129-52 Summer Rains and Snow Drought Intensity Affect Seasonal Vegetation and Groundwater Connections

Abstract:

In the mountainous western US, snow drought —when winter precipitation falls as rain instead of snow— promotes earlier plant green-up and potentially dire downstream water stress during the following summer, unless groundwater or summer rains ameliorate water stress. During droughts, proximity to a perennial spring has been shown to sustain riparian plant water use in quartzite parent material, but it is unknown whether spring-adjacent plants in limestone parent material exhibit similar drought response patterns. To address this gap, the rate of sapflow of a Serviceberry tree located in limestone parent material in a research watershed in southeastern Idaho was continuously recorded every 15 minutes starting in summer 2026. Soil moisture sensors were installed in a nearby soil pit at depths of 20 and 45 cm. Data collected from groundwater and stilling wells in the same watershed were used to compare water levels and streamflow during three drought years: 2021, 2022, and 2026. Accumulated precipitation and snow water equivalent relative to a 30-year average (1991-2020) were calculated for all three drought years, revealing that 2026 experienced the most intense snow drought of these three years. Nonetheless, sapflow patterns in limestone during 2026 were similar to sapflow patterns in quartzite during the previous droughts in 2021-2022. Because the 2026 drought was more severe compared to the previous 2021 and 2022 drought years, it remains unclear if quartzite would be able to match limestone springs’ ability to mitigate intense drought effects. Data from the full 2026 growing season will allow the evaluation of summer rain effects on the connections between vegetation and groundwater during droughts in the mountainous western US.

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