Analysis On The Characteristics Of Climate Change In The Upper And Middle Reaches Of The Yellow River And Its Impact On Runoff

The Yellow River Basin is one of the birthplaces of Chinese civilization,but there are also problems such as fragile ecological environment and insufficient water resources.Along with global warming,the ecological and hydrological process of the Yellow River Basin has become increasingly prominent in response to climate warming,especially the runoff of the mainstream of the Yellow River.The main stream is the main surface water resource of the Yellow River,and it is also the guarantee for the economic development of the basin.Therefore,studying the characteristics of climate change in the middle and upper reaches of the Yellow River and its impact mechanism on runoff has important practical significance for the ecological protection and high-quality development of the Yellow River Basin.Relying on the public welfare project of China Geological Survey,this dissertation takes the upper and middle reaches of the Yellow River as the research area.Using mathematical statistics,spatial information technology and other methods,the climatic elements and the characteristics of dry and wet state changes in the study area were analyzed.The response of the runoff of the main stream of the Yellow River to climate change and wet and dry conditions was studied,and the impact of climate change on the runoff of the main stream of the Yellow River was revealed.The following results and understanding have been achieved:1.According to the average temperature and precipitation changes in the upper and middle reaches of the Yellow River from 1961 to 2018,it can be seen that the basin is becoming dry and hot.However,the temperature and precipitation changes in the upper and middle reaches of the Yellow River are different,making the upper reaches of the Yellow River tend to become warmer and humid,and the middle reaches of the Yellow River tend to become dry and hot.The temperature rises most notably in winter,and the precipitation decreases most notably in summer.The spatial distribution of temperature and precipitation tendency rate shows that the most significant temperature change is in the Yinchuan-Baotou section,and the most significant precipitation is in the area above Tangnaihai Station and the Longmen-Huayuankou section.2.Significant changes occurred in the number and intensity of extreme weather in the upper and middle reaches of the Yellow River from 1961 to 2018.The number of days of extreme precipitation is decreasing,and the amount of heavy rain and torrential rain is increasing.It shows that the rainfall pattern of the basin is changing,showers are increasing,and continuous precipitation is decreasing.The sensitive areas for extreme precipitation index changes are the area above Tangnaihai Station and the Longmen-Huayuankou section.Extreme temperatures are rising significantly,with the lowest temperature rising the fastest and the highest temperature rising the slowest.The number of hot days is increasing and the number of cold days is decreasing,indicating that the basin is further warming.The most sensitive areas to extreme temperature changes are the area above Tangnaihai Station and the Yinchuan-Baotou section.3.From 1961 to 2018,the interannual potential evapotranspiration(PET)and drought index(SPEI)of the upper and middle reaches of the Yellow River are different in time and space.The PET in the upper reaches of the Yellow River is rising,while the middle reaches of the Yellow River is falling,similar to changes in precipitation.The middle and upper reaches of the drought continued.The upper and middle reaches of the PET Yellow River in the four seasons show differences,with summer and autumn decreasing,but spring and winter increasing.The frequency distribution of wet and dry grades shows spatial differences.SPEI has the best correlation with precipitation,followed by PET,and finally temperature.It shows that precipitation and PET are the main factors affecting the wet and dry state of the basin.4.From 1961 to 2018,the Toudaoguai and Huayuankou sections of the main stream of the Yellow River showed a significant downward trend.There was an abrupt change around 1985,with different changes before and after the abrupt change.The main period of the runoff was about 25 a.The research results show that runoff changes are more sensitive to the response of precipitation and SPEI,followed by PET,which further confirms that precipitation is a replenishment source of runoff and drought also directly affects the water resources of the basin.The change of runoff has no significant response to temperature.It reveals that precipitation and PET are the main controlling factors that dominate the runoff of the mainstream of the Yellow River,not temperature.5.Cross-wavelet analysis shows that precipitation and SPEI have the best correlation with runoff,showing a positive correlation,the runoff has a short time lag,about 10d;the average temperature is negatively correlated with PET and runoff,and the time lag is long,about 160 d.Among the five extreme rainfall indicators,runoff has the highest correlation with heavy rainfall events(R95p)and the shortest time lag(about 20 days).Except that the number of consecutive days without precipitation(CDD)has a low correlation with runoff and a long time lag,the others are positively correlated with a short time lag(35-90d).Among the eight extreme temperature indicators,the number of icing days(ID)has the best correlation with runoff,and the time lag is the shortest(about 6 days).Except for the number of frost days(FD),other extreme indexes are negatively correlated,with a long time lag(125d-180d).