Spatial–temporal changes of precipitation structure across the Pearl River basin, China

Using daily precipitation data covering 1960–2005 from 42 stations across the Pearl River basin, precipitation indices, defined by annual total precipitation amount, annual total rainy days, annual precipitation intensity and annual mean rainy days, are analyzed using the modified Mann–Kendall trend test method. Results indicate that: (1) decreasing precipitation is found mainly in the middle and upper Pearl River basin. However, a decreasing number of rainy days is detected almost over the entire basin. Thus, the Pearl River basin is characterized by increasing precipitation intensity, particularly in the middle and the eastern parts of the basin; (2) the occurrence and fractional contribution of wet periods (WPs) with longer durations are decreasing in recent decades and WPs with shorter durations, e.g., 2–5 days are tending to be predominant in recent decades with increasing total precipitation amount. Frequencies of shorter WPs with increased total precipitation amount can be expected, which can easily trigger occurrence of floods and droughts; (3) heavy precipitation is easy to occur in WPs with shorter durations which may further corroborate the intensified precipitation process in the Pearl River basin, particularly in the lower part. Reduction of water supply from the upper Pearl River basin due to decreased precipitation and higher risk of floods and droughts in the lower basin will increase uncertainty of water supply in the lower basin and hence pose new challenges for water supply and water resources management under the influence of climate change and human activities, such as increasing water demand as a result of booming socio-economy and fast population growth.