scholarly journals Forest summer albedo is sensitive to species and thinning: how should we account for this in Earth system models?

2014 ◽  
Vol 11 (8) ◽  
pp. 2411-2427 ◽  
Author(s):  
J. Otto ◽  
D. Berveiller ◽  
F.-M. Bréon ◽  
N. Delpierre ◽  
G. Geppert ◽  
...  
Keyword(s):  
Forest Management ◽  
Tree Species ◽  
Near Infrared ◽  
Model Parameters ◽  
Earth System ◽  
Forest Thinning ◽  
Area Index ◽  
System Models ◽  
Maximum Change ◽  
Earth System Models

Abstract. Although forest management is one of the instruments proposed to mitigate climate change, the relationship between forest management and canopy albedo has been ignored so far by climate models. Here we develop an approach that could be implemented in Earth system models. A stand-level forest gap model is combined with a canopy radiation transfer model and satellite-derived model parameters to quantify the effects of forest thinning on summertime canopy albedo. This approach reveals which parameter has the largest affect on summer canopy albedo: we examined the effects of three forest species (pine, beech, oak) and four thinning strategies with a constant forest floor albedo (light to intense thinning regimes) and five different solar zenith angles at five different sites (40° N 9° E–60° N 9° E). During stand establishment, summertime canopy albedo is driven by tree species. In the later stages of stand development, the effect of tree species on summertime canopy albedo decreases in favour of an increasing influence of forest thinning. These trends continue until the end of the rotation, where thinning explains up to 50% of the variance in near-infrared albedo and up to 70% of the variance in visible canopy albedo. The absolute summertime canopy albedo of all species ranges from 0.03 to 0.06 (visible) and 0.20 to 0.28 (near-infrared); thus the albedo needs to be parameterised at species level. In addition, Earth system models need to account for forest management in such a way that structural changes in the canopy are described by changes in leaf area index and crown volume (maximum change of 0.02 visible and 0.05 near-infrared albedo) and that the expression of albedo depends on the solar zenith angle (maximum change of 0.02 visible and 0.05 near-infrared albedo). Earth system models taking into account these parameters would not only be able to examine the spatial effects of forest management but also the total effects of forest management on climate.

scholarly journals Summertime canopy albedo is sensitive to forest thinning

2013 ◽  
Vol 10 (9) ◽  
pp. 15373-15414 ◽  
Author(s):  
J. Otto ◽  
D. Berveiller ◽  
F.-M. Bréon ◽  
N. Delpierre ◽  
G. Geppert ◽  
...  
Keyword(s):  
Forest Management ◽  
Tree Species ◽  
Structural Changes ◽  
Near Infrared ◽  
Canopy Structure ◽  
Model Parameters ◽  
Transfer Model ◽  
Forest Thinning ◽  
Crown Volume ◽  
The Difference

Abstract. Despite an emerging body of literature linking canopy albedo to forest management, understanding of the process is still fragmented. We combined a stand-level forest gap model with a canopy radiation transfer model and satellite-derived model parameters to quantify the effects of forest thinning, that is removing trees at a certain time during the forest rotation, on summertime canopy albedo. The effects of different forest species (pine, beech, oak) and four thinning strategies (light to intense thinning regimes) were examined. During stand establishment, summertime canopy albedo is driven by tree species. In the later stages of stand development, the effect of tree species on summertime canopy albedo decreases in favour of an increasing influence of forest thinning on summertime canopy albedo. These trends continue until the end of the rotation where thinning explains up to 50% of the variance in near-infrared canopy albedo and up to 70% of the variance in visible canopy albedo. More intense thinning lowers the summertime shortwave albedo in the canopy by as much as 0.02 compared to unthinned forest. The structural changes associated with forest thinning can be described by the change in LAI in combination with crown volume. However, forests with identical canopy structure can have different summertime albedo values due to their location: the further north a forest is situated, the more the solar zenith angle increases and thus the higher is the summertime canopy albedo, independent of the wavelength. Despite the increase of absolute summertime canopy albedo values with latitude, the difference in canopy albedo between managed and unmanaged forest decreases with increasing latitude. Forest management thus strongly altered summertime forest albedo.

Response of tropical rainfall to reduced evapotranspiration depends on continental extent

2021 ◽  
pp. 1-50
Author(s):  
Marianne Pietschnig ◽  
Abigail L. S. Swann ◽  
F. Hugo Lambert ◽  
Geoffrey K. Vallis
Keyword(s):  
Stomatal Conductance ◽  
General Circulation ◽  
Amazon Basin ◽  
Circulation Model ◽  
Complex Model ◽  
Earth System ◽  
Area Index ◽  
Tropical Rainfall ◽  
System Models ◽  
Earth System Models

AbstractFuture projections of precipitation change over tropical land are often enhanced by vegetation responses to CO2 forcing in Earth System Models. Projected decreases in rainfall over the Amazon basin and increases over the Maritime Continent are both stronger when plant physiological changes are modelled than if these changes are neglected, but the reasons for this amplification remain unclear. The responses of vegetation to increasing CO2 levels are complex and uncertain, including possible decreases in stomatal conductance and increases in leaf area index due to CO2-fertilisation. Our results from an idealised Atmospheric General Circulation Model show that the amplification of rainfall changes occurs even when we use a simplified vegetation parameterisation based solely on CO2-driven decreases in stomatal conductance, indicating that this mechanism plays a key role in complex model projections. Based on simulations with rectangular continentswe find that reducing terrestrial evaporation to zero with increasing CO2 notably leads to enhanced rainfall over a narrow island. Strong heating and ascent over the island trigger moisture advection from the surrounding ocean. In contrast, over larger continents rainfall depends on continental evaporation. Simulations with two rectangular continents representing South America and Africa reveal that the stronger decrease in rainfall over the Amazon basin seen in Earth System Models is due to a combination of local and remote effects, which are fundamentally connected to South America’s size and its location with respect to Africa. The response of tropical rainfall to changes in evapotranspiration is thus connected to size and configuration of the continents.

scholarly journals Carbon stocks and fluxes in the high latitudes: using site-level data to evaluate Earth system models

2017 ◽  
Vol 14 (22) ◽  
pp. 5143-5169 ◽  
Author(s):  
Sarah E. Chadburn ◽  
Gerhard Krinner ◽  
Philipp Porada ◽  
Annett Bartsch ◽  
Christian Beer ◽  
...  
Keyword(s):  
Soil Carbon ◽  
Nutrient Limitation ◽  
Vascular Plants ◽  
Carbon Stocks ◽  
The Arctic ◽  
Earth System ◽  
Area Index ◽  
System Models ◽  
Soil Carbon Stocks ◽  
Earth System Models

Abstract. It is important that climate models can accurately simulate the terrestrial carbon cycle in the Arctic due to the large and potentially labile carbon stocks found in permafrost-affected environments, which can lead to a positive climate feedback, along with the possibility of future carbon sinks from northward expansion of vegetation under climate warming. Here we evaluate the simulation of tundra carbon stocks and fluxes in three land surface schemes that each form part of major Earth system models (JSBACH, Germany; JULES, UK; ORCHIDEE, France). We use a site-level approach in which comprehensive, high-frequency datasets allow us to disentangle the importance of different processes. The models have improved physical permafrost processes and there is a reasonable correspondence between the simulated and measured physical variables, including soil temperature, soil moisture and snow. We show that if the models simulate the correct leaf area index (LAI), the standard C3 photosynthesis schemes produce the correct order of magnitude of carbon fluxes. Therefore, simulating the correct LAI is one of the first priorities. LAI depends quite strongly on climatic variables alone, as we see by the fact that the dynamic vegetation model can simulate most of the differences in LAI between sites, based almost entirely on climate inputs. However, we also identify an influence from nutrient limitation as the LAI becomes too large at some of the more nutrient-limited sites. We conclude that including moss as well as vascular plants is of primary importance to the carbon budget, as moss contributes a large fraction to the seasonal CO2 flux in nutrient-limited conditions. Moss photosynthetic activity can be strongly influenced by the moisture content of moss, and the carbon uptake can be significantly different from vascular plants with a similar LAI. The soil carbon stocks depend strongly on the rate of input of carbon from the vegetation to the soil, and our analysis suggests that an improved simulation of photosynthesis would also lead to an improved simulation of soil carbon stocks. However, the stocks are also influenced by soil carbon burial (e.g. through cryoturbation) and the rate of heterotrophic respiration, which depends on the soil physical state. More detailed below-ground measurements are needed to fully evaluate biological and physical soil processes. Furthermore, even if these processes are well modelled, the soil carbon profiles cannot resemble peat layers as peat accumulation processes are not represented in the models. Thus, we identify three priority areas for model development: (1) dynamic vegetation including (a) climate and (b) nutrient limitation effects; (2) adding moss as a plant functional type; and an (3) improved vertical profile of soil carbon including peat processes.

scholarly journals Spatially resolved evaluation of Earth system models with satellite column-averaged CO2

2021 ◽  
Author(s):  
Bettina K. Gier ◽  
Michael Buchwitz ◽  
Maximilian Reuter ◽  
Peter M. Cox ◽  
Pierre Friedlingstein ◽  
...  
Keyword(s):  
Satellite Data ◽  
Near Infrared ◽  
Early Period ◽  
Coupled Model ◽  
Negative Trend ◽  
Positive Trend ◽  
Earth System ◽  
Evaluation Tool ◽  
System Models ◽  
Earth System Models

<p>Earth system models (ESMs) participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5) showed large uncertainties in simulating atmospheric CO<sub>2</sub> concentrations. We utilize the Earth System Model Evaluation Tool (ESMValTool) to evaluate emission-driven CMIP5 and CMIP6 simulations with satellite data of column-average CO<sub>2</sub> mole fractions (XCO<sub>2</sub>). XCO<sub>2</sub> time series show a large spread among the model ensembles both in CMIP5 and CMIP6. Using the satellite observations as reference, the CMIP6 models have a <span>l</span>ower bias in the the multi-model mean than CMIP5, but the spread remains large. The satellite data are a combined data product covering the period 2003–2014 based on the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY)/Envisat (2003–2012) and Thermal And Near infrared Sensor for carbon Observation Fourier transform spectrometer/Greenhouse Gases Observing Satellite (TANSO-FTS/GOSAT) (2009–2014) instruments. While the combined satellite product shows a strong negative trend of decreasing <span>seasonal cycle amplitude (SCA)</span> with increasing XCO<sub>2</sub> in the northern midlatitudes, both CMIP ensembles instead show a non-significant positive trend in the multi-model mean. The negative trend is reproduced by the models when sampling them as the observations, attributing it to sampling characteristics. Applying a mask of the mean data coverage of each satellite to the models, the SCA is higher for the SCIAMACHY/Envisat mask than when using the TANSO-FTS/GOSAT mask. This induces an artificial negative trend when using observational sampling over the full period, as SCIAMACHY/Envisat covers the early period until 2012, with TANSO-FTS/GOSAT measurements starting in 2009. Overall, the CMIP6 ensemble shows better agreement with the satellite data than the CMIP5 ensemble in all considered quantities (mean XCO<sub>2</sub>, growth rate, SCA and trend in SCA). This study shows that the availability of column-integral CO<sub>2</sub> from satellite provides a promising new way to evaluate the performance of Earth system models on a global scale, complementing existing studies that are based on in situ measurements from single ground-based stations.</p>

scholarly journals Carbon stocks and fluxes in the high latitudes: Using site-level data to evaluate Earth system models

2017 ◽  
Author(s):  
Sarah Chadburn ◽  
Gerhard Krinner ◽  
Philipp Porada ◽  
Annett Bartsch ◽  
Christian Beer ◽  
...  
Keyword(s):  
Soil Carbon ◽  
Nutrient Limitation ◽  
Vascular Plants ◽  
Carbon Stocks ◽  
The Arctic ◽  
Earth System ◽  
Area Index ◽  
System Models ◽  
Soil Carbon Stocks ◽  
Earth System Models

Abstract. It is important that climate models can accurately simulate the terrestrial carbon cycle in the Arctic, due to the large and potentially labile carbon stocks found in permafrost-affected environments, which can lead to a positive climate feedback, along with the possibility of future carbon sinks from northward expansion of vegetation under climate warming. Here we evaluate the simulation of tundra carbon stocks and fluxes in three land surface schemes that each form part of major Earth System Models (JSBACH, Germany; JULES, UK and ORCHIDEE, France). We use a site-level approach where comprehensive, high-frequency datasets allow us to disentangle the importance of different processes. The models have improved physical permafrost processes and there is a reasonable correspondence between the simulated and measured physical variables, including soil temperature, soil moisture and snow. We show that if the models simulate the correct leaf area index (LAI), the standard C3 photosynthesis schemes produce the correct order of magnitude of carbon fluxes. Therefore, simulating the correct LAI is one of the first priorities. LAI depends quite strongly on climatic variables alone, as we see by the fact that the dynamic vegetation model can simulate most of the differences in LAI between sites, based almost entirely on climate inputs. However, we also identify an influence from nutrient limitation as the LAI becomes too large at some of the more nutrient-limited sites. We conclude that including moss as well as vascular plants is of primary importance to the carbon budget, as moss contributes a large fraction to the seasonal CO2 flux in nutrient-limited conditions. Moss photosynthetic activity can be strongly influenced by the moisture content of moss, and the carbon uptake can be significantly different from vascular plants with similar LAI. The soil carbon stocks depend strongly on the rate of input of carbon from the vegetation to the soil, and our analysis suggests that an improved simulation of photosynthesis would also lead to an improved simulation of soil carbon stocks. However, the stocks are also influenced by soil carbon burial (e.g. through cryoturbation) and the rate of heterotrophic respiration, which depends on the soil physical state. More detailed below-ground measurements are needed to fully evaluate soil biological and physical processes. Furthermore, even if these processes are well modelled, the soil carbon profiles cannot resemble peat layers as peat accumulation processes are not represented in the models. Thus we identify three priority areas for model development: 1. Dynamic vegetation including a. climate and b. nutrient limitation effects. 2. Adding moss as a plant functional type. 3. Improved vertical profile of soil carbon including peat processes.

scholarly journals Spatially resolved evaluation of Earth system models with satellite column-averaged CO<sub>2</sub>

2020 ◽  
Vol 17 (23) ◽  
pp. 6115-6144
Author(s):  
Bettina K. Gier ◽  
Michael Buchwitz ◽  
Maximilian Reuter ◽  
Peter M. Cox ◽  
Pierre Friedlingstein ◽  
...  
Keyword(s):  
Satellite Data ◽  
Missing Values ◽  
Near Infrared ◽  
Early Period ◽  
Negative Trend ◽  
Positive Trend ◽  
Earth System ◽  
Evaluation Tool ◽  
System Models ◽  
Earth System Models

Abstract. Earth system models (ESMs) participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5) showed large uncertainties in simulating atmospheric CO2 concentrations. We utilize the Earth System Model Evaluation Tool (ESMValTool) to evaluate emission-driven CMIP5 and CMIP6 simulations with satellite data of column-average CO2 mole fractions (XCO2). XCO2 time series show a large spread among the model ensembles both in CMIP5 and CMIP6. Compared to the satellite observations, the models have a bias of +25 to −20 ppmv in CMIP5 and +20 to −15 ppmv in CMIP6, with the multi-model mean biases at +10 and +2 ppmv, respectively. The derived mean atmospheric XCO2 growth rate (GR) of 2.0 ppmv yr−1 is overestimated by 0.4 ppmv yr−1 in CMIP5 and 0.3 ppmv yr−1 in CMIP6 for the multi-model mean, with a good reproduction of the interannual variability. All models capture the expected increase of the seasonal cycle amplitude (SCA) with increasing latitude, but most models underestimate the SCA. Any SCA derived from data with missing values can only be considered an “effective” SCA, as the missing values could occur at the peaks or troughs. The satellite data are a combined data product covering the period 2003–2014 based on the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY)/Envisat (2003–2012) and Thermal And Near infrared Sensor for carbon Observation Fourier transform spectrometer/Greenhouse Gases Observing Satellite (TANSO-FTS/GOSAT) (2009–2014) instruments. While the combined satellite product shows a strong negative trend of decreasing effective SCA with increasing XCO2 in the northern midlatitudes, both CMIP ensembles instead show a non-significant positive trend in the multi-model mean. The negative trend is reproduced by the models when sampling them as the observations, attributing it to sampling characteristics. Applying a mask of the mean data coverage of each satellite to the models, the effective SCA is higher for the SCIAMACHY/Envisat mask than when using the TANSO-FTS/GOSAT mask. This induces an artificial negative trend when using observational sampling over the full period, as SCIAMACHY/Envisat covers the early period until 2012, with TANSO-FTS/GOSAT measurements starting in 2009. Overall, the CMIP6 ensemble shows better agreement with the satellite data than the CMIP5 ensemble in all considered quantities (XCO2, GR, SCA and trend in SCA). This study shows that the availability of column-integral CO2 from satellite provides a promising new way to evaluate the performance of Earth system models on a global scale, complementing existing studies that are based on in situ measurements from single ground-based stations.

scholarly journals Projections of leaf area index in earth system models

2016 ◽  
Vol 7 (1) ◽  
pp. 211-229 ◽  
Author(s):  
Natalie Mahowald ◽  
Fiona Lo ◽  
Yun Zheng ◽  
Laura Harrison ◽  
Chris Funk ◽  
...  
Keyword(s):  
Climate Change ◽  
Leaf Area Index ◽  
Leaf Area ◽  
Climate Change Impacts ◽  
Earth System ◽  
Area Index ◽  
System Models ◽  
Clear Cut ◽  
The Tropics ◽  
Earth System Models

Abstract. The area of leaves in the plant canopy, measured as leaf area index (LAI), modulates key land–atmosphere interactions, including the exchange of energy, moisture, carbon dioxide (CO2), and other trace gases and aerosols, and is therefore an essential variable in predicting terrestrial carbon, water, and energy fluxes. Here our goal is to characterize the LAI projections from the latest generation of earth system models (ESMs) for the Representative Concentration Pathway (RCP) 8.5 and RCP4.5 scenarios. On average, the models project increases in LAI in both RCP8.5 and RCP4.5 over most of the globe, but also show decreases in some parts of the tropics. Because of projected increases in variability, there are also more frequent periods of low LAI across broad regions of the tropics. Projections of LAI changes varied greatly among models: some models project very modest changes, while others project large changes, usually increases. Modeled LAI typically increases with modeled warming in the high latitudes, but often decreases with increasing local warming in the tropics. The models with the most skill in simulating current LAI in the tropics relative to satellite observations tend to project smaller increases in LAI in the tropics in the future compared to the average of all the models. Using LAI projections to identify regions that may be vulnerable to climate change presents a slightly different picture than using precipitation projections, suggesting LAI may be an additional useful tool for understanding climate change impacts. Going forward, users of LAI projections from the CMIP5 ESMs evaluated here should be aware that model outputs do not exhibit clear-cut relationships to vegetation carbon and precipitation. Our findings underscore the need for more attention to LAI projections, in terms of understanding the drivers of projected changes and improvements to model skill.

scholarly journals Evaluation of CMIP5 earth system models in reproducing leaf area index and vegetation cover over the Tibetan Plateau

2014 ◽  
Vol 28 (6) ◽  
pp. 1041-1060 ◽  
Author(s):  
Yan Bao ◽  
Yanhong Gao ◽  
Shihua Lü ◽  
Qingxia Wang ◽  
Shaobo Zhang ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Leaf Area Index ◽  
Leaf Area ◽  
Vegetation Cover ◽  
The Tibetan Plateau ◽  
Earth System ◽  
Area Index ◽  
System Models ◽  
Earth System Models

scholarly journals Constraints to Vegetation Growth Reduced by Region-Specific Changes in Seasonal Climate

Climate ◽  
2019 ◽  
Vol 7 (2) ◽  
pp. 27 ◽  
Author(s):  
Hirofumi Hashimoto ◽  
Ramakrishna Nemani ◽  
Govindasamy Bala ◽  
Long Cao ◽  
Andrew Michaelis ◽  
...  
Keyword(s):  
Gross Primary Production ◽  
Earth System ◽  
Co2 Fertilization ◽  
Area Index ◽  
Vegetation Growth ◽  
System Models ◽  
Late 21St Century ◽  
Fertilization Effect ◽  
Physiological Benefits ◽  
Earth System Models

We qualitatively and quantitatively assessed the factors related to vegetation growth using Earth system models and corroborated the results with historical climate observations. The Earth system models showed a systematic greening by the late 21st century, including increases of up to 100% in Gross Primary Production (GPP) and 60% in Leaf Area Index (LAI). A subset of models revealed that the radiative effects of CO2 largely control changes in climate, but that the CO2 fertilization effect dominates the greening. The ensemble of Earth system model experiments revealed that the feedback of surface temperature contributed to 17% of GPP increase in temperature-limited regions, and radiation increase accounted for a 7% increase of GPP in radiation-limited areas. These effects are corroborated by historical observations. For example, observations confirm that cloud cover has decreased over most land areas in the last three decades, consistent with a CO2-induced reduction in transpiration. Our results suggest that vegetation may thrive in the starkly different climate expected over the coming decades, but only if plants harvest the sort of hypothesized physiological benefits of higher CO2 depicted by current Earth system models.

Better representing vegetation canopy structure in Earth System Models

2021 ◽  
Author(s):  
Renato Braghiere
Keyword(s):  
Weather Forecasting ◽  
Canopy Structure ◽  
Carbon Assimilation ◽  
Shortwave Radiation ◽  
Earth System ◽  
Area Index ◽  
System Models ◽  
Clumping Index ◽  
The Impact ◽  
Earth System Models

&lt;p&gt;Addressing the impact of 3D vegetation structure on shortwave radiation transfer in Earth System Models (ESMs) is important for accurate weather forecasting, carbon budget estimates, and climate predictions. While leaf-level photosynthesis is well characterized and understood, estimates of global level carbon assimilation in the literature range from 110 to 175 PgC.yr-1.&amp;#160;I will explore&amp;#160;how neglecting canopy structure leads to significant uncertainties in shortwave radiation partitioning, as well as second order derived canopy properties, such as leaf area index (LAI). I will also cover&amp;#160;how modeled carbon assimilation of the terrestrial biosphere is impacted when a satellite derived clumping index is incorporated into the UKESM.&amp;#160;Finally, I will touch on how the clumping index might be integrated into hyperspectral ESMs to explore the theoretical relationship between canopy structure and photosynthesis.&lt;/p&gt;

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