Quantifying the thermodynamic entropy budget of the land surface: is this useful?

Abstract. As a system is moved away from a state of thermodynamic equilibrium, spatial and temporal heterogeneity is induced. A possible methodology to assess these impacts is to examine the thermodynamic entropy budget and assess the role of entropy production and transfer between the surface and the atmosphere. Here, we adopted this thermodynamic framework to examine the implications of changing vegetation fractional cover on land surface energy exchange processes using the NOAH land surface model and eddy covariance observations. Simulations that varied the relative fraction of vegetation were used to calculate the resultant entropy budget as a function of fraction of vegetation. Results showed that increasing vegetation fraction increases entropy production by the land surface while decreasing the overall entropy budget (the rate of change in entropy at the surface). This is accomplished largely via simultaneous increase in the entropy production associated with the absorption of solar radiation and a decline in the Bowen ratio (ratio of sensible to latent heat flux), which leads to increasing the entropy export associated with the latent heat flux during the daylight hours and dominated by entropy transfer associated with sensible heat and soil heat fluxes during the nighttime hours. Eddy covariance observations also show that the entropy production has a consistent sensitivity to land cover, while the overall entropy budget appears most related to the net radiation at the surface, however with a large variance. This implies that quantifying the thermodynamic entropy budget and entropy production is a useful metric for assessing biosphere-atmosphere-hydrosphere system interactions.

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Quantifying the thermodynamic entropy budget of the land surface: is this useful?

Earth System Dynamics Discussions ◽

10.5194/esdd-2-71-2011 ◽

2011 ◽

Vol 2 (1) ◽

pp. 71-103

Author(s):

N. A. Brunsell ◽

S. J. Schymanski ◽

A. Kleidon

Keyword(s):

Heat Flux ◽

Entropy Production ◽

Eddy Covariance ◽

Latent Heat ◽

Latent Heat Flux ◽

Land Surface ◽

Simultaneous Increase ◽

Surface Model ◽

Thermodynamic Entropy ◽

Entropy Budget

Abstract. As a system is moved away from a state of thermodynamic equilibrium, spatial and temporal heterogeneity is induced. A possible methodology to assess these impacts is to examine the thermodynamic entropy budget and assess the role of entropy production and transfer between the surface and the atmosphere. Here, we adopted this thermodynamic framework to examine the implications of changing vegetation fractional cover on land surface energy exchange processes using the NOAH land surface model and eddy covariance observations. Simulations that varied the relative fraction of vegetation were used to calculate the resultant entropy budget as a function of fraction of vegetation. Results showed that increasing vegetation fraction increases entropy production by the land surface while decreasing the overall entropy budget (the rate of change in entropy at the surface). This is accomplished largely via simultaneous increase in the entropy production associated with the absorption of solar radiation and a decline in the Bowen ratio (ratio of sensible to latent heat flux), which leads to increasing the entropy export associated with the latent heat flux during the daylight hours and dominated by entropy transfer associated with sensible heat and soil heat fluxes during the nighttime hours. Eddy covariance observations also show that the entropy production has a consistent sensitivity to land cover, while the overall entropy budget appears most related to the net radiation at the surface. This implies that quantifying the thermodynamic entropy budget and entropy production is a useful metric for assessing biosphere-atmosphere-hydrosphere system interactions.

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The effect of chalk representation in land surface modelling

10.5194/hess-2016-244 ◽

2016 ◽

Author(s):

Mostaquimur Rahman ◽

Rafael Rosolem

Keyword(s):

Heat Flux ◽

Soil Moisture ◽

Latent Heat ◽

Latent Heat Flux ◽

Land Surface ◽

Unsaturated Zone ◽

Water Movement ◽

Hydrological Cycle ◽

Surface Model ◽

Surface Mass

Abstract. Modelling and monitoring of hydrological processes in the unsaturated zone of the chalk, which is a porous medium with fractures, is important to optimize water resources assessment and management practices in the United Kingdom (UK). However, efficient simulations of water movement through chalk unsaturated zone is difficult mainly due to the fractured nature of chalk, which creates high-velocity preferential flow paths in the subsurface. Complex hydrology in the chalk aquifers may also influence land surface mass and energy fluxes because processes in the hydrological cycle are connected via non-linear feedback mechanisms. In this study, it is hypothesized that explicit representation of chalk hydrology in a land surface model influences land surface processes by affecting water movement through the shallow subsurface. In order to substantiate this hypothesis, a macroporosity parameterization is implemented in the Joint UK Land Environment Simulator (JULES), which is applied on a study area encompassing the Kennet catchment in the Southern UK. The simulation results are evaluated using field measurements and satellite remote sensing observations of various fluxes and states in the hydrological cycle (e.g., soil moisture, runoff, latent heat flux) at two distinct spatial scales (i.e., point and catchment). The results reveal the influence of representing chalk hydrology on land surface mass and energy balance components such as surface runoff and latent heat flux via subsurface processes (i.e., soil moisture dynamics) in JULES, which corroborates the proposed hypothesis.

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Distinguishing between early- and late-covering crops in the land surface model Noah-MP: impact on simulated surface energy fluxes and temperature

Biogeosciences ◽

10.5194/bg-17-2791-2020 ◽

2020 ◽

Vol 17 (10) ◽

pp. 2791-2805

Author(s):

Kristina Bohm ◽

Joachim Ingwersen ◽

Josipa Milovac ◽

Thilo Streck

Keyword(s):

Land Use ◽

Heat Flux ◽

Surface Energy ◽

Latent Heat ◽

Latent Heat Flux ◽

Land Surface ◽

Land Surface Model ◽

Surface Model ◽

Energy Fluxes ◽

Surface Energy Fluxes

Abstract. Land surface models are essential parts of climate and weather models. The widely used Noah-MP land surface model requires information on the leaf area index (LAI) and green vegetation fraction (GVF) as key inputs of its evapotranspiration scheme. The model aggregates all agricultural areas into a land use class termed “cropland and pasture”. In a previous study we showed that, on a regional scale, the GVF has a bimodal distribution formed by two crop groups differing in phenology and growth dynamics: early-covering crops (ECC; e.g., winter wheat, winter rapeseed, winter barley) and late-covering crops (LCC; e.g., corn, silage maize, sugar beet). That result can be generalized for central Europe. The present study quantifies the effect of splitting the land use class cropland and pasture of Noah-MP into ECC and LCC on surface energy fluxes and temperature. We further studied the influence of increasing the LCC share, which in the study area (the Kraichgau region, southwest Germany) is mainly the result of heavily subsidized biomass production, on energy partitioning at the land surface. We used the GVF dynamics derived from high-resolution (5 m × 5 m) RapidEye satellite data and measured LAI data for the simulations. Our results confirm that the GVF and LAI strongly influence the partitioning of surface energy fluxes, resulting in pronounced differences between simulations of ECC and LCC. Splitting up the generic crop into ECC and LCC had the strongest effect on land surface exchange processes in July–August. During this period, ECC are at the senescence growth stage or already harvested, while LCC have a well-developed ground-covering canopy. The generic crop resulted in humid bias, i.e., an increase in evapotranspiration by +0.5 mm d−1 (latent heat flux is 1.3 MJ m−2 d−1), decrease in sensible heat flux (H) by 1.2 MJ m−2 d−1 and decrease in surface temperature by −1 ∘C. The bias increased as the shares of ECC and LCC became similar. The observed differences will impact the simulations of processes in the planetary boundary layer. Increasing the LCC share from 28 % to 38 % in the Kraichgau region led to a decrease in latent heat flux (LE) and a heating up of the land surface in the early growing season. Over the second part of the season, LE increased and the land surface cooled down by up to 1 ∘C.

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The Sensitivity of Latent Heat Flux to Changes in the Radiative Forcing: A Framework for Comparing Models and Observations

Journal of Climate ◽

10.1175/2009jcli3158.1 ◽

2010 ◽

Vol 23 (9) ◽

pp. 2345-2356 ◽

Cited By ~ 11

Author(s):

Jonathan M. Winter ◽

Elfatih A. B. Eltahir

Keyword(s):

Heat Flux ◽

Latent Heat ◽

Latent Heat Flux ◽

Land Surface ◽

Radiative Forcing ◽

Climate Model ◽

Regional Climate ◽

Surface Model ◽

Transfer Scheme ◽

Available Energy

Abstract A climate model must include an accurate surface physics scheme in order to examine the interactions between the land and atmosphere. Given an increase in the surface radiative forcing, the sensitivity of latent heat flux to available energy plays an important role in determining the energy budget and has a significant impact on the response of surface temperature. The Penman–Monteith equation is used to construct a theoretical framework for evaluating the climatology of evapotranspiration and the sensitivity of latent heat flux to available energy. Regional Climate Model version 3 coupled to Integrated Biosphere Simulator (RegCM3–IBIS); RegCM3 with its native land surface model, Biosphere–Atmosphere Transfer Scheme 1e (RegCM3–BATS1e); and Flux Network (FLUXNET) micrometeorological tower observations are compared and contrasted using the developed methodology. RegCM3–IBIS and RegCM3–BATS1e simulate the observed sensitivity of latent heat flux to available energy reasonably well during the summer on average; however, there are significant variations in the monthly values. Additional information provided by the physically based Penman–Monteith framework is employed for identifying deficiencies and guiding improvements in models, allowing calibration of both the climatology of evapotranspiration and the sensitivity of latent heat flux to available energy.

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WRF v.3.9 sensitivity to land surface model and horizontal resolution changes over North America

10.5194/gmd-2021-243 ◽

2021 ◽

Author(s):

Almudena García-García ◽

Francisco José Cuesta-Valero ◽

Hugo Beltrami ◽

Fidel González-Rouco ◽

Elena García-Bustamante

Keyword(s):

Heat Flux ◽

Latent Heat ◽

Latent Heat Flux ◽

Land Surface ◽

Land Surface Model ◽

Horizontal Resolution ◽

Convective Precipitation ◽

Surface Model ◽

Near Surface ◽

Low Latitudes

Abstract. Understanding the differences between regional simulations of land-atmosphere interactions and near-surface conditions is crucial for a more reliable representation of past and future climate. Here, we explore the effect of changes in the model's horizontal resolution on the simulated energy balance at the surface and near-surface conditions using the Weather Research and Forecasting (WRF) model. To this aim, an ensemble of twelve simulations using three different horizontal resolutions (25 km, 50 km and 100 km) and four different Land Surface Model (LSM) configurations over North America from 1980 to 2013 is developed. Our results show that finer resolutions lead to higher surface net shortwave radiation and maximum temperatures at mid- and high latitudes. At low latitudes over coastal areas, an increase in resolution leads to lower values of sensible heat flux and higher values of latent heat flux, as well as lower values of surface temperatures and higher values of precipitation and soil moisture in summer. The use of finer resolutions leads then to an increase in summer values of latent heat flux, convective and non-convective precipitation and soil moisture at low latitudes. The effect of the LSM choice is larger than the effect of horizontal resolution on the near-surface temperature conditions. By contrast, the effect of the LSM choice on the simulation of precipitation is weaker than the effect of horizontal resolution, showing larger differences among LSM simulations in summer and over regions with high latent heat flux. Comparison between observations and the simulation of daily maximum and minimum temperatures and accumulated precipitation indicates that the CLM4 LSM yields the lowest biases in maximum and minimum mean temperatures, but the highest biases in extreme temperatures. Increasing horizontal resolution leads to larger biases in accumulated precipitation over all regions particularly in summer. The reasons behind relate the partition between convective and non-convective precipitation, specially noticeable over western US.

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An Empirical Latent Heat Flux Parameterization for the Noah Land Surface Model

Journal of Applied Meteorology and Climatology ◽

10.1175/2010jamc2180.1 ◽

2010 ◽

Vol 49 (8) ◽

pp. 1696-1713 ◽

Cited By ~ 11

Author(s):

Christopher M. Godfrey ◽

David J. Stensrud

Keyword(s):

Heat Flux ◽

Latent Heat ◽

Latent Heat Flux ◽

Land Surface ◽

Initial Conditions ◽

Land Surface Model ◽

Vegetation Coverage ◽

Surface Model ◽

Oklahoma Mesonet ◽

Surface Observations

Abstract Proper partitioning of the surface energy fluxes that drive the evolution of the planetary boundary layer in numerical weather prediction models requires an accurate representation of initial land surface conditions. Unfortunately, soil temperature and moisture observations are unavailable in most areas and routine daily estimates of vegetation coverage and biomass are not easily available. This gap in observational capabilities seriously hampers the evaluation and improvement of land surface parameterizations, since model errors likely relate to improper initial conditions as much as to inaccuracies in the parameterizations. Two unique datasets help to overcome these difficulties. First, 1-km fractional vegetation coverage and leaf area index values can be derived from biweekly maximum normalized difference vegetation index composites obtained from daily observations by the Advanced Very High Resolution Radiometer onboard NOAA satellites. Second, the Oklahoma Mesonet supplies multiple soil temperature and moisture measurements at various soil depths each hour. Combined, these two datasets provide significantly improved initial conditions for a land surface model and allow an evaluation of the accuracy of the land surface model with much greater confidence than previously. Forecasts that both include and neglect these unique land surface observations are used to evaluate the value of these two data sources to land surface initializations. The dense network of surface observations afforded by the Oklahoma Mesonet, including surface flux data derived from special sensors, provides verification of the model results, which indicate that predicted latent heat fluxes still differ from observations by as much as 150 W m−2. This result provides a springboard for assessing parameterization errors within the model. A new empirical parameterization developed using principal-component regression reveals simple relationships between latent heat flux and other surface observations. Periods of very dry conditions observed across Oklahoma are used advantageously to derive a parameterization for evaporation from bare soil. Combining this parameterization with an empirical canopy transpiration scheme yields improved sensible and latent heat flux forecasts and better partitioning of the surface energy budget. Surface temperature and mixing ratio forecasts show improvement when compared with observations.

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Modelling evapotranspiration during precipitation deficits: identifying critical processes in a land surface model

Hydrology and Earth System Sciences Discussions ◽

10.5194/hessd-12-10789-2015 ◽

2015 ◽

Vol 12 (10) ◽

pp. 10789-10825 ◽

Cited By ~ 3

Author(s):

A. M. Ukkola ◽

A. J. Pitman ◽

M. Decker ◽

M. G. De Kauwe ◽

G. Abramowitz ◽

...

Keyword(s):

Heat Flux ◽

Stomatal Conductance ◽

Soil Properties ◽

Latent Heat ◽

Latent Heat Flux ◽

Land Surface ◽

Surface Model ◽

Area Index ◽

Seasonal Scale ◽

Rainfall Deficits

Abstract. Surface fluxes from land surface models (LSM) have traditionally been evaluated against monthly, seasonal or annual mean states. The limited ability of LSMs to reproduce observed evaporative fluxes under water-stressed conditions has been previously noted, but very few studies have systematically evaluated these models during rainfall deficits. We evaluated latent heat flux simulated by the Community Atmosphere Biosphere Land Exchange (CABLE) LSM across 20 flux tower sites at sub-annual to inter-annual time scales, in particular focusing on model performance during seasonal-scale rainfall deficits. The importance of key model processes in capturing the latent heat flux are explored by employing alternative representations of hydrology, leaf area index, soil properties and stomatal conductance. We found that the representation of hydrological processes was critical for capturing observed declines in latent heat during rainfall deficits. By contrast, the effects of soil properties, LAI and stomatal conductance are shown to be highly site-specific. Whilst the standard model performs reasonably well at annual scales as measured by common metrics, it grossly underestimates latent heat during rainfall deficits. A new version of CABLE, with a more physically consistent representation of hydrology, captures the variation in the latent heat flux during seasonal-scale rainfall deficits better than earlier versions but remaining biases point to future research needs. Our results highlight the importance of evaluating LSMs under water-stressed conditions and across multiple plant functional types and climate regimes.

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Evapotranspiration and CO2 exchange of wet and snow-loaded canopy in an evergreen temperate coniferous forest

10.5194/egusphere-egu21-3765 ◽

2021 ◽

Author(s):

Linjie Jiao ◽

Yoshiko Kosugi ◽

Yuichi Sempuku ◽

Ayaka Sakabe ◽

Ting-Wei Chang

Keyword(s):

Heat Flux ◽

Gas Exchange ◽

Eddy Covariance ◽

Latent Heat ◽

Latent Heat Flux ◽

Forest Canopy ◽

Surface Model ◽

Annual Average ◽

Process Gas ◽

Monsoon Area

Learning about the gas exchange dynamic (evapotranspiration and photosynthesis) relating to precipitation and leaf wetness is important for understanding the forest hydrological and carbon sink function. Precipitation can lead to the change in meteorological factors, depression on leaf gas exchange as well as increasing CO2 emission from soil. However, few studies fully consider the effect of these changes in ecosystem scale.This study conducted continuous eddy covariance measurement over a temperate evergreen Japanese cypress forest canopy in the Asian monsoon area from 2016 to 2019. By applying the eddy covariance method with the enclosed path gas analyzer, evapotranspiration and CO2 exchange from the canopy to the atmosphere during and after rainfall and snow are precisely monitored. The chamber method is used to simultaneously measure the soil respiration. Especially, to reveal the mechanism of wet canopy gas exchange mechanism, a SVAT multilayer model with two rainfall interception solution (Model 1: free gas exchange with interception only by the adaxial surface; Model 2: no gas exchange with interception by both surfaces) is applied to figure out the interception distribution over the leaf surface.The annual average daytime latent heat flux (&#955;E) was 70.92 W m-2, 22.31 W m-2, 139.40 W m-2 for wet canopy, snow-loaded canopy and the first 6 hours after wetness ended; the annual average daytime net ecosystem exchange was -1.9 &#956;mol m-2s-1, -0.42 &#956;mol m-2s-1, -7.43 &#956;mol m-2s-1 for wet canopy, snow-loaded canopy and the first 6 hours after wetness ended. Correspondingly, the annual average daytime soil CO2 flux was 2.53 &#956;mol m-2s-1, 0.26 &#956;mol m-2s-1, 2.93 &#956;mol m-2s-1 when the canopy was wet, snow-loaded and during the first 6 hours after wetness ended. The gas exchange at the first 6 hours after wet is more active than that of wet canopy and snow-loaded canopy despite rainfall increased the CO2 emission from the soil. Both measured data and simulation show the wet canopy can process gas exchange. The simulation showed that both interception situations are possible to happen but Model 1 is more suitable for this temperate forest. Meanwhile, the difference between the two models&#8217; performance is smaller during the rainfall than in the wet period after the rainfall, which means interception distribution had a larger impact on wet canopy gas exchange at the later wet period. Future studies should also concern about the mechanism and effect of gas exchange dynamics relating to different precipitation patterns and water sources for latent heat flux.

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Modelling evapotranspiration during precipitation deficits: identifying critical processes in a land surface model

Hydrology and Earth System Sciences ◽

10.5194/hess-20-2403-2016 ◽

2016 ◽

Vol 20 (6) ◽

pp. 2403-2419 ◽

Cited By ~ 14

Author(s):

Anna M. Ukkola ◽

Andy J. Pitman ◽

Mark Decker ◽

Martin G. De Kauwe ◽

Gab Abramowitz ◽

...

Keyword(s):

Heat Flux ◽

Stomatal Conductance ◽

Soil Properties ◽

Latent Heat ◽

Latent Heat Flux ◽

Land Surface ◽

Surface Model ◽

Area Index ◽

Seasonal Scale ◽

Rainfall Deficits

Abstract. Surface fluxes from land surface models (LSMs) have traditionally been evaluated against monthly, seasonal or annual mean states. The limited ability of LSMs to reproduce observed evaporative fluxes under water-stressed conditions has been previously noted, but very few studies have systematically evaluated these models during rainfall deficits. We evaluated latent heat fluxes simulated by the Community Atmosphere Biosphere Land Exchange (CABLE) LSM across 20 flux tower sites at sub-annual to inter-annual timescales, in particular focusing on model performance during seasonal-scale rainfall deficits. The importance of key model processes in capturing the latent heat flux was explored by employing alternative representations of hydrology, leaf area index, soil properties and stomatal conductance. We found that the representation of hydrological processes was critical for capturing observed declines in latent heat during rainfall deficits. By contrast, the effects of soil properties, LAI and stomatal conductance were highly site-specific. Whilst the standard model performs reasonably well at annual scales as measured by common metrics, it grossly underestimates latent heat during rainfall deficits. A new version of CABLE, with a more physically consistent representation of hydrology, captures the variation in the latent heat flux during seasonal-scale rainfall deficits better than earlier versions, but remaining biases point to future research needs. Our results highlight the importance of evaluating LSMs under water-stressed conditions and across multiple plant functional types and climate regimes.

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