Agricultural Water Management 201 (2018) 107–117

Contents lists available at ScienceDirect

Agricultural Water Management
journal homepage: www.elsevier.com/locate/agwat

Identifying the future water and salinity risks to irrigated viticulture in the
Murray-Darling Basin, South Australia

T⁎

V. Phogata,b, , J.W. Coxa,c, J. Šimůnekd
aSouth Australian Research and Development Institute, GPO Box 397, Adelaide, SA, 5001, Australia
CCS Haryana Agricultural University, Hisar, 125 004, Indiac
The University of Adelaide, PMB1 Glen Osmond, SA, 5064, AustraliadDepartment of Environmental Sciences, University of California, Riverside, CA, 92521, United Statesb

A R T I C L E I N F O

A B S T R A C T

Keywords:
Climate change
Viticulture
Irrigation demand
Salinity
HYDRUS-1D

Water and water related salinity risks to viticulture were assessed by running the HYDRUS-1D model with 100
ensembles of downscaled daily meteorological data obtained from the Global Climate Model (GCM) for
2020–2099. The modeling output was evaluated for seasonal irrigation requirements of viticulture (Ir), root zone
soil salinity at the beginning of the new season (ECswi), and the average seasonal salinity (ECsw) for all 100
realizations for four 20-year periods centred on 2030 (2020–2039), 2050 (2040–2059), 2070 (2060–2079), and2090 (2080–2099). The model showed a 4.2% increase in the mean seasonal Ir of viticulture during 2020–2039
as compared to Ir of 350.9 mm during 2004–2015. Similarly, the mean seasonal Ir increased by 7.5, 10.9, and16.9% during 2040–2059, 2060–2079, and 2080–2099, respectively, as compared to 2004–2015. These projections indicate that viticulture can face signiﬁcant deﬁcit conditions, which may have a drastic impact on thesustainability and productivity of the grapevine. Likewise, the average median ECswi increased by 40% during
2020–2039 as compared to the 2004–2015 mean ECswi value of 1.63 dS/m, but remained below the threshold(ECsw = 4.2 dS/m) for viticulture. The median seasonal ECswi almost doubled (3.15 dS/m) during 2040–2059,
varied from 1.73–8.15 dS/m during 2060–2079, and increased more than three times during 2080–2099 tosurpass the threshold salinity for grapevines. Similarly, the seasonal average root zone salinity (ECsw) showed a
47% increase during 2020–2039 over the baseline salinity. It continued increasing at a growing pace during
2040–2059 (1.5–8.64 dS/m) and 2060–2079 (2.78–9.52 dS/m), and increased to almost three times (6.04 dS/m)during 2080–2099 compared to the corresponding baseline salinity (1.97 dS/m). The continued presence of highsalt concentrations in the root zone can signiﬁcantly aﬀect the growth, yield, and wine quality. The modeling
results indicate that soil salinity at the beginning of the vine season and the average seasonal salinity are crucial
factors that may need special management to sustain the viticulture in this region.

1. Introduction
Water availability and climate change have played a crucial role inthe story of human development. The lack of available water for agricultural production, energy projects, other forms of anthropogenic
water consumption, and ecological use is already a major issue in many
parts of the world that is expected to grow more severe with increasing
population, higher food demand, rising temperatures, and changing
precipitation patterns (Elliott et al., 2014). Climate change is expected
to have a signiﬁcant impact on various economic sectors (IPCC, 2014)
but especially on agriculture because crops are heavily inﬂuenced byweather conditions during their life cycles (Bernetti et al., 2012). Future
projections foresee that climate change could reduce plant water⁎

availability and increase agricultural area under drought, aﬀecting crop
production (Collins et al., 2013). A rise in temperatures, for instance,
could lead to soil moisture deﬁcits and a growing risk of vegetation
desiccation due to increased evapotranspiration and decreased soil
moisture (Goyal, 2004; Riediger et al., 2014). On the other hand, increased CO2 concentrations in the atmosphere may provide an enhanced opportunity for higher carbon assimilation by crops and lead toan increase in the crop yield (Wang et al., 2012), provided that other
inputs are not limiting the crop growth. Ecological and economic consequences of climate change on agricultural ecosystems are expected tovary widely depending on the spatial patterns of land cover, land use
practices, and regional climate variability (Bindi and Olesen, 2011;
Iglesias et al., 2012).

Corresponding author at: South Australian Research and Development Institute, GPO Box 397, Adelaide, SA, 5001, Australia.
E-mail addresses: vinphogat@gmail.com, vinod.phogat@sa.gov.au (V. Phogat).

https://doi.org/10.1016/j.agwat.2018.01.025
Received 29 August 2017; Received in revised form 23 January 2018; Accepted 26 January 20180378-3774/ © 2018 Elsevier B.V. All rights reserved.

Agricultural Water Management 201 (2018) 107–117

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consequently poor decision-making and adaptation (Gohari et al.,2013).
There is a large number of models (e.g., https://soil-modeling.org/
resources-links/model-portal/model-collection; Vereecken et al., 2016)that have been used in similar studies as ours. All these models havetheir own pros and cons depending on their capabilities of addressing
climate, soil, and crop variables for the future climate. Among these,
HYDRUS-1D (Šimůnek et al., 2016) is one of the models that has been
most widely used for solving a wide range of irrigation related problems(see https://www.pc-progress.com/en/Default.aspx?h1d-references),
including those similar to ours. The key characteristics and recent developments of HYDRUS-1D can be found in its technical manual andpublished literature (e.g., Šimůnek et al., 2016). The main features of
HYDRUS-1D that are required in our study include an option to trigger
irrigation when a prescribed pressure head is reached at a speciﬁed soil
depth, to evaluate root water uptake as a function of soil water content
and daily potential transpiration, and to consider the coupled transportof water and solutes in the soil. HYDRUS-1D can also calculate surface
runoﬀ, evaporation, and inﬁltration ﬂuxes for atmospheric boundary
conditions, and drainage ﬂuxes through the bottom of the soil proﬁle.
Hence, HYDRUS-1D was selected to conduct the long-term simulations
for identifying future risks to irrigated viticulture.
This modeling study involves 100 ensembles of GCM projections
and considers a wide range of uncertainty in climate variables.
Irrigation requirements are evaluated using the HYDRUS-1D numericalmodel and a ﬁne temporal resolution (daily) of climatological data. The
goal of this study is to understand how the irrigation demand of viticulture is impacted by climate change and what unforeseen impacts(e.g., salinity) could arise due to the variability in the water use.
Understanding the impacts of climate change should help in eﬀectively
adapting to it and mitigating its eﬀects for sustainable viticulture.

Australia has the largest area under arid and semi-arid climate in theworld, with about 80% of the country receiving rainfall of less than
600 mm per year (Mushtaq et al., 2013). South Australia represents oneof the driest regions in Australia. Climate models expect a 10–20%
reduction in cold season rainfall in much of the southern Australia(CSIRO and BoM, 2016). A greater volatility in weather patterns is also
projected, particularly more frequent and more severe droughts (CSIRO
and BoM, 2016). South Australia is a major grape and wine producing
region in Australia, contributing 48% of the total wine grape crush.
92% of vineyards in South Australia use supplementary drip irrigation(ABS, 2015). The South Australian (SA) part of the Murry-Darling basin(Riverland) is the largest grapevine producing region, accounting for
61% of the South Australian production and 28% of the national production (Hayman and McCarthy, 2013). Climate change projections for
the Riverland show drier and hotter conditions, with an 11.4–21.7%
decrease in annual rainfall, a 1.9–3.6 °C increase in maximum temperatures, and a 1.5–3.1 °C increase in minimum temperatures by theturn of the 21st century (Charles and Fu, 2015). These projections canhave a dramatic impact on river ﬂow conditions, water allocation in theRiverland, and the future security of the quantity and quality of irrigation water for the irrigated horticulture including viticulture.
Water requirements of the viticulture production in the Riverland
region are met almost exclusively by irrigation from the Murray River.
The extent of ﬂow in the river decides the volume of water allocations
to irrigated industries. Given the economic importance of grapevine in
the region, a high seasonal variability of rainfall and water allocations,and an imminent prospect of climate change, it is critical to assess the
future irrigation demand and related risks to viticulture. Reduced ﬂows
in the Murray River and associated restricted irrigation may result inincreased root zone salinity to the detriment of wine quality. Even if
rainfall levels are unaﬀected, the risk of intense droughts will increase
due to the augmentation of the atmospheric evaporative demand as aresult of warming (Alcamo et al., 2007). Increased temperatures coupled with reduced rainfall may increase the salt accumulation in upper
soil layers and hence aﬀect plant growth (Cullen et al., 2009). It isessential to understand the impact of future climate drivers on irrigation requirements and soil salinity so that appropriate adaptation andmitigation strategies can be adopted for sustainable viticulture production.
Grapevine growth is sensitive to various environmental factors, including atmospheric CO2 concentrations, air temperatures, and water
availability (Salazar-Parra et al., 2010), and is thus vulnerable to climate change (Fraga et al., 2014; Kizildeniz et al., 2015). The mostcritical impact of climate change observed at the global scale is theadvancement of maturity of grapes by 4–8 days (Jones et al., 2005;
Webb et al., 2011). Webb et al. (2007) projected a 50-day advancementin the maturity of grapes in the Coonawarra region of South Australia
by 2050. The eﬀects of global warming and associated changes inprecipitation patterns may alter terroirs (White et al., 2009), i.e., unique combinations of climate and soils that are used to produce wines of
distinctive styles (Webb et al., 2012). However, the information on the
future irrigation requirements of viticulture and the magnitude of otherrelated risks (salinity) in the soil is sparse. A number of modeling studies have attempted to evaluate the eﬀects of climate change on water
use in agriculture for other crops (Fischer et al., 2007; Elgaali et al.,2007; De Silva et al., 2007; Xiong et al., 2010; Gondim et al., 2012; Saveet al., 2012; Lee and Huang, 2014; Woznicki et al., 2015). Most of thesestudies showed an increase in the irrigation demand for typical annual
crops. However, a majority of these studies were performed using a low
resolution data (e.g., monthly temperature and precipitation data) andthe impact of climate change on the irrigation demand was only examined for a small number of scenarios that may not have captured thewide variability and uncertainty in the projections of climate models.
Using only a limited number of ensembles of Global Climate Model(GCM) projections may result in a limited understanding of plausible
future climate scenarios, unreliable projections of the future, and

2. Materials and methods
2.1. Description of the study area
The South Australian Murray-Darling Basin region (Riverland)
covers 56,703 square kilometers or about 7% of the state’s land area
(Fig. 1). The landscape varies from the low-lying coastal plains to theﬂat lands of the Mallee. The Murray River is a dominant and inﬂuential
feature of the region due to the importance of its waters for irrigatedagriculture and the environment and in meeting domestic, livestock,and industrial needs. It supports a wide range of ﬂora, fauna, naturalenvironments, and human activities. Most irrigated industries are
spread along the Murray River corridor of about 10 km on either side.
The region’s climate can be characterized as Mediterranean, experiencing hot, dry summers and cold, wet winters.
The Riverland is famous in Australia for irrigated perennial horticulture and viticulture production. The productivity and sustainabilityof vineyards are fully dependent on the water allocation from the Murry
River. However, water ﬂow in the Murray River is highly erratic anddependent on the extent of rainfall in the eastern high reaches, which
feed the river system. During drought years, the water allocation issigniﬁcantly reduced; for example, during 2006–07 the water allocation
was only 18% of the total allocation. Hence, inadequate rainfall has adirect impact on ﬂow conditions in the Murray River, and South
Australia is usually impacted the most, being on the tail end of thebasin.
To undertake the long term (2015–2099) modeling study for evaluating future water requirements of viticulture and salinity dynamics inthe soils, the Loxton Research Centre (34.44°S and 140.59°E) was selected as a representative site. It has the typical Riverland climate andfalls within the central part of the viticulture production region. The
climate parameters were obtained from the Bureau of Meteorology for
Loxton, which is about 1 km away from the study site. Annual average
rainfall and reference crop evapotranspiration (ET0) during the last108

Agricultural Water Management 201 (2018) 107–117

V. Phogat et al.

Fig. 1. The location of the study area.

2.3. Model description

100 years amounted to 265 and 1369 mm, respectively, which indicatesa strong need for irrigation for crop production.
Prior to conducting the long-term simulations on future climate, themodel was run on the current climate (1st July 2004–30th June 2015)
data for the study site. This was done to stabilize the initial conditions
for the long-term simulations and to compare the current climate resultswith the future climate projections.

The HYDRUS-1D software can simulate one-dimensional variablysaturated water ﬂow, heat movement, and transport of solutes involved
in sequential ﬁrst-order decay reactions (Šimůnek et al., 2016). The
governing one-dimensional water ﬂow equation is described as follows:

∂θ
∂ ⎛
∂h
=
+ K (h) ⎞ − S (h, hs , z , t )
K (h)
∂t
∂z ⎝
∂z
⎠

2.2. Soil characteristics

3 −3

where θ is the soil water content (L L ), t is the time (T), h is the soil
water pressure head (L), hs is the osmotic head (L), z is the verticalcoordinate (positive upwards) (L), K(h) is the unsaturated hydraulicconductivity function (LT−1), and S(h,hs,z,t) is the sink term accounting
for an actual volume of water uptake by plant roots from a unit volume
of soil per unit of time (L3L−3T−1). Water extraction S(h,hs,z,t) from thesoil is computed according to the Feddes macroscopic approach (Feddes
et al., 1978). In this method, the potential transpiration rate, Tp, is
distributed over the root zone using the normalized root density distribution function and multiplied by the dimensionless water and salinity stress response functions. Hence, this model evaluates plant root
water uptake rates based on the local soil water and osmotic pressure
heads at any point in the root zone. Potential transpiration (Tp) is reduced below its potential value when the soil is no longer capable ofsupplying the amount of water required by the plant under the prevailing climatic conditions. Potential root water uptake is further reduced by the osmotic stress, resulting from the salinity of irrigationwater and the presence of salts in the soils. The eﬀect of water andsalinity stresses was assumed to be multiplicative so that diﬀerent stressresponse functions could be used for water and salinity stresses. Criticalvalues of pressure heads for root water uptake were taken from previous investigations on grapevine (Phogat et al., 2017) in the study
area. The threshold and slope model parameters were obtained from theprevious regional study (Zhang et al., 2002) evaluating salinity
thresholds (ECe = 2.1 dS/m) and percent reductions (12.8%) in different root stocks of grapevine.
The temporal and spatial distribution of soil solution salinity (ECsw)
was modeled as a non-reactive solute (e.g., Ramos et al., 2011; Wanget al., 2014; Phogat et al., 2014). These studies demonstrated that thisapproach could be successfully used in environments under intensive
irrigation and fertigation management. The longitudinal dispersivity
was assumed to be one tenth of the modeling domain (Cote et al., 2003)
and the molecular diﬀusion coeﬃcient for salts in water was considered
to be 1.66 cm2/day (Phogat et al., 2014, 2017). Since it is diﬃcult topredict changes in the river water quality under the future climatechange, the ECiw data for irrigation water was based on the water

The soils in the study area (Riverland) are characterized by thepresence of light-textured Aeolian deposits at the soil surface, underlain
by a heavy-textured soil at variable depths. These soils are known as
Duplex soils (Chittleborough, 1992), which covers a large cultivatedarea in Australia and are present is signiﬁcant extent in the Riverland.
However, there exists a huge variability of soils at diﬀerent locations in
the Riverland (Hall et al., 2009). The light-textured surface soils(0–30 cm) are predominately composed of sand particles with only asmall clay content (sand 90–94%, clay 5.5–9%, and silt 0.5–1.3%; Hallet al., 2009), whereas the soils at lower depths (below 30 cm) containappreciable amounts of clay content (20–40%). The soil texture at the
study site varies from a sandy loam topsoil (0–30 cm) overlying a sandy
clay loam subsoil (30–100 cm). The organic carbon content in the soil
varies from 0.3 to 1.14%, being higher in the surface soil, and pH increases from 7.8 to 8.1 from the soil surface to the 1 m depth. The soil
hydraulic parameters used in modeling were estimated from the particle size distribution and bulk density data from the study site. The soil
hydraulic parameters used in this investigation are given in Table 1.
Similar hydraulic parameters have also been used in other related
studies (Phogat et al., 2016, 2017) in the Riverland where HYDRUS has
been calibrated and validated for spatiotemporal water content distribution in the soil under viticulture.

Table 1
Soil hydraulic parameters used in the modeling study.
TexturallayersSandy
loam
Sandy clay

Soil
depth
(cm)

Bulk
density(g cm−3)

0–30
30–100

Soil hydraulic parametersθrθs(cm3 cm−3)αn(cm−1)Ksl(cm day−1)

1.6

0.05

0.37

0.031

1.94

120.81

0.5

1.5

0.07

0.41

0.02

1.26

14.14

0.5

(1)

109

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global climate model (GCM) projections for six climate variables:
rainfall, maximum and minimum temperature, areal potential evapotranspiration (APET), solar radiation, and vapor pressure deﬁcit. The
projections were obtained for intermediate and high emission scenarios, i.e., for representative concentration pathways RCP4.5 and
RCP8.5, respectively. Since the climate projections have a strong
variability, 100 stochastic datasets were generated by the downscaling
model (NHMM) for diﬀerent GCMs. Rather than selecting a few ensembles of a suite of models, as usually done in many studies (Fischer
et al., 2007; Xiong et al., 2010; Gondim et al., 2012; Save et al., 2012;
Lee and Huang, 2014; Woznicki et al., 2015), we adopted all 100 ensembles of a better performing model (Charles and Fu, 2015) so that theuncertainty in climate projections can be adequately addressed inmodeling scenarios. The GCM (GFDL ESM2 M) data downscaled for
RCP8.5 for Loxton in the Riverland were used in the current modelingstudy to consider the worst-case scenario for the water related risks toviticulture. Daily APET and rainfall data for the simulation period(2015–2099) were used to develop input parameters for the HYDRUS1D model.
A quick assessment of seasonal (1st July to 30th June) deviations indownscaled rainfall data for Loxton revealed a strong decreasing trend
throughout the 21st century (Fig. 2). During the ﬁrst 20-year period(2020–2039), a strong likelihood of drought conditions at Loxton
during 2025, 2029, 2035 and 2039 seasons is projected (Fig. 3a), whichshows that dry conditions often occur after every ﬁve years. Average
rainfall during this period is projected to decline by 13.7% as compared
to average rainfall during the last 100 years (1916–2015). Similarly,
during the second 20-year period (Fig. 3b), the reduction in medianrainfall increased to 17.8%, and by further 32.7% during the lastquarter of the century. The projections showed that one-half of years(10 years) is expected to receive seasonal rainfall less than 200 mm
during the second 20-year period (2040–2059). The second half of the
21st century is projected to have a more dramatic reduction in seasonalrainfalls. Especially during the 2080–2099 period, median rainfall
plummeted to less than 200 mm (Fig. 3d).
Similarly, the variation in the seasonal APET among all 100 realizations downscaled for Loxton for all 20-year future periods is box
plotted in Fig. 4. The seasonal median APET during the ﬁrst 20-year
period (2020–2039) ranged from 1332.8 to 1368.6 mm, which showed
only a small reduction in the average median value (1356.6 mm)compared to the average seasonal reference crop evapotranspiration(ET0 = 1369 mm) of the last 100 years, i.e., from 1916 to 2015. The
maximum median seasonal APET was observed during 2039. Similarly,
during the second 20-year period (2040–2059), the seasonal APET
varied from 1273 to 1473 mm and the average median APET slightly
increased (0.6%) as compared to the last 100 years APET. However,during the third (2060–2079) and fourth (2080–2099) 20-year periods,
the average median APET increased by 2.5 and 5.0%, respectively,
compared to the average 100-year value. Median seasonal APET of allquality analysis conducted by the Murray Darling Basin Authority at
Berri during 2004–2015. Since the measured ECiw values for several
irrigation schedules were missing, the average measured value of ECiw
(0.3 dS/m) during the 2004–2015 period was considered in all modeling simulations. The average salinity of rainfall in the Mildura region,
which is close to the SA Riverland, has been reported as 0.12 dS/m(Cresswell et al., 2010) and was adapted in the present modeling investigation.
2.4. Irrigation scheduling
The trigger irrigation option available in HYDRUS-1D (Dabach
et al., 2013) was used to generate irrigation schedules for grapevine.
Irrigation is triggered when the predeﬁned suction level in the soil
proﬁle is reached, the timing of which depends on the daily climate
conditions, plant water requirements, soil texture, and water availability in the soil proﬁle. Typically, irrigation is triggered using tensiometers, which are widely used for irrigation scheduling, including invineyards. Tensiometers measure the suction (pressure head) at the
point where the ceramic porous cup is placed in the soil and irrigation isapplied when the suction (e.g., 60 kPa for grapevines) is reached. Similarly, in HYDRUS-1D, when the suction in the soil reaches the trigger
value (e.g., 60 kPa), the irrigation of speciﬁed duration (5.5 h) and rate
(4.364 cm/day) is automatically applied. Total amount of irrigation
thus applied (10 mm/day/event) is similar to the amount normallyapplied to grapevine in the Loxton region (ICMS, 2007). The trigger
point in this study was located at a 30-cm soil depth, which is similar toother ﬁeld (Soar and Loveys, 2007) and modeling (Phogat et al., 2017)
studies in this region and coincides with the maximum root activity for
viticulture. Other studies also used a similar suction for irrigating
grapevines (Edwards and Clingeleﬀer, 2013) at a 30-cm soil depth forwell-watered conditions. The use of the same trigger irrigation option
used for current climate (2004–2015) matched the water budget
guidelines for 100% yield of grapevine in the Riverland (ICMS, 2007).
2.5. Domain depth and initial conditions
The simulation domain depth was selected based on the maximum
rooting depth of grapevine (100 cm) reported in the literature andprevious modeling studies on grapevine in the study area (e.g., Phogat
et al., 2017). Measured values from the experimental site were used as
the initial conditions for water content and soil solution salinity (ECsw)
for current climate (2004–2015). However, the terminal (30th June2015) water (0.09–0.28 cm3cm−3) and ECsw (0.68–2.35 dS/m) values
for the current climate were imposed as initial condition for the futureclimate (1st July 2016–30th June 2099) simulations. These values
provide a link between the modeling of future climate scenarios and thecurrent climate. The upper boundary condition for water ﬂow was set toatmospheric conditions with surface runoﬀ, and the bottom boundary
condition was set to free drainage. The concentration ﬂux boundary
condition was used at both top and bottom boundaries for solutetransport.
All simulations were performed on a daily basis from 1st July 2015
to 30th June 2099 for all 100 ensembles of downscaled climate data.
However, the modeling outputs of irrigation requirements and rootzone salinity dynamics have been reported from 1st July 2019 to 30th
June 2099 to align it with the 20-year periods (2020–2039, 2040–2059,
2060–2079, and 2080–2099) of future climate projections (Charles andFu, 2015).

200
100
0
-100
-200

2.6. Climatic parameters for modeling-300

The input parameters for HYDRUS-1D for the future climate scenarios were developed from a set of downscaled projections generated
by the Goyder Institute for Water Research for South Australia (Charles
and Fu, 2015). These projections were downscaled from a suite ofFig. 2. Predicted deviations of seasonal (1st July to 30th June) rainfall from the historicalmean value (265 mm) in 100 realizations of the downscaled GCM (GFDL ESM2 M) data
for Loxton.

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V. Phogat et al.

Fig. 3. Variability in seasonal rainfall (mm) at Loxton in 100 realizations of downscaled GCM data during a) 2020–2039, b) 2040–2059, c) 2060–2079, and d) 2080–2099 periods.

100 ensembles showed a linear increasing trend (R2 = 0.59–0.74)
during all 20-year time periods at Loxton.
Daily crop evapotranspiration (ETC) of grapevine was then estimated (Allen et al., 1998) using daily APET values and local crop
coeﬃcients (Kc). The Kc coeﬃcients for grapevine for local conditions
were obtained from the Irrigation Recording and Evaluation System(IRES) developed by the Crop Management Service (Rural Solutions SA,
2011). The leaf area index (LAI) for grapevine was taken from Nguyen
et al. (2013), which was estimated in a local vineyard. Similar Kc and
LAI values were adopted every year, assuming similar canopy and wellgrown vine conditions. The values of daily potential evapotranspiration(ETC) and LAI, along with daily rainfalls at the study site during thesimulation period, were then used as time-variable boundary conditionsin the model. 100 simulations of daily input data were used to run
HYDRUS-1D and to simulate water requirements and salinity dynamics

in the soil from 1st July 2015 to 30th June 2099. However, the results
reported below are in 20-year blocks (2020–2039, 2040–2059,
2060–2079, and 2080–2099) to align them with the climate projections. The model-triggered irrigation requirements (Ir) and the rootzone soil solution salinity at the beginning (September, ECswi) andaverage seasonal root zone salinity (ECsw) are processed on a seasonalbasis (1st July–30th June) for all 100 simulations.
3. Results and discussion
3.1. Seasonal irrigation and salinity in the current climate
The data on seasonal irrigation (Ir) and average rootzone salinity(ECsw) and salinity at the beginning of the season (ECswi) for current
climate is presented in Fig. 5. The amount of seasonal Ir varied from

Fig. 4. Deviations in yearly (1st July to 30th June) areal potential evapotranspiration (APET) in 100 realizations of downscaled GCM data for Loxton during a) 2020–2039, b) 2040–2059,
c) 2060–2079, and d) 2080–2099 periods.

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V. Phogat et al.

Fig. 5. Seasonal irrigation (Ir), soil solution salinity at the
beginning (ECswi) and seasonal average (ECsw) during thecurrent climate (2004–05 to 2014–15).

received higher rainfall than the mean of 265 mm of the past 100 years
at Loxton. The projected increase in the irrigation requirements during
this period is much higher than the corresponding values observed
during the previous 20-year period (Fig. 7b) because below average
rainfall was projected by the climate models during this time. The
maximum projected outlier was 460 mm, which is 30% more than themean current baseline value. However, the minimum outlier may
plummet as low as 260 mm. Hence, there exists a wide variability in theseasonal Ir for viticulture during this period. These scenarios indicatethat viticulture can face signiﬁcant deﬁcit conditions. This may have adramatic impact on the sustainability and productivity of the viticulturein the region.
The simulated yearly seasonal Ir of viticulture at Loxton during
2060–2079 varied from 240 to 480 mm, showing a 100% variability indiﬀerent realizations (Fig. 6c). The average median seasonal Ir increased by 10.9% compared to the corresponding current baseline
value (350.9 mm). Simulated seasonal Ir for viticulture again showed astrong relationship with the seasonal rainfall at Loxton. For example,
high rainfall years (2060, 2065, 2072, and 2077), which normally occur
every ﬁve years, had relatively lower water requirements. Conversely,
the irrigation requirement of viticulture increased during low seasonalrainfall years (2064, 2067, 2070, 2076, and 2078). Deviations in theseasonal Ir over the baseline in diﬀerent realizations showed an increasing trend over the years during this period (Fig. 7c).
Similarly, Ir continued to increase during the last 20-year(2080–2099) period of the 21st century (Fig. 6d). The seasonal Ir varied
from 280 to 500 mm, and the average median Ir increased by 16.9%
compared to the current baseline irrigation requirement. The occurrence of drought years during this period is projected to be more frequent and longer lasting compared to previous decades. Hence, waterrequirements of viticulture were also projected to increase in the same
fashion. For example, the periods during 2080–2081, 2086–2087,
2091, 2093, and 2096–2098 are projected to have higher irrigation
requirements. Even in the 2092 year, which had the lowest projected
median Ir (380 mm) of this period, it was 8.3% higher than the current
baseline value (350.9 mm). The deviations of seasonal Ir from the current Ir also showed an increasing trend over the years, which means thatwater requirements are expected to increase during this period(Fig. 7d).
The seasonal Ir for each ensemble and year is plotted in Fig. 8
against the corresponding seasonal rainfall to highlight the degree ofcorrelation between these two values. The seasonal Ir showed a linear
relationship (R2 = 0.56–0.66) with seasonal rainfall during all 20-year
periods. The seasonal Ir decreased linearly with an increase in theamount of rainfall received during the same period, indicating a strong
dependence of irrigation requirements on rainfall. The modeling results
indicated a continued upsurge of the water demand for irrigation for

180–430 mm and being higher during the less rainfall years(2006–2009). However, the average root zone salinity (ECsw and ECswi)
showed an increasing trend as during the same period. It shows that
extent of seasonal rainfall had tremendous impact on the root zone
salinity dynamics irrespective of normal irrigation application. Whenthe drought condition broke during 2010 and annual rainfall (542 mm)exceeded more than double of 100 years average, the irrigation requirement drastically reduced and remained half of the 11 years
average (330.9 mm) leading to a decrease in soil salinity. Notably, mostof the rainfall in the study area is received during winter season which
may generate higher leaching fraction due to less evapotranspiration
demand and hence greater salt leaching eﬀect. Cucci et al. (2016) also
found similar impact of winter season rainfall under the Mediterranean
climate in a sandy loam soil. Overall, the seasonal salinity and averagesalinity (1.97 dS/m) during the entire period of current climate(2004–2015) remained below threshold (ECsw = 4.2 dS/m) for viticulture.
3.2. Future irrigation requirement for viticulture
The extent of variability in the seasonal irrigation requirements (Ir)of viticulture during the 2020–2039 period projected by the model for
100 diﬀerent yearly realizations of meteorogical data is presented in thebox-plots in Fig. 6a. The seasonal Ir is in close agreement with projectedseasonal rainfall (Fig. 3). The median Ir values ﬂuctuated similarly as
rainfall received during the season. The median seasonal Ir during 2025,
2032, 2035, and 2039 increased by 9, 6, 9, and 6%, respectively,
compared to the average median Ir of 366 mm. Unavailability of water
for irrigation during these crucial intermittent dry years can have asigniﬁcant impact on the growth and yield of grapevine and the wine
quality. On the other hand, the reduction in seasonal Ir during highrainfall years (2027, 2028, 2034, and 2038) ranged between 7 and 10%
compared to the average median Ir. Overall, the mean seasonal Ir during
2020–2039 increased by 4.2% compared to the corresponding Ir requirement of 350.9 mm during 2004–2015. Deviations in the seasonal Ir
were estimated by subtracting the average seasonal Ir (350.9 mm)
during 2004–2015 from the seasonal Ir for each ensemble in diﬀerent
years (Fig. 7). The data showed that there was a slightly declining trend
among yearly mean values of Ir over this period (Fig. 7a).
During 2040–2059, the seasonal irrigation requirements of viticulture at Loxton were projected to vary from 260 to 460 mm in all
ensembles. However, the median seasonal Ir remained mostly higher
than the current value (350.9 mm), except during few low Ir seasons(2041 and 2056) (Fig. 6b). During this period, the average medianseasonal water requirement of viticulture increased by 7.5% comparedto the current requirement for 2004–2015. The seasonal irrigation requirements Ir were low in 2041 and 2056, which were wetter years that112

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Fig. 6. Predicted variability in the seasonal irrigation requirement (Ir) for viticulture at Loxton during the a) 2020–2039, b) 2040–2059, c) 2060–2079, and d) 2080–2099 periods.

increase over the years (Fig. 9a) despite irrigations being triggered at arequired pressure (60 kPa). However, there was a slight reduction in the
median ECswi during 2034, which coincided with higher rainfall during
two preceding seasons and when the occurrence of some high-intensity
rains could have leached a fraction of root zone salts out of the crop
root zone. But the ECswi increased again during 2035, which was acomparatively dry year. Despite these seasonal salinity dynamics, themedian root zone salinity remained below the crop threshold level(ECsw = 4.2 dS/m, the blue line in Fig. 9) over the entire 20-year period(2020–2039), which indicates a low water-related salinity hazard
during this period. However, some max outliers (see red crosses inviticulture during the whole 21st century in response to a reduction inseasonal rainfall. Hence, water security could be an important issue for
ensuring the viticulture production under the projected climate change.
Therefore, water deﬁcit conditions or low water allocations during theviticulture growing season can pose a signiﬁcant threat to the sustainability of grapevine in the Riverland.
3.3. Impact of climate change on root zone salinity dynamics
The root zone salinity at the beginning of the new viticulture season(ECswi) in September during the 2020–2039 period showed a gradualFig. 7. Deviations in the model-predicted seasonal irrigation requirements of viticulture at Loxton from the mean baseline (2005–2015) value (350.9 mm) during the a) 2020–2039, b)
2040–2059, c) 2060–2079, and d) 2080–2099 periods.

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Fig. 8. The relationship between predicted seasonal Ir of viticulture and downscaled seasonal rainfall at Loxton during the a) 2020–2039, b) 2040–2059, c) 2060–2079, and d) 2080–2099
periods.

Fig. 9. Predicted variability in the root zone soil salinity at the beginning of the viticulture season (ECswi) at Loxton during the a) 2020–2039, b) 2040–2059, c) 2060–2079, and d)
2080–2099 periods. The blue line represents the salinity tolerance threshold for viticulture. (For interpretation of the references to colour in this ﬁgure legend, the reader is referred to the
web version of this article.)3.15 dS/m compared to the corresponding mean value during thebaseline period (1.63 dS/m), indicating a signiﬁcant salt deposition in
the root zone. Only 10% of realizations showed seasonal ECswi higher
than the crop threshold during this period. These salts can pose a serious salinity-related threat to the vine growth and yield, and the wine
quality. A tendency of salts to build up in the soil during this period(2040–2059) is related to consistently below-average rainfall, which
was not suﬃcient to leach salts from the root zone. Isidoro and Grattan(2011) also found through modeling that rainfall distribution plays amajor role in determining seasonal soil salinity in the root zone.
During 2060–2079, the seasonal ECswi varied from 1.73 to 8.15 dS/
m (Fig. 9c) and the overall average median ECswi increased by 150%

Fig. 8a) showed ECswi much higher than the threshold salinity. Thissituation (Av. ECswi > 4.2 dS/m) occurred only in 1.7% of the realizations especially during drought conditions. Though, the average medianECswi during the 2020–2039 period increased by 40% compared to thecorresponding value of 1.63 dS/m during the baseline period(2004–2015), which indicates increased salts depositions in the rootzone. However, a gradual reduction in rainfall (Figs. 2 and 3) over theyears contributed to an increase in the root zone salinity. These salts
can pose increasing risks to the vine growth and its sustainable production.
Similarly, the seasonal ECswi during the 2040–2059 varied from 1.1
to 7.63 dS/m (Fig. 9b). The average median ECswi almost doubled to114

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median ECsw varied from 3.27 to 4.49 dS/m in diﬀerent realizations andgenerally showed an increasing trend with time. The simulated mediansalinity is higher than the threshold (4.2 dS/m) in 35% of modelingrealizations, which means that it can have a tremendous impact on thenormal vine growth, yield, and the wine quality. Though the projectedamount of seasonal irrigation showed an increasing trend during thisperiod, irrigation was unable to generate necessary leaching to remove
the salts from the root zone.
During 2060–2079, the seasonal ECsw showed a signiﬁcant variability and varied from 2.78 to 9.52 dS/m in diﬀerent climate change
realizations (Fig. 10c). The average median salinity (4.98 dS/m) increased almost two and half times compared to the corresponding value
during the baseline period (2004–2015). Yearly median ECsw values
remained above the crop threshold in 81% of climate change realizations, indicating a strong likelihood of salt related problems. High values of upper outliers occurred during drought periods due to insuﬃcient leaching because rainfall plays a key role in maintaining aproper salt balance in the crop root zone. High soil salinities during thisperiod can damage the growing tissues and can signiﬁcantly aﬀect thegrowth, yield, and the sustainability of the viticulture.
The ECsw continued to increase during the last 20-year period of the
21st century. It ranged from 2.98 to 10.44 dS/m in diﬀerent yearly
realizations (Fig. 10d). It is worth noting that ECsw showed a muchhigher increasing trend during the last decade of the 21st century. ECsw
showed a strong correlation with a similar reduction in rainfall and anincrease in the irrigation demand during this period. The average
median seasonal ECsw increased almost three times (6.05 dS/m) compared to the corresponding baseline value (1.97 dS/m) and remained
higher than the viticulture salinity threshold (4.2 dS/m) in 97% of climate change realizations. Eventually, enhanced levels of salt concentrations in the root zone exert an increased osmotic impact andreduce vine water uptake by roots, which in turn inﬂuences many
physiological processes of the plant such as transpiration, photosynthesis (Russo et al., 2009), stem and leaf water potential (Walker et al.,1981), stomatal conductance (Walker et al., 1981; Prior et al., 1992a),and net assimilation rate (Downton et al., 1990). Ultimately, negative
impacts of increased salinity and water stresses on physiological traits
are transmitted into the fruit yield reduction (Prior et al., 1992b;
Stevens et al., 1999; Walker et al., 2002; DeGaris et al., 2015) and thecompared to the average baseline value of 1.63 dS/m. This indicatesthat continued additions of salts into the soil through irrigation are notleached out of the root zone. Therefore, salt concentrations in the rootzone increased above the crop threshold in 45% of climate realizations
and increased the salinity risks to the irrigated viticulture in the Riverland.
Similarly, the seasonal ECswi varied from 1.67 to 9.18 dS/m in various realizations during the ﬁnal 20-year period (2080–2099) (Fig. 9d).
This period showed a slight increase in the upper outliers as comparedto the previous 20-year period. However, the average median ECswi atthe beginning of the season increased more than three times (5.0 dS/m)
as compared to the corresponding salinity during the baseline period.
The median ECswi for the entire ﬁnal 20-year period increased above thethreshold salinity (ECsw = 4.2 dS/m) of grapevine (Zhang et al., 2002)
in 78% of climate realizations. High salinity at the beginning of theseason can have a dramatic impact on the bud burst and initial growth,which can subsequently be reﬂected in vine growth such as the canopy
development, berry development, ripening, harvesting, and the qualityof the wine. The modeling results revealed that soil salinity at the beginning of the vine season is a crucial factor that needs special attention
to ensure sustainable viticulture.
The average root zone salinity during the growing season (ECsw)
varied from 1.33–8.49 dS/m and showed an increasing trend during
2020–2039 (Fig. 10). The median ECsw of 100 ensembles(2.21–3.26 dS/m) also showed an increasing trend with time, though it
remained below the salinity threshold for viticulture (Fig. 10a). However, several outliers, which occurred due to drought conditions insome of the realizations that provided less opportunity for proper saltleaching from the root zone, showed a signiﬁcantly higher ECsw. The
average median salinity was 47% higher than the corresponding baseline value (1.97 dS/m), which reﬂects increased salt depositions in theroot zone. This suggests that the extent of rainfall and irrigation is notadequate for salt leaching under viticulture irrigated at the full requirement with good quality water. Increased salinity may hamper theadequate vine growth and can inﬂuence the berry production and wine
quality.
The average salinity during the cropping season (ECsw) showed alarge variability among the yearly seasonal realizations as it varied
from 1.5 to 8.64 dS/m during 2040–2059 (Fig. 10b). However, theFig. 10. Predicted variability in the seasonal average soil solution salinity in the root zone (ECsw) of viticulture at Loxton during the a) 2020–2039, b) 2040–2059, c) 2060–2079, and d)
2080–2099. The blue line represents the salinity tolerance threshold for viticulture. (For interpretation of the references to colour in this ﬁgure legend, the reader is referred to the web
version of this article.)

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Acknowledgments

deterioration of the berry juice composition (Prior et al., 1992a;
DeGaris et al., 2015) and wine quality. Sometimes, the concentration ofindividual ions such as Cl− or Na+ can increase to a toxic level and candisturb the plant metabolism (Munns and Tester, 2008). Nonetheless,increased root zone salinity above the crop threshold can be controlled
by adopting an appropriate leaching fraction (LF) for salinity control.
This could have been done, for example, by triggering irrigations at alower suction than in current simulations (i.e., < 60 kPa). However, itis certain that adopting higher LF would further enhance the total irrigation requirement of viticulture under projected climate change inthe study area.
It is worth mentioning that soluble salts that are leached out of thecrop root zone may re-enter it in response to dynamic evaporative
ﬂuxes at the soil surface. Alternatively, these salts can leach deeper into
the soil and may enter the river system via groundwater, which may behydraulically connected, as reported in many previous studies (e.g.
Cook et al., 2004; Tan et al., 2007). Maintaining a proper leaching
fraction can help in leaching the salts from the crop root zone. Aragüés
et al. (2014) reported an increase in salinity and sodicity in soil undersustained deﬁcit irrigation of vineyards due to the reduction in theleaching fraction. However, a high leaching fraction may be needed in
low rainfall areas where seasonal salinity can increase above the crop
tolerance threshold. These results suggest that irrigation-induced salts
can pose an increased threat to the normal growth and yield ofgrapevine, and can at the same time enhance the salinity related environmental risks to the river system.

The work was conducted under the South Australian River Murray
Sustainability Program that was funded by the Australian Governmentand delivered by the Government of South Australia. The leaves granted
to Dr. Vinod Phogat by CCS Haryana Agricultural University foravailing Post-Doctoral studies are highly acknowledged.
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4. Conclusions
In this study, a numerical model HYDRUS-1D was used to evaluate
the water and water-related salinity risks to viticulture for 100 diﬀerent
downscaled ensembles of climate model (GFDL ESM2 M) projections.
Such an assessment of the impact of climate change in all plausible
scenarios of downscaled GCM projections can help in reducing theuncertainty in simulated outcomes of a model. The study suggests a
strong likelihood of an increase in the irrigation demand of viticulturein the future. Seasonal irrigation requirements increased by 4.2%
during the 2020–2039 period as compared to the baseline period(2004–2015). The irrigation-induced salinity risks were low during thisperiod as the initial and seasonal average salinities in the soil remained
below the crop threshold. However, the water allocation to the viticulture may be aﬀected due to a reduction in rainfall (13.7%) and anincreased occurrence of droughts projected by the climate model.
After that, model simulations showed continuously increasing irrigation requirements and increased salinity risks to viticulture in thefollowing 20-year periods (2040–59, 2060–2079, and 2080–2099). The
seasonal irrigation requirement (Ir) increased by 7.5, 10.9, and 16.9%
during 2040–2059, 2060–2079, and 2080–2099, respectively. Thislarge increase in the irrigation requirement was mainly associated witha reduction in rainfall projected by the climate models because a reduction in potential evapotranspiration was projected to be only 2.5
and 5% during 2060–2079 and 2080–2099, respectively. Model simulations also indicated a tremendous increase in the root zone salinity as
rainfall-induced salt leaching was reduced to a great extent. The simulated seasonal average salinity increased three and four times
compared to the base line and 81 and 97% of the climate ensembles
showed a root zone salinity higher than the crop threshold during the2060–2079 and 2080–2099 periods, respectively.
The study suggests that apart from an increase in the irrigation requirement, root zone salinity could be a much bigger problem to be
faced by the irrigated viticulture in the Riverland region of South
Australia and regions under similar climates around the world. If salts
are not properly managed in a timely fashion, they can pose a serious
risk for irrigated crops, including viticulture. These ﬁndings could help
the stakeholders of irrigated viticulture in adopting strategies leading to
the reduction in the salinity in the crop root zone.
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