Impact Of Groundwater Extraction On The Runoff Generation In The Huang-Huai-Hai Plain

In China,a series of environmental problems brought by groundwater exploitation is restricting the socio-economic development of cities,such as ground subsidence,land salinization,surface dryness,seawater backup.These problems are also causing significant limitations for local agricultural production and domestic water use,affecting the regional water cycle process and causing changes in the regional water balance storage relationship.As a major agricultural development area in China,the Huang-Huai-Hai Plain is rich in agricultural resources and is an essential source of grain and cotton.Its agricultural development and the resulting environmental hydrological problems are becoming increasingly prominent and are a hot spot in water science.This thesis presents a systematic explanation of the changes in flow production in plain areas under the influence of groundwater extraction.The main findings include the following three aspects.(1)Analysis of the changes in groundwater storage and depth of burial.Analysis of the changes in groundwater storage and depth of burial in the Huang Huaihai Plain from 2003 to 2016,based on GRACE gravity satellite inversions of water storage and measured groundwater depth of burial data,using spatial interpolation analysis,regression analysis and Mann-Kendall trend test,and other methods.The results show that:(i)the groundwater storage in the Huang Huaihai Plain has shown a significant decreasing trend in the last 14 years through the Mann-Kendall test with a significance level of 0.01,with a decrease rate of 1.2cm/a,among which the decrease rate in the Haihe Plain is 1.6cm/a and the decrease rate in the Huaihe Plain is 0.9cm/a;(ii)the groundwater depth of burial has increased by 0.09 m per year on average,showing a significant(3)Based on the regional water balance change pattern,human water extraction and the analysis of the impact on groundwater,it shows that groundwater over-exploitation is the main reason for the decline of water storage in the Huang Huaihai Plain.(2)Due to the construction of the hydrological model of the plain area and the analysis of the importance of the parameters of the machine learning algorithm.Taking the Huang Huaihai Plain as the research object,a hydrological simulation system for the Huang Huaihai Plain was constructed using the variable infiltration capacity(VIC)model based on the multi-source element datasets of regional water cycle fluxes and storage from actual measurements,remote sensing inversion and assimilation,and a model parameter rate method based on the synergistic rate of runoff,evapotranspiration and storage was proposed to assess its applicability in the hydrological simulation of the Huang Huaihai Plain.The model uncertainty is assessed using machine learning and generalized likelihood uncertainty estimation,and the parameter space of the hydrological model is optimised to reduce the uncertainty confidence interval of the parameter simulation.The results show that:(i)the VIC model has good applicability in the Huang Huaihai Plain,with correlation coefficients exceeding 0.9 for simulated runoff and evapotranspiration and 0.6 for water storage compared to the measured values;(ii)the second soil thickness d2 is the most sensitive compared to the six parameters of the VIC model,followed by the variable infiltration curve index B,while the rest of the parameters are less sensitive;(iii)compared to the traditional single runoff rate determination method Compared with the traditional single runoff rate method,the co-rate parameter rate method improves the simulation accuracy of evapotranspiration and water storage,reduces the preference space and uncertainty confidence interval of model parameters,and reduces the 90% confidence interval of simulated runoff by about 26%,which reduces the uncertainty of hydrological simulation.(3)Groundwater extraction impact assessment.As the previous study showed that the most serious area of groundwater and water storage decline in terms of spatial and temporal distribution was concentrated in this part of the Hai Nan River Plain,a VIC model was developed for the Hai Nan River Plain in order to study the impact of groundwater decline on the flow production in the plain area.The VIC model was developed for the Haihenan Plain in order to study the impact of groundwater decline on flow production in the plain area.Therefore,a 5-year sliding rate determination was carried out for the selected time period.The relationships between groundwater depth,water storage,model soil layer thickness and runoff coefficient were analysed for the whole time period and the remaining 10 sliding time periods,and the results showed that:(1)The VIC model has good applicability in the Haiyan River system,and the absolute value of the relative deviation of simulated runoff and evaporation from the observed values is within 8% in each sliding time period,and the correlation coefficient is basically above 0.8.The correlation coefficients of simulated water storage are also above 0.7;(2)The sliding rate results show that the second layer of soil thickness in the Hai Nan River system has a trend of increasing year by year,and shows a high correlation with groundwater and water storage;(3)The increase in soil layer thickness will lead to a decrease in the runoff coefficient,and the second layer of soil thickness in the Hai Nan River system increased from 0.36 m to 0.42 m from 2003 to 2016,and the runoff coefficient The runoff coefficient was reduced by about 0.02.The results of the study are supportive of the understanding of regional water cycle evolution patterns and water resources management and exploitation in the changing environment of the plain area.