降水日数及强度的变化特征研究对黄土高原应对气候变化及水资源开发利用具有重要的科学意义。利用1960—2017年黄土高原地区55个地面气象站逐日降水资料,分析了总降水和不同等级降水（小雨、中雨、大雨和暴雨）的日数、强度和降水量的时空变化规律,并量化各等级降水日数和强度对降水量增量的贡献。结果表明:（1） 近58 a黄土高原地区不同等级降水日数和降水量,以及大雨和暴雨强度皆呈减少趋势,而总降水、小雨和中雨强度呈增加趋势,小雨日是黄土高原地区降水最主要的形式。（2） 黄土高原地区总降水、小雨、中雨的降水日数和降水量及其变化趋势的空间分布格局基本一致,即总降水和小雨等级皆呈西南高、西北低,降幅呈南多北少格局;中雨等级自东南至西北方向递减,趋势呈南降北增的规律;大雨以上等级自东南至西北向递减,趋势呈中部增加、南北减少特征。各等级降水强度与对应降水量分布特征基本一致,但强度趋势的空间分布较为复杂。（3） 黄土高原多数地区的降水量下降趋势是由降水日数的减少所致。降水日数趋势变化对降水增量起主要贡献的有总降水、小雨和中雨等级,空间格局呈南高北低特征;降水强度趋势变化对降水增量起主要贡献的仅有大雨以上等级,呈东北至西南方向高,而两侧低的空间特征。

The study on the variation characteristics of precipitation days and intensity is significant for the Loess Plateau to cope with climate change and water resource exploitation. Based on the daily precipitation data of 55 surface meteorological stations in the Loess Plateau from 1960 to 2017, the temporal and spatial variability of rainfall, precipitation days, and intensity of the total precipitation and precipitation of different grades (light rain, moderate rain, heavy rain, and rainstorm) were analyzed. The contribution of precipitation days and intensity at each grade to precipitation increment was quantified. Results showed that the total precipitation, light rain, moderate rain, heavy rain, rainstorm days and rainfall, and the intensity of heavy rain and rainstorm all had a decreasing trend in the past 58 years. In contrast, the intensity of total precipitation, light rain, and moderate rain increased. Light rain day is the primary precipitation form in the Loess Plateau. The precipitation days of total precipitation, light rain, and moderate rain in the Loess Plateau were consistent with their respective spatial patterns; that is, the levels of total precipitation and light rain were higher in the southwest and lower in the northwest. The decreasing amplitude was more significant in the south than in the north; also, the moderate rain grades decreased from southeast to northwest, and trend showed the law of descending from south to increasing from north. The heavy rain and above grades decreased from southeast to northwest, and the trend also decreased in the middle and north and south. The precipitation intensity of each grade was consistent with the corresponding precipitation distribution characteristics. However, the spatial distribution of intensity trend was more complex. The decreasing trend of precipitation in most areas was due to the reduction in precipitation days. The primary contribution of precipitation days trend change to precipitation increment included total precipitation, light rain, and moderate rain. The spatial pattern of their contribution rate was high in the south and low in the north. While the primary contribution of precipitation intensity trend change to precipitation increment was for heavy rain and above, which was spatially characterized by high in the northeast-southwest and low in the east and west.