Testing a maximum evaporation theory over saturated land: implications for potential evaporation estimation

Tu, Zhuoyi; Roderick, Michael L.

doi:10.5194/hess-26-1745-2022

Cited by 13 publications

(13 citation statements)

References 44 publications

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“…This interpretation is, however, quite different to previous studies which applied MEP or related optimality approaches to evaporation (Wang et al, 2004(Wang et al, , 2007Wang and Bras, 2011;Kleidon and Schymanski, 2008;Porada et al, 2011;Yang and Roderick, 2019;Tu et al, 2022). Evaporation certainly produces entropy when saturated air is mixed with an unsaturated atmosphere near the surface.…”

Section: Evaporation and Hydrologic Cyclingcontrasting

confidence: 71%

Working at the limit: A review of thermodynamics and optimality of the Earth system

Kleidon

2022

Preprint

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Abstract. Optimality concepts related to energy and entropy have long been proposed in Earth system science, yet they remain obscure, seem contradictory regarding their goal to either maximize or minimize, and have so far only played marginal roles. This review aims to clarify the role of thermodynamics and optimality in Earth system science by showing that it plays a pivotal role in how, and how much, work can be derived from the solar forcing, and that this imposes a major constraint to the dynamics of dissipative structures of the Earth system. This is, however, not as simple as it may sound. It requires a consistent formulation of Earth system processes in thermodynamic terms, including their linkages and interactions. Thermodynamics then constrains the ability of the Earth system to derive work and generate free energy from the solar radiative forcing, which limits the ability to maintain motion, mass transport, geochemical cycling, and biotic activity. It thus limits directly the generation of atmospheric motion and other processes indirectly through their need for transport, such as hydrologic cycling or biotic activity. I demonstrate the application of this thermodynamic Earth system view by deriving first-order estimates associated with atmospheric motion, hydrologic cycling, and terrestrial productivity that agree very well with observations. This supports the notion that the emergent simplicity and predictability inherent in observed climatological variations can be attributed to these processes working as hard as they can, reflecting thermodynamic limits directly or indirectly. I discuss how this thermodynamic interpretation is consistent with established theoretical concepts in the respective disciplines, interpret other optimality concepts in light of this thermodynamic Earth system view, and describe its utility for Earth system science.

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Section: Evaporation and Hydrologic Cyclingcontrasting

confidence: 71%

Working at the limit: A review of thermodynamics and optimality of the Earth system

Kleidon

2022

Preprint

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“…Different from E pa , E po is defined as the evaporation that occurs from the same large‐size surface of E when the evaporating water is not a limiting factor. Here, we adopt the maximum evaporation approach, which is able to recover radiation and temperature to a (hypothetical) wet condition, to estimate E po (Tu et al., 2022; Yang & Roderick, 2019). Tu and Yang (2022) demonstrated that E po estimated from the maximum evaporation approach follows the E po definition.…”

Section: Estimations Of Epo and The Implications For The Complementar...mentioning

confidence: 99%

Potential Evaporation and the Complementary Relationship

Roderick

McVicar

2023

Water Resources Research

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The complementary relationship (CR) provides a framework for estimating land surface evaporation with basic meteorological observations by acknowledging the relationship between actual evaporation, apparent potential evaporation and potential evaporation (Epo). As a key variable in the CR, Epo estimates by conventional models have a long‐standing problem in practical applications. That is, the meteorological forcings (i.e., radiation and temperature) employed in conventional Epo models are observed under actual conditions that are generally not saturated. Hence, conventional Epo models do not conform to the original definition of Epo (i.e., the evaporation that would occur with an unlimited water supply). Here, we estimate Epo using the maximum evaporation approach (Epo_max) that does follow the original Epo definition. We find that adopting Epo_max considerably reduces the asymmetry of the CR compared to when the conventional Priestley‐Taylor Epo is used. We then employ Epo_max and develop a new physically based, calibration‐free CR model, which shows an overall good performance in estimating actual evaporation in 705 catchments at the mean annual scale and 64 flux sites at monthly and mean annual scales (R2 ranges from 0.73 to 0.75 and root‐mean‐squared error ranges from 9.8 to 18.8 W m−2).Both the 705 catchments and 64 flux sites cover a wide range of climates. More importantly, the use of Epo_max leads to a new physical interpretation of the CR.

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“…Following a recent study (Maes et al, 2019;Tu et al, 2022), we isolated non-water-stressed conditions by selecting data with evaporative fraction (EF) exceeding 95% of each site's EF distribution. This selection strategy was adopted since soil moisture observations are only available for a few FLUXNET2015 sites, and previous research found no significant difference between soil moisture-based and EF-based criteria (Maes et al, 2019).…”

Section: Fluxnet2015 In Situ Observationsmentioning

confidence: 99%

Land‐Atmosphere Coupling Constrains Increases to Potential Evaporation in a Warming Climate: Implications at Local and Global Scales

2023

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The magnitude and extent of runoff reduction, drought intensification, and dryland expansion under climate change are unclear and contentious. A primary reason is disagreement between global circulation models and current potential evaporation (PE) models for the upper limit of evaporation under warming climatic conditions. An emerging body of research suggests that current PE models including Penman‐Monteith and Priestley‐Taylor may overestimate future evaporation for non‐water‐stressed conditions. However, they are still widely used for climatic impact analysis although the underlying physical mechanisms for PE projections remain unclear. Here, we show that current PE models diverge from observed non‐water‐stressed evaporation across site (>1,500 flux tower site years), watershed (>10,000 watershed‐years), and global (25 climate models) scales. By not incorporating land‐atmosphere coupling processes, current models overestimate non‐water‐stressed evaporation and its driving factors for warmer and drier conditions. To resolve this, we introduce a land‐atmosphere coupled PE model by extending the Surface Flux Equilibrium theory. The proposed PE model accurately reproduces non‐water‐stressed evaporation across spatiotemporal scales. We find that terrestrial PE will increase at a similar rate to ocean evaporation but much slower than rates suggested by current PE models. This finding suggests that land‐atmosphere coupling moderates continental drying trends. Budyko‐based runoff projections incorporating our PE model are well aligned with those from coupled climate simulations, implying that land‐atmosphere coupling is key to improving predictions of climatic impacts on water resources. Our approach provides a simple and robust way to incorporate coupled land‐atmosphere processes into water management tools.

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Testing a maximum evaporation theory over saturated land: implications for potential evaporation estimation

Cited by 13 publications

References 44 publications

Working at the limit: A review of thermodynamics and optimality of the Earth system

Working at the limit: A review of thermodynamics and optimality of the Earth system

Potential Evaporation and the Complementary Relationship

Land‐Atmosphere Coupling Constrains Increases to Potential Evaporation in a Warming Climate: Implications at Local and Global Scales

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