Analysis Of Hydro-meteorological Elements And Driving Factors Of Runoff In The Source Region Of Yellow River Under The Changing Environment

Water resources in the source region of Yellow River are extremely important,but the ecological environment is fragile and vulnerable to damage.Climate change has been a common challenge for us in recent years.Global warming,acid rain,ozone layer destruction and other problems have seriously affected the natural resources and human life.In the source region of Yellow River,there are problems such as water shortage,melting of glaciers,soil erosion,and land desertification have occurred.The ecological function of the source region of Yellow River has declined,and the river health has been threatened.Studying the evolution of hydro-meteorological elements and runoff in the source region of Yellow River under changing environment is important scientific guidance and social practical significance for strengthening water resources protection,utilization and guarantee systems.The paper analyzed the evolution of hydro-meteorological elements in the source region of Yellow River,including its consistency,trend,periodicity and spatial distribution.Besides,it studied the evolution of runoff in the study area,including its changing characteristics and driving factors,and calculated the impact of climate change and human activities on runoff evolution.The achievements mainly include:(1)According to the hydro-meteorological data in the source region of Yellow River from 1961 to 2015,heuristic segmentation,modified Mann-Kendall and Complete Ensemble Empirical Mode Decomposition with Adaptive Noise(CEEMDAN)methods were used to study the consistencies,trends,and periods of hydro-meteorological elements in the study area,which including precipitation,temperature and potential evapotranspiration(PET).The results showed that the increase trend of precipitation in the study area is insignificant,the time series is consistent,and the main period is 2.04a.The increase trend of temperature is significant,the mutation occurred in 1997,and the main period is not detected.The PET showed a significant increase trend,the mutation of PET occurred in 1969 and 2001,and the main period of PET was 3.67a.In terms of spatial distribution,the main procedures of the three elements present a northwest-southeast direction,and the value gradually increases from the northwest to the southeast.(2)According to the drought index and extreme climate indices,the drought and extreme climate change in the source region were analyzed.The results showed that the source region of Yellow River is gradually changing to "warmer and wetter",and the drought index has an increase trend since 1991.The change point of drought index occured in 1990,and the main period of drought index is 2.04a.The drought is mainly distributed from east to west,with the eastern region being relatively humid and the western region being relatively arid.Among the 8 extreme precipitation indices,the severe precipitation event(R95p),maximum 5-day precipitation(RX5day)and precipitation intensity(SD?)showed an increase trend.The years of mutation and the main period of each index are not completely consistent.The spatial distribution of indices is mainly northwest-southeast,and the results gradually increaded from northwest to southeast.Among the 11 extreme temperature indices,the number of cold day(TX10P),cold night(TN10P),frost days(FD0)and icy day(ID0)showed significant downward trends,and the remaining indices showed significant increase trends.Each index has its own mutation year and main period.The spatial distribution of each index is mainly northwest-southeast or south-north.The spatial distribution of each index is different before and after the change point.(3)It can be found in the 7 Land Use and Land Cover Change(LUCC)maps that the source region of Yellow River is dominated by grassland,followed by unused land,while urban and rural areas,industrial and mining,and residential land is the least.As a result of the research,the area of water has decreased.The area of cultivated land and urban-rural,industrial,mining,and residential increased,while other types of land use remained basically unchanged.During the period of 1982-2013,the normalized vegetation index(NDVI)increased,and the time series changed suddenly in 1986,with a main period of 4.00a.NDVI is mainly characterized by northwest-southeast spatial distribution,and the value gradually increased from northwest to southeast.(4)According to the runoff data in the Tangnaihai Hydrological Station in the source region of Yellow River during 1961-2015,the runoff showed an insignificant decrease trend.The runoff time series has a change point in 1990,and the main period is 3.67a.In spring and autumn,the runoff decrease trend is significant.In March and June,runoff has a slight upward trend,while the other months have downward trend.Precipitation is the main driving factor of runoff,the correlation coefficient between the two is large,and the correlation coefficient and coupling oscillation between them are obvious and strong.The correlation between runoff and drought index is relatively large,and the resonance signal is obvious.Runoff has a strong correlation with annual rain-day precipitation(PRCPTOT)and warm days(TX90P).LUCC is an important factor that affects runoff,but runoff and the normalized vegetation index(NDVI)have a rather weak correlation.(5)Human activities are the main influence factors of runoff changes,and climate change is an important factor.The period of 1961-1990 was the reference period,and 1991-2015 was the change period.According to the SCRAQ method,the contribution rates of runoff reductions caused by human activities and climate change were 79.04%and 20.96%,respectively.Based on the Budyko elastic analysis method,the contribution rates of runoff reductions caused by human activities and climate change were 78.53%and 21.47%,respectively.