Présentations Colloques

Within the framework of the Transboundary Waters Assessment Programme (TWAP), initiated by the Global Environment Facility (GEF), we contributed to a comprehensive baseline assessment of transboundary aquifers (TBAs) by quantifying different groundwater indicators under current (2010) and projected conditions in 2030 and 2050 using the global water resources and water use model WaterGAP 2.2. The set of indicators included per-capita groundwater recharge, groundwater depletion, dependency on groundwater, and groundwater development stress (groundwater withdrawals to groundwater recharge, GWDS). Projected indicators were quantified using climate scenarios of five global climate models (GCMs) for the high-emissions scenario RCP 8.5 and two alternative water use projections consistent with SSP2.**According to our assessment, aquifers with the highest current groundwater depletion rates worldwide are not transboundary. Exceptions are the Neogene Aquifer System (Syria) and the Indus River Plain aquifer (India). For current conditions, we identified 20 out of 258 TBA-CUs (CU- country unit) suffering from medium to very high GWDS. Per-capita groundwater recharge is projected to decrease in 80-90% of all TBA-CUs until 2030 2050. Due to the strongly varying projections of the global climate models, we applied a worst-case scenario approach to define future hotspots of GWDS, taking into account the highest computed increase of GWDS until either 2030 or 2050 among the ten GCM water use scenarios. Based on this approach, the number of TBA-CUs under at least medium GWDS increases from 20 to 58, comprising all hotspots under current conditions. New hotspots are projected to develop mainly in Sub-Saharan Africa, China and Mexico.**The study provided a globally-consistent analysis of groundwater quantity-related stress in TBAs under current and future climatic and water use conditions. By applying a worst-case scenario analysis with a focus on the high-emissions scenario RCP 8.5, its results are appropriate for informing adaptation to climate change under a precautionary approach.