Abstract: This paper proposes a method on analyzing the asynchronism synchronism of precipitation in different hydrological regions related to South to North water transfer areas of eastern China. In general, the analysis process includes three steps. Firstly, we created a Thiessen map based on data obtained from representative stations of the regions concerned and calculated the relative area controlled by each station. Then the areas were regarded as the weight of the corresponding stations in calculating average rainfall of the regions concerned. Secondly, we made an assessment on the dryness or wetness of the rainfall time series. According to the result we found that the Gamma distribution function is the best to describe the stochastic characters of rainfall series. Thus Gamma distribution function was called for the rainfall series and the probability values of 62 5% and 37 5% were determined as indexes to classify the wetness, evenness and dryness of each sample of the time series. As we had divided the rainfall conditions of each region into three types, there were nine kinds of encountering of every two different regions. Finally, by comparing the dryness wetness assessments of different regions, we calculated the frequency of the dryness wetness encountering of the regions. According to the above discussed method, we carried out two case studies, one was between North China and mid lower reaches of the Changjiang River, the other was between North China and upper reaches of Han River. In the case studies, the monthly rainfall material used ranged from 1957 to 1998 and rainfall time series of the regions were calculated by three kinds of time scales, i.e. annual, seasonal and monthly. The investigation has shown that synchronous frequency of rainfall encountering of in the two cases in annual scale was about 45% for both, which included the frequency of wetness wetness (NW SW), evenness evenness (NE SE) and dryness dryness (ND SD). The results of the other two time scales were quite the same to that of the annual scale. On the consideration of the asynchronism between North China and Changjiang River, the total frequency of SW ND, SW NE and SE ND is a little higher than that of NW SD, NW SE and NE SD. However, in this case, the condition of North China to upper reaches of Han River is just in a different way. As to the total frequency of the conditions (i.e. SW ND, SW NE, SE ND and SE NE) that are fit for water transfer, in annual scale it is 40% and 24% respectively of the two cases. While in spring, it is 28% and 35% respectively. According to the results of the investigation, in order to enhance the effectiveness and reliability of South to North Water Transfer Project in China, we strongly suggested that the ability of water resources adjustment and the capacity of the project must be given careful consideration.

Key words: South to North Water Transfer, hydrological region, precipitation