1976-2010年榆林市降水时空变化趋势分析

利用榆林市及其周边的109个雨量站1976-2010年逐月降水资料,运用Mann-Kendall、经验正交函数(EOF)、小波分析,并结合Arcgis10.1的空间分析工具,分析了榆林市降水量35年来的时间变化趋势和空间演变特征。结果表明:榆林市年降水主要呈东南向西北递减的趋势;各站点35年的年、汛期、枯季降水量趋势变化增减不一,年降水量表现出减小的趋势。榆林市大致存在两种主要降水型:总体一致型和东北-西南走向型,其中,东北-西南降水型是榆林市的典型降水类型,这主要是由地形条件和气候因子决定的。时间系数表征了该空间型的时间变化特征,从时间系数的波动来看,年、汛期、枯季降水量年际震荡比较显著。通过小波分析揭示了降水空间结构的周期变化特征,结果显示年降水、汛期降水的周期变化显著,不仅存在6~7a的短周期高频变化,还存在20a以上的长周期低频变化特征,枯季降水则只存在一种周期变化。这种周期变化特征可能与东亚季风的周期变化规律有关,也符合大尺度天气系统的周期变化规律。

Trend analysis of spatial-temporal change of precipitation in Yulin from 1976 to 2010

The paper used monthly precipitation data from 109 stations over Yulin City from 1976 to 2010, applied Mann-Kendall test, empirical orthogonal function (EOF) and wavelet analysis, and combined with the spatial analysis tools of Arcgis10.1 to analyze the spatial-temporal variability characteristics of precipitation in Yulin during last 35 years. The results indicate that the annual precipitation decreases from the southeast to the northwest, and the precipitation of annual, flood period and dry season each site show different trends and annual precipitation shows a decreasing trend. There are two main types of precipitation in Yulin that are consistency of all precipitation and the northeast-southwest direction type.Among these distribution types,the northeast-southwest precipitation are the typical precipitation type in Yulin, which is determined by the terrain conditions and climate factors. The time coefficients each distribution type can describe time-varying characteristics of each type.From the fluctuation of time coefficient.there is a notable inter-annual oscillation of annual ,flood and dry season precipitation. The paper revealed the periodic variation of precipitation spatial structure by wavelet analysis.The result showed that the period change of annual precipitation and precipitation of flood period is remarkable.There is not only a short period and high frequency variation of 6-7a, but also a low frequency variation of 20 a. There is only one periodic variation in dry season. This period characteristics may be related to the periodic variation law of the east Asian monsoon,which is also conformed to cycle variation discipline in large-Scale climate system.