Atmospheric drought indices in future projections

In this Perspective we critically discuss future drought projections, focusing on key issues related to the concept of drought and its frequent confusion with aridity. We address the common misunderstanding between drought metrics and drought indices, as well as misconceptions about what drought indices represent. Our analysis emphasizes the role of atmospheric evaporative demand in shaping future drought severity, along with its drivers, impact processes, and responses to global warming, while highlighting related observational and theoretical challenges. We also shed light on the uncertainties and limitations of Earth system models (ESMs) in assessing future drought severity. We explore the complexities of ESMs in accurately representing plant physiological and hydrological processes, which are crucial for evaluating drought severity. Our discussion also delves into the nuanced effects of atmospheric CO<inf>2</inf> concentrations on these processes and on water dynamics within ESMs, helping to clarify conceptual issues related to atmospheric drought indices. Finally, we advocate for a balanced evaluation of drought metrics, emphasizing the importance of considering multiple atmospheric processes in drought projections.

This work has been supported by the research projects TED2021-129152B-C41 and PID2022-137244OB-I00, financed by the Spanish Ministry of Science and FEDER, the Ministry for the Ecological Transition and the Demographic Challenge (MITECO) and the European Commission NextGenerationEU (Regulation EU 2020/2094), project CSC2300000, through CSIC’s Interdisciplinary Thematic Platform Clima (PTI-Clima), and GLANCE ‘AGricultural Land AbandoNment and ClimatE change impacts on the water, energy and vegetation carbon cycles in the Mediterranean region’ (ESA contract no. 4000145543/24/I-LR). CSIC’s Interdisciplinary Thematic Platform Clima (PTI-Clima), contract no. CSC2023-02-00 financed by the Ministry for the Ecological Transition and the Demographic Challenge (MITECO) and the European Commission NextGenerationEU (Regulation EU 2020/2094) and GLANCE (ESA contract no. 4000145543/24/I-LR). L.G.-S. is partially financed by national funds through FCT – Fundação para a Ciência e a Tecnologia under the project UIDB/00006/2020 (https://doi.org/10.54499/UIDB/00006/2020), and project UID/00006/2025.

Peer reviewed