Implications of CMIP6 projected drying trends for 21st century Amazonian drought risk

Abstract

Recent exceptionally hot droughts in Amazonia have highlighted the potential role of global warming in driving changes in rainfall and temperatures in the region. The previous generation of global climate models projected that eastern Amazonia would receive less future precipitation while western Amazonia would receive more precipitation, but many of these models disagreed on future precipitation trends in the region. Here Coupled Modeling Intercomparison Project, Phase 6 (CMIP6) models are used to examine the shifting risk of eastern Amazonian droughts under high and low future greenhouse gas emissions scenarios. This new generation of models shows better agreement that most of the Amazonian basin will receive less future rainfall, with particularly strong agreement that eastern and southern Amazonia will dry in the 21st century. These models suggest that global warming may be increasing the likelihood of exceptionally hot drought in the region. With unabated global warming, recent particularly warm and severe droughts will become more common by midcentury, but reducing the rate of greenhouse gas emissions can make extremely hot and dry years less common in the future. Simulated future rainfall changes in Amazonia under high greenhouse gas emissions are associated with changes in the tropical Pacific, but many climate models struggle to reproduce observed trends in the tropical Pacific. These shortcomings highlight the need to improve confidence in global climate models' ability to simulate observed trends in the tropics, even if more CMIP6 models agree on the sign of future rainfall trends. Plain Language SummaryRecent exceptionally hot droughts in Amazonia have highlighted the potential role of global warming in driving changes in rainfall and temperatures in the region. The previous generation of global climate models projected that eastern Amazonia would receive less future rainfall while western Amazonia would receive more rainfall. Here the latest climate model simulations are used to examine future rainfall and temperature changes over tropical South America. The new generation of climate models shows that most of the Amazonian basin will receive less future rainfall, with particularly strong agreement that eastern and southern Amazonia will dry in the future if the planet continues to rapidly warm. These models suggest that global warming has already increased the likelihood of exceptionally hot drought in the region, and by midcentury under unabated global warming, recent particularly warm and severe droughts will become more common. Reducing future greenhouse gas emissions decreases these warming and drying trends but does not eliminate them. However, many climate models have traditionally struggled to reproduce several key climate features in the tropics.

Causal Impacts of El Niño–Southern Oscillation on Global Soil Moisture Over the Period 2015–2100

“…Our results emphasize the important role of the tropical Pacific in driving changes of surface soil moisture over many regions where more droughts are expected in the 21st century (e.g., Parsons, 2020). While precipitation is known as the input source of soil moisture, temperature may affect evapotranspiration processes and may cause the loss of soil moisture to the atmosphere (Legates et al., 2011).…”

Circulation Patterns and Associated Rainfall Over South Tropical South America: GCMs Evaluation During the Dry‐To‐Wet Transition Season

“…In this sense, GCMs representation of sea surface temperature (SST) should be also considered in future studies as specific SST patterns over the Atlantic Ocean preceding the wet‐season onset can influence the SAMS development (Yin et al., 2014). Likewise, given the projections of drying conditions over STSA (Almazroui et al., 2021; Parsons, 2020; Sena & Magnusdottir, 2020; Thaler et al., 2021; Wainwright et al., 2021), these findings motivate the study of the CPs changes during the 21st century in terms of their frequency, intensity, and associated rainfall, which will be addressed in future research.…”

“…In terms of long‐term variability, GCMs depicted general drying trends during the historical period, especially over most of Amazonia, which are expected to intensify in the future (Almazroui et al., 2021; Boisier et al., 2015; Fu et al., 2013; Reboita et al., 2021; Sena & Magnusdottir, 2020; Teodoro et al., 2021; Thaler et al., 2021; Wainwright et al., 2021). Even more, according to Parsons (2020), the new generation of GCMs showed major agreement that most of the Amazonia will receive less PP in the future, with particularly strong agreement in eastern and southern Amazonia.…”

Diminishing seasonality of subtropical water availability in a warmer world dominated by soil moisture–atmosphere feedbacks

“…Seasonal variations in P-E are closely related to extreme hydroclimate conditions, such as droughts and floods, which are projected to increase in many regions under climate change 3 , 4 , 29 . Future drought risks and associated carbon loss are likely to be especially strong over the subtropics and the Amazon 29 , 30 . Increased dry-season P-E due to SM feedbacks may somewhat attenuate the potential increase of drought risk expected from the thermodynamic hydrological changes.…”