Temporal and Spatial Characteristics of Dry and Wet Conditions in Shiyang River Basin during the Period of 1960-2009

Based on the climatic data of four meteorological stations from 1960 to 2009, using FAO Penman-Monteith model, ArcGIS IDW interpolation and Mann-Kendall test and T-test, the paper analyzes the changing trends, spatial and temporal differences and mutation characteristics of surface dry and wet conditions. The results show: Firstly, the overall trend of surface dry and wet conditions had been becoming wetter and wetter with the trend rate of humid index 0.006/10yr during the period of 1960-2009 in Shiyang River Basin. The surface was drier in the period of 1960s-1970s, and then became wetter after 1980s, especially after 2000. Secondly, the spatial differences of surface dry and wet conditions are significant. The mean annual humid index decreased from 0.404 of the upper reaches to 0.081 of the lower reaches gradually and the changing rates also changed from fast to slow. Furthermore, the lower reaches appeared the most dramatic fluctuation, followed by the upper reaches and the slightest fluctuation in the middle of river. Thirdly, the seasonal variations of surface dry/wet conditions were very different. The mean annual humid index was the largest in summer, followed by the autumn and the less in winter and spring. The overall changing trends of four seasons were all increasing, but the wetting trend was more significant in autumn and winter than that in spring and summer. Correlation analysis shows the correlation coefficients between summer, autumn, winter, spring and the mean annual were 0.665, 0.591, 0.397 and 0.334 respectively, which were all accepted for the 1% significance level, indicating the humid index increasing in the four seasons, especially for the two fomers, made greater contribution to the annual humid index changing. Finally, the mutation threshold of annual humid index occurred in the year around 1983, while the mutation years for the winter, spring and autumn were 1984, 1981 and 1999 respectively and the unconspicuous mutation in summer.