A Review of environmental droughts: Increased risk under global warming?

This article reviews current drought effects on environmental systems. It stresses the need for considering environmental drought as a relevant type to be included in drought classifications. Here we illustrate that drought has complex environmental effects and affects many different systems (e.g., soils, air, vegetation, and forests, aquatic systems and wildlife). Droughts can affect the quality, structure, and diversity of these systems. However, we find that most environmental systems show strong resistance and resilience to drought events, and the effects of drought are usually temporary. Structural effects of environmental droughts tend to only occur in areas that are perturbed or in communities near their distribution limits. There are few long-term experimental studies that quantify possible trends in drought effects on environmental systems. Nevertheless, existing studies of forests that are based on tree-ring chronologies or forest inventories indicate increased drought-related effects on environmental systems. Future climate change scenarios suggest increased drought severity worldwide, which could alter the vulnerability of different environmental systems and increase the number of structural drought effects.

. In humid regions, soil water deficits are less frequent; so in general, vegetation is less impacted by precipitation reductions of similar relative magnitude to those in dry regions. Droughts that affect humid regions usually are of shorter duration and they do not produce permanent impacts on vegetation (see further discussion in Vicente-Serrano, Quiring, Peña-Gallardo, Domínguez-castro, & Yuan, 2020), and the recovery is fast after the perturbation, with the exception of very extreme drought episodes, in which AED has a very relevant role (C. D. Allen et al., 2015;Eamus, Boulain, Cleverly, & Breshears, 2013). ...
... (b) Evolution of the global average annual AED based on observations (black line) and considering the different variables as constant no evidence of increased impact of drought based on global trends of streamflow and vegetation activity (Scheff, 2018). Thus, no long-term or permanent environmental drought impacts can be inferred from the recent scientific literature (Vicente-Serrano, Quiring, et al., 2020). Nevertheless, these results do not contradict the fact that when a precipitation deficit occurs in a region, the associated impacts can be reinforced as a consequence of stronger AED. ...
... Nevertheless, these precipitation projections show important discrepancies with the soil moisture projections obtained from land surface models (Berg & Sheffield, 2018;Berg, Sheffield, & Milly, 2017;Dai et al., 2018;Scheff, 2018), and also when compared to drought indices that use both precipitation and AED. Future trends in the PDSI and the SPEI, based on the AED calculated by means of the standard FAO-56 Penman-Monteith equation, show strong increase in the world surface area affected by drought (Dai, 2013;Dai et al., 2018;Naumann et al., 2018;Vicente-Serrano, Quiring, et al., 2020;. On the other hand, hydrological drought indices show limited drought trends in future projections (Y. ...

Keywordsdrought vulnerability, soils, wildlife management, forest fires, desertification, land degradation