The Extreme Precipitation Trend Analysis and Spatial Variation for 50 Years in the Northern Part of Haihe River Basin

The daily precipitation data, from 1962 to 2012, of 20 relative meteorological stations in the Northern part of Haihe River Basin (NHHRB) were collected and analyzed to test the spatial variation and evolution trend of the extreme precipitation in NHHRB. Eight extreme precipitation indexes were selected and calculated to check the sustainability, frequency and intensity of the extreme precipitation in NHHRB and it is hoped to predict the characteristics or the likely types of precipitation causing disasters in the future. The results proved that: (1) the extreme precipitation happening in the plain area have the higher frequency and are more intensive than in mountainous area, and the extreme precipitation in coast area and the mountainous hinterland is of longer duration, while that in flat area and piedmont area are shorter, relatively; (2) through trend test, the sustainability in the flat area is examined to rise and the frequency and the intensity both have decreasing trend. In converse, in the mountain area and piedmont area, the sustainability of the extreme precipitation will re-duce, the moderate rain and rainstorm will happen less frequently while the heavy rain frequency is to rise, and the intensity strengthens. Therefore, it can be concluded that, due to the climate change, human activities and other factors, the characteristics of the extreme precipitation in NHHRB has changed. In the future, the flat area is more likely to suffer the disaster-causing precipitation with long sustainability, weak intensity and low frequency, and the mountain area will encounter with short-time, strong and frequent rainstorm.