Projected increases in extreme drought frequency and duration by 2040 affect specialist habitats and species in Scotland.
Abstract
Climate-driven increases in drought occurrence are an overlooked risk in temperate climates, which may be less resilient to water scarcity than arid habitats. Scotland provides an example of a temperate oceanic climate in which drought risk is understudied, but could have substantial ecological impacts, particularly in combination with additional stressors. We modelled changes to risk of extreme drought occurrence in Scotland, and considered potential impacts of these changes on two key habitats, ombrotrophic (precipitation fed) wetlands and temperate rainforest. Using temperature and precipitation data from the UK Climate Projections 2018 and the drought index Standardized Precipitation-Evapotranspiration Index, we calculated and mapped likely changes in extreme drought for the near future (2021-2040) in comparison to a baseline (1981-2001). We found likelihood of extreme drought events increased from an average of one event every 20 years in the baseline period, to one event every 3 years by 2040. Typical events were projected to be up to 2-3 months longer, with an average of 11 extra drought months per decade. Increases were projected throughout the country, but the effect was most severe in the east, and during autumn. Ombrotrophic wetlands have some level of adaptive resilience to drought, but are considered at high risk as several key sites are in drought hotspot areas. In contrast, Scotland's temperate rainforest is located in lower risk areas, but is typically less drought resilient. Potential impacts on these habitats include reductions in ecosystem services including carbon capture, reduced breeding success for multiple taxa and increased competition among plant communities, which threatens drought-sensitive species. These projections suggest that climate-driven drought risk is a significant and imminent threat, even in wet climates. In Scotland, the results can direct mitigation and management actions to areas likely to be at greatest risk, as well as informing conservation interventions that can cope with drought. Additionally, other areas with a temperate oceanic climate may be at risk of extreme drought and could experience similar consequences. Therefore, these results have implications both for facilitating improved resilience to extreme drought in Scotland and for potentially overlooked impacts of drought in oceanic climates elsewhere.