Vulnerability to the impact of climate change on renewable groundwater resources: a global-scale assessment

Climate change will lead to significant changes of groundwater recharge and thus renewable groundwater resources. Using the global water resources and use model WaterGAP, the impact of climate change on groundwater recharge and the number of affected people was computed for four climate scenarios by two climate models. Vulnerability of humans to decreased groundwater resources depends on both the degree of decrease and the sensitivity of the human system to the decrease. For each grid cell, a sensitivity index composed of a water scarcity indicator, an indicator for dependence of water supply on groundwater and the Human Development Index was quantified. Combining per cent groundwater recharge decrease with the sensitivity index, global maps of vulnerability to the impact of decreased groundwater recharge in the 2050s were derived. In the A2 (B2) emissions scenario, 18.4-19.3% (16.1-18.1%) of the global population of 10.7 (9.1) billion would be affected by groundwater recharge decreases of at least 10%, and 4.8-5.7% (3.8-3.8%) of the global population would be in the two highest vulnerability classes. The highest vulnerabilities are found at the North African rim of the Mediterranean Sea, in southwestern Africa, in northeastern Brazil and in the central Andes, which are areas of moderate to high sensitivity. For most of the areas with high population density and high sensitivity, model results indicate that groundwater recharge is unlikely to decrease by more than 10% until the 2050s. However, a fifth to a third of the population may be affected by a groundwater recharge increase of more than 10%, with negative impacts in the case of shallow water tables. The spatial distribution of vulnerability, even at the continental scale, differs more strongly between the two climate models than between the two emissions scenarios.