Abstract
In China, irrigation is widespread in 40.7% cropland to sustain crop yields. By its action on water cycle, irrigation affects water resources and local climate. In this study, a new irrigation module, including flood and paddy irrigation technologies, was developed in the ORCHIDEE‐CROP land surface model which describes crop phenology and growth in order to estimate irrigation demands over China from 1982 to 2014. Three simulations were performed including NI (no irrigation), IR (with irrigation limited by local water resources), and FI (with irrigation demand fulfilled). Observations and census data were used to validate the simulations. Results showed that the estimated irrigation water withdrawal ( W) based on IR and FI scenarios bracket statistical W with fair spatial agreements ( r=0.68±0.07; p<0.01). Improving irrigation efficiency was found to be the dominant factor leading to the observed W decrease. By comparing simulated total water storage (TWS) with GRACE observations, we found that simulated TWS with irrigation well explained the TWS variation over China. However, our simulation overestimated the seasonality of TWS in the Yangtze River Basin due to ignoring regulation of artificial reservoirs. The observed TWS decrease in the Yellow River Basin caused by groundwater depletion was not totally captured in our simulation, but it can be inferred by combining simulated TWS with census data. Moreover, we demonstrated that land use change tended to drive W locally but had little effect on total W over China due to water resources limitation.
Highlights
Irrigation, accounting for 70% of global total water usage (FAO, 2019), contributed to more than 40% of food production increase in the past six decades (George et al, 2011)
We develop a new irrigation module in a physical-based land surface model ORCHIDEE-CROP (ORganizing Carbon and Hydrology in Dynamic EcosystEms, Wang, 2016) with a crop module for wheat, maize, and rice to simulate the patterns of irrigation demand in China
The irrigation module presented in this study and coupled to ORCHIDEE-CROP has the advantage to compute irrigation demand and application for specific irrigated crop soil tiles in each grid cell, allowing mass closure and avoiding to give irrigation water to other vegetation types
Summary
Irrigation, accounting for 70% of global total water usage (FAO, 2019), contributed to more than 40% of food production increase in the past six decades (George et al, 2011). With the growth of population and economy, irrigated cropland area grew fourfold in the last century (Siebert et al, 2015), implying a huge increase of water demand (Hanasaki et al, 2008; Wada et al, 2016). Climate change, such as extreme events (Ben-Ari et al, 2018; Seneviratne et al, 2014) and CO2 fertilization (Osborne, 2016), brings divergent impacts on soil moisture in agricultural systems, which indirectly affects water management. The amount of irrigation applied to crops is determined by the demand from different cultivar types and climate conditions and by irrigation techniques and water availability (Leng et al, 2017; Savva et al, 2002; Wada et al, 2016). Nazemi and Wheater (2015a, 2015b) summarized different approaches to assess irrigation demand in land surface models (LSMs) and global hydrological models (GHMs) and suggested that the computation of irrigation demand should be associated with specific techniques, as well as local farming habits, YIN ET AL
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