Nonlinearity and Multivariate Dependencies in the Terrestrial Leg of Land‐Atmosphere Coupling
Journal
Water Resources Research
Journal Volume
57
Journal Issue
2
ISSN
0043-1397
1944-7973
Date Issued
2021-02
Author(s)
Dirmeyer, Paul A.
Abstract
Most studies of land-atmosphere coupling have focused on bivariate linear statistics like correlation. However, more complex dependencies exist, including nonlinear relationships between components of land-atmosphere coupling and the transmutability of relationships between soil moisture and surface heat fluxes under different environmental conditions. In this study, a technique called multivariate mutual information, based on information theory, is proposed to quantify how surface heat fluxes depend on both surface energy and wetness conditions, that is, net radiation and soil moisture, seasonally across the globe using reanalysis data. Such interdependency is then decomposed into linear and nonlinear contributions, which are further decomposed as different components explainable as the unique contribution from individual surface conditions, redundant contributions shared by both surface conditions, and the synergistic contribution from the concurrent action of net radiation and soil moisture. In reanalysis data, the dependency linearly contributed from soil moisture bears a similar global pattern to previously identified hot spots of coupling. The linear unique contributions of net radiation and soil moisture are mainly nonoverlapping, which suggests two separate regimes are governed by either energy or water limitations. These patterns persist when the nonlinearity is superimposed, thus reinforcing the validity of the land-atmospheric coupling hot spot paradigm and the spatial division of energy-limited as well as water-limited regions. Nevertheless, strong nonlinear relationships are detected, particularly over subtropical regions. Synergistic components are found across the globe, implying widespread multidimensional physical relationships among net radiation, soil moisture, and surface heat fluxes that previously had only been inferred locally.
Subjects
Land-atmosphere coupling
Multivariate
Mutual information
Surface fluxes
Publisher
American Geophysical Union (AGU)
Type
journal article