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Characterizing soil moisture regimes and linear and nonlinear soil moisture-latent heat flux dependency
  • Hsin Hsu,
  • Paul Dirmeyer
Hsin Hsu
George Mason University

Corresponding Author:[email protected]

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Paul Dirmeyer
George Mason University
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Abstract

The control of latent heat flux (LE) by soil moisture (SM) variations is a key process affecting the moisture and energy balance at the land-atmosphere interface. SM-LE coupling is conventionally examined by identifying SM-LE relationships with metrics involving correlation. However, such a traditional approach, which fits a straight line across the full SM-LE space to evaluate the dependency, leaves out certain critical information: nonlinear SM-LE relationships and the long-recognized thresholds that lead to dramatically different behavior in different soil moisture regimes. This study examines three aspects of the SM-LE relationship to diagnose coupling globally: linear dependencies, nonlinear dependencies, and SM-LE threshold behavior. Using data from climate models, reanalyses, and observational-constrained datasets, global patterns of SM-LE regimes are determined by segmented regression. Mutual information analysis is applied only for days when SM is in the transitional regime between critical points defining high sensitivity in the SM-LE dependency. Sensitivity is further decomposed into linear and nonlinear components. Our results show discrepancies in the global pattern of existing SM regimes, but general consistencies among the linear and nonlinear components of SM-LE coupling. This implies that although models simulate different surface hydroclimates, the inherent behavior of how LE interacts with SM is well-described. The pattern of strong SM-LE coupling in the transition regime resembles the conventional distribution of “hot spots” of land-atmosphere interactions. This indicates that only the transitional SM range is necessary to determine the strength of coupling. This framework can be applied to investigate extremes and the shifting surface hydroclimatology in a warming climate.