# Quantification of ecohydrological sensitivities and their influencing factors at the seasonal scale

Yiping Hou, Mingfang Zhang, Xiaohua Wei, Shirong Liu, Qiang Li, Tijiu Cai, Wenfei Liu, Runqi Zhao, Xiangzhuo Liu

► To cite this version:

Yiping Hou, Mingfang Zhang, Xiaohua Wei, Shirong Liu, Qiang Li, et al. Quantification of ecohydrological sensitivities and their influencing factors at the seasonal scale. Hydrology and Earth System Sciences, 2021, 25 (3), pp.1447-1466. 10.5194/hess-25-1447-2021. hal-03201583

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# Quantification of ecohydrological sensitivities and their influencing factors at the seasonal scale

Yiping Hou<fnref n="1" />,<fnref n="2" />, Mingfang Zhang<fnref n="1" />,<fnref n="3" />, Xiaohua Wei<fnref n="2" />, Shirong Liu<fnref n="4" />, Qiang Li<fnref n="5" />, Tijiu Cai<fnref n="6" />, Wenfei Liu<fnref n="7" />, Runqi Zhao<fnref n="1" />,<fnref n="8" />, and Xiangzhuo Liu<fnref n="1" />,<fnref n="9" />

**Correspondence:** Mingfang Zhang (mingfangzhang@uestc.edu.cn)

Received: 2 July 2020 – Discussion started: 21 July 2020

Revised: 4 December 2020 – Accepted: 18 February 2021 – Published: 25 March 2021

**Abstract.** Ecohydrological sensitivity, defined as the response intensity of streamflow to per unit vegetation change is an integrated indicator for assessing hydrological sensitivity to vegetation change. Understanding ecohydrological sensitivity and its influencing factors is crucial for managing water supply, reducing water-related hazards and ensuring aquatic functions by vegetation management. Yet, there is still a systematic assessment on ecohydrological sensitivity and associated driving factors especially at a seasonal scale lacking. In this study, 14 large watersheds across various environmental gradients in China were selected to quantify their ecohydrological sensitivities at a seasonal scale and to examine the role of associated influencing factors such as climate, vegetation, topography, soil and landscape. Based on the variables identified by correlation analysis and factor analysis, prediction models of seasonal ecohydrological sensitivity were constructed to test their utilities for the design of watershed management and protection strategies. Our key findings were the following: (1) ecohydrological sensi-

tivities were more sensitive under dry conditions than wet conditions – for example, 1 % LAI (leaf area index) change, on average, induced 5.05 % and 1.96 % change in the dry and wet season streamflow, respectively; (2) seasonal ecohydrological sensitivities were highly variable across the study watersheds with different climate conditions, dominant soil types and hydrological regimes; and (3) the dry season ecohydrological sensitivity was mostly determined by topography (slope, slope length, valley depth and downslope distance gradient), soil (topsoil organic carbon and topsoil bulk density) and vegetation (LAI), while the wet season ecohydrological sensitivity was mainly controlled by soil (topsoil-available water-holding capacity), landscape (edge density) and vegetation (leaf area index). Our study provided a useful and practical framework to assess and predict ecohydrological sensitivities at the seasonal scale. The established ecohydrological sensitivity prediction models can be applied to ungauged watersheds or watersheds with limited hydrological data to help decision makers and watershed managers

<footnote n="1">¹School of Resources and Environment, University of Electronic Science and Technology of China, Chengdu 611731, China</footnote>

<footnote n="2">²Department of Earth, Environmental and Geographic Sciences, University of British Columbia (Okanagan campus), 1177 Research Road, Kelowna, British Columbia V1V 1V7, Canada</footnote>

<footnote n="3">³Center for Information Geoscience, University of Electronic Science and Technology of China, Chengdu 611731, China</footnote>

<footnote n="4">⁴Research Institute of Forest Ecology, Environment and Protection, Chinese Academy of Forestry, Beijing 100091, China</footnote>

<footnote n="5">⁵Center for Ecological Forecasting and Global Change, College of Forestry, Northwest A&F University, Yangling 712100, China</footnote>

<footnote n="6">⁶Department of Forestry, School of Forestry, Northeast Forestry University, Harbin 150040, China</footnote>

<footnote n="7">⁷Jiangxi Provincial Key Laboratory for Restoration of Degraded Ecosystems & Watershed Ecohydrology, Nanchang Institute of Technology, Nanchang 330099, China</footnote>

<footnote n="8">⁸Division of Ocean Science and Technology, Tsinghua Shenzhen International Graduate School, Tsinghua University, Shenzhen 518055, China</footnote>

<footnote n="9">⁹INRA, Centre INRA Bordeaux Aquitaine, URM 1391 ISPA, 33140 Villenave d'Ornon, France</footnote>
effectively manage hydrological impacts through vegetation
restoration programs. We conclude that ecohydrological sen-
sitivities at the seasonal scale are varied by climate, vege-
tation and watershed property, and their understanding can
greatly support the management of hydrological risks and
protection of aquatic functions.

# 1 Introduction

Natural rivers often have a distinctive seasonal pattern of
flow, where flow is highly related to precipitation and shows
large variations over dry and wet seasons. Seasonal flows
determine ecosystem functions (Toledo-Aceves et al., 2011;
Bruijnzeel et al., 2011; Salve et al., 2011), and their re-
sponses to vegetation change are highly variable and, con-
sequently, affect watershed ecosystem equilibrium (Maeda
et al., 2015). On the one hand, wet season flows and their
variability regulate flood magnitudes (Arias et al., 2012), de-
termine the structure of floodplains and channel morphol-
ogy (Jansen and Nanson, 2010) and provide opportunities
for the recruitment of large woody debris (Warfe et al., 2011;
de Paula et al., 2011). On the other hand, dry season flows
are critical for maintaining a stable water supply and pro-
tecting the aquatic ecosystem, as well as playing important
roles in sustaining aquatic biota and refuging juvenile fish
(Bunn et al., 2006; Palmer and Ruhi, 2019). However, sea-
sonal streamflow can be significantly affected by forest or
vegetation change (Dai, 2011; Hirabayashi et al., 2013). Re-
search has shown that vegetation change can influence water
retention time (Moore and Wondzell, 2005; Baker and Wi-
ley, 2009; Bisantino et al., 2015), alter snow accumulation
and snowmelt processes (Lin and Wei, 2008; Zhang and Wei,
2012; Calder, 2005) and route river flow quickly downstream
(Winkler et al., 2010; Chang, 2012) and, consequently, in-
crease the frequency and size of floods in wet season. Vege-
tation change can also affect dry season flows, which may in-
fluence baseflow level, and the risk of droughts, and degrade
or enrich in-channel habitat for aquatic species (Simonit and
Perrings, 2013; Sun et al., 2016). Thus, understanding sea-
sonal hydrological variations in vegetation change is criti-
cal for maintaining the sustainable water supply, preventing
large floods and droughts and developing the best watershed
management plans.

Obviously, seasonal streamflow responses to vegetation
change are highly variable among watersheds worldwide. To
better understand the general pattern of streamflow response
to vegetation change, Zhang et al. (2017) introduced a uni-
form indicator named ecohydrological sensitivity (defined as
the response intensity of streamflow to per unit forest change)
to express the hydrological sensitivity to forest change for
a given watershed. Ecohydrological sensitivity is believed
to be controlled not only by forest or vegetation coverage
but also by climate condition, hydrological regime and forest

or vegetation type (Zhang et al., 2017; Li et al., 2017). As-
sessing ecohydrological sensitivity can provide various ben-
efits. For example, it provides a dimensionless index on the
vegetation-water relationship so that any watersheds can be
effectively compared. It allows for the prediction of ecohy-
drological sensitivities for a landscape or region so that nega-
tive hydrological impacts in areas with high ecohydrological
sensitivities can be minimized through suitable arrangements
of vegetation or watershed management strategies.

Ecohydrological sensitivity is likely varied with
timescales. The hydrological responses to vegetation
change at the annual scale are the averaged and cumulative
effects from those at shorter time intervals, which are
typically associated with total annual magnitudes such as
water yield, while those at daily or monthly or seasonal
scales affect flow patterns and are normally related to floods
and droughts. The seasonal scale is a medium level between
daily and annual scales, which can affect both magnitude and
pattern in terms of hydrological response and sensitivity. For
example, the interactions between vegetation and water are
quite different between dry and wet seasons (Donohue et al.,
2010; Asbjornsen et al., 2011). Abundant water is available
for vegetation growth in the wet season, while vegetation
in the dry season mostly relies on limited soil moisture or
groundwater for limited photosynthesis and transpiration.
Besides, streamflow generation in the wet season is mainly
based on precipitation or water input, whereas dry season
flow is controlled by soil moisture in the antecedent wet
season and groundwater discharge. Thus, the contrasting
processes in different seasons suggest that ecohydrological
sensitivity must be examined at a seasonal scale.

Various factors, including climate, vegetation and water-
shed property, affect hydrological responses or sensitivities
(Zhou et al., 2015; Li et al., 2017; Zhang et al., 2017). For
example, hydrological responses to forest change tend to be
more sensitive in non-humid regions (Zhang et al., 2017).
Evapotranspiration change related to vegetation change is
controlled by energy and water (Zhang et al., 2004; Creed
et al., 2014; Yang et al., 2007). Topography controls hydro-
logical processes by affecting the distribution and routing of
water (Woods, 2007). Soil and landscape conditions are im-
portant for erosion, sediment and flow connectivity (Borselli
et al., 2008). Clearly, fully assessing and understanding eco-
hydrological sensitivity requires a consideration of various
influencing variables. Yet, current studies have only focused
on the hydrological influences of a single type of variable,
such as vegetation (Beck et al., 2013; Feng et al., 2016;
van Dijk et al., 2012), climate (Creed et al., 2014; Miara et
al., 2017), topography (Lyon et al., 2012; Jencso and McG-
lynn, 2011; Q. Li et al., 2018) and landscape (Nippgen et
al., 2011; Buma and Livneh, 2017; Teutschbein et al., 2018).
The inclusion of various types of variables into an integrated
assessment framework of hydrological responses remains a
challenging subject. Despite the acknowledgement that eco-
hydrological sensitivity can be a good index that facilitates
the understanding of variations in hydrological response to vegetation change, there is still a commonly accepted definition or framework for its quantitative assessment and comparisons especially at a seasonal scale lacking. To our best knowledge, there is no study on quantifying seasonal ecohydrological sensitivity.

China has experienced substantial and dynamic vegetation change over the past few decades. Deforestation and biomass loss dominated vegetation change from the 1950s to 1980s (Wei et al., 2008), while large-scale revegetation programs have been implemented since the 1980s (Y. Li et al., 2018). These large-scale vegetation changes can inevitably affect local and regional water cycles. However, given the large variations in climate, vegetation, soil, topography and landscapes in China, hydrological responses to vegetation change can be quite different among watersheds. Since assessing the hydrological impact of vegetation change in every single watershed can be very challenging and time-consuming, a general framework for an efficient evaluation of ecohydrological sensitivity at a watershed scale is in an urgent need for the support of future water and forest resource management. The objectives of this study were as follows: (1) to evaluate seasonal ecohydrological sensitivity in the selected large watersheds across environmental gradients, (2) to examine the role of climate, vegetation, topography, soil and landscape in seasonal ecohydrological sensitivity, and (3) to simulate and predict seasonal ecohydrological sensitivity based on the selected factors.

# 2 Study watersheds and data

## 2.1 Study watersheds

Given that the dominant climate zones in China include subtropical monsoon, alpine, temperate monsoon and temperate continental climate zones, two to four representative study watersheds in each climate zone are identified according to their hydrological data availability, watershed size, climate type and vegetation type. The selected watersheds in each climatic zone have a watershed size greater than 500 km² and long-time hydrological data available to meet the data requirements for statistical analysis (≥ 15 years). In addition, only vegetative watersheds with vegetation coverage greater than 30% are included since the climate (e.g., precipitation) is a more influencing factor than vegetation on river flows in watersheds with less vegetation coverage. With these criteria, 14 large watersheds across climatic zones, with areas ranging from 832 to 19189 km², are selected. They include the Pingjiang and Xiangshui watersheds in southeastern China, the Tangwang River and Xinancha River watersheds in northeastern China, the Upper Zagunao River, Zagunao River, Upper Heishui River, Heishui River, Gongbujiangda and Gengzhang watersheds in southwestern China and the Dongchuan, Heishuichuan, Jingchuan and Rui River watersheds in northwestern China (Fig. 1). In this study, the dry and wet seasons are defined according to the long-term mean monthly precipitation in a hydrological year. For subtropical-monsoon-climate-dominated watersheds (the Pingjiang and Xiangshui), the wet season is from March to August, with its precipitation amount accounting for over 70% of the annual total, while the dry season lasts from September to February. For those from the alpine, temperate monsoon and temperate continental climate zones, the wet season is from May to October, with the dry season from November to April. Table 1 provides a brief summary of seasonality, climate, vegetation, hydrology and topography in the study watersheds. Detailed descriptions of study watersheds can be found in Sect. S1 in the Supplement. In addition, substantial vegetation restoration programs caused large-scale vegetation change from the 1980s onwards. To evaluate seasonal ecohydrological sensitivity, the study periods start from 1983.

## 2.2 Data

Daily or monthly discharges for 14 watersheds were obtained from various government agencies. The details about the study periods and hydrometric stations can be found in the Supplement (Table S3). Discharges (in cubic meters per second) were converted into the unit of millimeters according to the drainage area. According to the definitions of seasonality in Table 1, a hydrological year was divided into the dry season and wet season, and then seasonal flows were calculated accordingly.

The historical climate data used in this study include three sources, namely daily climate records from the National Meteorological Information Centre of China Meteorological Administration (CMA; http://data.cma.cn/, last access: 20 June 2020), spatial-interpolated gridded climate data, by using the Australian National University Spline (ANUSPLIN) model, and meteorological data collected at the associated hydrological stations or rain gauges (Sect. S1.2 and Table S3). In this study, daily or monthly climate data, including mean temperature ($T_{mean}$), minimum temperature ($T_{min}$), maximum temperature ($T_{max}$) and precipitation ($P$), were derived and calculated accordingly. Monthly potential evapotranspiration (PET) was calculated based on estimated $T_{max}$ and $T_{min}$ by using Hargreaves’ equation (Eq. 1) (Hargreaves and Samani, 1985).

$$ \text{PET} = 0.0023 \times \text{Ra} \times \left[ \frac{(T_{\text{max}} + T_{\text{min}})/2 + 17.8}{(T_{\text{max}} - T_{\text{min}})^{0.5}} \right] \quad (1) $$

where, Ra is the extraterrestrial radiation, and $T_{min}$ and $T_{max}$ are the minimum and maximum temperatures in degrees Celsius.

The Moderate Resolution Imaging Spectroradiometer (MODIS) land cover product MODIS MCD12Q1, with the spatial resolution of 500 m, was downloaded from the Land Process Distributed Active Archive Center (LP DAAC; https://doi.org/10.5194/hess-25-1447-2021).
<figure><img src="image_2.png" /><figcaption>Figure 1. Locations of the study watersheds.</figcaption></figure>

https://lpdaac.usgs.gov/products/mcd12q1v006/, last access: 20 June 2020; Sulla-Menashe et al., 2019). There are 17 types of land covers in MODIS MCD12Q1, including evergreen needleleaf forests, deciduous needleleaf forests, evergreen broadleaf forests, deciduous broadleaf forests, mixed forests, closed shrublands, opened shrublands, woody savannas, savannas, grasslands, permanent wetlands, croplands, urban and built-up land, cropland/natural vegetation mosaics, permanent snow and ice, barren land and water bodies. We reclassified them into forest (evergreen needleleaf forests, deciduous needleleaf forests, evergreen broadleaf forests, deciduous broadleaf forests and mixed forests), shrubland (closed shrublands and opened shrublands), grassland (woody savannas, savannas and grasslands), agricultural (croplands and cropland/natural vegetation mosaics), snow (permanent snow and ice), and other lands (permanent wetlands, urban and built-up land, barren, and water bodies; Table S2). Vegetation coverage, including forest, shrubland and grassland, can be then calculated.

Leaf area index (LAI) derived from the Global Land Surface Satellite LAI (GLASS LAI) product was used as a vegetation index to express vegetation change in this study (GLASS; http://glass-product.bnu.edu.cn/, last access: 20 June 2020). The GLASS LAI product data set provides

continuous global LAI at a high temporal resolution of 8 d (Liang et al., 2013; Xiao et al., 2014). There are two types of GLASS LAI products with different spatial resolutions and available periods. The first GLASS LAI product is based on Advanced Very High Resolution Radiometer (AVHRR) reflectance data, with a spatial resolution of 0.05°, and this data set is available from 1982 to 2016. The other one, with a higher spatial resolution of 1 km, is retrieved from MODIS reflectance data, but it only covers a period of 17 years from 2000 to 2016. As the study watersheds are large watersheds (>500 km²), and the study periods ended before 2006, the former GLASS LAI product was chosen for this study, and from which two data series of LAI, namely dry season LAI (mean value of the LAIs in the dry season) and wet season LAI (mean value of the LAIs in the wet season), from the entire study period were generated.

The Harmonized World Soil Database (HWSD) was published by the Food and Agriculture Organization (FAO) and International Institute for Applied Systems Analysis (IIASA), with a spatial resolution of 1 km, and used to collect soil indices (Wieder, 2014). HWSD classifies soil into topsoil, from the surface to 30 cm belowground, and subsoil, between 30 and 100 cm belowground.
<table><caption>**Table 1.** Watershed characteristics in the study watersheds.</caption><thead><tr><th rowspan="2">Watersheds</th><th rowspan="2">Area (km²)</th><th rowspan="2">Mean elevation (m)</th><th rowspan="2">Slope (°)</th><th rowspan="2">Climate zone</th><th rowspan="2">Period</th><th colspan="4">Dry season</th><th colspan="4">Wet season</th></tr><tr><th>T<sub>mean</sub> (°C)</th><th>P (mm)</th><th>ET (mm)</th><th>Q (mm)</th><th>LAI (m²/m²)</th><th>Period</th><th>T<sub>mean</sub> (°C)</th><th>P (mm)</th><th>ET (mm)</th><th>Q (mm)</th><th>LAI (m²/m²)</th></tr></thead><tbody><tr><td>Pingjiang</td><td>2778</td><td>314</td><td>15.1</td><td>SMC</td><td>September</td><td>13.5</td><td>501.1</td><td>254.0</td><td>236.2</td><td>1.45</td><td>March</td><td>22.3</td><td>1310.7</td><td>585.5</td><td>604.3</td><td>1.90</td></tr><tr><td>Xiangshui</td><td>1742</td><td>440</td><td>17.6</td><td></td><td>February</td><td>14.3</td><td>472.0</td><td>274.6</td><td>242.5</td><td>2.54</td><td>August</td><td>22.0</td><td>1402.7</td><td>659.5</td><td>616.4</td><td>3.17</td></tr><tr><td>Tangwang River</td><td>19189</td><td>447</td><td>8.7</td><td>TCMC</td><td></td><td>-9.6</td><td>60.3</td><td>42.4</td><td>30.1</td><td>0.73</td><td></td><td>14.8</td><td>517.1</td><td>367.4</td><td>239.9</td><td>3.53</td></tr><tr><td>Xinancha River</td><td>2585</td><td>507</td><td>11.3</td><td></td><td></td><td>-11.1</td><td>81.0</td><td>47.5</td><td>37.3</td><td>0.71</td><td></td><td>12.8</td><td>567.5</td><td>398.9</td><td>293.6</td><td>3.59</td></tr><tr><td>Upper Zagunao</td><td>2442</td><td>3814</td><td>31.0</td><td></td><td></td><td>5.3</td><td>190.3</td><td>146.2</td><td>176.9</td><td>0.83</td><td></td><td>17.0</td><td>848.6</td><td>500.4</td><td>672.9</td><td>1.87</td></tr><tr><td>Zagunao</td><td>4629</td><td>3622</td><td>31.7</td><td></td><td></td><td>5.0</td><td>164.4</td><td>139.9</td><td>144.0</td><td>0.86</td><td></td><td>16.6</td><td>759.9</td><td>484.2</td><td>583.2</td><td>2.14</td></tr><tr><td>Upper Heishui River</td><td>1710</td><td>3858</td><td>27.8</td><td>AC</td><td>November</td><td>-1.8</td><td>121.1</td><td>102.7</td><td>136.9</td><td>0.50</td><td>May</td><td>9.7</td><td>599.8</td><td>408.6</td><td>630.0</td><td>1.78</td></tr><tr><td>Heishui River</td><td>7170</td><td>3619</td><td>27.3</td><td></td><td>April</td><td>-1.8</td><td>121.1</td><td>103.0</td><td>117.8</td><td>0.53</td><td>October</td><td>12.9</td><td>599.8</td><td>410.5</td><td>471.2</td><td>1.93</td></tr><tr><td>Gongbujiangda</td><td>6323</td><td>4946</td><td>27.2</td><td></td><td></td><td>2.5</td><td>61.0</td><td>52.3</td><td>60.8</td><td>0.11</td><td></td><td>13.4</td><td>783.6</td><td>404.8</td><td>880.3</td><td>0.59</td></tr><tr><td>Gengzhang</td><td>16000</td><td>4752</td><td>28.3</td><td></td><td></td><td>3.8</td><td>83.1</td><td>68.2</td><td>95.8</td><td>0.22</td><td></td><td>16.6</td><td>438.5</td><td>321.0</td><td>23.1</td><td>0.59</td></tr><tr><td>Dongchuan</td><td>3049</td><td>1415</td><td>16.3</td><td></td><td></td><td>0.1</td><td>68.1</td><td>59.2</td><td>6.6</td><td>0.19</td><td></td><td>17.0</td><td>471.9</td><td>336.8</td><td>14.6</td><td>1.51</td></tr><tr><td>Heshuichuan</td><td>832</td><td>1340</td><td>16.8</td><td>TCC</td><td></td><td>0.9</td><td>83.5</td><td>71.1</td><td>4.7</td><td>0.34</td><td></td><td>18.1</td><td>444.4</td><td>305.3</td><td>39.5</td><td>0.98</td></tr><tr><td>Jingchuan</td><td>3155</td><td>1678</td><td>13.5</td><td></td><td></td><td>2.2</td><td>81.1</td><td>66.7</td><td>16.6</td><td>0.26</td><td></td><td>15.2</td><td>488.3</td><td>364.0</td><td>55.1</td><td>1.23</td></tr><tr><td>Rui River</td><td>1688</td><td>1608</td><td>13.0</td><td></td><td></td><td>0.1</td><td>83.6</td><td>74.0</td><td>17.6</td><td>0.28</td><td></td><td></td><td></td><td></td><td></td><td></td></tr></tbody></table>

Note: T<sub>mean</sub>, P, ET, Q and LAI stand for mean temperature, precipitation, actual evapotranspiration, streamflow and leaf area index, respectively, during the study period. SMC, TCMC, AC and TCC refer to subtropical monsoon climate, temperate continental monsoon climate, alpine climate and temperate continental climate, respectively.

Digital elevation models (DEMs), with the spatial resolution of 30 m derived from the Global Digital Elevation Model (GDEM), were provided by the Geospatial Data Cloud site, Computer Network Information Centre, Chinese Academy of Sciences (http://www.gscloud.cn, last access: 20 June 2020). Topographic information for the study watersheds was derived from DEMs.

# 3 Methods

## 3.1 Definition and calculation of ecohydrological sensitivity

In this study, an improved single watershed approach was employed to quantify seasonal streamflow variations attributed to climate variability, vegetation change and other factors (Hou et al., 2018a, b). The modified double mass curve (MDMC) was firstly used to remove the effects of climate variability on seasonal streamflow variation. The multivariate ARIMA (AutoRegressive Integrated Moving Average; with an exogenous variable, ARIMA becomes ARI-MAX) model was then adopted to quantify seasonal streamflow variation attributed to non-climatic factors (vegetation change and other factors). The 95% confidence interval (95% CI) criterion was applied to separate the statistical errors and the seasonal streamflow variation attributed to other factors. The seasonal streamflow variation caused by vegetation change (ΔQ<sub>v</sub>) can be quantified eventually and be used to calculate the seasonal ecohydrological sensitivity. A more detailed description of the methodology is provided in Sect. S2 in the Supplement.

Similar to the concept of ecohydrological sensitivity proposed by Zhang et al. (2017), in this study, we defined seasonal ecohydrological sensitivity (S<sub>f</sub>) as the response intensity of seasonal streamflow variations to per unit vegetation change (using the LAI as a proxy), which can be computed with Eqs. (2)–(3). The value of seasonal ecohydrological sensitivity refers to the percentage of seasonal streamflow changes induced by 1% of the LAI change. Given that seasonal streamflow response to vegetation change in millimeters (ΔQ<sub>v</sub>) can be influenced by its background value (Q̄; the long-term mean seasonal streamflow during the study period), seasonal streamflow response to vegetation change in percent (ΔQ<sub>v</sub>%) is used for the calculation of ecohydrological sensitivity. Here, ΔQ<sub>v</sub> is divided by Q̄ to calculate ΔQ<sub>v</sub>. Through this normalization, ΔQ<sub>v</sub>%, representing relative change (%) in seasonal streamflow compared to its average state, can be a better indicator for hydrological sensitivity analysis than ΔQ<sub>v</sub>.

$$ \Delta Q_v \% = 100 \times \frac{\Delta Q_v}{\bar{Q}} \qquad (2) $$

$$ S_f = \left| \frac{\Delta Q_v \%}{\Delta LAI} \right|, \qquad (3) $$
where $\overline{Q}$ refers to the long-term mean seasonal streamflow during the study period, $\Delta Q_v$ is the seasonal streamflow response to vegetation change in millimeters, $\Delta Q_v\%$ is the seasonal streamflow response to vegetation change in percent (%), and $\Delta LAI$ is the LAI variation compared to average LAI in the reference period in percent.

## 3.2 Comparison of seasonal ecohydrological sensitivities between watershed conditions

According to the dryness index (DI), watersheds were grouped into energy-limited (EL), equitant (EQ) and water-limited (WL) conditions (McVicar et al., 2012). The most widely distributed soil type in a watershed was treated as the dominant soil type. Following our analysis, four dominant soil types (Lixisols, Luvisols, Leptosols and Cambisols) were found in this study. Additionally, the selected watersheds were categorized into rain-dominated (RD) and rain-snow hybrid (Hybrid) watersheds, according to their hydrological regimes. Table 2 shows the detailed classifications for each watershed in terms of climate condition, dominant soil type and hydrological regime.

A non-parametric Mann-Whitney *U* test was performed to detect the statistically significant differences between the watershed groups. A Mann-Whitney *U* test can determine whether there are significant differences in the median values of seasonal ecohydrological sensitivities between two groups (Birnbaum, 1956).

## 3.3 Prediction of seasonal ecohydrological sensitivity

A total of five types of indices, including climate, vegetation, topography, soil and landscape, were adopted in this study. Detailed information on the interpretations and calculations of 40 indices were presented in Table 3. Climate indices, including the dryness index and effective precipitation can demonstrate the water input and climate condition in a given watershed (van Dijk et al., 2012; Jones et al., 2012; Zhang et al., 2004). The dryness index is calculated at the annual scale to demonstrate the dryness condition, while effective precipitation (an integrated index of climatic variability) in the dry season and wet season denotes seasonal water inputs. Vegetation growth is highly dependent on temperature, water, soil and geographical location (Chang, 2012). Vegetation coverage or forest coverage indicates a proportion of vegetation or forest in a watershed, but it cannot express vegetation growth, mortality and seasonality. LAI is recognized as a better indicator, mainly because it is an important biophysical variable relating to photosynthesis, transpiration and energy balance (Launiainen et al., 2016; Verrelst et al., 2016; González-Sanpedro et al., 2008). Topographic indices can be classified into two groups, namely primary and secondary (also known as compounded topographic indices; Q. Li et al., 2018; Moore et al., 1991). Primary topographic indices can be directly derived from DEM, while compounded

topographic indices are based on one or more primary indices (Q. Li et al., 2018). Based on previously published studies, 17 topographic indices, including five primary indices and 12 compounded indices which are most frequently used in studying the topograohic effect on hydrological processes, were selected to describe watershed characteristics including visibility, generation process and morphology (Yokoyama et al., 2002; Park et al., 2001; Jenness, 2004; Q. Li et al., 2018). Calculations of the topographic indices were made in ArcGIS 10.2 (Esri) and SAGA GIS 2.1. Soil types were based on the FAO-85 system classification, while soil organic carbon and salinity were directly derived from HWSD in ArcGIS 10.2 (Esri), and soil-available water-holding capacity, saturated hydraulic conductivity and bulk density were calculated using the Soil-Plant-Air-Water (SPAW) hydrology model. We used the weighted-average value to represent watershed-scale soil indices. A total of seven landscape indices, including patch number (PN), patch density (PD), largest patch index (LPI), edge density (ED), contagion index (CONTAG), Shannon's diversity index (SHDI) and Simpson's diversity index (SIDI) at the landscape level which are most correlated with hydrological processes, were selected in the analysis (Zhou and Li, 2015; Boongaling et al., 2008). The calculations of landscape indices were performed by FRAGSTATS 4.2 software.

Obviously, the prediction with a large number of indices may cause model redundancy. Moreover, some of these indices can be correlated with each other, and a multicollinearity problem may arise. To address these issues, we have firstly performed a Kendall correlation analysis and linear regression to identify indices that are significantly correlated with seasonal ecohydrological sensitivities, and then we have conducted the factor analysis to further reduce the redundancy of indices. Eventually, only a few indices with key influences on seasonal ecohydrological sensitivity are retained for multiple linear regression.

To be specific, a Kendall correlation analysis and linear regression were used to identify statistically significant correlations between seasonal ecohydrological sensitivities and 40 indices at a significant level of *p* = 0.10. The insignificant indices were excluded for prediction, as described below. Factor analysis (FA) was introduced to further reduce the redundancy of indices. Similar to principal component analysis (PCA), indices after filtering by factor analysis could retain important information, which means that fewer indices can be used to represent most information (Lyon et al., 2012). A total of three criteria were used to pick highly related indices, namely the coefficient of Kaiser-Meyer-Olkin (KMO) test, the *p* value of Bartlett's test and the diagonal coefficients of the anti-image correlation matrix (Q. Li et al., 2018). Indices filtered by factor analysis, with the coefficient of KMO being greater than 0.50, the *p* value of Bartlett's test being less than 0.05 and the diagonal coefficients of the anti-image correlation matrix being greater than 0.50, were selected for further analysis. After filtering, only a few indices with key
<table><caption>**Table 2.** Classification of watersheds.</caption><thead><tr><td>Watersheds</td><td>Climate condition</td><td>Dominant soil type</td><td>Hydrological regime</td></tr></thead><tbody><tr><td>Pingjiang</td><td>Energy limited</td><td>Lixisols</td><td>Rain dominated</td></tr><tr><td>Xiangshui</td><td>Energy limited</td><td>Lixisols</td><td>Rain dominated</td></tr><tr><td>Tangwang River</td><td>Equitant</td><td>Luvisols</td><td>Rain dominated</td></tr><tr><td>Xinancha River</td><td>Equitant</td><td>Luvisols</td><td>Rain dominated</td></tr><tr><td>Upper Zagunao</td><td>Equitant</td><td>Leptosols</td><td>Hybrid</td></tr><tr><td>Zagunao</td><td>Equitant</td><td>Leptosols</td><td>Hybrid</td></tr><tr><td>Upper Heishui River</td><td>Equitant</td><td>Leptosols</td><td>Hybrid</td></tr><tr><td>Heishui River</td><td>Equitant</td><td>Leptosols</td><td>Hybrid</td></tr><tr><td>Gongbujiangda</td><td>Water limited</td><td>Leptosols</td><td>Hybrid</td></tr><tr><td>Gengzhang</td><td>Water limited</td><td>Leptosols</td><td>Hybrid</td></tr><tr><td>Dongchuan</td><td>Water limited</td><td>Cambisols</td><td>Rain dominated</td></tr><tr><td>Heshuichuan</td><td>Water limited</td><td>Cambisols</td><td>Rain dominated</td></tr><tr><td>Jingchuan</td><td>Water limited</td><td>Cambisols</td><td>Rain dominated</td></tr><tr><td>Rui River</td><td>Water limited</td><td>Cambisols</td><td>Rain dominated</td></tr></tbody></table>

influences on seasonal ecohydrological sensitivity were retained for the prediction models. In this way, the correlation between the influencing drivers could be greatly reduced. In addition, the collinearity of inputting variables for the multiple linear regression was assessed by a variance inflation factor (VIF). Models with a VIF of less than 10 were selected to address collinearity.

A multiple linear regression model modified by stepwise regression was employed to predict seasonal ecohydrological sensitivity. Influencing factors filtered by correlation analysis and factor analysis were regarded as independent variables, and ecohydrological sensitivity was considered as a dependent variable in a linear regression model. Independent variables were inputted into a model one by one, and the analysis of variance (ANOVA) test was conducted accordingly. Once the *p* value of the ANOVA test was greater than 0.10, the input-independent variable at this stage would be dropped. The optimal linear regression model was reached when no independent variables were inputted and no variables were dropped. The Akaike information criterion (AIC) and *R*² were used to find optimal multiple linear regression models for prediction. Except for quantitative indices, climate condition, dominant soil type and hydrological regime might also make contributions to the prediction of ecohydrological sensitivity. As a result, we introduced dummy variables to quantify the influence of the climate condition, dominant soil type and hydrological regime on model accuracy (Hardy, 1993). In this study, ecohydrological sensitivity based on the improved single watershed approach was called the observed *S*<sub>f</sub>, while ecohydrological sensitivity from the multiple linear regression model was named as the predicted *S*<sub>f</sub>.

# 4 Results

## 4.1 Seasonal ecohydrological sensitivity and its variations

Table 4 compares ecohydrological sensitivities between the dry and wet seasons. The ecohydrological sensitivities in the dry season were significantly greater than those in the wet season (Figs. 2 and S8–S10). As shown in Fig. 2, 1% LAI change, on average, induced 5.05% change in dry season streamflow, while in wet season, this value dropped to 1.96%. There were large variations in seasonal ecohydrological sensitivity among the study watersheds. The dry season ecohydrological sensitivity of the Tangwang River watershed was highest, up to 27.75, while the dry season ecohydrological sensitivity of the Upper Heishui River watershed was the lowest (1.01). Similarly, the wet season ecohydrological sensitivity, with the value of 4.36, in the Tangwang River watershed was also the highest among all watersheds in the wet season, whereas the lowest wet season ecohydrological sensitivity (0.40) was found in the Xiangshui watershed (Table S4).

Comparisons of seasonal ecohydrological sensitivities were made among the study watersheds grouped by their climate conditions, dominant soil types and hydrological regimes (Figs. 3, 4 and 5). As suggested by Fig. 3 and Table 5, significant differences in both dry season and wet season ecohydrological sensitivities between energy-limited (EL) and equitant (EQ) watersheds and between energy-limited and water-limited (WL) watersheds were found. Significant differences in the medians of wet season ecohydrological sensitivity in the pair of EQ–WL were also detected. A 1% vegetation change caused 2.11%, 5.86% and 5.23% change in dry season streamflow in the energy-limited, equitant and water-limited watersheds, respectively (Fig. 3a), while it only led to 0.58%, 2.82% and 1.64% change in wet
<table><caption>**Table 3.** Definition or description of the selected influencing factors.</caption><thead><tr><th>No.</th><th>Category</th><th>Abbreviation</th><th>Metrics</th><th>Definition or description</th></tr></thead><tbody><tr><td>1</td><td>Climate</td><td>DI</td><td>Dryness index</td><td>DI = PET / P; annual potential evaporation (PET) was calculated by the Hargreaves method (Hargreaves and Samani, 1985). It shows interactions between energy and water and indicates the water availability for vegetation growth.</td></tr><tr><td>2</td><td></td><td>P<sub>e</sub></td><td>Effective precipitation</td><td>P<sub>e</sub> = P - ET; actual evapotranspiration (ET) was calculated by Zhang's equation (Zhang et al., 2001).</td></tr><tr><td>3</td><td>Vegetation</td><td>LAI</td><td>Leaf area index</td><td>This is half of the total green leaf area per unit of horizontal ground surface area; derived from the GLASS product.</td></tr><tr><td>4</td><td></td><td>Forest coverage</td><td>Forest coverage</td><td>Forest coverage in a watershed.</td></tr><tr><td>5</td><td></td><td>Vegetation coverage</td><td>Vegetation coverage</td><td>Vegetation coverage in a watershed (total coverage of forest, shrubland and grassland).</td></tr><tr><td>6</td><td>Soil</td><td>Soil types</td><td>Number of soil types</td><td>Total number of soil types in a watershed.</td></tr><tr><td>7</td><td></td><td>T<sub>oc</sub></td><td>Topsoil organic carbon</td><td>Amount of carbon bound in human, animal and plant residues and microorganisms formed by microbial action in soil.</td></tr><tr><td>8</td><td></td><td>S<sub>oc</sub></td><td>Subsoil organic carbon</td><td></td></tr><tr><td>9</td><td></td><td>T<sub>ece</sub></td><td>Topsoil salinity</td><td>Soil total salinity.</td></tr><tr><td>10</td><td></td><td>S<sub>ece</sub></td><td>Subsoil salinity</td><td></td></tr><tr><td>11</td><td></td><td>T<sub>w</sub></td><td>Topsoil-available water-holding capacity</td><td>Soil moisture in a stable level.</td></tr><tr><td>12</td><td></td><td>S<sub>w</sub></td><td>Subsoil-available water-holding capacity</td><td></td></tr><tr><td>13</td><td></td><td>T<sub>hy</sub></td><td>Topsoil saturated hydraulic conductivity</td><td>Infiltration rate of each hydraulic gradient.</td></tr><tr><td>14</td><td></td><td>S<sub>hy</sub></td><td>Subsoil saturated hydraulic conductivity</td><td></td></tr><tr><td>15</td><td></td><td>T<sub>d</sub></td><td>Topsoil bulk density</td><td>Soil mass of each volume.</td></tr><tr><td>16</td><td></td><td>S<sub>d</sub></td><td>Subsoil bulk density</td><td></td></tr><tr><td>17</td><td>Landscape</td><td>PN</td><td>Patch number</td><td>Total number of patches within a specified land cover class.</td></tr><tr><td>18</td><td></td><td>PD</td><td>Patch density</td><td>The number of patches per unit area.</td></tr><tr><td>19</td><td></td><td>LPI</td><td>Largest patch index</td><td>The ratio of the largest patch area to total area.</td></tr><tr><td>20</td><td></td><td>ED</td><td>Edge density</td><td>The total length of patches per unit area.</td></tr><tr><td>21</td><td></td><td>CONTAG</td><td>Contagion index</td><td>Indicates the aggregation of patches.</td></tr><tr><td>22</td><td></td><td>SHDI</td><td>Shannon's diversity index</td><td>Based on information theory, this indicates the patch diversity in landscape.</td></tr><tr><td>23</td><td></td><td>SIDI</td><td>Simpson's diversity index</td><td>Indicates the patch diversity in landscape.</td></tr></tbody></table>
<table><caption>**Table 3. Continued.**</caption><thead><tr><th>No.</th><th>Category</th><th>Abbreviation</th><th>Metrics</th><th>Definition or description</th></tr></thead><tbody><tr><td>24</td><td rowspan="10">Topography</td><td>Area</td><td>Area of a watershed</td><td>Area draining to watershed outlet.</td></tr><tr><td>25</td><td>Perimeter</td><td>Perimeter of a watershed</td><td>Perimeter of a watershed.</td></tr><tr><td>26</td><td>Elevation</td><td>Mean elevation</td><td>Mean value of all DEM pixels in a watershed.</td></tr><tr><td>27</td><td>Elevation</td><td>Elevation difference</td><td>Difference between the highest elevation and the lowest elevation in a watershed.</td></tr><tr><td>28</td><td>Slope</td><td>Average slope</td><td>Slope degree of each DEM pixel; can be used in estimation of energy budgets.</td></tr><tr><td>29</td><td>LS</td><td>Slope length factor</td><td>A combined factor of slope length and slope gradient.</td></tr><tr><td>30</td><td>Length</td><td>Flow path length</td><td>The average flow path length, starting from the seeds.</td></tr><tr><td>31</td><td>Max length</td><td>Maximum flow path length</td><td>The maximum distance of water flow to a point.</td></tr><tr><td>32</td><td>TWI</td><td>Topographic wetness index</td><td>TWI = ln (SCA / tan(slope)); it shows the spatial distribution of zones of surface saturation and soil water content (Ambroise et al., 1996).</td></tr><tr><td>33</td><td>CON</td><td>Convergence</td><td>Convergence of a cell, which is calculated based on the surrounding eight cells – 100% convergence means all surrounding grid cells flow into the center cell.</td></tr><tr><td>34</td><td>DDG</td><td>Downslope distance gradient</td><td>An indicator for assessing the impact of the local slope characteristics on a hydraulic gradient. Values are lower on concave slope profiles and higher on convex slope profiles.</td></tr><tr><td>35</td><td>SA</td><td>Surface area</td><td>Land area of each DEM.</td></tr><tr><td>36</td><td>TPI</td><td>Topographic position index</td><td>TPI ≈ 0 indicates flat area. TPI > 0 tends towards ridge tops and hilltops. TPI < 0 tends towards the valley and canyon bottoms.</td></tr><tr><td>37</td><td>TRI</td><td>Terrain ruggedness index</td><td>The degree of difference in elevation among adjacent cells.</td></tr><tr><td>38</td><td>PO</td><td>Topographic positive openness</td><td>The degree of dominance or enclosure of a location on an irregular surface. Values are high for convex forms.</td></tr><tr><td>39</td><td>NO</td><td>Topographic negative openness</td><td>The degree of dominance or enclosure of a location on an irregular surface. Values are high for convex forms.</td></tr><tr><td>40</td><td>Depth</td><td>Valley depth</td><td>Difference between the elevation and an interpolated ridge level.</td></tr></tbody></table>

<table><caption>**Table 4.** Mann-Whitney *U* test for ecohydrological sensitivity between dry season and wet season.</caption><thead><tr><th>Season</th><th>Z</th><th>p</th></tr></thead><tbody><tr><td>Dry season vs. wet season</td><td><strong>5.63</strong></td><td><strong>0.00*</strong></td></tr></tbody></table>

Note: The bold number with the asterisk (*) indicates a statistically significant value at *p*<0.10.

season streamflow in the EL, EQ and WL watersheds, respectively (Fig. 3b). These results clearly demonstrated that ecohydrological sensitivity was greater in the EQ and WL conditions, particularly in the dry season.

When seasonal ecohydrological sensitivity in watersheds grouped by dominant soil types was compared (Fig. 4 and

Table 5), the median of dry season ecohydrological sensitivity in the Lixisols-dominated watersheds was significantly different from those of the Luvisols- and Cambisols-dominated watersheds at $\alpha$ = 0.05, and the significant differences in median of dry season ecohydrological sensitivity were also detected in the Luvisols-Leptosols, Lixisols-Leptosols, Luvisols-Cambisols and Leptosols-Cambisols pairs at $\alpha$ = 0.05 (Table 5). Similarly, the median of wet season ecohydrological sensitivity in the Lixisols-dominated watersheds was significantly different from those of the Luvisols-, Leptosols- and Cambisols-dominated watersheds at $\alpha$ = 0.05. On average, 1% change in vegetation led to 2.11%, 3.29%, 5.62% and 13.01% change in dry season streamflow in the Lixisols-, Leptosols-, Cambisols- and Luvisols-dominated watersheds, respectively (Fig. 4a), while
<table><caption>**Table 5.** Mann–Whitney *U* tests for the differences in seasonal ecohydrological sensitivity between climate condition, dominant soil type and hydrological regime.</caption><thead><tr><th rowspan="2">Watershed classification</th><th rowspan="2">Pairs</th><th colspan="2">S<sub>fd</sub></th><th colspan="2">S<sub>fW</sub></th></tr><tr><th>Z</th><th>p</th><th>Z</th><th>p</th></tr></thead><tbody><tr><td rowspan="3">Climate condition</td><td>EL-EQ</td><td>-2.14</td><td>0.03*</td><td>-3.98</td><td>&lt;0.001*</td></tr><tr><td>EL-WL</td><td>-3.09</td><td>&lt;0.002*</td><td>-3.15</td><td>&lt;0.002*</td></tr><tr><td>EQ-WL</td><td>-1.41</td><td>0.16</td><td>2.20</td><td>0.03*</td></tr><tr><td rowspan="6">Dominant soil type</td><td>Lixisols-Luvisols</td><td>-3.70</td><td>&lt;0.001*</td><td>-2.19</td><td>0.028*</td></tr><tr><td>Lixisols-Leptosols</td><td>-1.79</td><td>0.074*</td><td>-2.93</td><td>0.003*</td></tr><tr><td>Lixisols-Cambisols</td><td>-2.95</td><td>0.003*</td><td>-4.62</td><td>&lt;0.001*</td></tr><tr><td>Luvisols-Leptosols</td><td>3.53</td><td>&lt;0.001*</td><td>0.02</td><td>0.98</td></tr><tr><td>Luvisols-Cambisols</td><td>1.88</td><td>0.059*</td><td>-0.80</td><td>0.42</td></tr><tr><td>Leptosols-Cambisols</td><td>-2.20</td><td>0.027*</td><td>-1.42</td><td>0.15</td></tr><tr><td>Hydrological regime</td><td>RD-Hybrid</td><td>1.97</td><td>0.05*</td><td>-0.26</td><td>0.79</td></tr></tbody></table>

$S_{fd}$ and $S_{fW}$ are dry season and wet season ecohydrological sensitivity, respectively; EL, EQ and WL refer to energy-limited, equitant and water-limited watersheds, respectively; RD is the rain-dominated watershed. The bold numbers with the asterisk (*) indicate statistically significant values at $p<0.10$.

<figure><img src="image_3.png" /><figcaption>**Figure 2.** A comparison of ecohydrological sensitivity in the dry season and wet season ($S_{fd}$ and $S_{fW}$ show dry season ecohydrological sensitivity and wet season ecohydrological sensitivity).</figcaption></figure>

it caused only 0.58%, 2.20%, 2.11% and 2.24% change in wet season streamflow (Fig. 4b).

Figure 5 demonstrates the differences in seasonal ecohydrological sensitivity in watersheds grouped by hydrological regime. A Mann–Whitney *U* test showed that there were significant differences between rain-dominated and hybrid watersheds in the medians of dry season ecohydrological sensitivity (Table 5). A 1% vegetation change can result in 6.51% and 3.29% change in dry season streamflow in rain-dominated and hybrid watersheds, respectively (Fig. 5a), while it only leads to 1.75% and 2.20% change in wet season streamflow in rain-dominated and hybrid watersheds, respectively (Fig. 5b).

## 4.2 Prediction models for seasonal ecohydrological sensitivity

According to correlations between seasonal ecohydrological sensitivity and 40 indices detected by Kendall correlation and linear regression, 17 indices significantly related to dry season ecohydrological sensitivity were identified (Table 6). Dry season ecohydrological sensitivity was significantly and positively correlated with the dryness index (DI), topographic wetness index (TWI), downslope distance gradient (DDG), topographic positive openness (PO), topographic negative openness (NO), topsoil salinity ($T_{ece}$) and topsoil bulk density ($T_{d}$), while its correlations with all vegetation indices (LAI, vegetation coverage and forest coverage), slope, slope length factor (LS), terrain ruggedness index (TRI), valley depth (depth), topsoil organic carbon ($T_{oc}$), patch density (PD) and edge density (ED) were significantly negative. In contrast, only eight indices were significantly correlated with wet season ecohydrological sensitivity. Wet season ecohydrological sensitivity had a significantly positive correlation with convergence (CON), topsoil-available water-holding capacity ($T_{w}$), topsoil-saturated hydraulic conductivity ($T_{hy}$), subsoil-saturated hydraulic conductivity ($S_{hy}$) and subsoil salinity ($S_{ece}$), whereas there was a negative relation with effective precipitation ($P_e$), soil types and edge density (ED).

A total of 8 out of 17 indices significantly related to dry season ecohydrological sensitivity were further identified by factor analysis, which included factors such as DI, slope, LS, TWI, DDG, TRI, depth and NO. For the factor analysis of dry season ecohydrological sensitivity, the coefficient of KMO was 0.730, the *p* value of Bartlett's test was less than 0.05 and diagonal coefficients of the anti-image correlation matrix were greater than 0.53 (Table 7). Meanwhile, factor analysis
<table><caption>**Table 6.** Correlation analysis between seasonal ecohydrological sensitivities and contributing factors.</caption><thead><tr><th rowspan="2">Variables</th><th rowspan="2"></th><th colspan="3">S<sub>fd</sub></th><th colspan="3">S<sub>fW</sub></th></tr><tr><th>Kendall</th><th>a</th><th>R<sup>2</sup></th><th>Kendall</th><th>a</th><th>R<sup>2</sup></th></tr></thead><tbody><tr><td rowspan="2">Climate</td><td>DI</td><td><strong>0.44*</strong></td><td><strong>2.37*</strong></td><td><strong>0.41</strong></td><td>0.19</td><td>0.51</td><td>0.05</td></tr><tr><td>P<sub>e</sub></td><td>-0.23</td><td>-0.01</td><td>0.09</td><td>-0.32</td><td><strong>-0.03*</strong></td><td><strong>0.23</strong></td></tr><tr><td rowspan="3">Vegetation</td><td>Vegetation coverage</td><td><strong>-0.51*</strong></td><td><strong>-0.08*</strong></td><td><strong>0.53</strong></td><td>0.08</td><td>0.01</td><td>0.01</td></tr><tr><td>Forest coverage</td><td><strong>-0.36*</strong></td><td>-0.03</td><td>0.13</td><td>0.21</td><td>0.01</td><td>0.06</td></tr><tr><td>LAI</td><td><strong>-0.44*</strong></td><td><strong>-1.62*</strong></td><td><strong>0.05</strong></td><td>0.09</td><td>-0.08</td><td>0.00</td></tr><tr><td rowspan="15">Topography</td><td>Area<sup>c</sup></td><td>0.15</td><td>0.28</td><td>0.01</td><td>0.19</td><td>0.28</td><td>0.02</td></tr><tr><td>Perimeter<sup>c</sup></td><td>0.23</td><td>1.75</td><td>0.07</td><td>0.25</td><td>1.08</td><td>0.15</td></tr><tr><td>Elevation<sup>c</sup></td><td>0.00</td><td>-0.10</td><td>0.00</td><td>0.12</td><td>0.23</td><td>0.03</td></tr><tr><td>ΔElevation<sup>c</sup></td><td>0.10</td><td>0.71</td><td>0.05</td><td>0.27</td><td>0.5</td><td>0.06</td></tr><tr><td>Slope</td><td><strong>-0.39*</strong></td><td><strong>-0.15*</strong></td><td><strong>0.28</strong></td><td>-0.03</td><td>-0.01</td><td>0.00</td></tr><tr><td>LS</td><td><strong>-0.40*</strong></td><td><strong>-0.20*</strong></td><td><strong>0.24</strong></td><td>0.04</td><td>0.48</td><td>0.01</td></tr><tr><td>Length</td><td>-0.18</td><td>-4.3 × 10<sup>-3</sup></td><td>0.10</td><td>0.21</td><td>-1.2 × 10<sup>-2</sup></td><td>0.03</td></tr><tr><td>Max length</td><td>-0.23</td><td>-1.9 × 10<sup>-3</sup></td><td>0.15</td><td>0.32</td><td>-1.4 × 10<sup>-3</sup></td><td>0.10</td></tr><tr><td>TWI</td><td><strong>0.62*</strong></td><td><strong>4.30*</strong></td><td><strong>0.51</strong></td><td>0.19</td><td>1.05</td><td>0.15</td></tr><tr><td>CON</td><td>0.12</td><td>0.04</td><td>0.04</td><td>0.20</td><td><strong>0.05*</strong></td><td><strong>0.20</strong></td></tr><tr><td>DDG</td><td><strong>0.49*</strong></td><td><strong>0.10*</strong></td><td><strong>0.45</strong></td><td>0.03</td><td>0.02</td><td>0.05</td></tr><tr><td>SA</td><td>-0.13</td><td>1.5 × 10<sup>-3</sup></td><td>0.00</td><td>0.14</td><td>4.2 × 10<sup>-3</sup></td><td>0.15</td></tr><tr><td>TPI</td><td>-0.04</td><td>3.45</td><td>0.00</td><td>-0.05</td><td>8.86</td><td>0.03</td></tr><tr><td>TRI</td><td>-0.33</td><td><strong>-0.32*</strong></td><td><strong>0.23</strong></td><td>0.01</td><td>0.02</td><td>0.00</td></tr><tr><td>PO</td><td><strong>0.36*</strong></td><td><strong>14.23*</strong></td><td><strong>0.26</strong></td><td>0.08</td><td>0.63</td><td>0.00</td></tr><tr><td>NO</td><td>0.34</td><td><strong>14.78*</strong></td><td><strong>0.25</strong></td><td>0.03</td><td>0.43</td><td>0.00</td></tr><tr><td>Depth</td><td>-0.31</td><td><strong>-0.01*</strong></td><td><strong>0.32</strong></td><td>-0.10</td><td>-0.01</td><td>0.01</td></tr><tr><td rowspan="10">Soil</td><td>T<sub>w</sub></td><td>0.25</td><td>74.26</td><td>0.05</td><td><strong>0.53*</strong></td><td><strong>125.46*</strong></td><td><strong>0.38</strong></td></tr><tr><td>T<sub>hy</sub></td><td>-0.03</td><td>0.04</td><td>0.01</td><td><strong>0.41*</strong></td><td><strong>0.15*</strong></td><td><strong>0.25</strong></td></tr><tr><td>T<sub>d</sub></td><td>0.28</td><td><strong>32.32*</strong></td><td><strong>0.28</strong></td><td>0.10</td><td>2.49</td><td>0.01</td></tr><tr><td>T<sub>oc</sub></td><td>-0.21</td><td><strong>-3.99*</strong></td><td><strong>0.27</strong></td><td>-0.11</td><td>-0.29</td><td>0.00</td></tr><tr><td>T<sub>ece</sub></td><td><strong>0.39*</strong></td><td><strong>10.74*</strong></td><td><strong>0.28</strong></td><td>0.30</td><td>3.99</td><td>0.19</td></tr><tr><td>S<sub>w</sub></td><td>-0.09</td><td>-17.10</td><td>0.03</td><td>0.06</td><td>-3.80</td><td>0.01</td></tr><tr><td>S<sub>hy</sub></td><td>0.15</td><td>0.28</td><td>0.07</td><td>0.30</td><td><strong>0.30*</strong></td><td><strong>0.22</strong></td></tr><tr><td>S<sub>d</sub></td><td>0.00</td><td>13.30</td><td>0.06</td><td>0.15</td><td>8.66</td><td>0.08</td></tr><tr><td>S<sub>oc</sub></td><td>0.17</td><td>3.80</td><td>0.03</td><td>-0.09</td><td>1.76</td><td>0.02</td></tr><tr><td>S<sub>ece</sub></td><td>0.34</td><td>7.71</td><td>0.16</td><td>0.28</td><td><strong>3.87*</strong></td><td><strong>0.22</strong></td></tr><tr><td>Soil types</td><td>-0.30</td><td>-0.11</td><td>0.14</td><td><strong>0.37*</strong></td><td>0.06</td><td>0.13</td></tr><tr><td rowspan="7">Landscape</td><td>PN</td><td>-0.18</td><td>-5.2 × 10<sup>-4</sup></td><td>0.02</td><td>0.01</td><td>-4.2 × 10<sup>-5</sup></td><td>0.00</td></tr><tr><td>PD</td><td><strong>-0.54*</strong></td><td><strong>-10.83*</strong></td><td><strong>0.30</strong></td><td>-0.25</td><td>-4.73</td><td>0.15</td></tr><tr><td>LPI</td><td>0.08</td><td>0.02</td><td>0.04</td><td>0.06</td><td>0.04</td><td>0.00</td></tr><tr><td>ED</td><td><strong>-0.36*</strong></td><td>-0.27</td><td>0.17</td><td>-0.32</td><td><strong>-0.19*</strong></td><td><strong>0.23</strong></td></tr><tr><td>CONTAG</td><td>0.03</td><td>0.02</td><td>0.01</td><td>0.10</td><td>0.03</td><td>0.09</td></tr><tr><td>SHDI</td><td>-0.05</td><td>-0.31</td><td>0.00</td><td>-0.06</td><td>-0.66</td><td>0.03</td></tr><tr><td>SIDI</td><td>-0.08</td><td>-0.74</td><td>0.00</td><td>-0.03</td><td>-0.69</td><td>0.01</td></tr></tbody></table>

Note: linear regressions are built as $y = ax + b$, where *a* is the slope of the linear regression; the superscript *c* means parameters are transferred into ln() format. The bold numbers with the asterisks (*) indicate statistically significant values at *p*<0.10.

identified six indices (P<sub>e</sub>, CON, T<sub>w</sub>, T<sub>hy</sub>, S<sub>hy</sub> and ED) associated with wet season ecohydrological sensitivity based on a correlation analysis. For the wet season subset, the coefficient of KMO with the value of 0.634 was lower than that in the dry season subset, but diagonal coefficients of the anti-image correlation matrix were higher than those in the wet season subset (≥ 0.57). The *p* value of Bartlett's test was

0.00. Given that it is an important ecohydrological indicator for vegetation status in a watershed, LAI was also manually added as a predictor in the predicted model. Figure 6 shows the structure, parameters and statistics of the established prediction models for ecohydrological sensitivity. The dry season model had a better performance with a higher R<sup>2</sup>
<figure><img src="image_4.png" /><figcaption>**Figure 3.** Comparisons of ecohydrological sensitivity grouped by energy-limited (EL), equitant (EQ) and water-limited (WL) conditions in the (a) dry season and (b) wet season ($S_{fd}$ and $S_{fw}$ are dry season ecohydrological sensitivity and wet season ecohydrological sensitivity, respectively).</figcaption></figure>

of 0.966 (Fig. 6a), while the $R^2$ was only 0.501 for the wet season model (Fig. 6b).

# 5 Discussion

## 5.1 Seasonal ecohydrological sensitivity and climate conditions

Climate conditions in terms of energy (temperature) and water (precipitation) are the most important drivers for vegetation growth. Ecohydrological processes of vegetative watersheds vary greatly with climate conditions (Donohue et al., 2010). As suggested by our study, both dry season and wet season ecohydrological sensitivities of the water-limited watersheds were higher than those of the energy-limited watersheds (Fig. 3), and the dry season ecohydrological sensitivities were much higher than the wet season ecohydrological sensitivities (Fig. 2). In addition, the dry season ecohydro-

<figure><img src="image_5.png" /><figcaption>**Figure 4.** Comparisons of ecohydrological sensitivity grouped by dominant soil type in the (a) dry season and (b) wet season.</figcaption></figure>

logical sensitivity significantly increased with a rising dryness index, while the wet season ecohydrological sensitivity significantly decreased with increasing effective precipitation (Table 6). In other words, under dry conditions (during dry periods or in dry regions), streamflow is more sensitive to vegetation change than under wet conditions (during wet periods or in wet regions). These findings are in accordance with results from previous studies, which indicate streamflow response to vegetation in drier regions might be more pronounced than in wetter regions (Jackson et al., 2005; Vose et al., 2011; Li et al., 2017; Zhang et al., 2017). For example, Farley et al. (2005) demonstrated that afforestation produced 27% water yield reduction in wetter sites, while 62% water yield reduction was identified in drier sites, based on the analysis of 26 catchments globally. Sun et al. (2006) modeled streamflow responses to large-scale reforestation in China and found increased vegetation cover produced a nearly 30% reduction in streamflow in humid regions, but the streamflow reduction rose to approximately 50% in semi-arid and arid areas. Creed et al. (2014) indicated that water use efficiencies in forests were higher in drier years than in wetter years by
<table><caption>**Table 7.** Selected factor analysis models.</caption><thead><tr><th></th><th>Influencing factors</th><th>MSA</th><th>KMO</th><th>Bartlett's test</th></tr></thead><tbody><tr><td>Dry season</td><td>DI, slope, LS, TWI, DDG, TRI, depth, NO</td><td>≥ 0.53</td><td>0.730</td><td>0.000</td></tr><tr><td>Wet season</td><td>P<sub>e</sub>, CON, T<sub>w</sub>, T<sub>hy</sub>, S<sub>hy</sub>, ED</td><td>≥ 0.57</td><td>0.634</td><td>0.000</td></tr></tbody></table>

<figure><img src="image_6.png" /><figcaption>**Figure 5.** Comparisons of ecohydrological sensitivity grouped by rain-dominated (RD) and hybrid regimes in the (a) dry season and (b) wet season.</figcaption></figure>

assessing water yield variations in North America. The different ecohydrological sensitivities between dry and wet seasons might be explained by the various mechanisms of water use by vegetation. Vegetation growth in wet conditions with abundantly available water, sufficient soil moisture and saturated aquifers is more sensitive to energy factors including temperature, radiation and heat input (Newman et al., 2006; Hou et al., 2018a; Zhang et al., 2011; Brooks et al., 2012). Changes in energy input in wet conditions can alter stomatal conductance and transpiration and, consequently, affect the photosynthesis, transpiration and biomass of vegetation (de Sarrau et al., 2012; Van Dover and Lutz, 2004). In contrast,

<figure><img src="image_7.png" /><figcaption>**Figure 6.** Comparisons of observed and predicted ecohydrological sensitivity in the (a) dry season and (b) wet season (TR, XR, PJ, XS, GBJD, GZ, UZGN, ZGN, UHR, HR, DC, HSC, JC and RR refer to the Tangwang River, Xinancha River, Pingjiang, Xiangshui, Gongbujiangda, Gengzhang, Upper Zagunao, Zagunao, Upper Heishui River, Heishui River, Dongchuan, Heishuichuan, Jingchuan and Rui River watersheds, respectively).</figcaption></figure>

in dry conditions with limited precipitation input, water is more critical for vegetation growth as vegetation mainly rely on access to soil water through root systems to support photosynthesis and transpiration (Zhou et al., 2015).

## 5.2 Seasonal ecohydrological sensitivity and soils

Soils as the interface between streamflow and groundwater play vital roles in the water cycle (Bockheim and Genadiyev, 2010; Schoonover and Crim, 2015). Our study showed that watersheds with different dominant soil types could have contrasting seasonal ecohydrological sensitivity. As shown in Fig. 4, the ecohydrological sensitivities in both dry and wet seasons in the Lixisol-dominated water-
sheds were the lowest compared with those of Cambisols-, Leptosols- and Luvisols-dominated watersheds. This result clearly illustrates the importance of soil types in hydrological responses and sensitivities (Rieu and Sposito, 1991; Sri vastava et al., 2010; Chadli, 2016). Soil properties, including organic carbon, salinity, available water-holding capacity, saturated hydraulic conductivity and bulk density can affect soil water infiltration and lateral movement (Hillel, 1974; Leu et al., 2010). For example, soils with higher available water-holding capacity have the ability to store more water for vegetation growth (Mukundan et al., 2010). Saturated hydraulic conductivity is positively correlated to available water-holding capacity, suggesting that soils in a watershed with a higher value of saturated hydraulic conductivity might promote interactions between streamflow and groundwater (Sulis et al., 2010). Large differences between topsoil and subsoil bulk densities suggest a frequent moisture movement, leading to more active interactions and feedbacks above and below the soil (Zhao et al., 2010). Lixisols are characterized by the lowest saturated hydraulic conductivity and the smallest difference between topsoil and subsoil bulk densities, as compared to other three types of soils (Table S1), indicating that they have the lowest water storage capacity and less frequent water movement between topsoil and subsoil. Therefore, hydrological responses in the Lixisols-dominated watersheds were less sensitive to vegetation change, and, consequently, this led to the lowest seasonal ecohydrological sensitivity.

## 5.3 Seasonal ecohydrological sensitivity and hydrological regimes

The hydrological regime is another determinant for ecohydrological sensitivity (Zhang et al., 2017). Our study found that the dry season ecohydrological sensitivity in the rain-dominated watersheds was significantly higher than that in the hybrid watersheds (Fig. 5), while an insignificant difference in wet season ecohydrological sensitivity between the rain-dominated and hybrid watersheds was estimated (Table 5). The differences in dry season ecohydrological sensitivity between the rain-dominated and hybrid watersheds are associated with their differences in the mechanisms of streamflow generation. In the rain-dominated watersheds, dry season streamflow is mainly maintained by groundwater discharge, while both groundwater and snow water might be the sources of dry season streamflow in the hybrid watersheds. Thus, the generation of the dry season streamflow in the hybrid watersheds tends to be more complex and stable and can be more resilient to vegetation change in comparison with that of rain-dominated watersheds. This is supported by several reviews which found that forest cover change in rain-dominated watersheds can produce greater hydrological impacts than in snow-dominated watersheds (Zhang et al., 2017; Moore and Wondzell, 2005). In hybrid watersheds, forestation or vegetation removal can lead to changes in

snowmelt processes by altering snow accumulation, melting timing, energy input and wind speed in dry season (Frank et al., 2015), resulting in hydrological de-synchronization effects. These de-synchronization effects may offset the negative impacts of vegetation change on dry season streamflow and, eventually, lower dry season ecohydrological sensitivity in the hybrid watersheds.

The lack of a significant difference in the wet season ecohydrological sensitivity between the rain-dominated and hybrid watersheds might be due to the fact that the only precipitation form during the wet season is rainfall. It is expected that there are similar interactions and feedback mechanisms between vegetation and water in the wet season in all watersheds, leading to insignificant differences in wet season ecohydrological sensitivity between the rain-dominated and hybrid watersheds.

## 5.4 Seasonal ecohydrological sensitivity and topography

Topography, as a dominating factor for hydrological processes (Zeng et al., 2016; Jenness, 2004; Scown et al., 2015; Yokoyama et al., 2002; Park et al., 2001; Q. Li et al., 2018), plays an important role in determining streamflow response to vegetation change (Price, 2011; Smakhtin, 2001). According to the established prediction model of dry season ecohydrological sensitivity (Fig. 6a), topographic factors, including slope and downslope distance gradient, had positive effects on dry season ecohydrological sensitivity, while slope length factor and valley depth yielded negative effects. The vegetative watersheds with steeper slopes often have faster water movement from slopes to the river channel, and there is severe soil erosion in the wet season if vegetation is destroyed, which can greatly reduce wet season soil water storage for dry season streamflow, and this, therefore, leads to greater dry season ecohydrological sensitivity (Desmet and Govers, 1996; Zhang et al., 2012). Similarly, vegetative watersheds with a smaller slope length factor and valley depth can have greater dry season ecohydrological sensitivity. This is probably because these watersheds often have a generally flatter topography and longer water residence time, and consequently, this allows for more interactions between vegetation and water, which likely leads to greater ecohydrological sensitivity in the dry season.

Unlike the dry season ecohydrological sensitivity, no topographic indices were associated with wet season ecohydrological sensitivity (Fig. 6b). As we know, climate and vegetation are two major drivers of hydrological variations in vegetative watersheds (Wei et al., 2018; Li et al., 2017). This indicates that, in the wet season, climate plays a more dominant role in hydrological responses or variations, which means a decreasing role of vegetation on streamflow and, consequently, a reduction in ecohydrological sensitivity. The decreasing role of vegetation on streamflow in the wet season
may explain the insignificant impact of topographic indices
on wet season ecohydrological sensitivity.

**5.5 Seasonal ecohydrological sensitivity and landscape**

Landscape pattern can directly affect hydrological connectiv-
ity and indirectly influence hydrological processes by con-
trolling soil activities, such as soil erosion and sediment
(Buma and Livneh, 2017; Teutschbein et al., 2018; Karlsen
et al., 2016). Based on the prediction models (Fig. 6), the
landscape pattern played a more important role in wet season
ecohydrological sensitivity than in dry season ecohydrologi-
cal sensitivity. Only edge density was identified as an effec-
tive, negative landscape predictor for wet season ecohydro-
logical sensitivity. Watersheds with a higher value of edge
density are often characterized by landscape fragmentation
and segmentation, e.g., scatter-distributed vegetation, higher
road densities, leading to poor hydrological connectivity, and
a high risk of soil erosion. The increasing role of watershed
property (edge density) means that the relative role of vege-
tation in hydrological response would be lower, which conse-
quently leads to decreasing wet season ecohydrological sen-
sitivity.

5.6 Implications

Ecohydrological studies at the seasonal scale are limited
due to the lack of the understanding of complex and vari-
able streamflow responses to climate, vegetation, topogra-
phy, soil and landscape (McDonnell et al., 2018; Singh et
al., 2014; Wei et al., 2018; Q. Li et al., 2018; Oppel and
Schumann, 2020; Guswa et al., 2020). Our findings clearly
showed that seasonal ecohydrological sensitivity was not
only highly associated with climate and vegetation change
but also significantly related to watershed properties like
topography, soil and landscape. As indicated by the con-
structed prediction models, the dry season ecohydrological
sensitivity could be better described by vegetation, topogra-
phy and soil (Fig. 6a), while the wet season hydrological re-
sponse was mainly controlled by vegetation (leaf area index),
soil (topsoil-available water-holding capacity) and landscape
 edge density; Fig. 6b). Given the complex and variable hy-
drological responses to vegetation change among the study
watersheds due to their differences in watershed properties
(Zhou et al., 2015; Wei et al., 2018), our seasonal ecohydro-
logical sensitivity prediction model can provide valuable in-
formation for understanding the relative role of climate, veg-
etation and watershed characteristics.

Since many watersheds lack long-term monitoring data
on climate, hydrology and vegetation, a quantitative assess-
ment of the hydrological response to vegetation change at
the watershed scale is very challenging and time-consuming.
However, physical watershed data on climate, vegetation and
watershed properties can be easily derived from online cli-
mate data sets, remote-sensing-based products, DEMs and

soil databases. The development of a seasonal ecohydrolog-
ical sensitivity prediction model can be an efficient tool for
watershed managers to evaluate the hydrological impacts of
vegetation restoration programs with easily accessible data
on climate, vegetation, topography, soil and landscape. Once
seasonal ecohydrological sensitivity for different watersheds
can be predicted quickly, future forest management can be
implemented in a more sustainable way. We expect that the
assessment framework from this study can be effectively ap-
plied to any watershed for which physical watershed data are
available to support sustainable watershed planning and man-
agement.

5.7 Uncertainties and limitations

This study may have some uncertainties and limitations re-
garding the ecohydrological sensitivity quantification and its
prediction model development. The accuracy of ecohydro-
logical sensitivity quantification relies on the methodology
for quantifying seasonal streamflow variation attributed to
vegetation change. In this study, the improved single wa-
tershed approach used to separate the effects of vegetation
change, climate variability and other factors on seasonal
streamflow has several limitations. An important assumption
of this approach is that the vegetation-water relationship dur-
ing the study period must be stationary, which limits its ap-
plication under nonstationary conditions. In addition, vari-
ous watershed disturbances, such as urbanization, dam regu-
lations and other human activities, are considered as being an
integrated driver (other factors). Thus, the impact of each wa-
tershed disturbance (e.g., urbanization, dam regulation and
irrigation) cannot be quantified separately.

Given that the ecohydrological sensitivity prediction mod-
els were generated from only 14 large representative wa-
tersheds, an uncertainty associated with the sample size
may arise. Admittedly, a larger number of study watersheds
would yield more robust conclusions. However, the quan-
tification of vegetation impact on seasonal streamflow in-
volves tremendous data-processing analyses for each water-
shed, and there is a trade-off between the number of study
watersheds and workload.

The selection of indices and models may also give rise to
some uncertainties and limitations of the prediction models.
In this study, topographic and landscape indices were identi-
fied based on previously published studies, which were most
frequently used in studying the topographic and landscape
effects on hydrological processes. As is known, every fea-
ture can have a certain impact on the watershed hydrological
responses. For example, area, perimeter, mean elevation and
elevation differences provide basic topographic conditions
for each watershed, showing watershed heterogeneity. Slope,
flow path length (length) and slope length factor (LS) are
indices used for assessing the erosion hazard. Topographic
wetness index (TWI) is a critical topographic index related to
soil water content and surface saturation. Shannon’s diversity
index (SHDI) and Simpson's diversity index (SIDI) could be applied to indicate a patch diversity of the landscape. The ideal method is to include all indices in the analysis. Nevertheless, some of these indices are highly linearly related to others, possibly resulting in a multicollinearity problem in a prediction model. In this study, multicollinear relationships between these indices were detected and confirmed first and then used to identify the key factors mostly related to seasonal ecohydrological sensitivities by factor analysis and stepwise regression. The whole selection process is a trade-off between the model complexity and model performance. In addition, our linear prediction models fail to capture some nonlinear relationships between ecohydrological sensitivity and its influencing factors. Other methodologies, such as machine learning or neural network, could be applied to explore nonlinear relationships between ecohydrological sensitivity and its influencing factors with a sufficient sample size in future studies.

## 6 Conclusions

Ecohydrological sensitivities at the seasonal scale were quantified in 14 large watersheds across various environmental gradients in China. Our main conclusions are as follows: (1) hydrological responses were greater and more sensitive under dry conditions than wet conditions, (2) seasonal ecohydrological sensitivities were highly variable across climate gradient, dominant soil type and hydrological regime, and (3) dry season ecohydrological sensitivity could be better controlled by vegetation, topography and soil, while wet season hydrological sensitivity could be better controlled by vegetation, soil and landscape. Our study also demonstrated the usefulness of constructing an ecohydrological sensitivity prediction model for predicting ecohydrological sensitivity in ungauged watersheds or watersheds with insufficient hydrological data to help watershed managers to effectively manage hydrological impacts and risks through vegetation restoration programs.

*Data availability.* Climate data of this study can be downloaded from the National Meteorological Information Centre of China Meteorological Administration at http://data.cma.cn/ (CMA, 2008). Vegetation data (GLASS LAI product) are openly available from http://glass-product.bnu.edu.cn/ (GLASS, 2014). The MODIS land cover product can be accessed from Land Process Distributed Active Archive Centre (LP DAAC, 2015; https://lpdaac.usgs.gov/products/mcd12q1v006/). DEMs can be acquired from Geospatial Data Cloud site, Computer Network Information Centre, Chinese Academy of Sciences (http://www.gscloud.cn; Geospatial Data Cloud, 2010).

*Code availability.* Climate, vegetation, topography, soil and landscape indices of the study watersheds are freely available upon request to the corresponding author.

*Supplement.* The supplement related to this article is available online at: https://doi.org/10.5194/hess-25-1447-2021-supplement.

*Author contributions.* YH and MF proposed the analysis, designed the experiment, performed the result analysis and wrote the paper. QL and XW interpreted the results and reviewed the paper. SL, TC, WL and XL collected the data. RZ calculated landscape indices. All authors participated in the discussion (Sect. 5) and revision of the paper.

*Competing interests.* The authors declare that they have no conflict of interest.

*Acknowledgements.* The authors wish to thank the China Scholarship Council (CSC) for sponsoring Yiping Hou. We would like to thank the editor, Stacey Archfield, and the two anonymous reviewers for their constructive comments and suggestions on this paper.

*Financial support.* This paper was supported by National Program on Key Research and Development Project of China (grant no. 2017YFC0505006) and National Natural Science Foundation of China (grant no. 31770759).

*Review statement.* This paper was edited by Stacey Archfield and reviewed by two anonymous referees.

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