Keywords: 
• irrigation water requirement /
• climate change /
• rice /
• the mid-lower reaches of Yangtze River /
• statistic downscaling

Abstract: Projections of rice irrigation water requirements under future climate conditions can be beneficial in developing adaptation strategies for reducing the negative impact of climate change on rice productions and to ensuring the food security from the perspective of the sustainable use of water resources. Using a statistical downscaling model (SDSM), the projected daily reference evapotranspiration and precipitation of HadCM3 under A2 and B2 scenarios were downscaled to 45 local meteorological stations in the Mid-Lower Reaches of Yangtze River. Spatiotemporal variations of irrigation water requirements during the middle-season rice growing period for the past five decades (1961-2010) and future dates (2011-2099) were analyzed. The FAO (Food and Agricultural Organization) crop coefficient method and a water balance model considering the effective precipitation and deep percolation were used in the analysis. The results show that in the past five decades, significant decreasing trends in reference crop evapotranspiration and rice water demand can be detected in most regions of the Mid-Lower Reaches of Yangtze River except the Taihu Basin. While significant decreasing trends in paddy irrigation water requirements can only be observed in the Poyanghu Basin. Under both A2 and B2 scenarios, the mean reference crop evapotranspiration, paddy water demand and irrigation water requirements would decrease. However, the decrease in paddy irrigation water requirements would be greater than that in reference crop evapotranspiration and paddy water demand. Spatial heterogeneities could be found in changing trends in paddy water demand and irrigation water requirement. The region with greater decreasing paddy water demand would extend from the Taihu Basin to the Hanjiang River Basin and the Dongtinghu Basin. The decrease of paddy irrigation water requirements could be expected in the Taihu Basin, the eastern area of the Hanjiang River Basin and the northern area of the Dongtinghu Basin. The region with the decrease of paddy irrigation water requirements would be growing as time goes on.