scholarly journals The effects of varying drought-heat signatures on terrestrial carbon dynamics and vegetation composition

2021 ◽  
Author(s):  
Elisabeth Tschumi ◽  
Sebastian Lienert ◽  
Karin van der Wiel ◽  
Fortunat Joos ◽  
Jakob Zscheischler
Keyword(s):  
Heat Waves ◽  
Model Simulation ◽  
Vegetation Type ◽  
Carbon Dynamics ◽  
Scenario Tree ◽  
Tree Cover ◽  
Ecosystem Productivity ◽  
Terrestrial Carbon ◽  
Dynamic Global Vegetation Model ◽  
Tree Coverage

Abstract. The frequency and severity of droughts and heat waves are projected to increase under global warming. However, the differential impacts of climate extremes on the terrestrial biosphere and anthropogenic CO2 sink remain poorly understood. In this study, we analyse the effects of six hypothetical climate scenarios with differing drought-heat signatures, sampled from a long stationary climate model simulation, on vegetation distribution and land carbon dynamics, as modelled by a dynamic global vegetation model (LPX-Bern v1.4). The six forcing scenarios consist of a Control scenario representing a natural climate, a Noextremes scenario featuring few droughts and heatwaves, a Nocompound scenario which allows univariate hot or dry extremes but no co-occurring extremes, a Hot scenario with frequent heatwaves, a Dry scenario with frequent droughts, and a Hotdry scenario featuring frequent concurrent hot and dry extremes. We find that a climate with no extreme events increases tree coverage by up to 10 % compared to the Control and also increases ecosystem productivity as well as the terrestrial carbon pools. A climate with many heatwaves leads to an overall increase in tree coverage primarily in higher latitudes, while the ecosystem productivity remains similar to the Control. In the Dry and even more so in the Hotdry scenario, tree cover and ecosystem productivity are reduced by up to −4 % compared to the Control. Depending on the vegetation type, the effects from the Hotdry scenario are stronger than the effects from the Hot and Dry scenario combined, illustrating the importance of correctly simulating compound extremes for future impact assessment. Overall, our study illustrates how factorial model experiments can be employed to disentangle the effects from single and compound extremes.

The effect of differing drought-heat signatures on terrestrial carbon dynamics and vegetation composition

2021 ◽  
Author(s):  
Elisabeth Tschumi ◽  
Sebastian Lienert ◽  
Karin van der Wiel ◽  
Fortunat Joos ◽  
Jakob Zscheischler
Keyword(s):  
Carbon Cycle ◽  
Carbon Dynamics ◽  
Occurrence Frequency ◽  
Climate Variables ◽  
Vegetation Composition ◽  
Terrestrial Carbon ◽  
Dynamic Global Vegetation Model ◽  
Climate Conditions ◽  
Global Mean

<p>Droughts and heatwaves have large impacts on the terrestrial carbon cycle. They lead to reductions in gross and net carbon uptake or anomalous carbon emissions by the vegetation to the atmosphere because of responses such as stomatal closure, hydraulic failure and vegetation mortality. The impacts are particularly strong when drought and heat occur at the same time. Climate model simulations diverge in their occurrence frequency of compound hot and dry events, and so far it is unclear how these differences affect carbon dynamics. Furthermore, it is unknown whether a higher frequency of droughts and heatwaves leads to long-term changes in carbon dynamics, and how such an increase might affect vegetation composition.</p><p>To study the immediate and long-term effects of varying signatures of droughts and heatwaves on carbon dynamics and vegetation composition, we employ the state-of-the-art dynamic global vegetation model LPX-Bern (v1.4) under different drought-heat scenarios. We constructed six 100-yr long scenarios with different drought-heat signatures: a “control”, “no extremes”, “no compound extremes”, “heat only”, “drought only”, and “compound drought and heat” scenario. This was done by sampling daily climate variables from a 2000-year stationary simulation of a General Circulation Model (EC-Earth) for present-day climate conditions. Such a sampling ensures physically-consistent co-variability between climate variables in the climate forcing.</p><p>The scenarios differ little in their mean climate conditions (global mean land temperature differences of around 0.3°C and global mean land precipitation differences smaller than 7%), but vary strongly in the occurrence frequency of extremes such as droughts, heatwaves, and compound drought and heatwaves (up to five times more compound extremes in the “hotdry “scenario than in the “control”), allowing us to study the effects of the extremes on vegetation. Combined hot and dry extremes reduce all tree types and promotes grassland, while only hot extremes favours trees, especially in higher latitudes. No extremes are preferred by all tree types in LPX. Net Ecosystem Production (NEP) is expected to increase in most regions for the “noextremes” scenario, while the “hotdry” scenario is likely to reduce NEP.</p><p>Our results provide a better understanding of the links between hot and dry conditions and vegetation dynamics as well as carbon dynamics. These analyses may help to reduce uncertainties in carbon cycle projections, which is important for constraining carbon cycle-climate feedbacks. The presented scenarios can be used for a variety of purposes such as studying the effects of differing drought-heat signatures on crop yield or the occurrence of fire besides others.</p>

Investigating the impact of different drought-heat signatures on carbon dynamics using a dynamic global vegetation model

2020 ◽  
Author(s):  
Elisabeth Tschumi ◽  
Sebastian Lienert ◽  
Karin van der Wiel ◽  
Fortunat Joos ◽  
Jakob Zscheischler
Keyword(s):  
Carbon Cycle ◽  
Heat Waves ◽  
Carbon Dynamics ◽  
Climate Forcing ◽  
Carbon Uptake ◽  
Climate Variables ◽  
Vegetation Model ◽  
Dynamic Global Vegetation Model ◽  
Global Vegetation

<p><span>Droughts and heat waves have large impacts on the terrestrial carbon cycle. They lead to reductions in gross and net carbon uptake or anomalous increases in carbon emissions to the atmosphere because of responses such as stomatal closure, hydraulic failure and vegetation mortality. The impacts are particularly strong when drought and heat occur at the same time. Climate model simulations diverge in their occurrence frequency of compound hot and dry events, and it is unclear how these differences affect carbon dynamics. Furthermore, it is unknown whether an increase in frequency of droughts and heat waves leads to long-term changes in carbon dynamics, and how such an increase might affect vegetation composition.</span></p><p><span>To study the immediate and long-term effects of varying signatures of droughts and heat waves on carbon dynamics such as inter-annual variability of carbon fluxes and cumulative carbon uptake, we employ the state-of-the-art dynamic global vegetation model LPX-Bern (v1.4) under different drought-heat scenarios.</span></p><p><span>We have constructed five 100-yr long scenarios with different drought-heat signatures, representing a “control”, “close to mean seasonal cycle”, “drought only”, “heat only”, and “compound drought and heat” climate forcing to LPX-Bern. This is done by sampling daily climate variables from a 2000-year stationary simulation of a General Circulation Model (EC-Earth) for present-day climate conditions. Such a sampling ensures physically-consistent co-variability between climate variables in the climate forcing.</span></p><p><span>We investigate the carbon-cycle response and changes in vegetation structure to different drought-heat signatures on a global grid, representing different land cover types and climate zones. Our results provide a better understanding of the links between hot and dry conditions and carbon dynamics. This may help to reduce uncertainties in carbon cycle projections, which is important for constraining carbon cycle-climate feedbacks.</span></p>

scholarly journals Improvement of Soil Respiration Parameterization in a Dynamic Global Vegetation Model and Its Impact on the Simulation of Terrestrial Carbon Fluxes

2018 ◽  
Vol 32 (1) ◽  
pp. 127-143 ◽  
Author(s):  
Dongmin Kim ◽  
Myong-In Lee ◽  
Eunkyo Seo
Keyword(s):  
Spatial Distribution ◽  
Soil Respiration ◽  
Soil Temperature ◽  
Vegetation Type ◽  
Carbon Fluxes ◽  
Decomposition Process ◽  
Spatial And Temporal Variation ◽  
In Situ Observation ◽  
Terrestrial Carbon ◽  
Soil Temperature And Moisture

Abstract The Q10 value represents the soil respiration sensitivity to temperature often used for the parameterization of the soil decomposition process has been assumed to be a constant in conventional numerical models, whereas it exhibits significant spatial and temporal variation in the observations. This study develops a new parameterization method for determining Q10 by considering the soil respiration dependence on soil temperature and moisture obtained by multiple regression for each vegetation type. This study further investigates the impacts of the new parameterization on the global terrestrial carbon flux. Our results show that a nonuniform spatial distribution of Q10 tends to better represent the dependence of the soil respiration process on heterogeneous surface vegetation type compared with the control simulation using a uniform Q10. Moreover, it tends to improve the simulation of the relationship between soil respiration and soil temperature and moisture, particularly over cold and dry regions. The modification has an impact on the soil respiration and carbon decomposition process, which changes gross primary production (GPP) through controlling nutrient assimilation from soil to vegetation. It leads to a realistic spatial distribution of GPP, particularly over high latitudes where the original model has a significant underestimation bias. Improvement in the spatial distribution of GPP leads to a substantial reduction of global mean GPP bias compared with the in situ observation-based reference data. The results highlight that the enhanced sensitivity of soil respiration to the subsurface soil temperature and moisture introduced by the nonuniform spatial distribution of Q10 has contributed to improving the simulation of the terrestrial carbon fluxes and the global carbon cycle.

scholarly journals African biomes are most sensitive to changes in CO<sub>2</sub> under recent and near-future CO<sub>2</sub> conditions

2020 ◽  
Vol 17 (4) ◽  
pp. 1147-1167 ◽  
Author(s):  
Simon Scheiter ◽  
Glenn R. Moncrieff ◽  
Mirjam Pfeiffer ◽  
Steven I. Higgins
Keyword(s):  
Environmental Conditions ◽  
Climate Model ◽  
Mitigation Strategies ◽  
Tree Cover ◽  
Mixing Ratio ◽  
Vegetation Model ◽  
Rcp Scenarios ◽  
Dynamic Global Vegetation Model ◽  
Lag Effects ◽  
Near Future

Abstract. Current rates of climate and atmospheric change are likely higher than during the last millions of years. Even higher rates of change are projected in CMIP5 climate model ensemble runs for some Representative Concentration Pathway (RCP) scenarios. The speed of ecological processes such as leaf physiology, demography or migration can differ from the speed of changes in environmental conditions. Such mismatches imply lags between the actual vegetation state and the vegetation state expected under prevailing environmental conditions. Here, we used a dynamic vegetation model, the adaptive Dynamic Global Vegetation Model (aDGVM), to study lags between actual and expected vegetation in Africa under a changing atmospheric CO2 mixing ratio. We hypothesized that lag size increases with a more rapidly changing CO2 mixing ratio as opposed to slower changes in CO2 and that disturbance by fire further increases lag size. Our model results confirm these hypotheses, revealing lags between vegetation state and environmental conditions and enhanced lags in fire-driven systems. Biome states, carbon stored in vegetation and tree cover in Africa are most sensitive to changes in CO2 under recent and near-future levels. When averaged across all biomes and simulations with and without fire, times to reach an equilibrium vegetation state increase from approximately 242 years for 200 ppm to 898 years for 1000 ppm. These results have important implications for vegetation modellers and for policy making. Lag effects imply that vegetation will undergo substantial changes in distribution patterns, structure and carbon sequestration even if emissions of fossils fuels and other greenhouse gasses are reduced and the climate system stabilizes. We conclude that modelers need to account for lag effects in models and in data used for model testing. Policy makers need to consider lagged responses and committed changes in the biosphere when developing adaptation and mitigation strategies.

scholarly journals Depletion of Urban Green Space and Its Adverse Effect: A Case of Kumasi, the Former Garden City of West- Africa

2017 ◽  
Vol 8 (2) ◽  
pp. 1 ◽  
Author(s):  
Bernard Essel
Keyword(s):  
Adverse Effect ◽  
Land Use ◽  
Green Space ◽  
City Planning ◽  
Landscape Planning ◽  
Heat Waves ◽  
Urban Green Space ◽  
Tree Cover ◽  
Urban Green ◽  
The Impact

Incorporating greenery has been a vital aspect of city planning. Landscape planning has been a vital aspect of city planning since the 19th Century. Since then, landscape planning has become a social necessity. Assessing the impact of the decline in urban green space is very important. Hence, using Kumasi as a case study largely fit due to the decline of the city’s urban green space. Based on this the study assessed the Landcover change between 2000 to 2010 and projected the Landcover/land use for 2020. It also analyzed the temperature recordings from 2000 to 2016. The result revealed that the city has lost 19.59 km2 and 33.39 km2 of forest and agriculture lands respectively. It was also projected that it will further decline to 0.7 km2 and 8.2 km2 respectively. Among the various Landcover classes, agriculture lands were the most delicate land use which suffers massive decline in acreage. Moreover, the adverse effect of the decline in green spaces has been evident in high temperatures, unattractive environment, and atmospheric pollution. In the last decade (2000-2010), the city’s temperature increased by 0.2oC but has dropped in the past six years (2010-2016). Nevertheless, it doesn’t suggest that the impact of the heat waves has reduced due to the reduction in temperature. Conversely, the impact has increased due to the absence of tree cover. Ultimately, Kumasi’s landscape has depleted and has lost a touch of vegetation, hence appropriate measure needs to be put in place. 

scholarly journals Interactive Impacts of Fire and Vegetation Dynamics on Global Carbon and Water Budgets using Community Land Model version 4.5

2018 ◽  
Author(s):  
Hocheol Seo ◽  
Yeonjoo Kim
Keyword(s):  
Land Surface ◽  
Vegetation Dynamics ◽  
Carbon Sink ◽  
Vegetation Type ◽  
Water Fluxes ◽  
Carbon Sinks ◽  
Terrestrial Carbon ◽  
Moisture Profile ◽  
Community Land Model ◽  
Model Version

Abstract. Fire plays an important role in terrestrial ecosystems. The burning of biomass affects carbon and water fluxes and the distribution of vegetation. To understand the effect of the interactive processes of fire and ecological succession on land surface carbon and water fluxes, this study utilized the Community Land Model version 4.5 to conduct a series of experiments that included and excluded fire and dynamic vegetation processes. Results of the experiments that excluded dynamic vegetation showed a global increase in net ecosystem production (NEP) in post-fire regions, which has been shown in previous studies with the similar modeling practices. However, inclusion of dynamic vegetation revealed a fire-induced decrease in NEP in some regions. Additionally, the carbon sink in post-fire regions reduced when the dominant vegetation type was changed from trees to grasses. This study shows that inclusion of dynamic vegetation enhances carbon emissions from fire by reducing terrestrial carbon sinks; however, this effect is somewhat mitigated by the increase in terrestrial carbon sinks when dynamic vegetation is not used. Results also show that fire-induced changes in vegetation modify the soil moisture profile because grasslands are more dominant in post-fire regions; this results in less moisture within top soil layers compared to non-burned regions, even though transpiration is reduced overall. These findings are different from those of previous fire model evaluations, that ignore vegetation dynamics, and thus highlight the importance of interactive processes between fire and vegetation dynamics, particularly when evaluating recent model developments with respect to fire and vegetation dynamics.

scholarly journals Influence of dynamic vegetation on climate change and terrestrial carbon storage in the Last Glacial Maximum

2013 ◽  
Vol 9 (4) ◽  
pp. 1571-1587 ◽  
Author(s):  
R. O'ishi ◽  
A. Abe-Ouchi
Keyword(s):  
Carbon Storage ◽  
Last Glacial Maximum ◽  
Glacial Maximum ◽  
Atmospheric Co2 ◽  
Terrestrial Carbon ◽  
Dynamic Global Vegetation Model ◽  
Vegetation Feedback ◽  
Last Glacial ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract. When the climate is reconstructed from paleoevidence, it shows that the Last Glacial Maximum (LGM, ca. 21 000 yr ago) is cold and dry compared to the present-day. Reconstruction also shows that compared to today, the vegetation of the LGM is less active and the distribution of vegetation was drastically different, due to cold temperature, dryness, and a lower level of atmospheric CO2 concentration (185 ppm compared to a preindustrial level of 285 ppm). In the present paper, we investigate the influence of vegetation change on the climate of the LGM by using a coupled atmosphere-ocean-vegetation general circulation model (AOVGCM, the MIROC-LPJ). The MIROC-LPJ is different from earlier studies in the introduction of a bias correction method in individual running GCM experiments. We examined four GCM experiments (LGM and preindustrial, with and without vegetation feedback) and quantified the strength of the vegetation feedback during the LGM. The result shows that global-averaged cooling during the LGM is amplified by +13.5 % due to the introduction of vegetation feedback. This is mainly caused by the increase of land surface albedo due to the expansion of tundra in northern high latitudes and the desertification in northern middle latitudes around 30° N to 60° N. We also investigated how this change in climate affected the total terrestrial carbon storage by using offline Lund-Potsdam-Jena dynamic global vegetation model (LPJ-DGVM). Our result shows that the total terrestrial carbon storage was reduced by 597 PgC during the LGM, which corresponds to the emission of 282 ppm atmospheric CO2. In the LGM experiments, the global carbon distribution is generally the same whether the vegetation feedback to the atmosphere is included or not. However, the inclusion of vegetation feedback causes substantial terrestrial carbon storage change, especially in explaining the lowering of atmospheric CO2 during the LGM.

Response of terrestrial carbon dynamics to snow cover change: A meta-analysis of experimental manipulation (II)

2016 ◽  
Vol 103 ◽  
pp. 388-393 ◽  
Author(s):  
Weibin Li ◽  
Jiabing Wu ◽  
Edith Bai ◽  
Changjie Jin ◽  
Anzhi Wang ◽  
...  
Keyword(s):  
Snow Cover ◽  
Meta Analysis ◽  
Carbon Dynamics ◽  
Experimental Manipulation ◽  
Terrestrial Carbon

scholarly journals Multi-factor controls on terrestrial carbon dynamics in urbanized areas

2014 ◽  
Vol 11 (24) ◽  
pp. 7107-7124 ◽  
Author(s):  
C. Zhang ◽  
H. Tian ◽  
S. Pan ◽  
G. Lockaby ◽  
A. Chappelka
Keyword(s):  
Carbon Sequestration ◽  
Environmental Change ◽  
Carbon Dynamics ◽  
Individual Factors ◽  
Land Conversion ◽  
Terrestrial Carbon ◽  
Carbon Loss ◽  
Relative Contribution ◽  
Urbanized Areas ◽  
The Impact

Abstract. As urban land expands rapidly across the globe, much concern has been raised that urbanization may alter the terrestrial carbon cycle. Urbanization involves complex changes in land structure and multiple environmental factors. Little is known about the relative contribution of these individual factors and their interactions to the terrestrial carbon dynamics, however, which is essential for assessing the effectiveness of carbon sequestration policies focusing on urban development. This study developed a comprehensive analysis framework for quantifying relative contribution of individual factors (and their interactions) to terrestrial carbon dynamics in urbanized areas. We identified 15 factors belonging to five categories, and we applied a newly developed factorial analysis scheme to the southern United States (SUS), a rapidly urbanizing region. In all, 24 numeric experiments were designed to systematically isolate and quantify the relative contribution of individual factors. We found that the impact of land conversion was far larger than other factors. Urban managements and the overall interactive effects among major factors, however, created a carbon sink that compensated for 42% of the carbon loss in land conversion. Our findings provide valuable information for regional carbon management in the SUS: (1) it is preferable to preserve pre-urban carbon pools than to rely on the carbon sinks in urban ecosystems to compensate for the carbon loss in land conversion. (2) In forested areas, it is recommendable to improve landscape design (e.g., by arranging green spaces close to the city center) to maximize the urbanization-induced environmental change effect on carbon sequestration. Urbanization-induced environmental change will be less effective in shrubland regions. (3) Urban carbon sequestration can be significantly improved through changes in management practices, such as increased irrigation and fertilizer and targeted use of vehicles and machinery with least-associated carbon emissions.

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