This study provides a global analysis of drought metrics obtained from several climatic, hydrologic and ecological variables in a climate change framework using CMIP6 model data. A comprehensive analysis of the evolution of drought severity on a global scale is carried out for the historical experiment (1850-2014) and for future simulations under a high emissions scenario (SSP5-8.5). This study focuses on assessing trends in the magnitude and duration of drought events according to different standardised indices over the world land-surface area. The spatial and temporal agreement between the different drought indices on a global scale was also evaluated. Overall, there is a fairly large consensus among models and drought metrics in pointing to drought increase in southern North America, Central America, the Amazon region, the Mediterranean, southern Africa and southern Australia. Our results show important spatial differences in drought projections, which are highly dependent on the drought metric employed. While a strong relationship between climatic indices was evident, climatic and ecological drought metrics showed less dependency over both space and time. Importantly, our study demonstrates uncertainties in future projections of drought trends and their interannual variability, stressing the importance of coherent hydrological and plant physiological patterns when analysing CMIP6 model simulations of droughts under a warming climate scenario.

The spatiotemporal evolution of droughts in the Congo River Basin (CRB) from 1981–2018 was investigated using the Standardised Precipitation Index (SPI) and Standardised Precipitation–Evapotranspiration Index (SPEI) to assess the roles of precipitation and potential evapotranspiration. The results confirmed a notable trend toward drier conditions, particularly in parts of the northern and central basin, as well as in the south of the CRB, which was associated with increases in potential evapotranspiration and declining rainfall. Global outputs of the Lagrangian model FLEXPART were used to model air masses over four important climatological regions considered to be the main sources of precipitation in the CRB, and their contributions to precipitation over the basin were computed. These analyses confirmed that moisture in the CRB is ~60% self-sourced; African lands were the next greatest contributor, followed by the Indian and Atlantic Oceans. It was found that a reduction in contributions of the sources prevailed during 53 meteorological drought episodes that affected the CRB during the study period and it could be inferred that a reduction in moisture supplied from the Atlantic and Indian Oceans played an important role in the onset of drought episodes. It was also observed that the contribution of moisture from all sources to the CRB decreased during the study period, especially over the northern half of the basin, where the main humid forest of the CRB is located, confirming the importance of water transport and local hydroclimatological dynamics on the hydrological conditions, ecosystems, and local communities of the CRB.