A Study on Precipitation Concentration in Sichuan Province from 1960 to 2004
四川地区1960年-2004年降水集中程度研究

Based on daily precipitation data observed at 121 stations in Sichuan Province during the period 1960-2004, and employing the concepts of precipitation-concentration degree (PCD) and precipitation-concentration period (PCP), wavelet analysis and synthetic analysis, the authors systematically analyzed the characteristics of spatial and temporal distributions and variations in precipitation in Sichuan Province, southwestern China. Results demonstrate that the PCD and PCP can quantitatively characterize the heterogeneity of precipitation over space and time. The PCD generally showed a decreasing trend in Sichuan Province. The PCD of the eastern basin area was found to be smallest in Sichuan Province. It was also found that the PCD showed a weakening trend over the entire Sichuan Province. The PCD was greatest and the PCP remained stable over the western plateau area. The precipitation over the western plateau was relatively more concentrated, but the maximum precipitation of pentad seemed to be stable. Therefore, the weather predictability in the region is high. Droughts/floods are likely to occur at some local areas of the eastern basin and western plateau in the dry years. The precipitation predictability of the southern areas is stronger. In order to understand the mechanisms of the interactions between climate change and water resources, we made a synthesis on three regions in Sichuan Province. Droughts/floods are very likely to occur over part of the eastern basin areas in the dry years. Annual variation of droughts/floods presents continuity. The time of the maximum precipitation of pentad occurring each year remains invariant over the western plateau. The concentration of precipitation throughout the region is of local regularity. The southern area showed the same situation as the eastern basin did, prone to droughts/floods in the dry years but with high weather predictability. Using the wavelet analysis of annual precipitation in the eastern basin of Sichuan, it was indicated that there exist three marked characteristic time scales, i.e., 5-year, 14-year and 25-year or so. It is expected that the precipitation resources would decrease gradually and move to a dry period persisting a long period of time over the east of Sichuan Province. The western plateau has an obvious time scale of 22-year. The precipitation would increase over a short period in the western plateau. In the south of Sichuan, there is clearly a 10-year time scale of alternation of wetting and drying. The precipitation showed an obvious decreasing trend from the late 1990s to 2004, lying in a prolonged drought cycle.