Land–atmospheric feedbacks during droughts and heatwaves: state of the science and current challenges

Abstract

Droughts and heatwaves cause agricultural loss, forest mortality, and drinking water scarcity, especially when they occur simultaneously as combined events. Their predicted increase in recurrence and intensity poses serious threats to future food security. Still today, the knowledge of how droughts and heatwaves start and evolve remains limited, and so does our understanding of how climate change may affect them. Droughts and heatwaves have been suggested to intensify and propagate via land-atmosphere feedbacks. However, a global capacity to observe these processes is still lacking, and climate and forecast models are immature when it comes to representing the influences of land on temperature and rainfall. Key open questions remain in our goal to uncover the real importance of these feedbacks: What is the impact of the extreme meteorological conditions on ecosystem evaporation? How do these anomalies regulate the atmospheric boundary layer state (event self-intensification) and contribute to the inflow of heat and moisture to other regions (event self-propagation)? Can this knowledge on the role of land feedbacks, when available, be exploited to develop geo-engineering mitigation strategies that prevent these events from aggravating during their early stages? The goal of our perspective is not to present a convincing answer to these questions, but to assess the scientific progress to date, while highlighting new and innovative avenues to keep advancing our understanding in the future.

New Insights on Land Surface-Atmosphere Feedbacks over Tropical South America at Interannual Timescales

“…It is remarkable that under this structure of causalities, evaporation (E) is the only variable which non-linearly controls Θ. This agrees with the essential role of evaporation in the surface energy partitioning in wetter environments [74], taking into account that under this non-linear framework, precipitation presents a relative causality on soil moisture (Figure 7a). In general, Θ is essential over Tropical South America to structurally feedback on q 925 under the highest influence of ENSO at concurrent series (non-linear links).…”

“…Evaporation anomalies depend on surface conditions and these are relatively homogeneous in the region as shown by the spatial pattern depicted in Figure 4b,c [69,74]. This is the most representative ENSO-influenced area over tropical South America for all the variables.…”

Concurrent 2018 Hot Extremes Across Northern Hemisphere Due to Human‐Induced Climate Change

“…Multiple heat waves that occur subsequently in the same region can amplify heat wave impacts and are projected to increase with global warming (Baldwin et al, 2019). In particular, the co-occurrence rate of compound drought-heat wave events will increase even if there is no trend in drought occurrence (Diffenbaugh et al, 2015;Zscheischler & Seneviratne, 2017) and may exacerbate heat-related impacts (Miralles et al, 2018;Seneviratne et al, 2010). In particular, the co-occurrence rate of compound drought-heat wave events will increase even if there is no trend in drought occurrence (Diffenbaugh et al, 2015;Zscheischler & Seneviratne, 2017) and may exacerbate heat-related impacts (Miralles et al, 2018;Seneviratne et al, 2010).…”

Global characterization of hydrological and meteorological droughts under future climate change: The importance of timescales, vegetation‐CO2 feedbacks and changes to distribution functions

“…This severity is likely to occur even in regions that do not project a precipitation decrease. Future drought severities may be linked to the projected increase in AED by radiative forcing (Dai et al ., ) and/or enhanced thermodynamic processes (Miralles et al ., ). This would generate noticeable spatial differences in the global drought trends, supporting the notion that—even in a more humid future world—model outputs suggest enhanced climatic and hydrologic drought severity over large regions worldwide.…”