Study On Runoff Evolution Trend In Luojiang River Basin

Water resources have become a strategic resource for many countries,and the richness of its content can largely show the strength of a country’s comprehensive strength.The distribution of water resources in our country has been unbalanced since ancient times,and the water environment problems are complex and changeable.In addition,the narrow development concept and consciousness of all countries in the world in the last century have led to the continuous warming of global temperature,which fundamentally affects the circulation process of water resources.Furthermore,the scope of human activities has become deeper and wider,which has a certain impact on water resources and even the whole ecological environment.In China in 2012,the strictest water resource management system was implemented,in order to deal with the severe water resource problem,and build a water-saving society while promoting sustainable economic development.It can be seen that exploring the influence of climate change and human activities on runoff in different basins,is helpful to provide scientific theoretical guidance for local water resources management,land use planning,and friendly ecological environment construction.It will provide a constructive foundation for the development of digital water conservancy models and intelligent water conservancy in different regions.Although there are many researches on hydrological response processes in different regions under changing environment,the fundamental differences in different regions,the research methods adopted and the parameters selected can lead to different research processes and results.In view of this,this paper chooses the Luojiang River Basin as the study area.Firstly,analyzed the variation characteristics of hydrometeorological elements in the past 50 years,and then constructed SWAT model on this basis.Then,the meteorological scenario setting method,the comparison method of multi-period land use change,and the SWAT model were combined,in order to explore the spatio-temporal influence of climate and land use change on runoff.Finally,CA-Markov model was used to predict the future land use scenarios in Luojiang River,and combined with the climate prediction results the natural runoff in 2025 was simulated.At last,according to the forecast results,put forward targeted prevention plans.The main research results are as follows:(1)Nonlinear regression,Mann-Kendall nonparametric test method,Accumulative anomaly method and Morlet wavelet analysis method were used to analyze the trend,mutation and periodicity characteristics of the precipitation and temperature series from 1970to 2019,and the runoff series from 1975 to 2019 in the Luojiang Basin.(2)The SWAT hydrological model was constructed in Luojiang River Basin.The results show that the correlation coefficient(R~2),Nash coefficient(NSE)and percentage of deviation(PBIAS)can meet the evaluation criteria.The SWAT model can be used to simulate the monthly runoff process of Hejiang hydrological station in the Luojiang Basin,and can be used to explore the relationship between subsequent environmental changes and runoff.(3)Under fixed temperature,the runoff and precipitation were positively correlated,and runoff was more sensitive to precipitation decline,in Luojiang River.The spatial difference of runoff change rate is also mainly caused by precipitation characteristics in corresponding areas,but land use is also an important influencing factor:The conversion of garden land to forest land would make the underlying surface more complex and diverse,increase the interception rate of precipitation.Lengthen the time of runoff production and confluence,and reduce the formation rate,which would lead to the decrease of runoff coefficient and runoff.However,the increase of cultivated land and commercial land will lead to the decrease of water conservation capacity,the increase of runoff coefficient,and the increase of runoff.With the increase of cultivated land,the retention effect and water retention capacity of the underlying layer in the face of runoff decreased,which promoted the runoff convergence.With the increase of commercial land area,the hardened area of the region increases substantially,which changes the original pervious characteristics of the region,reduces the surface roughness,and the runoff yield and confluence are easy to form in a short time,resulting in the increase of surface runoff.(4)In Luojiang Basin in 2025,the land use will still be mainly garden land,accounting for more than 75%of the total area of the basin.The area of garden land and cultivated land will be substantially converted to commercial land.This change will lead to an increase in the overall runoff coefficient of Luojiang River Basin in the future,and the runoff would also increase.Based on this,it is proposed that the Luojiang River Basin should pay attention to the sensitivity of runoff change caused by precipitation characteristics in the middle and west of the basin,while accelerating the urbanization rate.At the same time,we should pay attention to the red line of cultivated land,garden and forest land in the north-central part of the basin,increase the construction of land use types with strong water conservation capacity,improve vegetation coverage,and promote the scientific management and positive development of water resources.