Abstract
AbstractEvapotranspiration (ET) is a crucial quantity through which land surface conditions can impact near‐surface weather and vice versa. ET can be limited by energy or water availability. The transition between water‐ and energy‐limited regimes is marked by the critical soil moisture (CSM), which is traditionally derived from small‐sample laboratory analyses. Here, we aim to determine the CSM at a larger spatial scale relevant for climate modeling, using state‐of‐the‐art gridded data sets. For this purpose, we introduce a new correlation‐difference metric with which the CSM can be accurately inferred using multiple data streams. We perform such an analysis at the continental scale and determine a large‐scale CSM as an emergent property. In addition, we determine small‐scale CSMs at the grid cell scale and find substantial spatial variability. Consistently from both analyses we find that soil texture, climate conditions, and vegetation characteristics are influencing the CSM, with similar respective importance. In contrast, comparable CSMs are found when applying alternative large‐scale energy and vegetation data sets, highlighting the robustness of our results. Based on our findings, the state of the vegetation and corresponding land‐atmosphere coupling can be inferred, to first order, from easily accessible satellite observations of surface soil moisture.
Highlights
Evapotranspiration is a crucial variable in land‐atmosphere interactions, since it affects the carbon, energy, and water balances
The transition between water‐ and energy‐limited regimes is marked by the critical soil moisture (CSM), which is traditionally derived from small‐sample laboratory analyses
Insignificant Δcorr values occur in northern Scandinavia due to a lack of available soil moisture data related to low surface temperatures and in between water‐ and energy‐limited regions across central Europe, marking the transitional regions
Summary
Evapotranspiration (hereafter referred to as ET) is a crucial variable in land‐atmosphere interactions, since it affects the carbon, energy, and water balances. We distinguish two evaporative regimes: (i) the water‐limited regime, where ET is mainly controlled by soil moisture availability, and (ii) the energy‐limited regime, where ET is mostly governed by energy (temperature and radiation) supply (Budyko, 1974; Seneviratne et al, 2010). Regime shifts potentially induce changes in the causality of energy and water availability for ET. This could dampen or amplify land‐atmosphere interactions, like evaporative cooling (Seneviratne et al, 2010). The critical soil moisture (hereafter referred to as CSM) associated with this regime shift in the conceptual framework is a crucial parameter
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