IJERD – International Journal of Environmental and Rural Development (2021) 12-2

Research article
erd

Impacts of Land Use-Land Cover Changes on Streamflow
and Water Balance of Stung Sangkae Catchment Using
SWAT
NARETH NUT*
Faculty of Agricultural Engineering, Royal University of Agriculture, Phnom Penh, Cambodia
Email: nnareth@rua.edu.kh

MACHITO MIHARA
Faculty of Regional Environment Science, Tokyo University of Agriculture, Tokyo, Japan

JAEHAK JEONG
Blackland Research & Extension Center, Texas, USA

BUNTHAN NGO
Royal University of Agriculture, Phnom Penh, Cambodia

SAKDANUPHOL CHAN
Faculty of Agricultural Engineering, Royal University of Agriculture, Phnom Penh, Cambodia

GILBERT SIGUA
United States Department of Agriculture, Agriculture Research Service,
Coastal Plains Research Center, South Carolina, USA

MANUEL R. REYES
Sustainable Intensification Innovation Lab., Kansas State University, Kansas, USA
Received 31 December 2020

Accepted 15 November 2021(*Corresponding Author)

Abstract Land use-land cover changes (LULCC) brought by increasing population and fooddemand could affect not only the fluxes of water, sediment, contaminants and energy, butalso ecological, physical and socioeconomic aspects in the environment. In this study, theSoil and Water Assessment Tool (SWAT) model was used to examine the effects of LULCC
on hydrological processes of Stung Sangkae catchment in Tonle Sap Basin, Cambodia. The
performance of the model was evaluated through uncertainty sensitivity analysis, calibration,and validation. The time series of LULCC were used to estimate the streamflow and the waterbalance in the catchment based on five interval years (1998, 2003, 2008, 2013, and 2018).
From 1998 to 2018, the coverages of forest land, wetland, and the paddy rice decreased by
5.1%, 1.4%, and 1.2%, respectively. The forest land and wetland were converted into
cultivated land with an increase of about 7.6% over the study periods. These changes resulted
in significant variations of water balance (2000-2018) namely: i) an increase of averageannual surface runoff (SURFQ) by 10 mm; ii) 3 mm reduction of the average annual lateralflow (LATQ); iii) 6.2 mm reduction of the average annual groundwater (GW); iv) reductionof the average annual evapotranspiration (ET) by 0.97 mm; and v) an increase of averageannual water yield by 0.9 mm. On a monthly basis, the model results had shown a reasonableagreement with the observed values as shown by the coefficient of determination (R2) = 0.41,
Nash Sutcliff efficiency (NSE) = 0.40, and percent of bias (PBIAS) = 0.34. Based on thevalidated water discharge and water balance results in 2018, LULCC have impacted theenvironmental sustainability, especially the streamflow that caused flooding at thedownstream watershed due to decline in forest cover at the watershed.
Keywords land use-land cover, Stung Sangkae Catchment, streamflow, SWAT model,water balanceⒸ ISERD

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INTRODUCTION
In Cambodia, the annual increase of population is always followed by the increasing demand forland, food, housing, and other social needs of the people. In Battambang, Cambodia in 2005, the total
population of the province was 952,306 (185,868 families) and increased to 1,066,928 (205,351
families) in 2018 (NCDD, 2010). Several studies have shown that the land changes caused by theincrease of urbanization, agricultural activities, and devastation of forest area have caused widechanges of streamflow and water balance in the watershed. As expected, there will be shortage ofwater due to the increase in water demand for all types of land use activities. However, the knowledgeof the effects of LULCC on various hydrological processes of Stung Sangkae catchment in Tonle
Sap Basin is not well understood. Additionally, the impact of LULCC on the streamflow and thewater balance in the catchment, where the research is targeted to create accessibility of important
information of water resources for sustainable resources management is not yet fully identified. Since
2005, people have cleared forested areas to cultivate maize and/or cassava. Most of these products
are being exported to Thailand. Over time, newly cleared land would require more and more fertilizer
to improve land productivity and this activity may contribute to degradation of water resources due
to eutrophication if no countermeasures are taken properly. Currently, an estimated 191,492 ha offorest cover is left, of which 150,992 ha is under the forestry administration’s management and40,000 ha is under the provincial department of the environment. However, protected areas are
increasingly under threat from land encroachment for large-scale agricultural land development(Sotheary, 2015).
As described above, the streamflow and water balance such as the surface runoff andgroundwater are being affected by LULCC. Despite progress in assessing and projecting LULCC
impacts, vulnerability and adaptation studies in Cambodia is still failing to provide sufficientunderstanding of existing vulnerabilities, thereby constraining mitigation responses, current andprojected risks in constantly changing contexts. Building resilience to LULCC variability,
understanding the hydrology-sensitive linkages between sectors and promoting sustainable
development and integrated hydrological cycle risk management require policies and plans that are
informed by scientific evidence.
To address the potential impacts of LULCC on hydrology and water balance, the Soil and Water
Assessment Tool (SWAT) model was used in Stung Sangkae catchment. Although, nowadays, there
are many hydrological models to help calculate the water discharge more accurately, easily andquickly than the traditional measurement method, SWAT was proven to be quite effective. Soil andWater Assessment Tool model, is a basin-scale model integrated with ArcGIS to help improve theaccuracy of the simulated result of streamflow from rainfall and physical properties of the basin. As
mentioned earlier, SWAT model has a good reputation for best use in agricultural watersheds and its
uses have been successfully calibrated and validated in many areas around the world (Ang andOeurng, 2018; Gassman et al., 2007). It has the most comprehensive literature database of 4200
articles compiled by the Center for Agriculture and Rural Development, Iowa State University(CARD-ISU, 2020).
OBJECTIVES
The objective of this research was to evaluate the impacts of LULCC on streamflow, surface runoff(SURFQ), lateral flow (LATQ), ground water (GW), evaporation and transpiration (ET) and water
yield in Stung Sangkae catchment in Tonle Sap Basin, Cambodia (Fig. 1).
METHODOLOGY
Site Description
This study was carried out in Stung Sangkae catchment containing the Tonle Sap Lake. This lake is
the greatest lake in South East Asia and one of the world richest biodiversity located in the NorthⒸ ISERD202

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western part of Cambodia (Fig. 1). Stung Sangkae catchment is the third largest of Tonle Sap Basinriver system with an area of 6,051 km2. Stung Sangkae River is one of the key sources of water in
Battambang, Cambodia. The natural habitats of this region form a complex network ofinterconnected landscapes and watersheds that provides important ecosystem services to the region(Killeen, 2012). The majority of the catchment area is mostly lowlands with elevations of less than
100 m above the mean sea level, and with gentle slopes. There are six (6) main soil types within thecatchment area and 13 land uses. Of the 13 land uses, 25% are planted with annual crops such as
cassava (Manihot esculenta L.), corn (Zea mays L.), sugarcane (Saccharum officinarum L.) etc. and
24% is under rice production. Battambang Province receives most of its rainfall during the southwest
monsoon from May to November, as most of the regions in Cambodia. According to the MekongRiver Commission in 2008, long-term rainfall between 1920 and 2004, with 60 years of complete
data, averaged 1,318 mm/year. Typically, there is very little rainfall from December to March (onaverage 5.6% of the annual total), and because of high temperatures and evaporation rates throughMay, there is usually little standing water in most paddy fields until June.

Fig. 1 A map of Stung Sangkae catchment showing the Great Lake, stream gauge andrainfall stations with a background of 30 m resolution DEM
SWAT Modeling
Soil and Water Assessment Tool is a physically based semi-distributed continuous time model
developed by United States Department of Agriculture-Agricultural Research Service (USDA-ARS)(Arnold et al., 1998). Soil and Water Assessment Tool can be operated to estimate, predict, andassess the effects of soil characteristics, land management, and climate change on water resource,
sediment, nutrient cycling and crop growth in the enormous complicated watersheds (Neitsch et al.,2002). Soil and Water Assessment Tool model simulates various hydrologic processes, including
surface runoff calculation, using either Natural Resources Conservation Service curve number
method or the Green and Ampt infiltration equation. For the quantification of evapotranspiration,
SWAT model offers several approaches such as, Pristley-Taylor, Hargreaves, or Penman-Monteith
methods. Groundwater flow, lateral flow and percolation are assessed through mass balance of theunderlying system (Anand et al., 2018).
In this research, the required input data of SWAT model in Stung Sangkae catchment werecollected from different sources both locally and globally. A digital elevation model (DEM) with a
30 m resolution was retrieved from the Shuttle Radar Topography Mission (SRTM). Stream/river in2010 and administrative province/district in 2014 data obtained from the open source site atⒸ ISERD

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www.opendevelopmentcambodia.net. A land use-land cover map was developed by the SERVIR
Mekong from 1998 to 2018 based on satellite imagery. A soils map of 16 soil types developed by
Crocker in 1962 and was classified based on the FAO/UNESCO in 1984 with the classification up
to two levels (0-30 cm and 30-100 cm) were utilized during the simulation process. Rainfall data
(1995‒2018) were obtained from Department of Meteorology (DoM) of Ministry of Water
Resources and Meteorology (MoWRAM) and satellite image from bias correction. Daily andmonthly streamflow data (2000‒2018) were obtained from Department of Hydrology and River
Work (DHRW) of Ministry of Water Resources and Meteorology (MoWRAW).
For a better estimation of model parameters in order to simulate the streamflow to match theobserved value, the model was calibrated manually by adjusting several default parameters. We
calibrated daily streamflow from 2000 to 2010 with a basis of LULCC from SERVIR-Mekong in
2003, where the simulation period between 1995 and 1999 serving as the warm-up period. Then themodel with modified parameters is validated by running different time period to ascertain model
consistency between the observed and simulated values. In the study, we validated daily streamflow
from 2011 to 2018 with a basis of LULC from SERVIR-Mekong in 2003. After the evaluation of
SWAT model rating, we modified different LULCC layers (1998, 2008, 2013, and 2018) as an input
parameter. All simulated results from calibration and validation were evaluated by three quantitative
statistics: i) Coefficient of determination (R2); ii) Nash-Sutcliffe efficiency (NSE); and iii) Percent
Bias (PBIAS).
RESULTS AND DISCUSSION
LULC Change Analysis
Table 1 summarized the relative areas of each land use class for the years 1998, 2003, 2008, 2013
and 2018. The result has shown that during the study period (1998-2018), the forest land, wetland,and paddy rice has decreased by 5.10%, 1.44%, and 1.20%, respectively. These land uses wereconverted into cultivated land with an increase of the agricultural land by 7.60%. The changes invarious land uses was due to increasing human influence through the development of urban area andthe process of industrialization and modernization.
Table 1 Summary of LULC change in Stung Sangkae catchment from 1998 to 2018 (%)
LULC
Agricultural land (AGRR,ORCD)
Forest (FRSD,FRSE,FRST)
Wetland Forest (WETF,WETL,WETN)
Rice (RICE)

1998
45.60
23.83
25.33
5.02

2003
47.62
20.74
24.44
6.97

2008
47.29
20.62
24.22
7.63

2013
48.07
20.43
23.99
7.25

2018
53.20
18.74
23.89
3.82

Change
7.60
-5.10
-1.44
-1.20

Model Sensitivity Analysis
In the study, we analyzed the five most sensitive parameters which influenced water quantity in
Stung Sangkae catchment namely: 1) Manning’s “n” (CH_N2); 2) Effective hydraulic conductivity(CH_K2); 3) Groundwater delay (GW_DELAY); 4) Threshold water depth in the shallow aquifer
for return flow (GWQMN); and 5) Threshold water depth in the shallow aquifer for “revap”(REVAPMN). The fitted value of model parameters was illustrated in Table 2. Sensitivity analysis
of different parameters was performed for streamflow.
Impact of LULCC on Streamflow
The model was calibrated for the 2000–2010 period, while the validation period was done from 2011
to 2018. The model performance was reasonably good with limited rainfall data as shown in Table
3. Fig. 2 presented the simulation results of LULCC in 1998, 2003, 2008, 2013 and 2018 about streamflow.
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Results of the simulation LULCC were not significantly different. However, the result of streamflow
has increased with the range from 1.6 m3/s to 781 m3/s due to the loss of forestland converted into
the agricultural land. Several simulation studies revealed that LULCC due to deforestation haveincreased the mean annual streamflow (Anand et al., 2018; Oeurng et al., 2019; Quyen et al., 2014).

Table 2 Parameters use for calibration and validation
Parameter
CH_N2
CH_K2
GW_DELAYGWQMNREVAPMN

Definition
Manning’s “n” value for the main channel
Effective hydraulic conductivity in the main
channel alluvium (mm/h)
Groundwater delay (days)
Threshold depth of water in the shallow aquifer
required for return flow to occur (mm H2O)
Threshold water depth in the shallow aquifer for“revap” ( mm )Default range-0.01‒0.3
0‒500

Fitted value
0.22
5

0‒500
0‒5000

40
1500

0‒500

500

Table 3 Summary result of model performance efficiency evaluation of the monthly stream
flow for Stung Sangkae catchment
Calibration (2000-2010)

Validation (2011-2018)

A basis of LULC from SERVIR-Mekong
R2
NSE
PBIAS

1998
0.40
0.40
1.06

2003
0.41
0.40
0.34

2008
0.41
0.40
-0.19

2013
0.41
0.41
-0.60

2018
0.41
0.40
0.88

1998
0.28
0.21
31.24

2003
0.28
0.22
30.52

2008
0.28
0.22
30.05

2013
0.28
0.22
29.73

2018
0.28
0.21
31.10

Fig. 2 Daily and monthly streamflow (cm) in calibration and validation periods
Impact of LULCC on Water Balance
Due to LULCC from 1998 to 2018, the average annual change in SURFQ, LATQ, GW, ET and water
yield was approximately 277 mm, 77 mm, 297 mm, 764 mm, and 668 mm, respectively. Fig. 3
presented the spatial distribution of water balance in Stung Sangkae catchment under the gauging
station. The water yield and the surface runoff came to catchment has increased by 0.9 mm and 10Ⓒ ISERD

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IJERD – International Journal of Environmental and Rural Development (2021) 12-2mm, respectively; the lateral flow, the ground water and the evapotranspiration has declined by 3
mm, 6.2 mm, and 0.97 mm, respectively. Moreover, the changes shown in Fig. 3, in terms of thedifferent hydrologic components such as surface runoff, water yield, and ET were in agreement withthe results reported by other researchers (Anand et al., 2018; Dey and Mishra, 2017; Kundu et al.,2017; Remondi et al., 2016; Wagner et al., 2017). However, we noted that the impacts of LULCC on
the water balance varied significantly for each sub-basin due to urbanization. Our results were similar
to several studies that investigated the correlation between urbanization and the water balance intropical regions (Anand et al., 2018; Gumindoga et al., 2014; Remondi et al., 2016; Wagner et al.,2013).

Fig. 3 Change in water balance from 1998 to 2018 for Stung Sangkae catchment
CONCLUSION
Based on the LULCC data provided by SERVIR Mekong, results showed that from 1998 to 2018,
the forest land, wetland, and paddy rice had decreased by 5.10%, 1.44%, and 1.20%, respectively.
These led to the increase of agricultural land by 7.6%. This increase in agricultural land resulted in
the increase of average annual surface runoff (SURFQ) by 10 mm, reduction of 3 mm in the averageannual lateral flow (LATQ), reduction of the average annual ground water (GW) by 6.2 mm, decreaseof 0.97 mm in average annual evapotranspiration (ET), and an increase of average annual water yieldby 0.9 mm. Moreover, the model captured a reasonable agreement with the observed values inmonthly basis. Based on the validated water discharge and water balance results in 2018, LULCC
have impacted the environmental sustainability, especially the streamflow that caused flooding at thedownstream watershed due to declined forest cover at the watershed.
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ACKNOWLEDGEMENTS
This research and publication are made possible by the generous support of the American People
provided to the Royal University of Agriculture through Partnerships for Enhanced Engagement in
Research (PEER) Cycle 7 funded by the United States Agency for International Development(USAID) and implemented by the National Academy of Sciences (NAS) under Sponsor Cooperative
Agreement No. AID-OAA-A-11-00012 of Subaward Number: 2000010295. The contents are thesole responsibility of the authors and do not necessarily reflect the views of NAS, USAID or theUnited States Government. Moreover, the research and publication are made possible by thegenerous support of the American people through support by the United States Agency forInternational Development to the Feed the Future Innovation Labs for Collaborative Research on
Sustainable Intensification (Cooperative Agreement No. AID-OAA-L-14-00006, Kansas State
University). Thanks to Kelly Robbins, Senior Program Officer, the National Academy of Sciences(NAS), for her support and guidance on the research grant implementation, and also thanks to theUnited State Department of Agriculture (USDA), as well as the Institute of Technology of Cambodia(ITC), and International Fertilizer Development Center (IFDC) for data provision, technical support,
assistance, and consultation.
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