Widespread drought-driven declines in streamflows and water quality in the Upper Colorado River Basin during 1998-2022

The cascading effects of meteorological droughts on river flows and water quality in mountainous regions are poorly understood. Using a data-driven framework, we studied drought impacts on streamflow, water temperature (WT), specific conductance (SC) in the Upper Colorado River Basin (1998-2022). Severe meteorological droughts in 2001-2002, 2012, 2018, 2020-2021 reduced annual streamflows by 15%, increased WT by 9% and SC by 5% relative to normal adjacent years. Declines were greatest in spring and summer, with reduced peak flows. Streamflow and SC recovered until 2018, after which successive droughts prolonged impacts, whereas WT effects were transient. Catchments with higher freshwater withdrawals, deciduous forest cover, air temperatures, residence times, finer soils had greater streamflow declines, while higher subsurface flows and infiltration enabled resilience. WT increases were associated with higher elevation, slopes, precipitation and lower agriculture, shrub cover. Open water and reservoirs mitigated SC increases. Thus, catchment attributes influence drought vulnerability in mountainous regions.