Shifts in Irrigation Water Demand and Supply Patterns during Critical
Crop Growth Stages under Changing Impacts of Climate and Socio-Economic
Dynamics in South Asia
Abstract
Changing irrigation water demand (IWD) and supply (IWS) patterns (size
and time) under increased climate variability and socio-economic
development is significantly effecting the water and food production in
the densely populated South Asia (SA). Considering food security
paradigm of SA, where rice and wheat are major staple and
water-intensive crops, this study aims to investigate the linkages in
IWD by crops and IWS by sources (surface and groundwater) using
integrated climate and socio-economic projections. The novel aspect of
this study is to explore IWD and IWS pattern shifts during critical crop
growth stages (CW’s), which is previously less studied with no
remarkable research evidence for IGB region. Quantification of shifts in
IWD and IWS patterns in future is crucial for long-term integrated water
resources and agricultural planning. For this, LPJmL crop-water model is
forced with an ensemble of eight state of the art downscaled GCM at 5
arc-min resolution. To assess the combined impacts of climate and
socio-economic changes, RCP-SSP framework is used. Our statistical
analysis results show that IWD is higher in vegetative stage (CW1) than
the reproductive stage (CW2) during both Rabi and Kharif cropping
seasons. Water demand is decreasing in future for wheat while increasing
for rice. IWS is decreasing substantially from surface while increasing
largely from groundwater resources during Rabi. Though, IWS during
kharif season is increasing largely from both surface and groundwater
resources. There is mismatch in demand and supply as evident from the
results suggesting 10 days early wheat planting reduces IWD by 8.0% in
F1, 18.7% in F2 and 28.4% in F3 during CW1 with a decrease of 7%, 30
% and 62.56% during F1, F2 and F3 in CW2. Increased IWS with larger
contribution from groundwater resources is projected for both crops in
future. Water gap between demand and supply during both CW’s in future
is increasing for Rabi and Kharif suggesting 10 days early planting of
wheat while 20 days delay in kharif planting. Estimation of IWS by
sources helped in assessing shifts in percent (%) dependency of water
supply from different sources. Moreover, Spatio-temporal mismatch
between water demand and supply help exploring geospatially driven water
gap trends consequently, highlighting water stress hotspots during CW’s
in future.