Abstract
Abstract. A common parameter in hydrological modeling frameworks is root zone water storage capacity (SR[L]), which mediates plant water availability during dry periods as well as the partitioning of rainfall between runoff and evapotranspiration. Recently, a simple flux-tracking-based approach was introduced to estimate the value of SR (Wang-Erlandsson et al., 2016). Here, we build upon this original method, which we argue may overestimate SR in snow-dominated catchments due to snow melt and evaporation processes. We propose a simple extension to the method presented by Wang-Erlandsson et al. (2016) and show that the approach provides a lower estimate of SR in snow-dominated watersheds. This SR dataset is available at a 1 km resolution for the continental USA, along with the full analysis code, on the Google Colab and Earth Engine platforms. We highlight differences between the original and new methods across the rain–snow transition in the Southern Sierra Nevada, California, USA. As climate warms and precipitation increasingly arrives as rain instead of snow, the subsurface may be an increasingly important reservoir for storing plant-available water between wet and dry seasons; therefore, improved estimates of SR will better clarify the future role of the subsurface as a storage reservoir that can sustain forests during seasonal dry periods and episodic drought.
Highlights
Root zone water storage capacity (SR[L]) quantifies the maximum amount of subsurface water that can be stored for use by vegetation
Actual SR should generally exceed estimated SR values presented in our revised method, because some evapotranspiration occurs during times when snow cover is present
We argue that an existing method for estimating root zone water storage capacity (SR) will tend to overestimate SR in snowy areas due to unaccounted for snow melt, evaporation, and sublimation processes
Summary
Root zone water storage capacity (SR[L]) quantifies the maximum amount of subsurface water that can be stored for use by vegetation This ecohydrological parameter plays a central role in the determination of plant community composition and drought resilience (Hahm et al, 2019a, b), runoff generation mechanisms (Botter et al, 2007; Salve et al, 2012), landslide triggering (Montgomery and Dietrich, 1994), landscape evolution (Deal et al, 2018), and the partitioning of precipitation into evapotranspiration and runoff (Porporato et al, 2004). High-resolution maps of soil plant-available water storage capacity exist (Reynolds et al, 2000), such maps incompletely describe the water used by plants. Within seasonally dry environments in particular, a significant volume of water accessed during the growing season can be derived from depths below mapped soils
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