Impact of global change on large river basins: Example of the Yellow River basin

The Yellow River basin (YRB) is the breadbasket of China and the “cradle of Chinese civilization.” The basin is characterized by severe water scarcity; the ratio of surface water withdrawal to water resources, at 64 percent in 2008, is among the highest in the world. Particular climatic conditions, the rapid socioeconomic development, and the absence of defined water rights have led to excessive water abstraction. During the last 50 years agricultural water use has increased by more than 250 percent, while water demand from industry and domestic use has grown even more steeply. Climate change is likely to add pressure to water resources by affecting the stream-flow in two regions of the YRB, which account for approximately three-fourths of total runoff in the basin. Using stream-flow data as input, the Yellow River Conservancy Commission (YRCC) water supply-and-demand model projects that climate change may result in annual water shortages of 9 km3 by 2020. In extremely dry years this value may increase to 15 or even 26 km3. Similarly, the International Food Policy Research Institute's (IFPRI's) IMPACT (International Model for Policy Analysis of Agricultural Commodities and Trade) model shows a decline in overall availability of water for irrigation in the YRB under climate change. The model also shows that large food-producing basins, such as the YRB, can strongly impact international food prices. We implement two scenarios of reduced irrigation water availability in the YRB (declines by 30 percent and 50 percent) under climate change, which reflect Chinese estimates of future dry-season water shortages in the YRB. By 2030, with climate change and irrigation water reduction of 30 percent, international wheat prices increase by 6 percent, maize prices by 4 percent, and rice prices by 3 percent. With a 50 percent irrigation water reduction, increases would be even higher: 9 percent for wheat, 10 percent for maize, and 6 percent for rice. Furthermore, calorie availability in developing countries declines by 1.2 percent and 2.2 percent under a 30 percent and 50 percent irrigation water reduction, respectively, by 2030. To preserve economic growth and food security in the basin and to reduce potentially adverse impacts on global food markets, managers will need to tackle inefficient water use. YRCC experts show that technological advances are important but insufficient to meet projected gaps in water supply. The focus will thus need to remain on measures to control water demand as well as on increased agricultural and crop water productivity. China has both the potential and the resources to make this happen.