Spatio-temporal effect of climate change on water balance and interactions between groundwater and surface water in plains

The analysis of the impact of climate change on water resources in plains requires integral simulation tools that quantify topographic complexity and the strong interaction of groundwater and surfacewater components (GW-SW). The objective of this study is to implement a coupled hydrological-hydrogeological model under climate change scenarios in order to quantify the spatio-temporal dynamics of water balance and GW-SW interactions for the upper creek basin of Del Azul, which is located in the center of the province of Buenos Aires. The simulation was carried out for a baseline scenario calibrated and validated for the period 2003-2015 and contrasted with two scenarios of the regional climate model CCSM4, RCP (4.5 and 8.5) simulated for the period 2020-2050. First, the annual andmonthly anomalies of precipitation, temperature, surface runoff, evapotranspiration, soilmoisture, recharge, flow, aswell as the discharge, head level and reserves of groundwater are studied. Then the spatio-temporal anomalies of the GW-SWinteraction were analyzed and finallywet and dry periods by means of the standardized precipitation index and the annual water balance were studied. Simulation results show that climate change will significantly alter the spatio-temporal patterns of the GW-SW interaction as well as the water balance. These showed monthly, seasonal and annual variations. They show an increase in most of the components of the water balance towards the middle of the 21st century, except soil moisture. Regarding GW-SW interactions, the average annual discharge of the aquifer to the stream is expected to increase by 5% with RCP 4.5while itwill increase 24% with RCP 8.5. The recharge fromthe streamto the aquifer is expected to increase by 12% with RCP 4.5while a decrease by 5% with RCP 8.5. Concerning the SPI related to the water balance for the period 2020-2050, alternations of both the time and the length of dry and wet periods are expected for the two scenarios, with RCP 4.5 lowfrequency ofwet episodes, butwith a greater severity and permanence in time in contrast to RCP 8.5 that presents less frequency in dry periods, but with high permanence and severity. Climate change could alter groundwater mainly through changes in the recharge, leading tomodify groundwater levels and this will cause GW-SWflow to be reversed in some sectors of the stream by increasing or decreasing groundwater discharge into the stream. (C) 2020 Elsevier B.V. All rights reserved.