Partitioning Of Available Energy Research Articles

Can changes in land use in a semi-arid region of Brazil cause seasonal variation in energy partitioning and evapotranspiration?

Changes to forests due to deforestation, or their replacement by agricultural areas, alter evapotranspiration and the partitioning of available energy. This study investigated seasonal variations in the energy balance and evapotranspiration in landscapes under different levels of anthropogenic intervention in the semi-arid region of Brazil. Micrometeorological data was obtained from September 2020 to October 2022 for three areas of the semi-arid region: preserved Caatinga (CAA, native vegetation), Caatinga under regeneration (REGE) and a deforested area (DEFA). Here, we use the Bowen ratio energy balance method. Measurements were taken of global solar radiation, air temperature, relative humidity, vapour pressure deficit, rainfall, net radiation, latent heat flux, sensible heat flux, soil heat flux, evapotranspiration, volumetric soil water content and Normalised Difference Vegetation Index. Sensible heat flux was the dominant flux in both areas with 66% for preserved Caatinga vegetation, 63% for Caatinga under regeneration and 62% deforested area. The latent heat flux was equivalent to 28% of the net radiation for preserved Caatinga vegetation, Caatinga under regeneration and deforested area. The evapotranspiration in turn responded as a function of water availability, being higher during the rainy seasons, with average values of 1.82 mm day−1 for preserved Caatinga vegetation, 2.26 mm day−1 for Caatinga under regeneration and 1.25 mm day−1 for deforested area. The Bowen ratio presented values > 1 in deforested area, preserved Caatinga vegetation and Caatinga under regeneration. Thus, it can be concluded that the change in land use alters the energy balance components, promoting reductions in available energy and latent and sensible heat fluxes during the rainy-dry transition in the deforested area. In addition, the seasonality of energy fluxes depends on water availability in the environment.

Partitioning of available energy in canopy and soil surface in croplands with different irrigation methods

Partitioning of available energy in canopy and soil surface in croplands with different irrigation methods

Diurnal cycle of surface energy fluxes in high mountain terrain: High‐resolution fully coupled atmosphere‐hydrology modelling and impact of lateral flow

AbstractWater and energy fluxes are inextricably interlinked within the interface of the land surface and the atmosphere. In the regional earth system models, the lower boundary parameterization of land surface neglects lateral hydrological processes, which may inadequately depict the surface water and energy fluxes variations, thus affecting the simulated atmospheric system through land‐atmosphere feedbacks. Therefore, the main objective of this study is to evaluate the hydrologically enhanced regional climate modelling in order to represent the diurnal cycle of surface energy fluxes in high spatial and temporal resolution. In this study, the Weather Research and Forecasting model (WRF) and coupled WRF Hydrological modelling system (WRF‐Hydro) are applied in a high alpine catchment in Northeastern Tibetan Plateau, the headwater area of the Heihe River. By evaluating and intercomparing model results by both models, the role of lateral flow processes on the surface energy fluxes dynamics is investigated. The model evaluations suggest that both WRF and coupled WRF‐Hydro reasonably represent the diurnal variations of the near‐surface meteorological fields, surface energy fluxes and hourly partitioning of available energy. By incorporating additional lateral flow processes, the coupled WRF‐Hydro simulates higher surface soil moisture over the mountainous area, resulting in increased latent heat flux and decreased sensible heat flux of around 20–50 W/m2 in their diurnal peak values during summertime, although the net radiation and ground heat fluxes remain almost unchanged. The simulation results show that the diurnal cycle of surface energy fluxes follows the local terrain and vegetation features. This highlights the importance of consideration of lateral flow processes over areas with heterogeneous terrain and land surfaces.

Soil moisture signature in global weather balloon soundings

The land surface influences the atmospheric boundary layer (ABL) through its impacts on the partitioning of available energy into evaporation and warming. Previous research on understanding this complex link focused mainly on site-scale flux observations, gridded satellite observations, climate modeling, and machine-learning experiments. Observational evidence of land surface conditions, among which soil moisture, impacting ABL properties at intermediate landscape scales is lacking. Here, we use a combination of global weather balloon soundings, satellite-observed soil moisture, and a coupled land-atmosphere model to infer the soil moisture impact on the ABL. The inferred relationship between soil moisture and surface flux partitioning reflects distinctive energy- and water-limited regimes, even at the landscape scale. We find significantly different behavior between those two regimes, associating dry conditions with on average warmer (≈3 K), higher (≈400 m) and drier (≈1 kPa) afternoon ABLs than wet conditions. This evidence of land–atmosphere coupling from globally distributed atmospheric measurements highlights the need for an accurate representation of land–atmosphere coupling into climate models and their climate change projections.

Feasibility of Estimating Turbulent Heat Fluxes via Variational Assimilation of Reference-Level Air Temperature and Specific Humidity Observations

This study investigated the feasibility of partitioning the available energy between sensible (H) and latent (LE) heat fluxes via variational assimilation of reference-level air temperature and specific humidity. For this purpose, sequences of reference-level air temperature and specific humidity were assimilated into an atmospheric boundary layer model (ABL) within a variational data assimilation (VDA) framework to estimate H and LE. The VDA approach was tested at six sites (namely, Arou, Audubon, Bondville, Brookings, Desert, and Willow Creek) with contrasting climatic and vegetative conditions. The unknowns of the VDA system were the neutral bulk heat transfer coefficient (CHN) and evaporative fraction (EF). EF estimates were found to agree well with observations in terms of magnitude and day-to-day fluctuations in wet/densely vegetated sites but degraded in dry/sparsely vegetated sites. Similarly, in wet/densely vegetated sites, the variations in the CHN estimates were found to be consistent with those of the leaf area index (LAI) while this consistency deteriorated in dry/sparely vegetated sites. The root mean square errors (RMSEs) of daily H and LE estimates at the Arou site (wet) were 25.43 (Wm−2) and 55.81 (Wm−2), which are respectively 57.6% and 45.4% smaller than those of 60.00 (Wm−2) and 102.21 (Wm−2) at the Desert site (dry). Overall, the results show that the VDA system performs well at wet/densely vegetated sites (e.g., Arou and Willow Creek), but its performance degrades at dry/slightly vegetated sites (e.g., Desert and Audubon). These outcomes show that the sequences of reference-level air temperature and specific humidity have more information on the partitioning of available energy between the sensible and latent heat fluxes in wet/densely vegetated sites than dry/slightly vegetated sites.

Mapping regional evapotranspiration in cloudy skies via variational assimilation of all-weather land surface temperature observations

Recently, a number of studies estimated evapotranspiration (ET) via variational assimilation of land surface temperature (LST) data from Moderate Resolution Imaging Spectroradiometer (MODIS). Their unknown parameters are neutral bulk heat transfer coefficient (CHN) (that scales the sum of sensible and latent heat fluxes), and evaporative fraction (EF) (that represents the partitioning of available energy between sensible and latent heat fluxes). The variational data assimilation (VDA) approaches estimate CHN and EF by minimizing the difference between the MODIS LST observations and model estimates. The applicability of these studies is limited only to clear-sky conditions where MODIS LST data are available. Even when the sky is clear, they cannot robustly update the initial guess of EF (i.e., the a priori EF value) because of the low temporal resolution of MODIS LST data. This study overcomes these shortcomings by 1) using the random forest (RF) method to obtain a reasonable the a priori EF value, and 2) assimilating the all-weather LST data (which are obtained by merging thermal infrared and passive microwave observations) into the VDA approach. The VDA approach is applied to the Source Regions of Rivers (SRR) in southwest China with heavy cloud covers. Results show that the RF method obtains a reasonably accurate the a priori EF value. Compared to assimilating the MODIS LST product, assimilation of all-weather LST data lead to an improvement in the ET estimates, especially in regions with dense clouds. Comparison of ET estimates with the measurements at four sites (i.e., Dangxiong, Linzhi, Naqu, and Qomolangma) in the SRR shows that the VDA approach can accurately estimate ET in cloudy conditions. Finally, the three-cornered hat (TCH) method is employed to assess the relative uncertainty of ET estimates over the SRR.

Ecosystem scale evapotranspiration and CO2 exchange in burned and unburned peatlands: Implications for the ecohydrological resilience of carbon stocks to wildfire

AbstractBoreal peatlands represent a significant global store of soil carbon, which are subject to increasing natural and anthropogenic disturbance. Wildfire is the single largest disturbance to boreal forest and wetlands annually. Critical to the long‐term carbon storage function in peatlands is the (re‐)establishment of a near‐surface water table following wildfire. This has been recently shown to in part be facilitated by post‐fire reductions in water losses via evapotranspiration (ET). However, reduced ET may also have cascade impacts on other ecohydrological processes in recovering peatlands, such as a reduction in carbon sequestration. To investigate the linked cycles of evaporative loss and carbon exchange in burned peatlands, the burned and unburned peatlands in Alberta, Canada, were instrumented with eddy covariance systems to monitor continuous fluxes of energy, carbon dioxide, and water vapour, over two summer seasons (2013 and 2014; 2–3 years post‐burn). The burned site showed significant changes to respiration and productivity and a shift in the partitioning of available energy (significantly larger Bowen ratio; mean values of 1.19 and 1.10 at the burned and unburned sites, respectively), as well as a significant reduction in ET rates. Decreases in respiration did not offset the decrease in primary productivity, and the burned site was significantly less productive than the reference site on a net production basis for the available data period. This provides direct observations of ET and CO2 fluxes at a novel ecosystem scale to show the impacts of fire on short‐term (2–3 years) post‐burn ecosystem ecohydrological function.

Comparing the Performance of the Maximum Entropy Production Model With a Land Surface Scheme in Simulating Surface Energy Fluxes

AbstractHydrological projections under future climate change have been shown to be sensitive to the formulation of evapotranspiration. Many hydrological models still rely on empirical formulations of this flux, and hence do not take into account the surface energy budget. On the other hand, land surface schemes, which are used within the climate models to describe land hydrology and associated surface heat fluxes (SHF), rely on the energy conservation. Due to land surface schemes complexity, they are not suitable for integration in traditional hydrological models. A newly developed and relatively simple Maximum Entropy Production model, which operates under the constraint of energy conservation and allows for an appropriate partitioning of available energy into SHF, appears to be a good alternative for integration in hydrological models. However, the MEP's performances still need to be evaluated under various environmental conditions. This study aims to evaluate the SHF simulated by MEP using observations over a multiyear period from several carefully chosen snow‐free sites located in low‐latitude regions. Moreover, simulated fluxes were compared to those derived from the Canadian Land Surface Scheme (CLASS), which was run at the same sites. The analysis of simulated and observed fluxes associated with different water stress conditions suggests that the abilities of MEP and CLASS in estimating sensible and latent heat fluxes are comparable. It was also found that the MEP and CLASS fluxes are in a good agreement with observations. However, the simulated nocturnal fluxes show that both models are in less agreement with the observations.

Comparison of energy partitioning between artificial pasture and degraded meadow in three-river source region on the Qinghai-Tibetan Plateau: A case study

To reveal the differences in energy exchange between a degraded alpine meadow (DM) and an artificial pasture (AP, that was artificially planted with Elymus nutans on the ploughed degraded meadow), the energy partitioning and its biophysical controls were compared between the two study sites in the Three-River Source Region (TRSR) on the Qinghai-Tibetan Plateau. The mean maximum leaf area index (LAI) for AP and DM was 2.66 and 1.08 m2 m−2, respectively. The net radiation (Rn), sensible heat flux (H), latent heat flux (λE), and soil heat flux (G) showed similar seasonal changes for the two study sites; no obvious differences in energy partitioning were noted between AP and DM during the non-growing season. However, during the growing season, Rn of DM was about 5.4% higher than that of AP, although almost the same downward shortwave and longwave radiation was received at both sites. Moreover, the mean albedo (α) of DM was lower by 0.02 than that of AP, and the mean soil surface temperature of DM was 4.1 °C lower than that of AP. The partitioning of available energy into H and λE of DM differed markedly from those of AP, and the λE/Rn ratio of DM was 16.4% higher than that of AP, whereas the H/Rn ratio of the former was 20.9% lower than that of the latter during the growing season. The growing season (annual) mean Bowen ratio (β) was 0.69 ± 0.04 and 0.90 ± 0.03 (2.38 ± 0.09 and 2.93 ± 0.12) at DM and AP, respectively, indicating that more available energy of DM was used for λE in comparison with that for AP. The difference in vegetation was considered to be the major factor leading to differences in the energy partitioning between the two sites. The results of the case study suggest that meadow degradation increases water loss through evapotranspiration and that enlarging the area of artificial pasture can increase the plant productivity and improve the water conservation capacity in this region.

Impacts of Fire and Flood on Land-Surface–Atmosphere Energetics in a Sub-tropical Barrier Island Freshwater Swamp

Climate change is predicted to lead to a drier and warmer climate in sub-tropical eastern Australia. Drier landscapes are more susceptible to fire, however, increases in daily precipitation extremes, and possible expansion of tropical weather systems into higher latitudes, implies that flooding may also become more common. We use the eddy-covariance technique to evaluate turbulent heat fluxes, and a net radiometer to measure surface albedo, over a groundwater dependent barrier island swamp. Measurements are made for dry and vegetated surface conditions, and following the natural occurrences of a wildfire and flooding. Results show that the wetland Bowen ratio has a value near 1 for typical dry and vegetated conditions, and is dominated by the latent heat flux when inundated by water. The largest changes in the partitioning of available energy into turbulent heat fluxes occur in the days immediately after the wildfire when the surface is dry, with the midday sensible heat flux nearly eight times greater than the latent heat flux. The key influences on energy partitioning are the atmospheric conditions for a dry and vegetated surface, and the surface conditions for either a burnt or a flooded surface.

Spatially variable evapotranspiration over salt affected pistachio orchards analyzed with satellite remote sensing estimates

Recent prolonged droughts in California have emphasized the urgent need to implement more efficient water management practices for high value tree crops. Accurate estimation of evapotranspiration (ET), a main component of consumptive water use, is critical for improving management of micro-irrigated pistachio orchards grown in the San Joaquin Valley of California. We estimated ET of three mature commercial pistachio orchards on non-saline and increasingly saline soils in 2015 and 2016, using the Mapping Evapotranspiration at high Resolution with Internalized Calibration (METRIC) method and Landsat 8 satellite observations. Based on a comparison with field observations at 8 sites, we modified the parameterizations of the momentum roughness length and net radiation for pistachio tree crops and reduced the uncertainty of daily ET estimates. When compared with field data, the recalibrated METRIC ET estimates had an R2 of 0.59, a mean absolute error of 1.1 mm/day, and a RMSE of 1.4 mm/day during Landsat overpass dates (n = 72). The METRIC ET map captured the temporal dynamics and spatial heterogeneity both within and among the orchards. The mean annual crop season estimated ET (mid-March to mid-October in 2016) with remote sensing decreased by 32% from 1064 ± 99 mm in the non-salt affected control orchard to 725 ± 82 mm in the orchard with the highest level of soil-water salinity. The ET reduction was consistent with canopy volume differences among the study orchards, as shown by summer Normalized Difference Vegetation Index (NDVI) from Landsat observations, e.g., 0.72 ± 0.06 in the control vs. 0.52 ± 0.06 in the most saline orchard. The available energy was controlled mostly by canopy features and explained 64% of daily ET variation among all Landsat pixels and satellite overpass days. The normalized differenced water index (NDWI) could be considered as an important parameter to capture the partitioning of available energy for ET (R2 = 0.38), suggesting that the lower soil osmotic potential in saline orchards further reduced crop ET.

A comparison of energy partitioning and evapotranspiration over closed maize and sparse grapevine canopies in northwest China

Energy exchanges and turbulent fluxes were simultaneously measured using eddy covariance technique over closed maize and sparse grapevine canopies during two growth seasons in an arid region of northwest China. Canopy conductance (Gc) and decoupling coefficient (Ω) were calculated to evaluate differences of fluxes and controlling factors over the two types of canopies. Atmosphere over grapevine canopy was drier, higher evaporative demand and aerodynamical transfer than maize canopy because air temperature, vapor pressure deficit and wind speed over grapevine were higher. Seasonal averaged net radiation (Rn) and soil heat flux (G) over maize canopy was higher and lower, respectively, than grapevine, resulting in that averaged available energy (Rn – G) was higher for maize than grapevine canopies, with 125.0 and 85.6 W m−2 in 2009 and 121.9 and 99.5 W m−2 in 2010, respectively. Energy partitioning of available energy to latent heat flux (λET) was higher for maize than grapevine canopies, with seasonal averaged ratio of 79.8% and 75.0% for maize and 62.3% and 59.8% for grapevine for both years, respectively. Seasonal averaged Bowen ratio (β) was lower for maize than grapevine canopies, with 0.26 and 0.72, respectively. Gc for maize canopy was higher than grapevine, varying nearly from 1 to above 30 mm s−1 and from 0 to above 15 mm s−1, respectively. Ω of maize canopy was higher than grapevine, with averaged values of 0.52 and 0.30, respectively, suggesting that there was a stronger coupling between grapevine canopy and the above air. The slope of linear regression between evapotranspiration (ET) and Rn were higher for maize canopy, indicating that maize ET was mostly controlled by Rn. The relationship between the Priestley-Taylor coefficient (α) and Gc fits an exponential increase for both types of crop canopies, suggesting that grapevine ET was more controlled by Gc because most grapevine Gc was lower than the threshold of 15 mm s−1. The slope of linear regression between α and leaf area index (LAI) <2.8 m2 m−2 was higher for maize canopy, indicating that maize ET was more sensitive to LAI below the threshold. These results are important for water management and agricultural sustainable development across similar croplands in arid regions.

Quantifying Water and Energy Fluxes Over Different Urban Land Covers in Phoenix, Arizona

AbstractThe impact of urbanization on water and energy fluxes varies according to the characteristics of the urban patch type. Nevertheless, urban flux observations are limited, particularly in arid climates, given the wide variety of land cover present in cities. To help address this need, a mobile eddy covariance tower was deployed at three locations in Phoenix, Arizona, to sample the surface energy balance at a parking lot, a xeric landscaping (irrigated trees with gravel) and a mesic landscaping (irrigated turf grass). These deployments were compared to a stationary eddy covariance tower in a suburban neighborhood. A comparison of the observations revealed key differences between the mobile and reference sites tied to the urban land cover within the measurement footprints. For instance, the net radiation varied substantially among the sites in manners consistent with albedo and shallow soil temperature differences. The partitioning of available energy between sensible and latent heat fluxes was modulated strongly by the presence of outdoor water use, with the irrigated turf grass exhibiting the highest evaporative fraction. At this site, we identified a lack of sensitivity of turbulent flux partitioning to precipitation events, which suggests that frequent outdoor water use removes water limitations in an arid climate, thus leading to mesic conditions. Other urban land covers with less irrigation, however, exhibited sensitivity to the occurrence of precipitation, as expected for an arid climate. As a result, quantifying the frequency and magnitude of outdoor water use is critical for understanding evapotranspiration losses in arid urban areas.

Impacts of future urban expansion on summer climate and heat-related human health in eastern China

China is the largest and most rapidly urbanizing nation in the world, and is projected to add an additional 200 million city dwellers by the end of 2030. While this rapid urbanization will lead to vast expansion of built-up areas, the possible climate effect and associated human health impact remain poorly understood. Using a coupled urban-atmospheric model, we first examine potential effects of three urban expansion scenarios to 2030 on summer climate in eastern China. Our simulations indicate extensive warming up to 5°C, 3°C, and 2°C in regard to low- (>0%), high- (>75%), and 100% probability urban growth scenarios, respectively. The partitioning of available energy largely explains the changes in 2-m air temperatures, and increased sensible heat flux with higher roughness length of the underlying urban surface is responsible for the increase of nighttime planetary boundary layer height. In the extreme case (the low-probability expansion pathway), the agglomeration of impervious surfaces substantially reduces low-level atmospheric moisture, consequently resulting in large-scale precipitation reduction. However, the effect of near-surface warming far exceeds that of moisture reduction and imposes non-negligible thermal loads on urban residents. Our study, using a scenario-based approach that accounts for the full range of urban growth uncertainty by 2030, helps better evaluate possible regional climate effects and associated human health outcomes in the most rapidly urbanizing areas of China, and has practical implications for the development of sustainable urban regions that are resilient to changes in both mean and extreme conditions.

A modeling study of the sensitivity of urban heat islands to precipitation at climate scales

The impacts of urban surface characteristics on urban heat islands have been extensively studied. However, the influence of local climate on the urban heat island intensity remains elusive. This study aims to quantify the influence of precipitation on the urban heat island intensity over the Continental United States (CONUS) at climate scales. Results from numerical experiments show that across the CONUS, the urban heat island intensities are positively correlated with the precipitation amounts in summer but not in winter. The sensitivity of urban heat island intensity to precipitation varies spatially and seasonally. In summer, the urban heat island intensity in mid-south CONUS is particularly sensitive to changes in precipitation and the sensitivity shows a generally negative correlation with the precipitation amount. The sensitivity is found to largely come from the rural temperature rather than the urban temperature, and is mostly controlled by the partition of available energy to sensible and latent heat fluxes. In winter the albedo effect is also important. This study highlights the climatic conditions as important controls on the urban heat island intensity, and thus climate change has significant implications for the urban thermal environment even if urban surface characteristics remain the same.

The Role of Circulation and Land Surface Conditions in Current and Future Australian Heat Waves

Understanding the physical drivers of heat waves is essential for improving short-term forecasts of individual events and long-term projections of heat waves under climate change. This study provides the first analysis of the influence of the large-scale circulation on Australian heat waves, conditional on the land surface conditions. Circulation types, sourced from reanalysis, are used to characterize the different large-scale circulation patterns that drive heat wave events across Australia. The importance of horizontal temperature advection is illustrated in these circulation patterns, and the pattern occurrence frequency is shown to reorganize through different modes of climate variability. It is further shown that the relative likelihood of a particular synoptic situation being associated with a heat wave is strongly modulated by the localized partitioning of available energy between surface sensible and latent heat fluxes (as measured through evaporative fraction) in many regions in reanalysis data. In particular, a several-fold increase in the likelihood of heat wave day occurrence is found during days of reduced evaporative fraction under favorable circulation conditions. The atmospheric circulation and land surface conditions linked to heat waves in reanalysis were then examined in the context of CMIP5 climate model projections. Large uncertainty was found to exist for many regions, especially in terms of the direction of future land surface changes and in terms of the magnitude of atmospheric circulation changes. Efforts to constrain uncertainty in both atmospheric and land surface processes in climate models, while challenging, should translate to more robust regional projections of heat waves.

Evaluation of Surface Fluxes in the WRF Model: Case Study for Farmland in Rolling Terrain

The partitioning of available energy into surface sensible and latent heat fluxes impacts the accuracy of simulated near surface temperature and humidity in numerical weather prediction models. This case study evaluates the performance of the Weather Research and Forecasting (WRF) model on the simulation of surface heat fluxes using field observations collected from a surface flux tower in Oregon, USA. Further, WRF-modeled heat flux sensitivities to North American Mesoscale (NAM) and North American Regional Reanalysis (NARR) large-scale input forcing datasets; U.S. Geological Survey (USGS) and the Moderate Resolution Imaging Spectroradiometer (MODIS) land use datasets; Pleim-Xiu (PX) and Noah land surface models (LSM); Yonsei University (YSU) and Mellor-Yamada-Janjic (MYJ) planetary boundary layer (PBL) schemes using the Noah LSM; and Asymmetric Convective Model version 2 (ACM2) PBL scheme using PX LSM are investigated. The errors for simulating 2-m temperature, 2-m humidity, and 10-m wind speed were reduced on average when using NAM compared with NARR. Simulated friction velocity had a positive bias on average, with the YSU PBL scheme producing the largest overestimation in the innermost domain (0.5 km horizontal grid resolution). The simulated surface sensible heat flux had a similar temporal behavior as the observations but with a larger magnitude. The PX LSM produced lower and more reliable sensible heat fluxes compared with the Noah LSM. However, Noah latent heat fluxes were improved with a lower RMSE compared to PX, when NARR forcing data was used. Overall, these results suggest that there is not one WRF configuration that performs best for all the simulated variables (surface heat fluxes and meteorological variables) and situations (day and night).

Explaining sex differences in lifespan in terms of optimal energy allocation in the baboon.

We provide a quantitative test of the hypothesis that sex role specialization may account for sex differences in lifespan in baboons if such specialization causes the dependency of fitness upon longevity, and consequently the optimal resolution to an energetic trade-off between somatic maintenance and other physiological functions, to differ between males and females. We present a model in which females provide all offspring care and males compete for access to reproductive females and in which the partitioning of available energy between the competing fitness-enhancing functions of growth, maintenance, and reproduction is modeled as a dynamic behavioral game, with the optimal decision for each individual depending upon his/her state and the behavior of other members of the population. Our model replicates the sexual dimorphism in body size and sex differences in longevity and reproductive scheduling seen in natural populations of baboons. We show that this outcome is generally robust to perturbations in model parameters, an important finding given that the same behavior is seen across multiple populations and species in the wild. This supports the idea that sex differences in longevity result from differences in the value of somatic maintenance relative to other fitness-enhancing functions in keeping with the disposable soma theory.

Performance of five surface energy balance models for estimating daily evapotranspiration in high biomass sorghum

Robust evapotranspiration (ET) models are required to predict water usage in a variety of terrestrial ecosystems under different geographical and agrometeorological conditions. As a result, several remote sensing-based surface energy balance (SEB) models have been developed to estimate ET over large regions. However, comparison of the performance of several SEB models at the same site is limited. In addition, none of the SEB models have been evaluated for their ability to predict ET in rain-fed high biomass sorghum grown for biofuel production. In this paper, we evaluated the performance of five widely used single-source SEB models, namely Surface Energy Balance Algorithm for Land (SEBAL), Mapping ET with Internalized Calibration (METRIC), Surface Energy Balance System (SEBS), Simplified Surface Energy Balance Index (S-SEBI), and operational Simplified Surface Energy Balance (SSEBop), for estimating ET over a high biomass sorghum field during the 2012 and 2013 growing seasons. The predicted ET values were compared against eddy covariance (EC) measured ET (ETEC) for 19 cloud-free Landsat image. In general, S-SEBI, SEBAL, and SEBS performed reasonably well for the study period, while METRIC and SSEBop performed poorly. All SEB models substantially overestimated ET under extremely dry conditions as they underestimated sensible heat (H) and overestimated latent heat (LE) fluxes under dry conditions during the partitioning of available energy. METRIC, SEBAL, and SEBS overestimated LE regardless of wet or dry periods. Consequently, predicted seasonal cumulative ET by METRIC, SEBAL, and SEBS were higher than seasonal cumulative ETEC in both seasons. In contrast, S-SEBI and SSEBop substantially underestimated ET under too wet conditions, and predicted seasonal cumulative ET by S-SEBI and SSEBop were lower than seasonal cumulative ETEC in the relatively wetter 2013 growing season. Our results indicate the necessity of inclusion of soil moisture or plant water stress component in SEB models for the improvement of their performance, especially under too dry or wet environments.

Characterizing the Effect of Vegetation Dynamics on the Bulk Heat Transfer Coefficient to Improve Variational Estimation of Surface Turbulent Fluxes

Abstract Estimation of turbulent heat fluxes by assimilating sequences of land surface temperature (LST) observations into a variational data assimilation (VDA) framework has been the subject of numerous studies. The VDA approaches are focused on the estimation of two key parameters that regulate the partitioning of available energy between sensible and latent heat fluxes. These parameters are neutral bulk heat transfer coefficient CHN and evaporative fraction (EF). The CHN mainly depends on the roughness of the surface and varies on the time scale of changing vegetation phenology. The existing VDA methods assumed that the variations in vegetation phenology over the period of one month are negligible and took CHN as a monthly constant parameter. However, during the growing season, bare soil may turn into a fully vegetated surface within a few weeks. Thus, assuming a constant CHN may result in a significant error in the estimation of surface fluxes, especially in regions with a high temporal variation in vegetation cover. In this study the VDA approach is advanced by taking CHN as a function of leaf area index (LAI). This allows the characterization of the dynamic effect of vegetation phenology on CHN. The performance of the new VDA model is tested over three sites in the United States and one site in China. The results show that the new model outperforms the previous one and reduces the root-mean-square error (and bias) in sensible and latent heat flux estimates across the four sites on average by 31% (61%) and 21% (37%), respectively.