Time of emergence (TOE) of potential aridification in the western United States

• The western United States is projected to experience a continuous decrease in TWS during the 21st century across the entire region. • The TOE of the TWS reveals significant regional variation, with the interior and high-elevation regions experiencing the TOE earlier. • The Upper Colorado River Basin is highlighted as an emerging aridification hotspot. Quantifying the timing of hydroclimatic changes due to global warming is crucial for water resources management. This study investigates the hydroclimatic changes based on the Time of Emergence (TOE) analysis in the western United States, with a focus on the impacts of climate change and aridification. Utilizing the Community Earth System Model Version 2 Large Ensemble (CESM2-LE), we investigate projected changes in temperature, precipitation, evapotranspiration, runoff, snow, and Total Water Storage (TWS). Despite precipitation increases in the future, our results project a robust decrease in TWS by the end of the 21st century, mainly driven by higher evapotranspiration and reduced snow. Total Water Storage, which is an integrated measure of all terrestrial hydrological processes, exhibits a more pronounced climate change signal compared to precipitation. Significant regional variations also emerge in the TOE of TWS, with states around the interior and high-elevation regions experiencing changes faster, as early as in the 2030 s, than those on the Pacific Coast or in southern regions. The study highlights the Upper Colorado River Basin as an emerging aridification hotspot, emphasizing the need for targeted research and adaptive water resource management strategies. This research underscores the importance of jointly considering TWS and the aridity index to comprehensively assess hydrologic regime shifts under global warming. Climate change is leading to shifts in temperature, rainfall, evapotranspiration, river flow, snow, and other factors. These changes collectively affect what we call the ’hydroclimate,’ which includes changes in groundwater and aridity. Our study finds that as climate change progresses, there will be a noticeable decrease in groundwater, particularly in the interior states. Additionally, we observe an expansion of dry areas, especially in the Upper Colorado River Basin due to reduced snow. This information is crucial for policymakers who need to plan and prepare for future water resource management in the face of a warming climate.