Improving representation of canopy temperatures for modeling subcanopy incoming longwave radiation to the snow surface

Webster, Clare; Rutter, Nick; Jonas, Tobias

doi:10.1002/2017jd026581

Cited by 35 publications

(41 citation statements)

References 32 publications

(77 reference statements)

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“…This result is because α IIS bs characterizes the surface intrinsic reflection property that is related to incident solar zenith, as α HHF bs depends on the SZA over the horizontal surface. Although some different patterns occur at the α IIS bs of sparse discontinuous forest over a large slope due to the canopy gap effect (Webster et al, 2017), similar surface albedo patterns are observed for medium and dense forests ( Figures S1-S3). The maximum absolute (relative) differences between α HHS bs and α IIS bs are up to 0.026 (61.8%), 0.134 (62.4%), and 0.114 (62.3%) in the VIS, NIR, and SW broadbands over a 60°sloped surface.…”

Section: /2018jd028283supporting

confidence: 60%

Characterization of Remote Sensing Albedo Over Sloped Surfaces Based on DART Simulations and In Situ Observations

Wen

You

et al. 2018

JGR Atmospheres

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In situ albedo measurement over sloped surfaces is pivotal to a wide range of remote sensing applications, such as the estimation and evaluation of surface energy budget at regional and global scales. However, existing albedo measurements over rugged terrain are limited and controversial and remain a major challenge. In this paper, two commonly measured broadband albedos, which depend on incoming/outgoing geometric conditions, were characterized over sloped surfaces and illustrated. These albedos are the horizontal/horizontal sloped surface albedo (HHSA) and inclined/inclined sloped surface albedo (IISA). The 3‐D Discrete Anisotropic Radiative Transfer (DART) model simulations over varying slopes were utilized to quantify differences in the albedos. In particular, the effects of the slope, aspect, the solar zenith angle, and the proportion of diffuse skylight were investigated. The results show that absolute (relative) biases between HHSA and IISA are significant, reaching up to 0.026 (61.8%), 0.134 (62.4%), and 0.114 (62.3%) in the visible, near‐infrared, and shortwave broadbands, respectively. In addition, the diurnal cycle differences between HHSA and IISA were also compared using DART simulations and in situ observations over four typical slopes. Comparisons reveal that topographic parameters (e.g., slope and aspect) and atmospheric conditions (e.g., diffuse skylight and atmospheric visibility) are the primary factors, while the optical and structural parameters have a smaller effect.

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Section: /2018jd028283supporting

confidence: 60%

Characterization of Remote Sensing Albedo Over Sloped Surfaces Based on DART Simulations and In Situ Observations

Wen

You

et al. 2018

JGR Atmospheres

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“…Additional testing should also better characterize the insulation properties of ground cover under different management scenarios. Third, the calculation of T rad is simple and applicable in data-sparse environments, but other approaches for adjusting a temperature value based on topography and land cover are available (Fox, 1992;Kang, 2005;Webster et al, 2017) and could be further tested. Fourth, future research should also determine the effects of spatial heterogeneity of snow and frost depth on runoff and streamflow at both the local and watershed scales.…”

Section: Resultsmentioning

confidence: 99%

A simple temperature-based method to estimate heterogeneous frozen ground within a distributed watershed model

Follum

Niemann

Parno

et al. 2018

Hydrol. Earth Syst. Sci.

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Abstract. Frozen ground can be important to flood production and is often heterogeneous within a watershed due to spatial variations in the available energy, insulation by snowpack and ground cover, and the thermal and moisture properties of the soil. The widely used continuous frozen ground index (CFGI) model is a degree-day approach and identifies frozen ground using a simple frost index, which varies mainly with elevation through an elevation-temperature relationship. Similarly, snow depth and its insulating effect are also estimated based on elevation. The objective of this paper is to develop a model for frozen ground that (1) captures the spatial variations of frozen ground within a watershed, (2) allows the frozen ground model to be incorporated into a variety of watershed models, and (3) allows application in data sparse environments. To do this, we modify the existing CFGI method within the gridded surface subsurface hydrologic analysis watershed model. Among the modifications, the snowpack and frost indices are simulated by replacing air temperature (a surrogate for the available energy) with a radiation-derived temperature that aims to better represent spatial variations in available energy. Ground cover is also included as an additional insulator of the soil. Furthermore, the modified Berggren equation, which accounts for soil thermal conductivity and soil moisture, is used to convert the frost index into frost depth. The modified CFGI model is tested by application at six test sites within the Sleepers River experimental watershed in Vermont. Compared to the CFGI model, the modified CFGI model more accurately captures the variations in frozen ground between the sites, inter-annual variations in frozen ground depths at a given site, and the occurrence of frozen ground.

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“…The forest canopy also affects the amount of long‐wave radiation reaching an animal from above (Webster, Rutter, & Jonas, ). In the absence of a canopy, long‐wave radiation from the air ( L a ) is calculated as (Buckley, ; Campbell & Norman, ; Sears et al, ):

L_{normala} = ε_{a c} σ {(T_{normala normali normalr} + 273)}^{4}

…”

Section: Methodsmentioning

confidence: 99%

“…where ε ac is clear‐sky emissivity. Under a canopy, long‐wave radiation ( L a,sub ) comes from the sky and from the canopy, in proportion to the amount of clear sky (Webster et al, ):

L_{a, s u b} = V_{normals} L_{normala} + (1 - V_{s}) ε_{normalc} σ {(T_{normalc normala normaln} + 273)}^{4}

…”

Section: Methodsmentioning

confidence: 99%

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Remote sensing restores predictability of ectotherm body temperature in the world’s forests

Algar

Morley

Boyd

2018

Global Ecol Biogeogr

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Aim Rising global temperatures are predicted to increase ectotherms’ body temperatures, benefitting some species but threatening others. Biophysical models predict a key role for shade in buffering these effects, but the difficulty of measuring shade across broad spatial extents limits predictions of ectotherms’ thermal futures at the global scale. Here, we extend biophysical models of ectotherm body temperature to include effects of forest canopy shade, via leaf area index, and test whether considering remotely‐sensed canopy density improves predictions of body temperature variation in heavily shaded habitats. Location Worldwide. Time period 1990–2010. Major taxa studied Lizards. Methods We test predictions from biophysical ecological theory for how body temperature should vary with microclimate for 269 lizard populations across open, semi‐open and closed habitats worldwide. We extend existing biophysical models to incorporate canopy shade effects via leaf area index, test whether body temperature varies with canopy density as predicted by theory, and evaluate the extent to which incorporating canopy density improves model performance in heavily shaded areas. Results We find that body temperatures in open habitats, like deserts, vary with air temperature and incident solar radiation as predicted by biophysical equations, but these relationships break down in forests, where body temperatures become unpredictable. Incorporating leaf area index into our models revealed lower body temperatures in more heavily shaded environments, restoring the predictability of body temperature in forests. Conclusions Although biophysical ecological theory can predict ectotherm body temperature in open habitats, like deserts, these relationships decay in closed forests. Models incorporating remotely‐sensed data on canopy density improved predictability of body temperatures in these habitats, providing an avenue to incorporate canopy shade effects into predictions of animals’ vulnerability to climate change. These results highlight the thermal threat of changes in canopy structure and loss of forest cover for the world's ectotherms.

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Improving representation of canopy temperatures for modeling subcanopy incoming longwave radiation to the snow surface

Cited by 35 publications

References 32 publications

Characterization of Remote Sensing Albedo Over Sloped Surfaces Based on DART Simulations and In Situ Observations

Characterization of Remote Sensing Albedo Over Sloped Surfaces Based on DART Simulations and In Situ Observations

A simple temperature-based method to estimate heterogeneous frozen ground within a distributed watershed model

Remote sensing restores predictability of ectotherm body temperature in the world’s forests

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