Net radiation in a snow‐covered discontinuous forest gap for a range of gap sizes and topographic configurations

Seyednasrollah, Bijan; Kumar, Mukesh

doi:10.1002/2014jd021809

Cited by 38 publications

(38 citation statements)

References 51 publications

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“…We estimated diffuse shortwave radiation in the canopy gap ( R d,g ) using the original DHSVM formulation as in Equation with the adjusted sky view factor ( θ ) given as a function of solar elevation and gap radius:

R_{sans-serif-italicd, sans-serif-italicg} = R_{d} ([], θ + τ_{d} ((), sans-serif1 - θ))

where R d is the diffuse atmospheric radiation and τ d is the canopy transmittance of diffuse radiation. We took the approach of Seyednasrollah and Kumar () to estimate the sky view factor θ over the gap base:

\begin{matrix} lefttrue \\ SVF (sans-serif-italicy, sans-serif-italicx) = \frac{sans-serif1}{π^{2}} \int_{sans-serif0}^{2 π} {tan}^{- 1} (\frac{\sqrt{R^{2} - x^{2} \cdot {sin}^{2} α} - sans-serif-italicx \cdot cos α}{h}) d α \\ θ = \int_{sans-serif0}^{sans-serif-italicR} SVF (sans-serif-italicy, sans-serif-italicx) dx \end{matrix}

…”

Section: Methodsmentioning

confidence: 99%

“…In the Cedar River Watershed located on the western slope of the Cascade Range (characterized by a maritime climate) in the Pacific Northwest, the mean snow duration in a circular gap cut in the forest with a diameter of 20 m (equal to approximately one tree height) was observed to be 1–2 weeks longer than in the adjacent control forest covered by untreated second‐growth forest dominated by western hemlock and Douglas‐fir (Dickerson‐Lange et al, ). These unique benefits of forest gaps have led to recent modelling developments that address the distinct radiation scheme in a forest gap from entirely open or forested areas (Lawler & Link, ; Musselman, Molotch, Margulis, Lehning, & Gustafsson, ), the energy budget at the forest gap floor (Seyednasrollah & Kumar, ), net canopy interception (Moeser, Morsdorf, & Jonas, ; Moeser, Stähli, & Jonas, ), and snow distributions (Broxton et al, ) in the presence of forest gaps.…”

Section: Introductionmentioning

confidence: 99%

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Evaluating the functionality and streamflow impacts of explicitly modelling forest–snow interactions and canopy gaps in a distributed hydrologic model

Sun

Wigmosta

Zhou

et al. 2018

Hydrological Processes

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Many plot‐scale studies have shown that snow‐cover dynamics in forest gaps are distinctly different from those in open and continuously forested areas, and forest gaps have the potential to alter the magnitude and timing of snowmelt. However, the watershed‐level impacts of canopy gap treatment on streamflows are largely unknown. Here, we present the first research that explicitly assesses the impact of canopy gaps on seasonal streamflows and particularly late‐season low flows at the watershed scale. To explicitly model forest–snow interactions in canopy gaps, we made major enhancements to a widely used distributed hydrologic model, distributed hydrology soil vegetation model, with a canopy gap component that represents physical processes of snowpack evolution in the forest gap separately from the surrounding forest on the subgrid scale (within a grid typically 10–150 m). The model predicted snow water equivalent using the enhanced distributed hydrology soil vegetation model showed good agreement (R2 > 0.9) with subhourly snow water equivalent measurements collected from open, forested, and canopy gap sites in Idaho, USA. Compared with the original model that does not account for interactions between gaps and surrounding forest, the enhanced model predicted notably later melt in small‐ to medium‐size canopy gaps (the ratio of gap radius (r) to canopy height (h) ≤ 1.2), and snow melt rates exhibited great sensitivity to changing gap size in medium‐size gaps (0.5 ≤ r/h ≤ 1.2). We demonstrated the watershed‐scale implications of canopy gaps on streamflow in the snow‐dominated Chiwawa watershed, WA, USA. With 24% of the watershed drainage area (about 446 km2) converted to gaps of 60 m diameter, the mean annual 7‐day low flow was increased by 19.4% (i.e., 0.37 m3/s), and the mean monthly 7‐day low flows were increased by 13.5% (i.e., 0.26 m3/s) to 40% (i.e., 1.76 m3/s) from late summer through fall. Lastly, in practical implementation of canopy gaps with the same total gap areas, a greater number of distributed small gaps can have greater potential for longer snow retention than a smaller number of large gaps.

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R_{sans-serif-italicd, sans-serif-italicg} = R_{d} ([], θ + τ_{d} ((), sans-serif1 - θ))

\begin{matrix} lefttrue \\ SVF (sans-serif-italicy, sans-serif-italicx) = \frac{sans-serif1}{π^{2}} \int_{sans-serif0}^{2 π} {tan}^{- 1} (\frac{\sqrt{R^{2} - x^{2} \cdot {sin}^{2} α} - sans-serif-italicx \cdot cos α}{h}) d α \\ θ = \int_{sans-serif0}^{sans-serif-italicR} SVF (sans-serif-italicy, sans-serif-italicx) dx \end{matrix}

…”

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Evaluating the functionality and streamflow impacts of explicitly modelling forest–snow interactions and canopy gaps in a distributed hydrologic model

Sun

Wigmosta

Zhou

et al. 2018

Hydrological Processes

View full text Add to dashboard Cite

show abstract

“…Further away from these heated tree trunks, the trunk view component decreases and the heated tree trunks have less influence on the radiation budget at the snow surface. This suggests the two-part model can work sufficiently in the center of forest gaps where V f is high [Lawler and Link, 2011;Seyednasrollah and Kumar, 2014]. Consequently, prediction of snowmelt initiation and evolution is therefore dependent on accurate representations of the tree trunk and its temperature, which can be better achieved by accounting for canopy and tree trunk temperatures when modeling subcanopy incoming longwave radiation.…”

Section: à2mentioning

confidence: 99%

“…During the snowmelt period the presence of forest can lead to enhanced melt as the total contribution of longwave radiation increases, particularly in midlatitude environments where daytime temperatures increase above 0°C [Lundquist et al, 2013]. This phenomenon is particularly prevalent in canopy discontinuities where there is heightened exposure to solar radiation and increased emission of longwave radiation from heated canopy elements [Lawler and Link, 2011;Seyednasrollah and Kumar, 2014]. As solar angles and incoming shortwave radiation increase through the snowmelt period, the formation of tree wells in forest environments and WEBSTER ET AL.…”

Section: Introductionmentioning

confidence: 99%

“…The effect of these heated canopy elements remains a source of uncertainty when modeling incoming longwave radiation dynamics within discontinuous canopies [Ellis et al, 2010;Lawler and Link, 2011]. In particular, the assumption that a single air temperature can be used to represent that of the entire canopy remains a limitation in both local and distributed incoming longwave radiation modeling [Pomeroy et al, 2009;Seyednasrollah and Kumar, 2014].…”

Section: Introductionmentioning

confidence: 99%

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Modeling subcanopy incoming longwave radiation to seasonal snow using air and tree trunk temperatures

et al. 2016

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Citation: Webster, Clare, Rutter, Nick, Zahner, Franziska and Jonas, Tobias (2016) Modelling sub-canopy incoming longwave radiation to seasonal snow using air and tree trunk temperatures. Journal of Geophysical 121 (3 Northumbria University has developed Northumbria Research Link (NRL) to enable users to access the University's research output. Copyright © and moral rights for items on NRL are retained by the individual author(s) and/or other copyright owners. Single copies of full items can be reproduced, displayed or performed, and given to third parties in any format or medium for personal research or study, educational, or not-for-profit purposes without prior permission or charge, provided the authors, title and full bibliographic details are given, as well as a hyperlink and/or URL to the original metadata page. The content must not be changed in any way. Full items must not be sold commercially in any format or medium without formal permission of the copyright holder. The full policy is available online: http://nrl.northumbria.ac.uk/policies.html This document may differ from the final, published version of the research and has been made available online in accordance with publisher policies. To read and/or cite from the published version of the research, please visit the publisher's website (a subscription may be required.)Modeling subcanopy incoming longwave radiation to seasonal snow using air and tree trunk temperatures Abstract Data collected at three Swiss alpine forested sites over a combined 11 year period were used to evaluate the role of air temperature in modeling subcanopy incoming longwave radiation to the snow surface. Simulated subcanopy incoming longwave radiation is traditionally partitioned into that from the sky and that from the canopy, i.e., a two-part model. Initial uncertainties in predicting longwave radiation using the two-part model resulted from vertical differences in measured air temperature. Above-canopy (35 m) air temperatures were higher than those within (10 m) and below (2 m) canopy throughout four snow seasons (December-April), demonstrating how the forest canopy can act as a cold sink for air. Lowest model root-mean-square error (RMSE) was using above-canopy air temperature. Further investigation of modeling subcanopy longwave radiation using above-canopy air temperature showed underestimations, particularly during periods of high insolation. In order to explicitly account for canopy temperatures in modeling longwave radiation, the two-part model was improved by incorporating a measured trunk view component and trunk temperature. Trunk temperature measurements were up to 25°C higher than locally measured air temperatures. This three-part model reduced the RMSE by up to 7.7 W m À2 from the two-part air temperature model at all sensor positions across the 2014 snowmelt season and performed particularly well during periods of high insolation when errors from the two-part model were up to 40 W m À2. A parameterization predicting tree trunk temperatures using measured air t...

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

Webster

Rutter

Jonas³

2017

JGR Atmospheres

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A comprehensive analysis of canopy surface temperatures was conducted around a small and large gap at a forested alpine site in the Swiss Alps during the 2015 and 2016 snowmelt seasons (March–April). Canopy surface temperatures within the small gap were within 2–3°C of measured reference air temperature. Vertical and horizontal variations in canopy surface temperatures were greatest around the large gap, varying up to 18°C above measured reference air temperature during clear‐sky days. Nighttime canopy surface temperatures around the study site were up to 3°C cooler than reference air temperature. These measurements were used to develop a simple parameterization for correcting reference air temperature for elevated canopy surface temperatures during (1) nighttime conditions (subcanopy shortwave radiation is 0 W m−2) and (2) periods of increased subcanopy shortwave radiation >400 W m−2 representing penetration of shortwave radiation through the canopy. Subcanopy shortwave and longwave radiation collected at a single point in the subcanopy over a 24 h clear‐sky period was used to calculate a nighttime bulk offset of 3°C for scenario 1 and develop a multiple linear regression model for scenario 2 using reference air temperature and subcanopy shortwave radiation to predict canopy surface temperature with a root‐mean‐square error (RMSE) of 0.7°C. Outside of these two scenarios, reference air temperature was used to predict subcanopy incoming longwave radiation. Modeling at 20 radiometer locations throughout two snowmelt seasons using these parameterizations reduced the mean bias and RMSE to below 10 W m s−2 at all locations.

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Net radiation in a snow‐covered discontinuous forest gap for a range of gap sizes and topographic configurations

Cited by 38 publications

References 51 publications

Evaluating the functionality and streamflow impacts of explicitly modelling forest–snow interactions and canopy gaps in a distributed hydrologic model

Evaluating the functionality and streamflow impacts of explicitly modelling forest–snow interactions and canopy gaps in a distributed hydrologic model

Modeling subcanopy incoming longwave radiation to seasonal snow using air and tree trunk temperatures

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

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