西北各省季节降水变化及其贡献的差异分析

利用中国西北地区124个气象台站1951?2015年逐日降水资料，通过计算各季节降水量及降水日数贡献率，解析西北五省（区）不同季节各等级降水量及降水日数贡献率差异，明确不同季节降水量和降水日数变化对年降水量和降水日数变化，以及同季节内不同等级降水量和降水日数变化对当季降水量和降水日数变化的作用，以探究西北地区降水的时空变化特征。结果表明：（1）1951-2015年，西北地区年降水日数以0.1d·10a-1（P＜0.01）的速率极显著减少，各站点年平均降水日数及线性变化趋势差异较大；（2）1951-2015年，西北地区年平均降水量以3.9mm·10a-1（P＜0.01）的速率极显著增加，变化显著区域主要分布在新疆及青海地区；（3）研究区域降水季节分布不均，主要集中在夏季，其中各省（区）夏季降水量贡献率在50%～63%，降水日数贡献率在35%～48%，春秋两季降水接近，冬季降水最少；各季节降水均以小雨和中雨为主，各省（区）两者降水日数累计贡献率均在90%以上，暴雨仅发生在夏季且降水日数贡献率低于1%，秋季各等级降水分布与春季基本一致；（4）夏、秋季节降水量和降水日数变化是年降水和降水日数变化的主要原因，小雨至中雨降水量和日数变化是导致季节总降水量和降水日数变化的最主要原因，而春、冬季降水在年降水、大雨至暴雨在当季（年）降水中不占优势，故其作用不明显。

Seasonal Variation about the Occurrence Frequency of Different Types of Precipitation and Their Relative Contribution over Northwest China

Based on the long-term daily precipitation data measured at 124 meteorological station in Northwest China from 1951 to 2015, the difference of the contribution rate of precipitation amount and precipitation days among different precipitation grades in each season were investigated and the variation characteristics of spatial and temporal were clarified in this study. How the changes of precipitation amount (days) in different seasons affect annual precipitation amount (days) and how the changes of precipitation amount (days) in different grades affect seasonal precipitation amount (days) were also figured out. The results showed that: (1) annual precipitation days decreased significantly with an averaging downward trend of 0.1 days per decade in Northwest China from 1951 to 2015. Significant difference was shown in both precipitation days and its temporal variation among different observation stations. (2) The annual precipitation amount in Northwest China also increased significantly from 1951 to 2015, with an average increasing trend of 3.9mm per decade. (3) Strong seasonal variations were shown in precipitation amount and days, with the most in summer and the least in winter. The contribution rate of summer precipitation amount and days in each province was 50%-63% and 35%-48%. The precipitation amount was similar in spring and autumn. In each season, the light and moderate rain was mainly, which accumulative contribution rate of precipitation days was above 90%. The rainstorm only occurred in summer, which contribution rate was less than 1%. (4) The variation of precipitation amount(days) in summer and autumn was the most important reason for the change of annual precipitation amount(days), and the change of light and moderate rain was the most important reason for the change of total seasonal precipitation amount(days). The precipitation in spring and winter was not dominant in the annual precipitation, and the heavy and rainstorm were not dominant in the current season (annual) precipitation, so their effect were not obvious.