Spatial and temporal patterns of precipitation variability over mainland China: Ⅱ: Recent trends

Applying precipitation indices series of quality-controlled daily data from over 2 300 stations, the characteristics of long-term precipitation variations over the past 60 years for mainland China are analyzed. The main conclusions are as follows: ① No significant long-term trends of annual and seasonal precipitation percentage anomalies have been found for mainland China as a whole, though a relatively significant decrease and increase have been seen for the seasonal precipitation percentage anomalies for autumn and winter respectively; ② Decrease in annual and summer precipitation mainly occurred in central and southern Northeast China, North China, western Central China and Southwest China. Increase mainly occurred in southeastern coastal region, the mid and lower reaches of the Yangtze River, the Qinghai-Tibetan Plateau and Northwest China; ③ The spatial patterns of the annual and seasonal precipitation trends were relatively stable. The decrease areas migrated from the Loess Plateau and North China toward northeast and southwest after 1990s, the increase areas in Northwest China and the Qinghai-Tibetan Plateau did not change much or marginally expanded, and the increase areas in northern Northeast China and the mid and lower reaches of the Yangtze River obviously shrank. In the eastern monsoon region, the areas with either increasing or decreasing trends reduced for the last two decades; ④ Significant increases in annual amount and frequency of rainstorms, 3.18 mm/10 a and 0.03 d/10 a respectively, have been observed for the past 60 years, though the intensity of rainstorms remained unchanged. The increase mostly appeared in the Pearl River basin and the rivers of southeastern region. The Haihe River and the rivers of Southwest China witnessed a remarkable decrease in annual amount, frequency and intensity of rainstorms; ⑤ Proportions of the stations with increase (decrease) annual maximum 1 d, continuous maximum 3 d and continuous maximum 5 d precipitation were 59.2% (40.8%), 54.4% (45.6%) and 51.5% (48.5%) respectively, and those with statistically significant increase (decrease) are 5.1% (1.2%), 4.2% (2.5%) and 3.7% (2.8%) respectively, indicating an increasing frequency and intensity of extreme intense precipitation events, and a tendency toward shorter duration for single extreme intense precipitation events.