LAN Yongchao, ZHU Yuntong, LIU Gensheng, LA Chengfang, SHEN Yongping, SHI Mingxing
Based on the observation data at the relevant stations, the seasonal variation and regional variations of temperature and precipitation in the four sub-regions in the source region of the Yellow River, that is, the area above Huangheyan hydrological station, the area between Huangheyan hydrological station and Jimai hydrological station, the area between Jimai hydrological station and Maqu hydrological station and the area between Maqu hydrological station and Tangnag hydrological station, and whole of the four sub-regions (named source region) during the period from 1960 to 2014 and their regional differences were analyzed.The result shows that the changing processes of all annual and seasonal temperatures in all sub-regions had risen, which were consistent with the global temperature changing trend, and the rising rates of the annual mean and seasonal temperatures in the four sub-regions were significantly higher than those of global and China's mean temperature.The annual difference of rising rate of mean temperature was small, and the seasonal differences of the rising rate of the temperature in sub-regions were very large.Abrupt change had occurred on temperature in all sub-regions after 1996, and all mean temperature series after abrupt change rose substantially as compared with that before abrupt change.The variation of precipitation in the source regions of the Yellow River was very complicated and the variation of seasonal precipitations had a distinct difference because of the influence of geographical environment.As a whole, the interannual variation of the mean precipitation in the source regions has presented an increasing trend indistinctively in the past more than 50 years.Thereinto, the increase of precipitation on the top half of the source regions with higher altitude, that is, in the areas above Huangheyan and between Huangheyan and Jimai, has been more significant, while the precipitation in the lower half of the regions, that is, the areas between Jimai and Maqu and between Maqu and Tangnag, had decreased and the decreasing precipitation in the area between Jimai and Maqu, in which the contribution of precipitation and runoff yield was the maximum among the whole source regions of the river, was most remarkable.The precipitation in winter, spring and summer in the sub-regions had generally increased, while precipitation in autumn had decreased.Thereinto, the decrease of precipitation in autumn in the area between Jimai and Maqu had been most remarkable.The difference of interdecadal variation of seasonal precipitations in the four sub-regions had been larger than that of interannual variation, merely the seasonal precipitation in the four sub-regions had been generally larger than the average since 2010.The time of abrupt change of annual and seasonal precipitation didn't agreed with that of temperature.The abrupt changes in annual and summer precipitations occurred mostly in 2005 and that in autumn occurred mostly in 1986, and the abrupt changes in winter and spring precipitations were rough and tumble.After and before abrupt changes, there were both increasing and decreasing of the precipitation series with different changing ranges.
