The impact of future changes in climate variables and groundwater abstraction on basin-scale groundwater availability

Abstract. Groundwater is under pressure from a changing climate and increasing anthropogenic demands. In this study, we project the effect of these two processes onto future groundwater status. Climate projections of Representative Concentration Pathway 4.5 (RCP4.5) and Representative Concentration Pathway 8.5 (RCP8.5) from the Coupled Model Intercomparison Project Phase 6 (CMIP6) drive a one-way coupled fully distributed hydrological and groundwater model. In addition, three plausible groundwater abstraction scenarios with diverging predictions from increasing, constant, and decreasing volumes and spatial distributions are used. Groundwater status projections are assessed for short-term (2030), mid-term (2050), and long-term (2100) periods. We use the Bandung groundwater basin as our case study; it is located 120 km from the current capital city of Indonesia, Jakarta, which is currently scheduled for relocation. It is selected as the future anthropogenic uncertainties in the basin, related to the projected groundwater abstraction, are in agreement with our developed scenarios. Results show that changes in the projected climate input, including intensifying rainfall and rising temperature, do not propagate notable changes in groundwater recharge. At the current unsustainable groundwater abstraction rate, the confined piezometric heads are projected to drop by maxima of 7.14, 15.25, and 29.51 m in 2030, 2050, and 2100, respectively. When groundwater abstraction expands in proportion to present population growth, the impact is worsened almost 2-fold. In contrast, if groundwater abstraction decreases because of the relocated capital city, groundwater storage starts to show replenishment potential. As a whole, projected groundwater status changes are dominated by anthropogenic activity and less so by changes in climatic forcing. The results of this study are expected to show and inform responsible parties in operational water management about the issue of the impact of projected climate forcing and anthropogenic activity on future groundwater status.