Understanding the hydrological trends of river basins in China

SummaryIn order to predict future hydrological trends, it is important to understand those that have occurred in the past. In this study, the entire area of China was divided into 10 basins to analyze the country’s hydrological trends. 317 weather stations with data from 1956 to 2005 were selected for trend analysis. Based on the observations, we found that precipitation has decreased in the north but has increased in the south due to weakening monsoon winds over the past 50 years. In the same period, the pan evaporation decreased as a whole but it was not uniform in either timing or spatial dimension. With the stepwise regression method, we concluded that precipitation had a greater impact on pan evaporation in the north than in the south. Furthermore, sun duration had a more significant impact on hydrological processes in the south than in the north. On the assumption that water storage and water use for irrigation has not changed, which is reasonable when the actual evaporation is decreasing, the actual evaporation estimated by the water balance equation showed a decreasing trend in both the north and south. Using complementary relation curves, we concluded that the decrease in the north was caused by the decrease in precipitation while the decrease in the south was caused by a decrease in potential evaporation.