Changing climate and implications for water use in the Hetao Basin, Yellow River, China

Balancing water allocations in river basins between upstream irrigated agriculture and downstream cities, industry and environments is a global challenge. The effects of changing allocations are exemplified in the arid Hetao Irrigation District on the Yellow River, one of China's three largest irrigation districts. Amongst the many challenges there, the impact of changing climate on future irrigation water demand is an underlying concern. In this paper we analyse trends in local climate data from the late 1950s and consider the implications for irrigation in the Basin. Since 1958, daily minimum temperatures, Tmin in the Basin have increased at three times the rate of daily maximum temperatures, Tmax. Despite this, there has been no significant increases in annual precipitation, P or pan evaporation, Epan. The difference between the increasing trends in Tmax and Tmin means that the average annual diurnal temperature range, DTR, has decreased very significantly, part of a global phenomenon. Hargreaves empirical approach is used to estimate changes in both incoming solar radiation, Rs, and potential evaporation, ET0. Changes in estimated ET0 correlated well with changes in measured pan evaporation, Epan. Paradoxically, the estimated decreasing trend in Rs does not correspond to a significant decreasing trend in Epan. Implications of changing climate on water use and soil salinity in the Basin are discussed.