Forest sensitivity to a changing climate: Investigating the role of bedrock water storage

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Forest health and stream water quality are threatened by ongoing shifts in climate, which have resulted in decreased snowpack, increased drought, dead trees, and dry rivers. The role of the deep subsurface (including bedrock below the soil) has emerged as a key factor in determining water availability and therefore the fate of forests and streams. However, our understanding of when, where, and how the subsurface buffers ecosystems from climate shifts is poorly understood. The overarching, long-term goal of this research program is to quantify how the interaction between climate and subsurface weathering patterns regulates water storage and release to plants and streams. This enables us to better understand present-day water storage dynamics as well as future dynamics under a warmer, drier climate. The short-term objectives are to: (1) advance our understanding of seasonal water storage sensitivity to year-to-year precipitation variability in winter-wet, summer-dry climates in particular (e.g., those along the central west coast of North America), including rain-snow transition areas; and (2) reveal the consequences for plant biome and streamflow resilience to drought. This will be achieved by instrumenting field observatories located across gradients of rock type, climate, and tectonic history. We will monitor eco-hydrologic processes at relevant spatial scales and develop mechanistic models that can be used to predict future forest and stream states and interpret paleo-records. We anticipate that this work will enable us to understand and predict the scenarios in which plants rely on water storage in weathered bedrock to survive drought and how declining snowpacks will impact the magnitude of summer low flows in streams. Our findings will also result in the novel development and incorporation of deep subsurface water storage processes into Earth system models, which are used to predict the coupled response of the water and carbon cycles to a shifting climate.