scholarly journals Disentangling residence time and temperature sensitivity of microbial decomposition in a global soil carbon model

2014 ◽  
Vol 11 (3) ◽  
pp. 4995-5021 ◽  
Author(s):  
J.-F. Exbrayat ◽  
A. J. Pitman ◽  
G. Abramowitz
Keyword(s):  
Soil Carbon ◽  
Residence Time ◽  
Carbon Balance ◽  
Coupled Model ◽  
Historical Period ◽  
Microbial Decomposition ◽  
Total Soil ◽  
Industrial Soil ◽  
The Future ◽  
The Impact

Abstract. Recent studies have identified the first-order parameterization of microbial decomposition as a major source of uncertainty in simulations and projections of the terrestrial carbon balance. Here, we use a reduced complexity model representative of the current state-of-the-art parameterization of soil organic carbon decomposition. We undertake a systematic sensitivity analysis to disentangle the effect of the time-invariant baseline residence time (k) and the sensitvity of microbial decomposition to temperature (Q10) on soil carbon dynamics at regional and global scales. Our simulations produce a range in total soil carbon at equilibrium of ~ 592 to 2745 Pg C which is similar to the ~ 561 to 2938 Pg C range in pre-industrial soil carbon in models used in the fifth phase of the Coupled Model Intercomparison Project. This range depends primarily on the value of k, although the impact of Q10 is not trivial at regional scales. As climate changes through the historical period, and into the future, k is primarily responsible for the magnitude of the response in soil carbon, whereas Q10 determines whether the soil remains a sink, or becomes a source in the future mostly by its effect on mid-latitudes carbon balance. If we restrict our simulations to those simulating total soil carbon stocks consistent with observations of current stocks, the projected range in total soil carbon change is reduced by 42% for the historical simulations and 45% for the future projections. However, while this observation-based selection dismisses outliers it does not increase confidence in the future sign of the soil carbon feedback. We conclude that despite this result, future estimates of soil carbon, and how soil carbon responds to climate change should be constrained by available observational data sets.

scholarly journals Disentangling residence time and temperature sensitivity of microbial decomposition in a global soil carbon model

2014 ◽  
Vol 11 (23) ◽  
pp. 6999-7008 ◽  
Author(s):  
J.-F. Exbrayat ◽  
A. J. Pitman ◽  
G. Abramowitz
Keyword(s):  
Soil Carbon ◽  
Residence Time ◽  
Carbon Balance ◽  
Carbon Stocks ◽  
Historical Period ◽  
Microbial Decomposition ◽  
Total Soil ◽  
Industrial Soil ◽  
The Future ◽  
The Impact

Abstract. Recent studies have identified the first-order representation of microbial decomposition as a major source of uncertainty in simulations and projections of the terrestrial carbon balance. Here, we use a reduced complexity model representative of current state-of-the-art models of soil organic carbon decomposition. We undertake a systematic sensitivity analysis to disentangle the effect of the time-invariant baseline residence time (k) and the sensitivity of microbial decomposition to temperature (Q10) on soil carbon dynamics at regional and global scales. Our simulations produce a range in total soil carbon at equilibrium of ~ 592 to 2745 Pg C, which is similar to the ~ 561 to 2938 Pg C range in pre-industrial soil carbon in models used in the fifth phase of the Coupled Model Intercomparison Project (CMIP5). This range depends primarily on the value of k, although the impact of Q10 is not trivial at regional scales. As climate changes through the historical period, and into the future, k is primarily responsible for the magnitude of the response in soil carbon, whereas Q10 determines whether the soil remains a sink, or becomes a source in the future mostly by its effect on mid-latitude carbon balance. If we restrict our simulations to those simulating total soil carbon stocks consistent with observations of current stocks, the projected range in total soil carbon change is reduced by 42% for the historical simulations and 45% for the future projections. However, while this observation-based selection dismisses outliers, it does not increase confidence in the future sign of the soil carbon feedback. We conclude that despite this result, future estimates of soil carbon and how soil carbon responds to climate change should be more constrained by available data sets of carbon stocks.

scholarly journals Response of microbial decomposition to spin-up explains CMIP5 soil carbon range until 2100

2014 ◽  
Vol 7 (6) ◽  
pp. 2683-2692 ◽  
Author(s):  
J.-F. Exbrayat ◽  
A. J. Pitman ◽  
G. Abramowitz
Keyword(s):  
Soil Carbon ◽  
Carbon Storage ◽  
Land Surface ◽  
Coupled Model ◽  
Surface Fluxes ◽  
Cmip5 Models ◽  
Historical Period ◽  
Microbial Decomposition ◽  
Transient Simulations ◽  
Business As Usual

Abstract. Soil carbon storage simulated by the Coupled Model Intercomparison Project (CMIP5) models varies 6-fold for the present day. Here, we confirm earlier work showing that this range already exists at the beginning of the CMIP5 historical simulations. We additionally show that this range is largely determined by the response of microbial decomposition during each model's spin-up procedure from initialization to equilibration. The 6-fold range in soil carbon, once established prior to the beginning of the historical period (and prior to the beginning of a CMIP5 simulation), is then maintained through the present and to 2100 almost unchanged even under a strong business-as-usual emissions scenario. We therefore highlight that a commonly ignored part of CMIP5 analyses – the land surface state achieved through the spin-up procedure – can be important for determining future carbon storage and land surface fluxes. We identify the need to better constrain the outcome of the spin-up procedure as an important step in reducing uncertainty in both projected soil carbon and land surface fluxes in CMIP5 transient simulations.

scholarly journals Permafrost carbon−climate feedback is sensitive to deep soil carbon decomposability but not deep soil nitrogen dynamics

2015 ◽  
Vol 112 (12) ◽  
pp. 3752-3757 ◽  
Author(s):  
Charles D. Koven ◽  
David M. Lawrence ◽  
William J. Riley
Keyword(s):  
Soil Nitrogen ◽  
Carbon Balance ◽  
Nitrogen Availability ◽  
Nitrogen Dynamics ◽  
Permafrost Region ◽  
Deep Soil ◽  
Surface Soils ◽  
Permafrost Thaw ◽  
The Future ◽  
The Impact

Permafrost soils contain enormous amounts of organic carbon whose stability is contingent on remaining frozen. With future warming, these soils may release carbon to the atmosphere and act as a positive feedback to climate change. Significant uncertainty remains on the postthaw carbon dynamics of permafrost-affected ecosystems, in particular since most of the carbon resides at depth where decomposition dynamics may differ from surface soils, and since nitrogen mineralized by decomposition may enhance plant growth. Here we show, using a carbon−nitrogen model that includes permafrost processes forced in an unmitigated warming scenario, that the future carbon balance of the permafrost region is highly sensitive to the decomposability of deeper carbon, with the net balance ranging from 21 Pg C to 164 Pg C losses by 2300. Increased soil nitrogen mineralization reduces nutrient limitations, but the impact of deep nitrogen on the carbon budget is small due to enhanced nitrogen availability from warming surface soils and seasonal asynchrony between deeper nitrogen availability and plant nitrogen demands. Although nitrogen dynamics are highly uncertain, the future carbon balance of this region is projected to hinge more on the rate and extent of permafrost thaw and soil decomposition than on enhanced nitrogen availability for vegetation growth resulting from permafrost thaw.

scholarly journals Phenology of Tempranillo and Cabernet-Sauvignon varieties cultivated in the Ribera del Duero DO: observed variability and predictions under climate change scenarios

OENO One ◽  
2018 ◽  
Vol 52 (1) ◽  
Author(s):  
Maria Concepción Ramos ◽  
Gregory V Jones ◽  
Jesús Yuste
Keyword(s):  
Climate Change ◽  
Emission Scenario ◽  
Coupled Model ◽  
Late Winter ◽  
Cabernet Sauvignon ◽  
Climate Change Scenarios ◽  
Wine Quality ◽  
Rcp Scenarios ◽  
The Future ◽  
The Impact

Aim: This research examined relationships between grapevine phenology and climate in the Ribera del Duero DO (Spain). The observed varieties included Tempranillo, the main variety planted in the region, and Cabernet-Sauvignon.Methods and Results: Phenological events for stages C (budbreak), I (bloom), M (véraison) and N (maturity) were analyzed for 2004-2015. Dormant period chilling and late winter heating requirements to initiate growth were evaluated and accumulated temperature (growing degree days-GDD) prior to each phenological event and in between events were examined for the role they play in influencing growth timing. The results were then used to examine future phenological changes due to climate change using eight models integrated in the Coupled Model Intercomparison Project (CMIP5) and for two Representative Concentration Pathways (RCP) scenarios – RCP4.5 and RCP8.5 – for 2030, 2050, and 2070. Accumulated temperatures after March 20th become important for initiating phenology and are strongly correlated to all growth events. The influence of water availability between budbreak and bloom and between bloom and véraison on phenological timing was also confirmed.Conclusions: The projections showed that for the RCP4.5 emission scenario, budbreak is predicted earlier by approximately 2 days for 2030, 3 days for 2050 and 5 days for 2070, while bloom is predicted to be 3 to 8 days earlier and véraison 6 to 19 days earlier for the same time periods. For the RCP8.5 emission scenario, budbreak is modeled to take place about 3 days, 5 days and 9 days earlier, respectively for 2030, 2050 and 2070. Bloom is predicted to occur about 5, 10 and 16 days earlier; véraison is predicted earlier by 10 days for 2030, 19 days for 2050, and 28 days for 2070. Maturity and the timing of harvest could be up to 23 days earlier under the RCP4.5 emission scenario and up to 35 days earlier under the RCP8.5 emission scenario. Compared to Cabernet-Sauvignon, Tempranillo exhibited greater phenological sensitivity to temperature changes in the observed time period that is likely to continue into the future with greater changes to earlier growth events projected. This sensitivity could be problematic for the region due to the variety’s historic importance and points to the need to examine adaptive measures that can help growers to respond to projected changes in climate.Significance and impact of the study: The projected climate changes in the future indicate the potential for significant changes in the phenology of Tempranillo in the Ribera del Duero DO, Spain. Given that this variety has the largest contribution and importance in this region, these changes could have impacts on wine quality, indicating the need of establishing strategies to reduce or mitigate the impact from future changes in climate.

More extreme El Niño events reduce ocean carbon uptake in the future

2021 ◽  
Author(s):  
Enhui Liao ◽  
Laure Resplandy ◽  
Junjie Liu ◽  
Kevin Bowman
Keyword(s):  
Biogeochemical Model ◽  
Historical Period ◽  
Terrestrial Biosphere ◽  
The Future ◽  
Thermally Driven ◽  
High Emission ◽  
Ocean Carbon ◽  
High Emission Scenario ◽  
Flux Response ◽  
The Impact

<p>El Niño events weaken the strong natural oceanic source of CO<sub>2</sub> in the Tropical Pacific Ocean, partly offsetting the simultaneous release of CO<sub>2</sub> from the terrestrial biosphere during these events. Yet, uncertainties in the magnitude of this ocean response and how it will respond to the projected increase in extreme El Niño in the future (Cai et al., 2014) limit our understanding of the global carbon cycle and its sensitivity to climate. Here, we examine the mechanisms controlling the air-sea CO<sub>2</sub> flux response to El Niño events and how it will evolve in the future, using multidecadal ocean pCO<sub>2</sub> observations in conjunction with CMIP6 Earth system models (ESMs) and a state‐of‐the‐art ocean biogeochemical model. We show that the magnitude, spatial extent, and duration of the anomalous ocean CO<sub>2</sub> drawdown increased with El Niño intensity in the historical period. However, this relationship reverses in the CMIP6 projections under the high emission scenario. ESMs project more intense El Niño events, but weaker CO<sub>2</sub> flux anomalies in the future. This unexpected response is controlled by two factors: a stronger compensation between thermally-driven outgassing and non-thermal drawdown (56% of the signal); and less pronounced wind anomalies limiting the impact of El Niño on air-sea CO<sub>2</sub> exchanges (26% of the signal). El Niños should no longer reinforce the net global oceanic sink in the future, but have a near-neutral effect or even release CO<sub>2</sub> to the atmosphere, reinforcing the concurrent release of CO<sub>2</sub> from the terrestrial biosphere.</p>

scholarly journals Response of microbial decomposition to spin-up explains CMIP5 soil carbon range until 2100

2014 ◽  
Vol 7 (3) ◽  
pp. 3481-3504 ◽  
Author(s):  
J.-F. Exbrayat ◽  
A. J. Pitman ◽  
G. Abramowitz
Keyword(s):  
Soil Carbon ◽  
Coupled Model ◽  
Cmip5 Models ◽  
Soil Carbon Storage ◽  
Microbial Decomposition ◽  
Transient Simulations ◽  
Intercomparison Project ◽  
Business As Usual ◽  
Carbon Stores

Abstract. Soil carbon storage simulated by the Coupled Model Intercomparison Project (CMIP5) models varies 6-fold for the present day. We show that this range already exists at the beginning of the historical simulations and demonstrate that it is mostly an artifact of the representation of microbial decomposition and its response during the spin-up procedure used by the models. The 6-fold range in soil carbon, once established, is maintained through the present and to 2100 almost unchanged even under a strong business-as-usual emissions scenario. By highlighting the role of the response of decomposition to spin-up in explaining why current CMIP5 soil carbon stores vary widely, we identify the need to better constrain the outcome of this procedure as a means to reduce uncertainty in transient simulations.

Modelling the effects of stover harvest on soil organic carbon in the Pampas of Argentina

Soil Research ◽  
2019 ◽  
Vol 57 (3) ◽  
pp. 257
Author(s):  
Roberto Alvarez ◽  
Josefina L. De Paepe
Keyword(s):  
Organic Carbon ◽  
Soil Organic Carbon ◽  
Soil Carbon ◽  
Carbon Balance ◽  
Crop Residues ◽  
Triticum Aestivum L ◽  
Management Scenarios ◽  
Retention Efficiency ◽  
Steady State Current ◽  
The Impact

Our objective was to estimate the impact of harvesting stover from agricultural crops to generate biofuels or electricity on the soil organic carbon levels of the Pampean Region in Argentina. For this purpose, a carbon balance methodology based on artificial neural networks was used. Contrasting soil carbon scenarios for different subregions were constructed using a current map of organic carbon and statistical data for crop rotations. Average yields were also estimated using this information. The neural network methodology allowed calculating the annual carbon balance as the difference between estimating the contribution of carbon in crop residues (stover+roots) to the soil and losses as heterotrophic respiration. The model was run for each level of residue input until the soil carbon attained a steady-state. Current rotations were modelled, with predominance of soybean (Glycine max (L.) Merr.) and alternatives that included a greater proportion of wheat (Triticum aestivum L.) and corn (Zea mays L.). Only the stover of these latter two crops was considered to be partially harvested (30% and 60%). The input of carbon to soil was highly dependent on rotation, increasing as the proportion of wheat and corn in the rotation and the level of yield increased. In contrast, stover harvest had little impact on the carbon input due to the low proportion of both crops in the predominant current rotation. By increasing the proportion of cereal crops or the technological level and yield, it was possible to compensate for the effect of stover harvest on soil carbon. The carbon input from residue needed to maintain soil carbon ranged within 2.0–6.0 t C ha–1 year–1 depending on the initial soil carbon level. Retention efficiency of residue carbon was ~30% across different management scenarios. It is not recommended to harvest more than 30% of the stover in order to maintain the level of carbon in the soil organic matter of many Pampean soils.

scholarly journals Statistical–Dynamical Downscaling Projections of Tropical Cyclone Activity in a Warming Climate: Two Diverging Genesis Scenarios

2020 ◽  
Vol 33 (11) ◽  
pp. 4815-4834 ◽  
Author(s):  
Chia-Ying Lee ◽  
Suzana J. Camargo ◽  
Adam H. Sobel ◽  
Michael K. Tippett
Keyword(s):  
Tropical Cyclone ◽  
Environmental Conditions ◽  
Dynamical Downscaling ◽  
Coupled Model ◽  
Historical Period ◽  
Future Scenario ◽  
Warming Climate ◽  
Increasing Trend ◽  
The Future ◽  
Intercomparison Project

AbstractTropical cyclone (TC) activity is examined using the Columbia Hazard model (CHAZ), a statistical–dynamical downscaling system, with environmental conditions taken from simulations from phase 5 of the Coupled Model Intercomparison Project (CMIP5) for both the historical period and a future scenario under the representative concentration pathway 8.5. Projections of individual global and basin TC frequency depend sensitively on the choice of moisture variable used in the tropical genesis cyclone index (TCGI) component of CHAZ. Simulations using column relative humidity show an increasing trend in the future, while those using saturation deficit show a decreasing trend, although both give similar results in the historical period. While the projected annual TC frequency is also sensitive to the choice of model used to provide the environmental conditions, the choice of humidity variable in the TCGI is more important. Changes in TC frequency directly affect the projected TCs’ tracks and the frequencies of strong storms on both basin and regional scales. This leads to large uncertainty in assessing regional and local storm hazards. The uncertainty here is fundamental and epistemic in nature. Increases in the fraction of major TCs, rapid intensification rate, and decreases in forward speed are insensitive to TC frequency, however. The present results are also consistent with prior studies in indicating that those TC events that do occur will, on average, be more destructive in the future because of the robustly projected increases in intensity.

scholarly journals Future Changes in Water Supply and Demand for Las Vegas Valley: A System Dynamic Approach based on CMIP3 and CMIP5 Climate Projections

Hydrology ◽  
2020 ◽  
Vol 7 (1) ◽  
pp. 16 ◽  
Author(s):  
Neekita Joshi ◽  
Kazi Tamaddun ◽  
Ranjan Parajuli ◽  
Ajay Kalra ◽  
Pankaj Maheshwari ◽  
...  
Keyword(s):  
Water Supply ◽  
Las Vegas ◽  
Supply And Demand ◽  
Coupled Model ◽  
Climate Projections ◽  
Lake Mead ◽  
Las Vegas Valley ◽  
The Future ◽  
Water Supply And Demand ◽  
The Impact

The study investigated the impact on water supply and demand as an effect of climate change and population growth in the Las Vegas Valley (LVV) as a part of the Thriving Earth Exchange Program. The analyses evaluated future supply and demand scenarios utilizing a system dynamics model based on the climate and hydrological projections from the Coupled Model Intercomparison Project phases 3 and 5 (CMIP3 and CMIP5, respectively) using the simulation period expanding from 1989 to 2049. The main source of water supply in LVV is the water storage in Lake Mead, which is directly related to Lake Mead elevation. In order to assess the future water demand, the elevation of Lake Mead was evaluated under several water availability scenarios. Fifty-nine out of the 97 (27 out of the 48) projections from CMIP5 (CMIP3) indicated that the future mean elevation of Lake Mead is likely to be lower than the historical mean. Demand forecasts showed that the Southern Nevada Water Authority’s conservation goal for 2035 can be significantly met under prevalent conservation practices. Findings from this study can be useful for water managers and resource planners to predict future water budget and to make effective decisions in advance to attain sustainable practices and conservation goals.

The impact of thermokarst lakes on streamflow generation in Central Yakutia (Russia): data assessment and modelling

2020 ◽  
Author(s):  
Olga Makarieva ◽  
Nataliia Nesterova ◽  
Alexander Fedorov ◽  
Andrey Shikhov
Keyword(s):  
River Basin ◽  
Hydrological Modeling ◽  
Hydrological Regime ◽  
Historical Period ◽  
Annual Streamflow ◽  
Landsat Images ◽  
Thermokarst Lakes ◽  
Central Yakutia ◽  
The Future ◽  
The Impact

<p>Central Yakutian Plain (Russia) is situated in Eastern Siberia in the Lena River basin and is characterized by severe continental climate, continuous permafrost and flat relief. The combination of semi-arid climate, gentle topography and ice-rich permafrost provides favorable conditions for the development of thermokarst lakes. Poorly developed river drainage system and the distribution of thermokarst lakes within the river basins form the areas with internal drainage which contribute runoff to river network only in wet conditions. The results of such environment are the special hydrological regime of the region which is characterized by extreme seasonal and annual variability of streamflow.</p><p>In this project we study the hydrological processes in four rivers of Central Yakutia with the basin area from 1270 to 8290 km<sup>2</sup> and available long-term streamflow data. Thermokarst lakes take up to 5-10 % of the area of those basins. Annual precipitation of this area is about 240 mm, while average annual streamflow varies from 1 to 15 mm depending on the river basin. Due to climate warming the number and area of thermokarst lakes in Central Yakutia is increasing (Kravsova, Tarasenko, 2011). The aim of the project is to investigate the impact of thermokarst lakes on hydrological regime and provide some reasonable projections of its changes in the future. Previous study (Lebedeva, 2018) has shown that the results of streamflow simulations in this region based on standard hydrological modeling approach were not satisfactory.</p><p>We used remote sensing data (Landsat images) to assess the seasonal and annual variation of thermokarst lakes area and their contributing area and combined that data with hydrological modelling of runoff formation processes. The hydrological model Hydrograph (Vinogradov et al., 2011) was applied in this study. The model contains the algorithms of heat and moisture dynamics in the upper part of soil profile which allow its use in the permafrost conditions. New part of the model algorithm was developed which considers the variations of thermokarst area depending on meteorological conditions, evaporation from open water areas and the dynamic of surface runoff retention depth. These model improvements allowed for the satisfactory results in streamflow simulations for historical period and future projections. In general, with the future development of thermokarst lakes in Central Yakutia one may expect the decrease of annual streamflow and its higher variation from one year to another.</p><p>Th results of the study will be presented. The study was funded by RFBR, project number 19-35-50030.</p>

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