| Groundwater is one of the most important water sources in arid and semi-arid regions,but it is increasingly scare under the dual influence of climate change and human activities.Studying the groundwater recharge processes and spatio-temporal variation has important practical significance for the sustainable utilization of regional water resources.The vadose zone is thick in the loess tableland,and the recharge mechanism of groundwater is controversial.The sustainability of regional groundwater resources is not clear.Therefore,it is urgent to estimate the current groundwater recharge and predict recharge in future scenarios.Taking the Changwu tableland as the study area,and taking the water level data of5 monitoring wells in the Changwu tableland from 1976 to 2017 as an example,based on the analysis of the groundwater level fluctuation characteristics of each well,the water table fluctuation method was used to estimate the recharge.The mechanism of the spatio-temporal variation of groundwater recharge was explained by combining climatic and non-climatic factors.The contribution rate of each influencing factor to the recharge variation was quantified.Finally,the data of rainfall,maximum temperature and minimum temperature under the 5 regional climate models(RCM)were corrected,and the variation in future recharge of two emission scenarios were predicted.The main conclusions are as follows:(1)The variation characteristics of groundwater depth were explored and its influencing factors were identified in Changwu tableland from 1976 to 2017.The groundwater depth of Changwu tableland was between 25-95 m,and the wells showed different fluctuation characteristics due to differences in hydrogeology and human interference degree.Generally,it showed a downward trend,with a decrease of 0.08-0.21m/a.Meteorological factors,vegetation and human factors(population,GDP and apple orchard area)all had certain influence on the water table in the annual or interannual scale,but the dominance were different.On the interannual scale,human factors dominated the groundwater depth change;on the intraannual scale,vegetation was the main factor affecting the water table.(2)The groundwater recharge in Changwu tableland was estimated and its changes were attributed.Groundwater recharge was estimated using the water table fluctuation method and the mean annual recharge(lateral flow excluded)was 13±4 mm/a, equivalent to 2%of the mean annual precipitation.Spatially,the recharge gradually decreased from the center to the edge of the tableland.Temporally,the rate of decrease in recharge was 3±1 mm/a.The results of cross-correlation and wavelet coherence analysis showed that there was a time lag of 1-8 months between recharge and precipitation.The relative contributions of climate,vegetation,lateral flow and human impacts(population and land use change)to recharge variation were 22%,11%,17%and 50%,respectively,indicating that human activities was the dominant factor controlling the recharge rate in the tableland.(3)Future climate change and groundwater recharge were projected in multiple scenarios.The bias-correction of rainfall,maximum temperature and minimum temperature under the five RCM climate models were carried out.The processed RCMs data could well reproduce and predict the historical and future climate change trend.From 2021 to 2050,the climate of the study area tends to be warm and dry,with decreasing precipitation and increasing temperature.This change in RCP8.5 emission mode is more significant than that in RCP4.5.Compared with the historical period,groundwater recharge under different future scenarios shows a decreasing trend in general.The recharge rate under RCP4.5 is generally greater than that under RCP8.5.Compared with the single climate change scenario,the decrease in recharge is greater under the co-change scenario of climate,vegetation,and human activities.This study mainly used the water table fluctuation method to estimate the groundwater recharge in Changwu tableland,and used multiple methods to explore the dominance factors of recharge variation at different time scales.Finally,based on the future climate data of five RCM models under two emission scenarios,we achieved the prediction of future groundwater recharge in the study area.It will improve the understanding of the groundwater system in the loessial tableland,and provide scientific basis and reference for the management of groundwater resources in the Loess Plateau and related researches in similar regions. |
