scholarly journals The challenges of an in situ validation of a nonequilibrium model of soil heat and moisture dynamics during fires

2021 ◽  
Vol 25 (2) ◽  
pp. 685-709 ◽  
Author(s):  
William J. Massman
Keyword(s):  
Boundary Condition ◽  
Heat Flux ◽  
Soil Surface ◽  
Vapor Source ◽  
Nonequilibrium Model ◽  
Apparent Thermal Conductivity ◽  
The Impact ◽  
Energy Balance Approach ◽  
Upper Boundary

Abstract. With the increasing frequency and severity of fire, there is an increasing desire to better manage fuels and minimize, as much as possible, the impacts of fire on soils and other natural resources. Piling and/or burning slash is one method of managing fuels and reducing the risk and consequences of wildfire, but the repercussions to the soil, although very localized, can be significant and often irreversible. In an effort to provide a tool to better understand the impact of fire on soils, this study outlines the improvements to and the in situ validation of a nonequilibrium model for simulating the coupled interactions and transport of heat, moisture and water vapor during fires. Improvements to the model eliminate the following two important (but heretofore universally overlooked) inconsistencies: one that describes the relationship between evaporation and condensation in the parameterization of the nonequilibrium vapor source term, and the other that is the incorrect use of the apparent thermal conductivity in the soil heat flow equation. The first of these made a small enhancement in the stability and performance of the model. The second is an important improvement in the physics underpinning the model but had less of an impact on the model's performance and stability than the first. This study also (a) develops a general heating function that describes the energy input to the soil surface by the fire and (b) discusses the complexities and difficulties of formulating the upper boundary condition from a surface energy balance approach. The model validation uses (in situ temperature, soil moisture and heat flux) data obtained in a 2004 experimental slash pile burn. Important temperature-dependent corrections to the instruments used for measuring soil heat flux and moisture are also discussed and assessed. Despite any possible ambiguities in the calibration of the sensors or the simplicity of the parameterization of the surface heating function, the difficulties and complexities of formulating the upper boundary condition and the obvious complexities of the dynamic response of the soil's temperature and heat flux, the model produced at least a very credible, if not surprisingly good, simulation of the observed data. This study then continues with a discussion and sensitivity analysis of some important feedbacks (some of which are well known and others that are more hypothetical) that are not included in the present (or any extant) model, but that undoubtedly are dynamically influencing the physical properties of the soil in situ during the fire and, thereby, modulating the behavior of the soil temperature and moisture. This paper concludes with a list of possible future observational and modeling studies and how they would advance the research and findings discussed here.

scholarly journals The challenges of an in situ validation of a non-equilibrium model of soil heat and moisture dynamics during fires

2020 ◽  
Author(s):  
William J. Massman
Keyword(s):  
Heat Flux ◽  
Equilibrium Model ◽  
Soil Heat Flux ◽  
Flow Equation ◽  
Vapor Source ◽  
Apparent Thermal Conductivity ◽  
And Performance ◽  
The Impact ◽  
Non Equilibrium

Abstract. With the increasing frequency and severity of fire there is an increasing desire to better manage fuels and minimize, as much as possible, the impacts of fire on soils and other natural resources. Piling and/or burning slash is one method of managing fuels and reducing the risk and consequences of wildfire, but the repercussions to the soil, although very localized, can be significant and often irreversible. In an effort to provide a tool to better understand the impact of fire on soils, this study outlines the improvements to and the in-situ validation of a non-equilibrium model for simulating the coupled interactions and transport of heat, moisture and water vapor during fires. Improvements to the model eliminate two important (but heretofore universally overlooked) inconsistencies: one that describes the relationship between evaporation and condensation in the parameterization of the non-equilibrium vapor source term and the other, is the incorrect use of the apparent thermal conductivity in the soil heat flow equation. The first of these enhanced the stability and performance of the model. The second is an important improvement in the model's physical realism, but had less of an impact on the model's performance and stability than the first. The model validation uses (in-situ temperature, soil moisture, and heat flux) data obtained in a 2004 experimental slash pile burn. Important temperature dependent corrections to the instruments used for measuring soil heat flux and moisture are also discussed and assessed. Despite any possible ambiguities in the calibration the sensors or the simplicity of the parameterization of the surface heating function, the difficulties and complexities of formulating the upper boundary condition, and the obvious complexities of the dynamic response of the soil's temperature and heat flux, the model produced at least a very credible, if not surprisingly good, simulation of the observed data. This study then continues with a discussion and sensitivity analysis of some important feedbacks (some of which are well known and others that are more hypothetical) that are not included in the present (or any extant) model, but undoubtedly are dynamically influencing the physical properties of the soil in-situ during the fire and thereby modulating the behavior of the soil temperature and moisture. This manuscript concludes with a list of possible future observational and modeling studies and how they would advance the research and findings discussed here.

In situ thermal-conductivity measurements and morphological characterization of intumescent coatings for fire protection

2018 ◽  
Vol 36 (5) ◽  
pp. 419-437 ◽  
Author(s):  
Jiyuan Kang ◽  
Fumiaki Takahashi ◽  
James S T’ien
Keyword(s):  
Thermal Conductivity ◽  
Heat Flux ◽  
Fire Protection ◽  
Heat Fluxes ◽  
Loss Cone ◽  
Char Layer ◽  
Intumescent Coatings ◽  
Apparent Thermal Conductivity ◽  
Initial Coating

Thermal insulating performance and char-layer properties have been studied for water-based intumescent coatings for structural steel fire protection using a new laboratory-scale mass-loss cone apparatus. A specimen (100 × 100 mm mild steel plate; the initial coating thickness: 0.3–2.0 mm) is placed horizontally and exposed to a constant incident radiant heat flux (25, 50, or 75 kW/m2). The apparent thermal conductivity of the expanding char layer is determined in situ based on real-time measurements of the temperature distribution in the char layer and the heat flux transmitted through the char layer. Three-dimensional morphological observations of the expanded char layer are made using a computed tomographic–based analytical method. The vertical variation of the porosity of the expanded char layer is measured. The measured heat-blocking efficiency is correlated strongly with the incident heat flux, which increases the expanded char-layer thickness, and porosity for sufficiently large initial coating thicknesses (>0.76 mm). For a thin coating (0.30 mm), violent off-gassing disrupts the intumescing processes to form a consistent char layer after abrupt exposure to higher incident heat fluxes, thus resulting in lower heat-blocking efficiency. Therefore, the product application thickness must exceed a proper threshold value to ensure an adequate thermal insulation performance.

scholarly journals HEPPA-II model–measurement intercomparison project: EPP indirect effects during the dynamically perturbed NH winter 2008–2009

2017 ◽  
Vol 17 (5) ◽  
pp. 3573-3604 ◽  
Author(s):  
Bernd Funke ◽  
William Ball ◽  
Stefan Bender ◽  
Angela Gardini ◽  
V. Lynn Harvey ◽  
...  
Keyword(s):  
Boundary Condition ◽  
Indirect Effect ◽  
Climate Model ◽  
Good Representation ◽  
Atmospheric Models ◽  
Model Simulations ◽  
Upper Lid ◽  
Odd Nitrogen ◽  
The Impact ◽  
Upper Boundary

Abstract. We compare simulations from three high-top (with upper lid above 120 km) and five medium-top (with upper lid around 80 km) atmospheric models with observations of odd nitrogen (NOx  =  NO + NO2), temperature, and carbon monoxide from seven satellite instruments (ACE-FTS on SciSat, GOMOS, MIPAS, and SCIAMACHY on Envisat, MLS on Aura, SABER on TIMED, and SMR on Odin) during the Northern Hemisphere (NH) polar winter 2008/2009. The models included in the comparison are the 3-D chemistry transport model 3dCTM, the ECHAM5/MESSy Atmospheric Chemistry (EMAC) model, FinROSE, the Hamburg Model of the Neutral and Ionized Atmosphere (HAMMONIA), the Karlsruhe Simulation Model of the Middle Atmosphere (KASIMA), the modelling tools for SOlar Climate Ozone Links studies (SOCOL and CAO-SOCOL), and the Whole Atmosphere Community Climate Model (WACCM4). The comparison focuses on the energetic particle precipitation (EPP) indirect effect, that is, the polar winter descent of NOx largely produced by EPP in the mesosphere and lower thermosphere. A particular emphasis is given to the impact of the sudden stratospheric warming (SSW) in January 2009 and the subsequent elevated stratopause (ES) event associated with enhanced descent of mesospheric air. The chemistry climate model simulations have been nudged toward reanalysis data in the troposphere and stratosphere while being unconstrained above. An odd nitrogen upper boundary condition obtained from MIPAS observations has further been applied to medium-top models. Most models provide a good representation of the mesospheric tracer descent in general, and the EPP indirect effect in particular, during the unperturbed (pre-SSW) period of the NH winter 2008/2009. The observed NOx descent into the lower mesosphere and stratosphere is generally reproduced within 20 %. Larger discrepancies of a few model simulations could be traced back either to the impact of the models' gravity wave drag scheme on the polar wintertime meridional circulation or to a combination of prescribed NOx mixing ratio at the uppermost model layer and low vertical resolution. In March–April, after the ES event, however, modelled mesospheric and stratospheric NOx distributions deviate significantly from the observations. The too-fast and early downward propagation of the NOx tongue, encountered in most simulations, coincides with a temperature high bias in the lower mesosphere (0.2–0.05 hPa), likely caused by an overestimation of descent velocities. In contrast, upper-mesospheric temperatures (at 0.05–0.001 hPa) are generally underestimated by the high-top models after the onset of the ES event, being indicative for too-slow descent and hence too-low NOx fluxes. As a consequence, the magnitude of the simulated NOx tongue is generally underestimated by these models. Descending NOx amounts simulated with medium-top models are on average closer to the observations but show a large spread of up to several hundred percent. This is primarily attributed to the different vertical model domains in which the NOx upper boundary condition is applied. In general, the intercomparison demonstrates the ability of state-of-the-art atmospheric models to reproduce the EPP indirect effect in dynamically and geomagnetically quiescent NH winter conditions. The encountered differences between observed and simulated NOx, CO, and temperature distributions during the perturbed phase of the 2009 NH winter, however, emphasize the need for model improvements in the dynamical representation of elevated stratopause events in order to allow for a better description of the EPP indirect effect under these particular conditions.

scholarly journals Potential evaporation at eddy-covariance sites across the globe

2018 ◽  
Author(s):  
Wouter H. Maes ◽  
Pierre Gentine ◽  
Niko E. C. Verhoest ◽  
Diego G. Miralles
Keyword(s):  
Eddy Covariance ◽  
Poor Performance ◽  
Drought Severity ◽  
Potential Evaporation ◽  
Diverse Range ◽  
Eddy Covariance Measurements ◽  
Priestley And Taylor Method ◽  
The Impact ◽  
Energy Balance Approach

Abstract. Potential evaporation (Ep) is a crucial variable for hydrological forecast and in drought monitoring systems. However, multiple interpretations of Ep exist, and these reflect a diverse range of methods to calculate Ep. As such, a comparison of the performance of these methods against field observations in different global ecosystems is badly needed. In this study, we used eddy-covariance measurements from 107 sites of the FLUXNET2015 database, covering 11 different biomes, to parameterize and compare the main Ep methods and uncover their relative performance. For each site, we extracted the days for which ecosystems are unstressed based on both an energy balance approach and on a soil water content approach. The evaporation measurements during these days were used as reference to validate the different methods to estimate Ep. Our results indicate that a simple radiation-driven method calibrated per biome consistently performed best, with a mean correlation of 0.93, an unbiased RMSE of 0.56 mm day−1, and a bias of −0.02 mm day−1 against in situ measurements of unstressed evaporation. A Priestley and Taylor method, calibrated per biome, performed just slightly worse, yet substantially and consistently better than more complex Penman, Penman-Monteith-based or temperature-based approaches. We show that the poor performance of Penman-Monteith based approaches relates largely to the fact that the unstressed stomatal conductance was assumed constant. Further analysis showed that the biome-specific parameters required for the simple radiation-driven methods are relatively constant per biome. This makes this simple radiation-driven method calibrated per biome a robust method that can be incorporated into models for improving our understanding of the impact of global warming on future global water use and demand, drought severity and ecosystem productivity.

scholarly journals Application of Multilayer Perceptron Method on Heat Flow Meter Results for Reducing the Measurement Time

2020 ◽  
Vol 2 (1) ◽  
pp. 29
Author(s):  
Sanjin Gumbarević ◽  
Bojan Milovanović ◽  
Mergim Gaši ◽  
Marina Bagarić
Keyword(s):  
Neural Network ◽  
Heat Flux ◽  
Multilayer Perceptron ◽  
Heat Losses ◽  
Measurement Time ◽  
Flux Rate ◽  
U Value ◽  
The Impact ◽  
Building Elements

To reduce the impact on climate change, many countries have developed strategies for the building sector with a goal to reduce the energy demands and carbon emission of buildings. As most buildings that exist today will very likely exist in foreseeable future, many buildings will need to undergo major renovations. One of the most important parameters in determining the transmission heat losses through the building envelope is the U-value, i.e., thermal transmittance, and it is simply the rate of heat transfer per unit temperature. Since the U-value is one of the most important parameters regarding building energy performance, envelope elements that do not perform well in terms of transmission heat losses must undergo a renovation processes. The in-situ U-value of building elements is usually determined by the Heat Flux Method (HFM). One of the issues of current application of the HFM is the measurement duration. This paper explores the possibilities of reducing the measurement time by predicting the heat flux rate using a multilayer perceptron (MLP), a class of artificial neural network. The MLP uses two input layers that are the interior and exterior air temperatures, and the output layer that is the predicted heat flux rate. The predicted value is trained by comparing the predicted heat flux rates with the measured values, and by rearranging the neural network parameters (weights and biases) in corresponding neurons by minimizing the mean squared error defined for trained values (measured versus predicted heat flux rates). The use of MLP shows promising results for predicting the heat flux rates for the analyzed cases (4 days HFM results) when the training is performed on 2/3 or 1/2 of the overall measurement time. The application of the MLP could be in reducing the in-situ measurement time when determining heat losses through building elements in shorter time periods.

scholarly journals The impact of imperfect heat transfer on the convective instability of a thermal boundary layer in a porous media

2016 ◽  
Vol 794 ◽  
pp. 154-174 ◽  
Author(s):  
Joseph Hitchen ◽  
Andrew J. Wells
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Boundary Condition ◽  
Porous Layer ◽  
Biot Number ◽  
Heat Sink ◽  
Convective Instability ◽  
The Impact ◽  
Biot Numbers ◽  
Upper Boundary

We consider convective instability in a deep porous medium cooled from above with a linearised thermal exchange at the upper surface, thus determining the impact of using a Robin boundary condition, in contrast to previous studies using a Dirichlet boundary condition. With the linearised surface exchange, the thermal flux out of the porous layer depends linearly on the temperature difference between the effective temperature of a heat sink at the upper boundary and the temperature at the surface of the porous layer. The rate of this exchange is characterised by a dimensionless Biot number, $\mathit{Bi}$, determined by the effective thermal conductivity of exchange with the heat sink relative to the physical thermal conductivity of the porous layer. For a given temperature difference between the heat sink at the upper boundary and deep in the porous medium, we find that imperfectly cooled layers with finite Biot numbers are more stable to convective instabilities than perfectly cooled layers which have large, effectively infinite Biot numbers. Two regimes of behaviour were determined with contrasting stability behaviour and characteristic scales. When the Biot number is large the near-perfect heat transfer produces small corrections of order $1/\mathit{Bi}$ to the perfectly conducting behaviour found when the Biot number is infinite. In the insulating limit as the Biot number approaches zero, a different behaviour was found with significantly larger scales for the critical wavelength and depth of convection both scaling proportional to $1/\sqrt{\mathit{Bi}}$.

scholarly journals HEPPA-II model-measurement intercomparison project: EPP indirect effects during the dynamically perturbed NH winter 2008–2009

2016 ◽  
Author(s):  
Bernd Funke ◽  
William Ball ◽  
Stefan Bender ◽  
Angela Gardini ◽  
V. Lynn Harvey ◽  
...  
Keyword(s):  
Boundary Condition ◽  
Indirect Effect ◽  
Climate Model ◽  
Atmospheric Models ◽  
Modeling Tools ◽  
Model Simulations ◽  
Upper Lid ◽  
Odd Nitrogen ◽  
The Impact ◽  
Upper Boundary

Abstract. We compare simulations from three high-top (with upper lid above 120 km) and five medium-top (with upper lid around 80km) atmospheric models with observations of odd nitrogen (NOx = NO + NO2), temperature, and carbon monoxide from seven satellite instruments (ACE-FTS on SciSat, GOMOS, MIPAS, and SCIAMACHY on Envisat, MLS on Aura, SABER on TIMED, and SMR on Odin) during the Northern Hemisphere (NH) polar winter 2008/2009. The models included in the comparison are the 3d Chemistry Transport model (3dCTM), the ECHAM5/MESSy Atmospheric Chemistry (EMAC) model, FinROSE, the Hamburg Model of the Neutral and Ionized Atmosphere (HAMMONIA), the Karlsruhe Simulation Model of the Middle Atmosphere (KASIMA), the modeling tools for SOlar Climate Ozone Links studies (SOCOL and CAO-SOCOL), and the Whole Atmosphere Community Climate Model (WACCM4). The comparison focuses on the energetic particle precipitation (EPP) indirect effect, that is, the polar winter descent of NOx largely produced by EPP in the mesosphere and lower thermosphere. A particular emphasis is given to the impact of the sudden stratospheric warming (SSW) in January 2009 and the subsequent elevated stratopause (ES) event associated with enhanced descent of mesospheric air. The chemistry climate model simulations have been nudged toward reanalysis data in the troposphere and stratosphere while being unconstrained above. An odd nitrogen upper boundary condition obtained from MIPAS observations has further been applied to medium-top models. Most models provide a good representation of the mesospheric tracer descent in general, and the EPP indirect effect in particular, during the unperturbed (pre-SSW) period of the NH winter 2008/2009. The observed NOx descent into the lower mesosphere and stratosphere is generally reproduced within 20 %. Larger discrepancies of a few model simulations could be traced back either to the impact of the models' gravity wave drag scheme on the polar wintertime meridional circulation or to a combination of prescribed NOx mixing ratio at the uppermost model layer and low vertical resolution. In March–April, after the ES event, however, modelled mesospheric and stratospheric NOx distributions deviate significantly from the observations. The too fast and early downward propagation of the NOx tongue, encountered in most simulations, coincides with a temperature high bias in the lower mesosphere (0.2–0.05 hPa) being likely caused by an overestimation of descent velocities. On the other hand, upper mesospheric temperatures (at 0.05–0.001 hPa) are generally underestimated by the high-top models after the onset of the ES event, being indicative for too slow descent and hence too low NOx fluxes. As a consequence, the magnitude of the simulated NOx tongue is generally underestimated by these models. Descending NOx amounts simulated with medium-top models are on average closer to the observations but show a large spread of up to several hundred percent. This is primarily attributed to the different vertical model domains in which the NOx upper boundary condition is applied. In general, the intercomparison demonstrates the ability of state-of-the-art atmospheric models to reproduce the EPP indirect effect in dynamically and geomagnetically quiescent NH winter conditions. The encountered differences between observed and simulated NOx, CO, and temperature distributions during the perturbed phase of the 2009 NH winter, however, emphasize the need for model improvements in the dynamical representation of elevated stratopause events in order to allow for a better description of the EPP indirect effect under these particular conditions.

HOW CLIMATE CHANGE CAN INFLUENCE THE AGRICULTURE IN UKRAINE: A REVIEW

2020 ◽  
Author(s):  
N. Maidanovych ◽  
Keyword(s):  
Climate Change ◽  
Crop Yields ◽  
Soil Surface ◽  
Winter Period ◽  
Negative Consequences ◽  
Resource Saving ◽  
Impact Of Climate Change ◽  
Positive Effects ◽  
Average Annual Temperature ◽  
The Impact

The purpose of this work is to review and analyze the main results of modern research on the impact of climate change on the agro-sphere of Ukraine. Results. Analysis of research has shown that the effects of climate change on the agro-sphere are already being felt today and will continue in the future. The observed climate changes in recent decades have already significantly affected the shift in the northern direction of all agro-climatic zones of Europe, including Ukraine. From the point of view of productivity of the agro-sphere of Ukraine, climate change will have both positive and negative consequences. The positives include: improving the conditions of formation and reducing the harvesting time of crop yields; the possibility of effective introduction of late varieties (hybrids), which require more thermal resources; improving the conditions for overwintering crops; increase the efficiency of fertilizer application. Model estimates of the impact of climate change on wheat yields in Ukraine mainly indicate the positive effects of global warming on yields in the medium term, but with an increase in the average annual temperature by 2 ° C above normal, grain yields are expected to decrease. The negative consequences of the impact of climate change on the agrosphere include: increased drought during the growing season; acceleration of humus decomposition in soils; deterioration of soil moisture in the southern regions; deterioration of grain quality and failure to ensure full vernalization of grain; increase in the number of pests, the spread of pathogens of plants and weeds due to favorable conditions for their overwintering; increase in wind and water erosion of the soil caused by an increase in droughts and extreme rainfall; increasing risks of freezing of winter crops due to lack of stable snow cover. Conclusions. Resource-saving agricultural technologies are of particular importance in the context of climate change. They include technologies such as no-till, strip-till, ridge-till, which make it possible to partially store and accumulate mulch on the soil surface, reduce the speed of the surface layer of air and contribute to better preservation of moisture accumulated during the autumn-winter period. And in determining the most effective ways and mechanisms to reduce weather risks for Ukrainian farmers, it is necessary to take into account the world practice of climate-smart technologies.

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