Quantitative Evaluation Of Generalized Water Resources In Changing Environment Based On Water Cycle Simulation

In recent years,with the rapid development of social economy,water resources have become an important factor restricting regional economic and social development.The evaluation of the quantity of water resources is the basis for the rational allocation and efficient use of water resources.The traditional water resources assessment only focuses on runoff water resources such as river runoff and lakes that can be directly used by humans,while ignoring non-runoff water resources.The Weihe River is a tributary of the Weihe River and a secondary tributary of the Yellow River.It is located in the Loess Plateau and has serious water and soil loss.It is the main sand producing area and water producing area of the Yellow River.Since the beginning of the 21st century,the vigorous promotion of the policy of“returning farmland to forests”and“closing mountains and prohibiting grazing”,the adjustment of agricultural planting structure and the changes of meteorological elements have greatly increased the area of forest and grass vegetation in the basin,and the area of cultivated land has been decreasing.This paper takes the Weihe River Basin as a research area,introduces the concept of generalized water resources,analyzes the temporal and spatial distribution of generalized water resources in the study area and its evolution,and further analyzes the response of generalized water resources to climate change and land use.The main findings are as follows:(1)Using linear estimation and Mann-Kendall rank correlation test to analyze the evolution of temperature,rainfall and runoff in the study area,it is found that from 1960to 2013,the annual average temperature of the study area showed a clear upward trend..Rainfall showed a downward trend but was not significant,and the runoff in the study area showed a significant downward trend.In terms of land use,the main land use types in the study area are cultivated land and grassland,and the main direction of change is from cultivated land to forest land and grassland.(2)Establish the SWAT model of the Weihe River Basin and carry out parameter calibration and verification.The rate regularity coefficient and Nash coefficient are 0.84and 0.76,and the verification period is 0.80 and 0.76.The fitting effect is better.The SWAT model simulation results can be used to evaluate the generalized water resources in the study area.(3)Using SWAT model to analyze the spatial and temporal distribution of generalized water resources in the study area.The results show that the average annual water resources of the study area is 208.84 billion m~3,of which the runoff and non-runoff water resources are 15.9 billion m~3 and 192.95 billion m~3,respectively,accounting for 7.6%and 92.4%of the general water resources.In terms of spatial distribution,the three are generally showing a trend of decreasing from south to north.(4)Using linear propensity estimation and Mann-Kendall rank correlation test to analyze the evolution law of generalized water resources in the study area,it is found that the generalized water resources in the study area showed a downward trend from1963 to 2013,and the non-runoff water resources showed a downward trend.In terms of space,the amount of runoff water resources in all sub-basins of the study area showed a significant downward trend;the non-runoff water resources and generalized water resources in most sub-basins showed a downward trend,and some sub-basins in the south and north showed an upward trend.However,the upward trend is not obvious.(5)Using the control variable method to analyze the impact of climate and land use on the generalized water resources in the study area,the results show that the amount of runoff water resources and non-runoff water resources are proportional to rainfall,and the amount of runoff water resources and temperature are In contrast,the amount of non-runwater resources is proportional to the temperature.Using multiple linear regression,it is found that the amount of runoff water resources and non-runoff water resources are more sensitive to changes in precipitation.At the same time,land use change is an important cause of the change in runoff water resources and non-runoff water resources in the study area.(6)Analyze the impact of meteorological conditions and land use change on runoff water resources and non-runoff water resources in the study area by setting scenarios of meteorological and land use combinations in different periods.It shows that due to the small change in land use during the evaluation period,the change of meteorological conditions is the main reason for the change of water resources during the evaluation period.