Variation Characteristics And Quantitative Separation Of Runoff In Karst Watershed

The karst watershed is affected by the external changing environment and its own complex underlying surface,and the water resources are more fragile than ordinary watersheds,posing a threat to the sustainable development and water security of the region.As the main source of regional water resources,runoff can directly affect the regional socio-economic and ecological environment.In view of this,this thesis takes the Chengbi River Basin,which belongs to the karst area of Southwest China,as the research object,to study the characteristics of runoff variation in this basin,and to quantify the impact of climate and human activities on runoff variation at multiple scales.The driving mechanism is expected to reveal the change mechanism of runoff in the karst area from multiple perspectives,so as to better guide the social and economic development and ecological protection of the area.The main results of this study have been drawn as follows:(1)Heuristic segmentation algorithm,sliding T test,Pettitt test,and MannKendall test were used to comprehensively diagnose the mutation points of runoff sequences,and based on Mann-Kendall nonparametric test,linear trend,and moving average method,concentration degree,concentration period,Gini method were introduced.Coefficient,distribution inhomogeneous coefficient and complete distribution coefficient are used to study the interannual and intraannual variation characteristics of runoff.The results show that: the runoff of the watershed changed abruptly in 1998,and the base period 1963～1998 and the change period 1999～2019 were divided by this;the interannual runoff was 0.22mm/a and 10.27 mm/a in the base period and the change period,respectively.The runoff showed a fluctuating downward trend as a whole;the distribution of runoff in the base period,the change period and the whole period gradually tended to be uniform,and the degree of inhomogeneity in the base period was the highest.(2)The weighting factor method based on Budyko complementary relationship,the extended Budyko model and the ABCD model are used to construct a quantitative impact framework to explore the impact of climate change and human activities on annual,seasonal and monthly runoff changes.The results show that precipitation and underlying surface parameters are the main controlling factors for climatic changes and human activities to affect annual runoff changes,respectively.When the annual-scale runoff completely follows the change path of the underlying surface,the change of runoff is the largest;climatic changes and human activities cause the runoff to decrease by 29.41 mm and 39.54 mm in the energy-limiting season(May-October),resulting in a waterlimiting season(January-April)month,November to December)runoff increased by 5.24 mm and 3.56 mm,indicating that human activities and climate change are the main driving factors of runoff changes in the energy-limited and moisturelimited seasons,respectively;climatic changes resulted in an increase of0.63～24.36 mm in runoff from January and March to June,a decrease of0.13～18.51 mm in runoff from February and July to December,a decrease of1.30～7.08 mm in runoff from January and October to December,and a decrease of 3.11～14.69 mm in runoff from March to September.(3)The underlying surface variation of the watershed are studied from land use change and vegetation cover change,and the driving mechanism of vegetation cover change is analyzed by using geographic detectors.The results show that:from 1990 to 2019,the grassland area in the basin decreased year by year,and the construction land area increased year by year.The expansion of construction land and the continuous change of cultivated land caused by human activities may cause certain pressure on water resources and change the underlying surface characteristics of the watershed;From 1987 to 2019,the NDVI of vegetation in the watershed showed an overall upward trend,and all regions except the southwest showed a significant improvement trend.From 2010 to 2019,the NDVI of the watershed showed an accelerated upward trend,and each region showed a significant improvement trend;soil vegetation and topography were largely improved.It determines the spatial differentiation of vegetation coverage,and as time went on,the influence of climate and economic factors on it is gradually strengthened.In addition,the interaction between factors further drove the change of vegetation coverage.