Crop water demand in China under the SRA1B emissions scenario

Projections of the crop demand under future climate scenarios would help us to understand the potential influence of climate change on food safety and water resources.Using the United Nations Food & Agriculture Organization (FAO)modified Penman-Monteith equation and the output from the Model for interdisciplinary Research on Climate (MIROC3.2)for the SRA1B emissions scenario,the reference evapotranspiration (ET0)can be calculated for China for the next 50 years.Using the FAO crop coefficients and the K-ppen climate classification system,the crop coefficient can thus be determined for every calculation unit.The estimation of crop water demands is achieved using ET0 and the crop coefficient,and the corresponding irrigation water requirement can also be worked out by matching the effective precipitation with the crop water demand.The result shows that on average,China's ET0 could increase by about 8%,and so does for the crop water demand and the irrigation water requirement.Over the northeast region, this increase in irrigation water requirement could reach above 10%,and the increase over South China is also significant.The upward trends in water demands are mainly due to the increase in future temperatures,which can result in an increase of ET0 values.The matter could be further complicated by the reduction of the projected precipitation for the northeast and south regions of China.However,the projected increase in precipitation over the north region could moderate the issue of water demands.