Beneath the Soil: Bedrock Moisture and Watershed Recovery from Multi-Year Drought Multi-year droughts can cause persistent watershed deficits and widespread plant mortality. Traditional runoff models, which often rely on surface metrics and snowpack, may overestimate water availability during these periods. Here, we present insights from deep drilling across diverse hillslopes to reveal the role of the weathered bedrock vadose zone in explaining these discrepancies and contextualizing watershed recovery. Field observations show that woody plants rely heavily on bedrock moisture; the depletion of this subsurface storage directly limits plant ecophysiology and correlates with canopy die-off during successive dry years. Furthermore, we link hillslope recharge and groundwater behavior in drought to critical streamflow and aquatic ecosystem habitat. To expand these site-specific observations, we use remotely sensed root-zone storage deficits to scale up estimates of landscape vulnerability and water availability. Ultimately, predicting post-drought recovery requires integrating weathering patterns at the hillslope scale and their interaction with vegetation and climate. Bio: Jesse Hahm is an assistant professor in the Department of Geography at Simon Fraser University, British Columbia, Canada, who studies how the subsurface mediates water availability to plant communities and streams in the context of climate change.

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Lan Wang

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