The Role of Spring Ecosystems as Climate Refugia in a Semi-Arid Environment

Wet and cool microenvironments often serve as climate refugia in semiarid regions. However, springs—locations where groundwater reaches the Earth's surface—remain underexplored as climate refugia. This study investigated the potential of spring ecosystems as climate refugia in a semiarid mountainous region of central Idaho, USA. Using high-resolution PlanetScope imagery (2017–2024), we derived seasonal phenophases from a normalized difference vegetation index (NDVI) time series to assess ecological stability at 40 springs and surrounding non-spring areas. We fit a linear mixed-effects model with phenophase as the dependent variable, spring and water year as random effects and climatic water balance (CWB), snow disappearance date (SDD), heat load index (HLI), topographic wetness index (TWI) and their interactions with site type (spring or non-spring) as predictors. We found that springs exhibited significantly lower interannual variability in end of growing season (EOS) timing (24 days less than non-springs). Higher annual CWB, reflecting greater precipitation relative to potential evapotranspiration, corresponded with later EOS timing for both springs and non-springs, but springs were less sensitive to annual CWB as shown by lower effect sizes. Springs phenology showed weak associations with TWI and HLI, underscoring their independence from topographically driven refugia. Our findings highlight springs as climate refugia due to their buffering of water limitations that stabilise late season phenology. Under climate change, water deficits will become more severe, making climate refugia like springs increasingly important. Future research should examine spring recharge processes and incorporate additional snowpack variables to monitor stability across a range of climate conditions.