An assessment of global net irrigation water requirements from various water supply sources to sustain irrigation: rivers and reservoirs (1960–2050)

Abstract

Abstract. Water supply sources for irrigation (e.g. rivers and reservoirs) are critically important for agricultural productivity. The current rapid increase in irrigation water use is considered unsustainable and threatens food production. In this study, we estimated the time-varying dependence of irrigation water requirements from water supply sources, with a particular focus on variations in irrigation area during past and future periods using the global water resources model, H08. The H08 model can simulate water requirements on a daily basis at a resolution of 1.0 • × 1.0 • latitude and longitude. The sources of irrigation water requirements in the past simulations were specified using four categories: rivers (RIV), large reservoirs (LR) with a storage capacity greater than 1.0 × 10 9 m 3 , mediumsize reservoirs (MSR) with storage capacities ranging from 1.0 × 10 9 m 3 to 3.0 × 10 6 m 3 , and non-local non-renewable blue water (NNBW). The simulated results from 1960 to 2001 showed that RIV, MSR and NNBW increased significantly from the 1960s to the early 1990s globally, but LR increased at a relatively low rate. After the early 1990s, the increase in RIV declined as it approached a critical limit, due to the continued expansion of irrigation area. MSR and NNBW increased significantly, during the same time period, following the expansion of the irrigation area and the increased storage capacity of the medium-size reservoirs. We also estimated future irrigation water requirements from the above four water supply sources and an additional water supply source (ADD) in three future simulation designs; irrigation area change, climate change, and changes in both irrigation area and climate. ADD was defined as a future increase in NNBW. After the 2020s, MSR was predicted to approach the critical limit, and ADD would account for 11-23 % of the total requirements in the 2040s.

Uncertainties in modelling the climate impact of irrigation

“…2) and in much better agreement with other studies (e.g. Yoshikawa et al 2013 and references therein). The gross irrigation constitutes only a rough approximation of the amount of water that has a direct impact on the simulated climate, as a significant fraction of the water merely results in increased runoff and drainage.…”

“…In these studies the focus is mainly on the extent of the irrigated areas or timing and mode of delivery, e.g. Sacks et al (2009) and Yoshikawa et al (2013). The present study aims to improve our understanding by performing complementary investigations using the Max Planck Institute for Meteorology's Earth System Model (MPI-ESM, Stevens et al 2013;Raddatz et al 2007;Brovkin et al 2009).…”

“…Currently, the amount of water that is being redistributed on the land surface via irrigation, is estimated to be more than 2500 km 3 a −1 which is equal to about 2% of precipitation over land (Shiklomanov 2000). Studies using a variety of models have investigated how this redistribution affects the availability of freshwater (Döll and Siebert 2002;Tiwari et al 2009;Liu and Yang 2010;Wada et al 2012Wada et al , 2013Yoshikawa et al 2013) and climate. The majority of the studies that investigate irrigation's climate impact is focused on regional climate (Douglas et al 2006;Kueppers et al 2007;Douglas et al 2009;Lobell et al 2009;Saeed et al 2009;Lawston et al 2015), but also larger scales have been addressed in recent studies (Boucher et al 2004;Sacks et al 2009;Wei et al 2013;de Vrese et al 2016a;Krakauer et al 2016;Thiery et al 2017).…”

On inclusion of water resource management in Earth system models – Part 1: Problem definition and representation of water demand

“…As an offline example, Hanasaki et al (2008a) assumed that paddy and nonpaddy crops require soil moisture content of 100 or 75 % of the field capacity at the root zone with constant depth at the global scale. Yoshikawa et al (2014) later updated the assumption for non-paddy soil moisture requirement and used 60 % of field capacity, referring to the requirement for wheat. This is again rather unrealistic as (1) by assuming a constant percentage of the field capacity for all crop types, the diversity in crop water requirement is ignored; and (2) a constant root zone depth at the global scale can result in misestimating the irrigation demand.…”

On inclusion of water resource management in Earth system models – Part 2: Representation of water supply and allocation and opportunities for improved modeling

“…Similarly, climate change is expected to perturb both water demand and supply, as it also results in greater seasonal and inter-annual variability with increase in the risk of extreme conditions (e.g., Prudhomme et al, 2014). Looking to the future, Yoshikawa et al (2014) argued that current sources can only account for 74 % of the global net irrigation requirements of the 2050s and supply-demand imbalance will cause a major increase in global water scarcity (Alcamo et al, 2007;Hanasaki et al, 2008aHanasaki et al, , b, 2013aSchewe et al, 2014). In water-scarce conditions, competition for water resources becomes increasingly important and the details of water allocation practice play a key role in the spatial and temporal distribution of water stress.…”