Abstract:

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.

Key words: precipitation days, precipitation intensity, precipitation increment, precipitation grades, the Loess Plateau