The influence of temperature–moisture coupling on the occurrence of compound hot and dry events over South America: historical and future perspectives

The strong global warming observed in the past 50 years has intensified the Earth’s water cycle, triggering more frequent and severe rainfall and drought episodes, a trend that is expected to be aggravated in many regions^1,2. Consequently, significant changes in the distribution of temperature, precipitation and evaporation are foreseen. Such changes will likely cause disturbances to the physical coupling between temperature and moisture and, ultimately, to the occurrence of compound hot and dry (CDH) extremes, leading to severe environmental and socio-economic impacts^3–5. These coupling interactions can be conceptualized by (1) the correlation between temperature and precipitation to characterize atmospheric coupling, and (2) the correlation between temperature and evaporation, as a proxy for land–atmosphere coupling.

Data from ERA5 reanalysis and from a weighted CORDEX-CORE ensemble⁶ assuming two different emission scenarios (RCP2.6 and RCP 8.5), was used to assess, for seven climate regions in South America, the influence of these coupling interactions on the occurrence of CDH conditions.

Results obtained by applying multivariate regression models for the historical period (1980–2005) demonstrate that the dependence of CDH conditions on these two metrics of coupling varies considerably from region to region. While in some areas of South America a monotonical influence of a particular coupling mechanism dominates, in other regions of the continent a jointly impact of both coupling processes in the occurrence of CDH conditions is present.  We also investigate how the distribution levels of these two coupling processes will change in future due to long-term disturbances expected by climate change in temperature and in the water balance, and how a higher or lower occurrence of CDH episodes can be explained by changes in the type and strength of the dominant coupling mechanism.  

References

• Chagas, V. B. P. et al. Climate and land management accelerate the Brazilian water cycle. Nat. Commun. 13, 5136 (2022).
• Donat, M. G. et al. More extreme precipitation in the world’s dry and wet regions. Nat. Clim. Chang. 6, 508–513 (2016).
• Berg, A. et al. Interannual Coupling between Summertime Surface Temperature and Precipitation over Land: Processes and Implications for Climate Change. J. Clim. 28, 1308–1328 (2015).
• Miralles, D. G. et al. Land–atmospheric feedbacks during droughts and heatwaves: state of the science and current challenges. Ann. N. Y. Acad. Sci. 1436, 19–35 (2019).
• Lesk, C. et al. Stronger temperature–moisture couplings exacerbate the impact of climate warming on global crop yields. Nat. Food 2, 683–691 (2021).
• Lima, D. C. A. et al. A multi-variable constrained ensemble of regional climate projections under multi-scenarios for Portugal – Part I: An overview of impacts on means and extremes. Clim. Serv. 30, 100351 (2023).

Acknowledgments:

JG is grateful to Fundação para a Ciência e a Tecnologia I.P./MCTES (FCT) for the PhD Grant 2020.05198.BD. JG, AR, RMT, and DCAL also thank FCT I.P./MCTES through national funds (PIDDAC) – UIDB/50019/2020 (https://doi.org/10.54499/UIDP/50019/2020) and LA/P/0068/2020 (https://doi.org/10.54499/LA/P/0068/2020). AR, RMT, RL, JG and AFSR thank also FCT for project DHEFEUS (https://doi.org/10.54499/2022.09185.PTDC). AR was supported by FCT through https://doi.org/10.54499/2022.01167.CEECIND/CP1722/CT0006. DCAL was supported by FCT through https://doi.org/10.54499/2022.03183.CEECIND/CP1715/CT0004. DGM acknowledges support from the European Research Council (HEAT, 101088405).