Spatial and Temporal Characteristics of Precipitation Changes from 1962 to 2000 in Northwestern China
西北地区1962 年至2000 年降水量变化的时空特征分析

Using daily precipitation data from 46 meteorological stations during the period 1962 to 2000 in northwestern China, and the linear trend analysis, wavelet analysis, as well as Mann-Kendall method, the authors investigated spatial and temporal characteristics of precipitation changes in northwestern China. Results indicated that over the past 40 years, in general, the precipitation fluctuated with a certain periodicity. There was a major oscillation period of 25 years, as well as an inter-annual oscillation period of approximately 4 years and 9 years. The slope of the linear regression showed that the precipitation over the northwestern regions as a whole decreased due primarily to a large geographic span of northwestern China, resulting in greater precipitation variability in eastern and western China. The precipitation error of each site was found to be larger on average; consequently it was not able to reflect details across the study region. To that end, the mean annual precipitation can only reflect a general trend over a large area, without reflecting the regional differences in the degree of fluctuation in precipitation. It was also found that the spatial distribution of precipitation showed essentially an incrementally decreasing trend from the southeast to the northwest. The least precipitation occurred at the central and eastern parts of the Tarim Basin in Xinjiang Uygur Autonomous Region, as well as the eastern part of the Turpan basin. The mean precipitation gradually increased from the center. The region where precipitation increased was principally distributed in areas with relatively less precipitation, whereas the region where precipitation decreased was mainly distributed over areas with more precipitation. The region with little precipitation change was observed to be in the transition zone of the first two regions. Areas with little precipitation exhibited a strong increasing trend, and areas with large precipitation showed a strong decreasing trend. In principle, the precipitation did not change significantly across the region between the former two transition zones. The precipitation in northwestern China as a whole has not decreased, but increased centered on some regions. The increasing rate of precipitation across the whole northwestern China tended to be particularly small. In terms of the age results of the interpolation of variability in precipitation, it was suggested that the overall precipitation in northwestern China did not decline, increasing to a small degree across the entire northwestern region.