Study Of Groundwater Recharge In The Sanjiang Plain Under The Influence Of Land Use Change

In recent years,the high-intensity exploitation of water resources,mainly groundwater,has supported large-scale agricultural development,resulting in dramatic changes in the regional land use pattern.The Sanjiang Plain is a key area for China’s food security,blackland ecological security and water security guarantee.In order to further rationalize the allocation of regional water and soil resources and achieve reasonable utilization of groundwater,it is necessary to identify the process of land use changes in recent years,accurately assess the impact of land use type changes on the amount of groundwater recharge in the Sanjiang Plain region,and provide an important basis for the optimal allocation of regional water and soil resources.In this paper,based on“Strategic Priority Research Program of the Chinese Academy of Sciences”(XDA28100105),in the Sanjiang Plain as the research area,using multiphase remote sensing products and mathematical statistics method,calculate degree of land use dynamic degree and the comprehensive index,build the transfer matrix of land use,The temporal and spatial evolution characteristics of regional land use were expounded.Soil water balance method was used to calculate groundwater recharge in typical years of land use change,and the relationship between land use change,groundwater recharge and its recharge factors was discussed.The SWAT model was constructed,and the verified groundwater recharge results were calculated by combining the historical runoff and comprehensive recharge calculation method,and the numerical simulation of regional water cycle process and groundwater recharge was established.From the perspective of historical land use distribution and specific spatial distribution,the historical change scenario of regional land use scenario and the change scenario of main land use types were set up.The SWAT model was used to calculate the total groundwater recharge and groundwater recharge of paddy field,dryland and wetland,and to elaborate the impact of groundwater recharge change under the main land use change.The results are as follows:(1)Using multi-year remote sensing data(1980,2000,2010 and 2018),the main land use types within the study were identified as paddy fields,drylands,woodlands and wetlands,with drylands and woodlands being the main dominant land types.Under the influence of human activities,the arable land area showed an increasing trend,while wetlands,woodlands and grasslands showed a decreasing trend.Among them,the land use area trends of paddy fields,drylands and wetlands are closely related to the three land use transformation processes,and the main driving force of the land use evolution process is agricultural activities.(2)Using the soil water balance model,the years 2000-2018 were selected as typical years of land use change,and the precipitation,evaporation and soil water content showed an increasing trend under the influence of human activities,and the average amount of underground water resources in the main years was calculated to be 8,496million m~3.The evaporation showed a positive correlation with the change of paddy field area and a negative correlation with the change of dry land area.The comprehensive trend of each element determined that the regional soil water balance was affected by agricultural activities to a greater extent than the change of climatic elements,and the regional groundwater recharge was mainly changed by the change of land use pattern.(3)Using the SWAT hydrological model,a spatial database and an attribute database covering the complete study area were constructed to complete the regional hydrological model.By setting the threshold values of land use type,soil type and slope at 5%,5%and 5%,respectively,and delineating HRUs,28 sub-basins with 873 HRUs were finally delineated.using monthly runoff information,based on parameter sensitivity analysis and parameter rate determination,the best parameter passage rate of the model was determined regularly compared with the simulated and actual measured runoff during the validation period,and the integrated model evaluation index and the integrated recharge calculation method The groundwater recharge calculation result of the model and the integrated recharge calculation method,the multi-year groundwater recharge in this area is calculated as 7.450 billion m~3.And the results of wetland seepage and total groundwater recharge were compared and verified,showing that the model simulation is effective.(4)Setting up different land use scenarios,comparing the simulation results under the historical trend land use scenario and land use evolution conditions,it shows that compared with the base year scenario(1980),the unit area groundwater recharge generated by paddy fields increases by 1.71 times on average,and the unit area groundwater recharge generated by wetlands increases by 13.4%,and the concentrated distribution of paddy fields or wetlands will bring more groundwater recharge to the region.The order of influence on the total groundwater recharge by major land use types is dryland>wetland>paddy field;from the perspective of groundwater recharge per unit area,the order of influence on groundwater recharge by three major land use types is dryland>paddy field>wetland.