Global exposure of population and land-use to meteorological droughts under different warming levels and SSPs: a CORDEX-based study.

Global warming is likely to cause a progressive drought increase in some regions, but how population and natural resources will be affected is still underexplored. This study focuses on global population, forests, croplands and pastures exposure to meteorological drought hazard in the 21st century, expressed as frequency and severity of drought events. As input, we use a large ensemble of climate simulations from the Coordinated Regional Climate Downscaling Experiment (CORDEX), population projections from the NASA- SEDAC dataset and land-use projections from the Land-Use Harmonization 2 project for 1981–2100. The exposure to drought hazard is presented for five Shared Socioeconomic Pathways (SSP1-SSP5) at four Global Warming Levels (GWLs: 1.5C to 4 C). Results show that considering only Standardized Precip- itation Index (SPI; based on precipitation), the SSP3 at GWL4 projects the larg- est fraction of the global population (14%) to experience an increase in drought frequency and severity (versus 1981–2010), with this value increasing to 60% if temperature is considered (indirectly included in the Standardized Precipitation-Evapotranspiration Index, SPEI). With SPEI, considering the highest GWL for each SSP, 8 (for SSP2, SSP4, SSP5) and 11 (SSP3) billion peo- ple, that is, more than 90%, will be affected by at least one unprecedented drought. For SSP5 at GWL4, approximately 2 × 106 km2 of forests and crop- lands (respectively, 6% and 11%) and 1.5 × 106 km2 of pastures (19%) will be exposed to increased drought frequency and severity according to SPI, but for SPEI this extent will rise to 17 × 106 km2 of forests (49%), 6 × 106 km2 of pas- tures (78%) and 12 × 106 km 2 of croplands (67%), being mid-latitudes the most affected. The projected likely increase of drought frequency and severity signif- icantly increases population and land-use exposure to drought, even at low GWLs, thus extensive mitigation and adaptation efforts are needed to avoid the most severe impacts of climate change.

Figure 11. Population and land-use progressive exposure to significant increase of both DF and DS at different GWLs under the SSP5 scenario, according to SPI (left) and SPEI (right). White represents areas with population below 1 inhabitant/ km2 and land-use below 5% over the grid point.