Response Of Runoff Process To Climate And Land Use Change In Shilin Bajiang River Basin

The Shilin karst area in Yunnan is famous for its unique and diverse karst type.The water resources,which is one of the karst development powers,not only participate in the natural changes of the karst area,but also the industrial and agricultural production,social construction and domestic water in the karst area.And so on.Therefore,we need to understand the development and evolution characteristics of water resources in karst areas,and provide a basis for the sustainable development of local economic and ecological.The Shilin Bajiang River Basin is located in the karst karst area of the Yunnan-Guizhou Plateau.It is the first-level tributary of the Nanpan River in the upper reaches of the Pearl River.The hydrology and water resources and hydrological ecosystems in the basin are special,and the trend of rocky desertification is prominent.Due to the influence of special geographical environment and human factors,the sustainability of water resources and ecosystems in the basin has become an important factor restricting local economic development.Therefore,based on the previous studies,this paper analyzes the trend of climate change and land use change in the Bajiang River Basin by using mathematical statistics,remote sensing technology and hydrological model combined with existing meteorological hydrological data.The response of the basin runoff process to climate and land use change is discussed in order to provide reference for the rational use of water resources in the basin,soil erosion control,and improvement of the ecological environment.The important research results of the thesis are as follows:(1)The temperature tendency of the Bajiang River Basin from 1965 to 2017 was 0.38 °C/10 a,and the overall trend was fluctuating.During the year,the winter temperature rose the fastest,with a tendency rate of 0.50 °C/10 a.The basin temperature series produced a mutation in 1996.And the temperature change showed a significant upward trend after the mutation in 1996;there were periodic oscillations in temperature changes in 21 and 28 years,of which 28 years were the main oscillation period and throughout the study period.The rainfall in the basin has a significant downward trend at the rate of-16.32mm/10 a in the past 53 years.Since the basin is located in the north subtropical monsoon climate zone and has obvious dry and wet seasons,the seasonal variation trend of the rainfall season is quite different.The seasons showed a downward trend with a tendency rate of-3.09 mm/10 a and-3.22 mm/10 a,while the spring and winter seasons showed an upward trend with a tendency of 0.17 mm/10 a and 0.87 mm/10 a,respectively.In 1975,the mutation occurred;the analysis of the rainfall wavelet period in the basin showed that there are multiple oscillation periods of 5a,10 a,15a and 28 a in the basin,28 a is the main oscillation period and has full time domain.(2)From 1980 to 2009,the overall trend of runoff in the Bajiang River Basin decreased at a rate of-545.69 million cubic meters/10 a,and the runoff changes in the spring and winter seasons increased at a rate of 848,800 cubic meters per 10 a and 575,300 cubic meters per 10 a,respectively.The overall trend of runoff in the basin is quite different;the runoff in the basin has a sudden change in 1983;the runoff in the basin has an oscillation period in 2a,4a,and 8a during the study period,and the oscillation period of 8a has the full-time characteristics of the study period.Through the analysis of the uniformity coefficient,concentration and concentration period of the annual inner diameter flow during the study period,the results are analyzed.It shows that the distribution of runoff is extremely uneven during the year,and the highest difference reaches 0.39.In 1983,the unevenness coefficient of runoff sudden change reached the lowest;the runoff water concentration in the basin mainly occurred in summer and autumn,and these two seasons accounted for the annual inner diameter flow.The total amount is 78.9%,and 67% of the year's runoff is generated in July and August.(3)The characteristics of land use change in Bajiang River Basin from 1988 to 2015 were analyzed.The research shows that the annual change rate of comprehensive land use in the Bajiang River Basin during the study period is 0.83%.The construction land area and grassland area generally increase during the study period.,respectively,at a rate of 3.11% and 3.33% per year;while waters,woodlands,cultivated land,and unused land showed a decreasing trend during the study period,but the downward trend was small,and the annual decline rate was less than 1%,respectively,at-0.17 per year.The rates of %,-0.79%,-0.20%,and-0.55% decreased,and the changes in the transfer of cultivated land,unused land,and forest land were relatively large,while the changes in the area of water,grassland,and construction land during the study period were relatively flat.(4)Based on the multiple linear regression model and correlation analysis method,the corresponding analysis of the runoff and climate change in the Bajiang River Basin from 1980 to 2009 was carried out.The results show that the runoff of the basin has a strong correlation with the rainfall during the study period.Therefore,the multivariate linear regression model is used to quantitatively analyze the response relationship between runoff and rainfall,and it is found that when the rainfall is 0,±1%,± When the change rate of 5% and ±10% changes,the corresponding change amount of runoff is 0,±2.06%,±9.79%,±19.59%.It can be seen that rainfall is a sensitive factor causing the change of runoff in the basin.(5)Using ANN neural network and Mboost machine learning model,combined with the principle of separation and evaluation,the contribution rate of climate factors and land use change to runoff in the Bajiang River Basin from 1980 to 2009 was analyzed.Taking 2002 as the boundary,the base period was established in the early stage and the human activity period after 2002.The contribution rate of the land use change calculated by the ANN model was 94.4%,and the contribution rate of the land use change calculated by the Mboost machine learning model was 96.9%.It follows that the impact of land use change on river basin runoff during human activities after 2002 is much greater than that of climate.Overall,the above research results have added new ideas and methods for the further study of water resources in the Bajiang River Basin.It not only helps to improve people's understanding of the evolution law of water resources in the Bajiang River Basin,but also provides a theoretical basis for the rational use of water resources in the basin and the sustainable development of ecological hydrology.