Spatial distribution characteristics of irrigation water requirement for main crops in China

Temporal and spatial distribution characteristics of crop water requirement and irrigation requirement are the bases for determining the irrigation quota in different areas. Based on the daily meteorological data over the past 30 years from more than 200 stations in China and the statistical data of crop growth stages from different areas, crop water requirement (ETc) and net irrigation requirement (IR) of 30 kinds of crops were estimated by using FAO Penman-Monteith equation and crop coefficient method. The results were validated with the observed data form different irrigation stations in different areas. Isolines of the average ETc and IR of main crops were obtained by GIS and IDW interpolation methods. The spatial distribution characteristics of ETc and IR for wheat, maize, cotton and rice were analyzed, which were the most widely planted crops in China. The irrigation requirement indexes of main crops in different areas were obtained by IR/ETc. Results revealed that mean irrigation requirement index in Northeast China, middle and lower reaches of the Yangtze River and South China were generally less than 0.5, and the crop irrigation water requirement in these areas was not high. In North China Plain, Inner Mongolia, Ningxia, Shanxi, Shaanxi and Gansu, 30%-50% of the crop water requirements depended on irrigation for dryland crops, 55%-80% of water consumption came from irrigation for rice. In Xinjiang Uygur Autonomous Region, the irrigation requirement indexes of main crops were over 0.7, and the development of agriculture relied entirely on irrigation.