Thermodynamic Bounds of Terrestrial Water-Energy Coupling and Resiliency in Global Ecosystems

Abstract

Increasing climatic variability has resulted in an unprecedented surge in extreme events, pressing global ecosystems towards systematic breakdown. Yet, the resilience of the soil-vegetation-atmosphere (SVA) system to revert to its natural state indicates the existence of energetic barriers forbidding systems from tipping. Observational and theoretical constraints limit our understanding of these energetic barriers which are crucial for assessing ecosystem sensitivity to atmospheric perturbations. We provide a novel coherent theory on the dissipative energy barriers (𝛥e) which decides the resilience potential of an ecosystem. These barriers are manifestation of lower bounds of entropy produced ( Σ *) for unit anomaly transference from soil moisture (SM) to evapotranspiration (ET). Using remote sensing data, we compute these global entropy bounds by introducing a new metric (Wasserstein distance, ) for SM-ET coupling. Quantifying these lower bounds from SM-ET coupling, places terrestrial ecosystems in the hierarchy of dissipative energy states spanning from forested regions to barren lands. Furthermore, we show that the optimization of SM-ET coupling translates to entanglement of water potential gradient (∆ω) between land surface and atmospheric boundary layer, and the resulting memory timescale or residence time (τ). This (τ.∆ω) entanglement propels moisture-rich and moisture-deficit systems in complementary evolutionary pathways in responding to imposed anomalies. As a result, we witness an emergence of coupling-aridity tradeoff with temperate climates operating as least efficient systems for unit SM to ET anomaly transfer. Physical basis, and transferability across space and scale makes this theory a potential benchmark for process improvement in the climate and earth system models.