Estimating changes in the green water productivity of cropping systems in Northern Shaanxi Province in China's Loess Plateau

Water shortages limit agricultural production in the world's arid and semi-arid regions. The Northern region of China's Shaanxi Province, in the Loess Plateau, is a good example. Raising the water productivity of rainfed grain production in this region is essential to increase food production and reduce poverty, thereby improving food security. To support efforts to increase crop water productivity (CWP), we accounted for limitations of most existing studies (experimental studies of specific crops or hydrological modeling approaches) by using actual field data derived from statistical reports of cropping patterns. We estimated the CWPs of nine primary crops grown in four counties in Northern Shaanxi from 1994 to 2008 by combining statistics on the cultivated area and yields with detailed estimates of evapotranspiration based on daily meteorological data. We further calculated both the caloric CWP of water (CCWP) and the CWP of productive water (i.e., water used for transpiration). We found that regional CWP averaged 6.333 kg mm^-1 ha^-1, the CCWP was 17,683.81 cal mm^-1 ha^-1, the CWP of productive green water was 8.837 kg mm^-1 ha^-1, and the CCWP of productive green water was 24,769.07 cal mm^-1 ha^-1. Corn, sorghum, and buckwheat had the highest CWP, and although potatoes had the largest planted area and relatively high CWP, they had a low CCWP.