Exposure and sensitivity of threatened plant species to changing drought regimes: A global analysis

Climate change is driving substantial impacts on plants, including widespread increases in drought frequency, duration, and intensity. Changes to these elements of the drought regime can elevate plant mortality and extinction risk, yet they remain largely overlooked in International Union for the Conservation of Nature's (IUCN) Red List assessments. We quantified the exposure of Red Listed plant species to future drought regimes by intersecting species' geographic ranges with global projections of drought duration and frequency. Across climate scenarios (SSP2–4.5, SSP5–8.5) 96 % of threatened species examined were projected to experience increases in drought frequency and duration in at least part of their range. On average, drought duration is projected to increase by 2–4 weeks, with one additional drought every 25–30 years across species ranges. The most exposed species include 28 threatened palms, 20 of which are Critically endangered, and 454 Proteaceae species, including four Critically endangered proteas ( Protea holosericea , P. inopina , P. odorata , P. namaquana ). Trees, shrubs and geophytes are most exposed of all plant growth forms to drought regime shifts. In threatened trees and shrubs species, data on hydraulic measures of sensitivity to drought are scarce, with key data available for only six species assessed for expsoure. Of these, three Endangered species ( Coffea arabica , Eucalyptus albida , Isopogon gardneri ) exhibit sensitivity to changing drought regimes. Our findings highlight the substantial risk to threatened plants posed by increased drought exposure, with important implications for conservation planning. Incorporating drought-regime shifts into future threat assessments will more accurately capturing emerging climate-related extinction risk. • Over 95% of the 2,866 threatened plants examined from the Red List are projected to face longer and/or more frequent drought • Threatened species are projected to experience longer increases in drought stress relative to non-threatened species • Woody species (shrubs and trees) are exposed to significantly longer and more frequent drought compared to other growth forms • Drought response data are lacking for nearly all high-risk woody species, with only six species currently characterised • Drought regime-shifts remain largely absent from extinction-risk assessments, despite globally widespread exposure