Impacts Of Crop Production On Groundwater Depletion In The Hebei Plain

Hebei Plain is one of the important food production areas in China.Because of the monsoon climate,the shortage of surface water makes groundwater a major supply for food production.Over the past few decades,the excessive groundwater exploitation has caused sharply decline of groundwater levels,and various environmental problems appear,thus,it is urgent to develop the efficient water-saving agriculture.It has a very important practical significance to accurately estimate the amount of water consumed by crop production and evaluate the impacts of that on the decline of groundwater level.In this study,based on argo-hydrological model and remote sensing evapotranspiration(ET),we use the model inversion method to estimate the crop water consumption(the effective irrigation amount)at county level.We use the PEST to optimize the irrigation parameter in SWAP so as the simulated ET by SWAP is closest to the remote sensing ET,which we regard as the observed ET.Then,we expect that the simulated irrigation amount from the optimized parameter is the estimated effective irrigatiom amount.The results show that the SWAP-PEST method can meet the simulation applicability at field scale and county grid scale.During the period,the average effective irrigation amout in typical counties is not significant,except for few drought or wet years.The effective irrigation amount in maize season is much smaller than that in wheat season,and wheat is the main water consuming crop during the year,whose water consumption accounts for about 90% of the year.In addition,the annual effective irrigation amount of the typical counties has spatial variability.Combined with the results of the effective irrigation amount estimation and the groundwater balance equation,the study evaluates the groundwater balance of the typical counties in 2010-2015.The results show that the groundwater levels of the five counties are continuously declining,and the average contribution rate of food production on the groundwater consumption 68%,which indicates that the current cropping system(winter wheat-summer maize)is the main reason of the excessive groundwater consumption.In order to find the possible measures to alleviate the above situation,we set up four different cropping system scenarios,winter wheat single cropping system,summer maize single cropping system,triple cropping system(winter wheat/summer maize followed by fallow and early maize in two years)and spring potato-summer maize double cropping system,and use hydrological model to analyse the situation of the groundwater consumption in of each scenarios.The results show that the winter wheat single cropping system has high crop production reduction rate(65%)but the net groundwater exploitation reduction rate is small.The crop production reduction rate of summer maize single cropping system is 35% and it has little water consumption.There are similar performances in crop production and the water consumption of the triple cropping system and the double cropping system,which shows low crop production reduction rate and moderate net groundwater exploitation reduction rate,and their performances are better than those of the above two single cropping systems.