Two questions motivated this study: 1) Will meteorological droughts become more frequent and severe during the twenty-first century? 2) Given the projected global temperature rise, to what extent does the inclusion of temperature (in addition to precipitation) in drought indicators play a role in future meteorological droughts? To answer, we analyzed the changes in drought frequency, severity, and historically undocumented extreme droughts over 1981–2100, using the standardized precipitation index (SPI; including precipitation only) and standardized precipitation-evapotranspiration index (SPEI; indirectly including temperature), and under two representative concentration pathways (RCP4.5 and RCP8.5). As input data, we employed 103 high-resolution (0.44°) simulations from the Coordinated Regional Climate Downscaling Experiment (CORDEX), based on a combination of 16 global circulation models (GCMs) and 20 regional circulation models (RCMs). This is the first study on global drought projections including RCMs based on such a large ensemble of RCMs. Based on precipitation only, ~15% of the global land is likely to experience more frequent and severe droughts during 2071–2100 versus 1981–2010 for both scenarios. This increase is larger (~47% under RCP4.5, ~49% under RCP8.5) when precipitation and temperature are used. Both SPI and SPEI project more frequent and severe droughts, especially under RCP8.5, over southern South America, the Mediterranean region, southern Africa, southeastern China, Japan, and southern Australia. A decrease in drought is projected for high latitudes in Northern Hemisphere and Southeast Asia. If temperature is included, drought characteristics are projected to increase over North America, Amazonia, central Europe and Asia, the Horn of Africa, India, and central Australia; if only precipitation is considered, they are found to decrease over those areas.

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Regional climate models have been used since 1989 in order to improve climate simulation in regions where mesoscale forcings modulate the regional climate. These models are driven by time-dependent lateral boundary conditions from global climate models or reanalysis, and this process is called dynamical downscaling. Here, we review the evolution of regional climate modeling, as well as present the studies developed for South America.

The value added from dynamic downscaling in climate projections of extratropical cyclones over the southwestern South Atlantic Ocean (SAO) is evaluated. For this purpose, the Regional Climate Model version 4 (RegCM4) is nested in the Hadley Global Environment Model 2 ‐ Earth System (HadGEM2‐ES) global climate model under the RCP8.5 scenario. The analyses focus on three time slices: the present (1979–2005), near future (NF: 2020–2050) and far future (FF: 2070–2098) climates. The cyclone tracking used an algorithm that searches for minima of relative vorticity at 925 hPa. Simulations of the present climate are compared to data from an ensemble of five reanalyses (ERA‐40, ERA‐Interim, NCEP‐NCAR, NCEP‐DOE and CFSR). For present climate, there is good agreement among reanalyses and models in associating austral winter and summer with higher and lower cyclone frequency, respectively. In addition, the simulations present the mean features of the cyclones (lifetime, distance travelled and mean velocity) as similar to those of the reanalysis. Moreover, RegCM4 outperforms the HadGEM2‐ES by simulating more realistically the spatial pattern of the cyclogenesis density over the SAO, which indicates value added from the RegCM4 downscaling. For the future climates, a decrease is projected for the annual frequency of cyclones, which reaches −6.5% (−3.6%) in RegCM4 (HadGEM2‐ES) in the NF and −11.4% (−10.4%) in the FF. Future projections do not indicate changes in the mean intensity of the cyclones. The negative trend of the cyclone frequency affects the precipitation. For FF, a decrease of approximately 15% in the precipitation associated with cyclones is projected.

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