Spatio-temporal variations of different grade precipitation in the pastoral area on the northern slope of Qilian Mountains during vegetation growing season
Taking the grassland pastoral area of Sunan County on the northern slope of Qilian Mountains as the research area, we selected the daily precipitation data of seven nearby weather stations from 1961 to 2016 to analyze the spatio-temporal variations of different grade precipitation in Sunan County during the vegetation growing season using the climate tendency method, Hurst index method, Mann-Kendall test and inverse distance weighted interpolation. The results show that the anomalous percentages of the quantity and intensity of precipitation in Sunan County during vegetation growing season showed a significant increasing trend, whereas the precipitation days presented an insignificant increase. Significant abrupt changes of the quantity and intensity of precipitation occurred in 1988, but no significant abrupt change of precipitation days occurred. The precipitation was dominated by light rainfall and the variation coefficient of moderate rainfall was large, but it tended to rise steadily in recent years. The spatial distribution of the days and intensity of precipitation decreased from the southeast to the northwest, which was similar to the distribution of light rainfall. To the opposite, the distribution of moderate rainfall decreased from the north to the south. Compared with the contribution of moderate rainfall, light rainfall contributed more to the precipitation; however, the increase of moderate rainfall was more significant than that of light rainfall in recent years, and the spatial and temporal distribution of precipitation showed an unbalanced trend.