Distribution characteristics of runoff in Shiyang River basin and its responses to climate change——The case study of Xiying River

Based on the runoff observation and meteorological data at Xiying River in the Shiyang River basin during 1961—2009,the change trend and annual distribution of runoff as well as their relationship with meteorological factors were analyzed.The results showed that the overall change trend of runoff was going down in the recent 49a,and the decrease range was greater in winter and summer than in spring and autumn.The seasonal runoff decreased obviously in 1990s,especially the evident abrupt changes were found in yearly,spring and summer runoff.The annual runoff came mainly from rainwater during flood seasons,and the proportion of rainwater in total runoff was gradually increased,while that of snow melt water in total runoff was decreased.There was a small increasing trend of precipitation in the river basin,but it was not obvious in summer.The temperature increased significantly,and the trend coefficient of temperature was the largest in winter,which caused the increase trend of evaporation.Correlative analysis showed that the runoff was positively correlated with the monthly precipitation during June to September,but it was negatively correlated with monthly temperature and evaporation during July to August.The probable influences of future temperature and precipitation changes on runoff under different conditions was also analyzed,which showed that the temperature would play a main negative role on runoff,and the rise of temperature along with the increase of evaporation during flood periods would bring out the decrease of total annual runoff.Climate warming would be unfavorable to the increase of runoff in general.