scholarly journals Impacts of extreme summers on European ecosystems: a comparative analysis of 2003, 2010 and 2018

2020 ◽  
Vol 375 (1810) ◽  
pp. 20190507 ◽  
Author(s):  
A. Bastos ◽  
Z. Fu ◽  
P. Ciais ◽  
P. Friedlingstein ◽  
S. Sitch ◽  
...  
Keyword(s):  
Comparative Analysis ◽  
Gross Primary Production ◽  
Severe Drought ◽  
Summer Drought ◽  
Climate Anomalies ◽  
Continental Scale ◽  
Vegetation Models ◽  
Global Vegetation ◽  
Autumn And Winter ◽  
The Impact

In Europe, three widespread extreme summer drought and heat (DH) events have occurred in 2003, 2010 and 2018. These events were comparable in magnitude but varied in their geographical distribution and biomes affected. In this study, we perform a comparative analysis of the impact of the DH events on ecosystem CO 2 fluxes over Europe based on an ensemble of 11 dynamic global vegetation models (DGVMs), and the observation-based FLUXCOM product. We find that all DH events were associated with decreases in net ecosystem productivity (NEP), but the gross summer flux anomalies differ between DGVMs and FLUXCOM. At the annual scale, FLUXCOM and DGVMs indicate close to neutral or above-average land CO 2 uptake in DH2003 and DH2018, due to increased productivity in spring and reduced respiration in autumn and winter compensating for less photosynthetic uptake in summer. Most DGVMs estimate lower gross primary production (GPP) sensitivity to soil moisture during extreme summers than FLUXCOM. Finally, we show that the different impacts of the DH events at continental-scale GPP are in part related to differences in vegetation composition of the regions affected and to regional compensating or offsetting effects from climate anomalies beyond the DH centres. This article is part of the theme issue ‘Impacts of the 2018 severe drought and heatwave in Europe: from site to continental scale’.

scholarly journals Analysis of floodplain forest sensitivity to drought

2020 ◽  
Vol 375 (1810) ◽  
pp. 20190518
Author(s):  
Natalia Kowalska ◽  
Ladislav Šigut ◽  
Marko Stojanović ◽  
Milan Fischer ◽  
Ina Kyselova ◽  
...  
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Gross Primary Production ◽  
Floodplain Forest ◽  
Severe Drought ◽  
Summer Drought ◽  
Negative Effects ◽  
Eddy Covariance Method ◽  
Continental Scale

Floodplain forests are very complex, productive ecosystems, capable of storing huge amounts of soil carbon. With the increasing occurrence of extreme events, they are today among the most threatened ecosystems. Our study's main goal was to assess the productivity of a floodplain forest located at Lanžhot in the Czech Republic from two perspectives: carbon uptake (using an eddy covariance method) and stem radius variations (using dendrometers). We aimed to determine which conditions allow for high ecosystem production and what role drought plays in reducing such production potential. Additionally, we were interested to determine the relative soil water content threshold indicating the onset and duration of this event. We hypothesized that summer drought in 2018 had the most significant negative effects on the overall annual carbon and water budgets. In contrast with our original hypothesis, we found that an exceptionally warm spring in 2018 caused a positive gross primary production (GPP) and evapotranspiration (ET) anomaly that consequently led in 2018 to the highest seasonal total GPP and ET from all of the investigated years (2015–2018). The results showed ring-porous species to be the most drought resistant. Relative soil water content threshold of approximately 0.45 was determined as indicating the onset of drought stress. This article is part of the theme issue ‘Impacts of the 2018 severe drought and heatwave in Europe: from site to continental scale’.

scholarly journals The impact of occasional drought periods on vegetation spread and greenhouse gas exchange in rewetted fens

2020 ◽  
Vol 375 (1810) ◽  
pp. 20190685
Author(s):  
Franziska Koebsch ◽  
Pia Gottschalk ◽  
Florian Beyer ◽  
Christian Wille ◽  
Gerald Jurasinski ◽  
...  
Keyword(s):  
Carbon Sink ◽  
Severe Drought ◽  
Summer Drought ◽  
Theme Issue ◽  
Vegetation Development ◽  
Continental Scale ◽  
Rapid Spread ◽  
Carry Over ◽  
The Impact

Peatland rewetting aims at stopping the emissions of carbon dioxide (CO 2 ) and establishing net carbon sinks. However, in times of global warming, restoration projects must increasingly deal with extreme events such as drought periods. Here, we evaluate the effect of the European summer drought 2018 on vegetation development and the exchange of methane (CH 4 ) and CO 2 in two rewetted minerotrophic fens (Hütelmoor—Hte and Zarnekow—Zrk) including potential carry-over effects in the post-drought year. Drought was a major stress factor for the established vegetation but also promoted the rapid spread of new vegetation, which will likely gain a lasting foothold in Zrk. Accordingly, drought increased not only respiratory CO 2 losses but also photosynthetic CO 2 uptake. Altogether, the drought reduced the net CO 2 sink in Hte, while it stopped the persistent net CO 2 emissions of Zrk. In addition, the drought reduced CH 4 emissions in both fens, though this became most apparent in the post-drought year and suggests a lasting shift towards non-methanogenic organic matter decomposition. Occasional droughts can be beneficial for the restoration of the peatland carbon sink function if the newly grown vegetation increases CO 2 sequestration in the long term. Nonetheless, care must be taken to prevent extensive peat decay. This article is part of the theme issue ‘Impacts of the 2018 severe drought and heatwave in Europe: from site to continental scale'.

scholarly journals Evaluation of a Global Vegetation Model using time series of satellite vegetation indices

2011 ◽  
Vol 4 (4) ◽  
pp. 1103-1114 ◽  
Author(s):  
F. Maignan ◽  
F.-M. Bréon ◽  
F. Chevallier ◽  
N. Viovy ◽  
P. Ciais ◽  
...  
Keyword(s):  
Climate Change ◽  
Time Series ◽  
Vegetation Index ◽  
Vegetation Indices ◽  
Global Scale ◽  
Vegetation Dynamic ◽  
Rate Of Increase ◽  
Vegetation Models ◽  
Global Vegetation ◽  
The Impact

Abstract. Atmospheric CO2 drives most of the greenhouse effect increase. One major uncertainty on the future rate of increase of CO2 in the atmosphere is the impact of the anticipated climate change on the vegetation. Dynamic Global Vegetation Models (DGVM) are used to address this question. ORCHIDEE is such a DGVM that has proven useful for climate change studies. However, there is no objective and methodological way to accurately assess each new available version on the global scale. In this paper, we submit a methodological evaluation of ORCHIDEE by correlating satellite-derived Vegetation Index time series against those of the modeled Fraction of absorbed Photosynthetically Active Radiation (FPAR). A perfect correlation between the two is not expected, however an improvement of the model should lead to an increase of the overall performance. We detail two case studies in which model improvements are demonstrated, using our methodology. In the first one, a new phenology version in ORCHIDEE is shown to bring a significant impact on the simulated annual cycles, in particular for C3 Grasses and C3 Crops. In the second case study, we compare the simulations when using two different weather fields to drive ORCHIDEE. The ERA-Interim forcing leads to a better description of the FPAR interannual anomalies than the simulation forced by a mixed CRU-NCEP dataset. This work shows that long time series of satellite observations, despite their uncertainties, can identify weaknesses in global vegetation models, a necessary first step to improving them.

Sensitivity of global gross primary production to elevated CO2

2021 ◽  
Author(s):  
Wenjia Cai ◽  
Iain Colin Prentice
Keyword(s):  
Field Experiments ◽  
Carbon Sink ◽  
Gross Primary Production ◽  
Light Response ◽  
Terrestrial Ecosystems ◽  
Percentage Increase ◽  
Terrestrial Plants ◽  
Fertilization Effect ◽  
Vegetation Models ◽  
The Impact

<p>Terrestrial ecosystems have accounted for more than half of the global carbon sink during the past decades and offset 25%-30% of current anthropogenic CO<sub>2</sub> emissions. The projected increase in CO<sub>2</sub> concentration will depend on the magnitude of terrestrial plants’ feedback to CO<sub>2</sub>: i.e. the sensitivity of plant carbon uptake in response to elevated CO<sub>2</sub>, and the strength of the CO<sub>2</sub> fertilization effect (CFE) in a changing (and warming) environment. Projecting vegetation responses to future increases in CO<sub>2</sub> concentration under climate change is a major uncertainty, as ecosystem models, field experiments and satellite-based models show large disagreements. In this study, using a recently developed, parameter-sparse model (the ‘P model’), we assess the sensitivity of GPP to increasing CO<sub>2</sub> under idealized conditions, in comparison with other vegetation models and field experiments. We investigate the impact of two central parameters, the ratio of J<sub>max </sub>to V<sub>cmax</sub> (at a common temperature) and the curvature of the light response curve, on the sensitivity of GPP to CO<sub>2</sub>. We also quantified the spatial-temporal trend of CFE using the β factor, defined as the percentage increase in GPP in response to a 100-ppm increase in atmospheric CO<sub>2</sub> concentration over a defined period. We show how modelled β has changed over the satellite era, and infer the possible effect of climatic variables on changes of CFE from spatial patterns of the modelled trend in β.</p>

scholarly journals Effects of drought and meteorological forcing on carbon and water fluxes in Nordic forests during the dry summer of 2018

2020 ◽  
Vol 375 (1810) ◽  
pp. 20190516
Author(s):  
Anders Lindroth ◽  
Jutta Holst ◽  
Maj-Lena Linderson ◽  
Mika Aurela ◽  
Tobias Biermann ◽  
...  
Keyword(s):  
Surface Conductance ◽  
Severe Drought ◽  
Water Fluxes ◽  
Multilinear Regression ◽  
Evaporative Demand ◽  
Meteorological Forcing ◽  
Continental Scale ◽  
The Difference ◽  
Effects Of Drought ◽  
The Impact

The Nordic region was subjected to severe drought in 2018 with a particularly long-lasting and large soil water deficit in Denmark, Southern Sweden and Estonia. Here, we analyse the impact of the drought on carbon and water fluxes in 11 forest ecosystems of different composition: spruce, pine, mixed and deciduous. We assess the impact of drought on fluxes by estimating the difference (anomaly) between year 2018 and a reference year without drought. Unexpectedly, the evaporation was only slightly reduced during 2018 compared to the reference year at two sites while it increased or was nearly unchanged at all other sites. This occurred under a 40 to 60% reduction in mean surface conductance and the concurrent increase in evaporative demand due to the warm and dry weather. The anomaly in the net ecosystem productivity (NEP) was 93% explained by a multilinear regression with the anomaly in heterotrophic respiration and the relative precipitation deficit as independent variables. Most of the variation (77%) was explained by the heterotrophic component. Six out of 11 forests reduced their annual NEP with more than 50 g C m −2 yr −1 during 2018 as compared to the reference year. The NEP anomaly ranged between −389 and +74 g C m −2 yr −1 with a median value of −59 g C m −2 yr −1 . This article is part of the theme issue ‘Impacts of the 2018 severe drought and heatwave in Europe: from site to continental scale’.

scholarly journals The impact of drought on total ozone flux in a mountain Norway spruce forest

2020 ◽  
Vol 66 (No. 7) ◽  
pp. 280-278 ◽  
Author(s):  
Thomas Agyei ◽  
Stanislav Juráň ◽  
Kojo Kwakye Ofori-Amanfo ◽  
Ladislav Šigut ◽  
Otmar Urban ◽  
...  
Keyword(s):  
Norway Spruce ◽  
Stomatal Closure ◽  
Severe Drought ◽  
Summer Drought ◽  
Spruce Forest ◽  
Soil Humidity ◽  
Drought Period ◽  
The Impact ◽  
Mild Drought ◽  
Norway Spruce Forest

In order to understand the impact of summer drought on dry deposition of tropospheric ozone (O<sub>3</sub>), we compared severe and mild drought periods of summer 2018 in a mountain Norway spruce forest at Bílý Kříž, Beskydy Mts. An eddy covariance technique was applied to measure diurnal courses of the ecosystem O<sub>3</sub> and CO<sub>2</sub> fluxes. Low O<sub>3</sub> deposition was recorded in the morning and evening, while the highest CO<sub>2</sub> and O<sub><sup>3</sup></sub> fluxes were recorded during the central hours of the day. Total O<sub>3</sub> deposition during severe drought (soil humidity 13%) was significantly higher than the deposition during the mild drought period (soil humidity 19%). Our data indicate that high vapour pressure deficit and low soil humidity during severe drought led to the stomatal closure, while non-stomatal O<sub>3</sub> deposition, associated with chemical reactions of O<sub>3</sub> with NO and volatile organic compounds, are responsible for higher total O<sub>3</sub> deposition during the severe drought period. Therefore, we assume that under severe drought stomatal O<sub>3</sub> uptake decreases but non-stomatal depositions to forest ecosystems substantially increase.

scholarly journals Land-use and land-cover change carbon emissions between 1901 and 2012 constrained by biomass observations

2017 ◽  
Vol 14 (22) ◽  
pp. 5053-5067 ◽  
Author(s):  
Wei Li ◽  
Philippe Ciais ◽  
Shushi Peng ◽  
Chao Yue ◽  
Yilong Wang ◽  
...  
Keyword(s):  
Land Use ◽  
Land Cover ◽  
Land Cover Change ◽  
Regional Scale ◽  
Model Estimate ◽  
Tropical Regions ◽  
Vegetation Models ◽  
Global Vegetation ◽  
Constraint Approach ◽  
The Impact

Abstract. The use of dynamic global vegetation models (DGVMs) to estimate CO2 emissions from land-use and land-cover change (LULCC) offers a new window to account for spatial and temporal details of emissions and for ecosystem processes affected by LULCC. One drawback of LULCC emissions from DGVMs, however, is lack of observation constraint. Here, we propose a new method of using satellite- and inventory-based biomass observations to constrain historical cumulative LULCC emissions (ELUCc) from an ensemble of nine DGVMs based on emerging relationships between simulated vegetation biomass and ELUCc. This method is applicable on the global and regional scale. The original DGVM estimates of ELUCc range from 94 to 273 PgC during 1901–2012. After constraining by current biomass observations, we derive a best estimate of 155 ± 50 PgC (1σ Gaussian error). The constrained LULCC emissions are higher than prior DGVM values in tropical regions but significantly lower in North America. Our emergent constraint approach independently verifies the median model estimate by biomass observations, giving support to the use of this estimate in carbon budget assessments. The uncertainty in the constrained ELUCc is still relatively large because of the uncertainty in the biomass observations, and thus reduced uncertainty in addition to increased accuracy in biomass observations in the future will help improve the constraint. This constraint method can also be applied to evaluate the impact of land-based mitigation activities.

scholarly journals Standardized Drought Indices for Pre-Summer Drought Assessment in Tropical Areas

Atmosphere ◽  
2020 ◽  
Vol 11 (11) ◽  
pp. 1209
Author(s):  
David Romero ◽  
Eric Alfaro ◽  
Roger Orellana ◽  
Maria-Engracia Hernandez Cerda
Keyword(s):  
Vegetation Index ◽  
Temporal Variations ◽  
Climatic Conditions ◽  
Drought Indices ◽  
Drought Severity ◽  
Severe Drought ◽  
Summer Drought ◽  
Tropical Zone ◽  
Drought Assessment ◽  
The Impact

The main climatic indices used for the determination of pre-summer drought severity were developed for temperate zones with very different climatic conditions from those found in the tropical climate zones, particularly with respect to seasonal rainfall variations. The temporal evolution of pre-summer drought leads the authors to compute the indices for each year over a defined period according to the climatic normals of each meteorological station and to consider the months inside the dry episode differently, according to the law of emptying the water reserves. As a function of this, standardized drought indices are proposed for the evaluation of the pre-summer drought in tropical zone. Two new indices were tested: one developed from precipitation and the other also considering temperature. These indices were validated by correlation with Advanced very-high-resolution radiometer (AVHRR) normalized difference vegetation index (NDVI) time series and used to identify the most severe drought conditions in the Yucatan Peninsula. The comparison between the indices and their temporal variations highlighted the importance of temperature in the most critical events and left indications of the impact of global warming on the phenomenon.

scholarly journals Periodic Relations between Terrestrial Vegetation and Climate Factors across the Globe

2020 ◽  
Vol 12 (11) ◽  
pp. 1805
Author(s):  
Boyi Liang ◽  
Hongyan Liu ◽  
Xiaoqiu Chen ◽  
Xinrong Zhu ◽  
Elizabeth L. Cressey ◽  
...  
Keyword(s):  
Time Lag ◽  
Climate Factors ◽  
Vegetation Types ◽  
Terrestrial Vegetation ◽  
Area Index ◽  
Vegetation Growth ◽  
Annual Cycles ◽  
Vegetation Models ◽  
Global Vegetation ◽  
The Impact

In this paper, cross-spectrum analysis was used to verify the agreement of periodicity between the global LAI (leaf area index) and climate factors. The results demonstrated that the LAI of deciduous forests and permanent wetlands have high agreement with temperature, rainfall and radiation over annual cycles. A low agreement between the LAI and seasonal climate variables was observed for some of the temperate and tropical vegetation types including shrublands and evergreen broadleaf forests, possibly due to the diversity of vegetation and human activities. Across all vegetation types, the LAI demonstrated a large time lag following variation in radiation (>1 month), whereas relatively short lag periods were observed between the LAI and annual temperature (around 2 weeks)/rainfall patterns (less than 10 days), suggesting that the impact of radiation on global vegetation growth is relatively slow, which is in accord with the results of previous studies. This work can provide a benchmark of the phenological drivers in global vegetation, from the perspective of periodicity, as well as helping to parameterize and refine the DGVMs (Dynamic Global Vegetation Models) for different vegetation types.

scholarly journals A comprehensive benchmarking system for evaluating global vegetation models

2013 ◽  
Vol 10 (5) ◽  
pp. 3313-3340 ◽  
Author(s):  
D. I. Kelley ◽  
I. C. Prentice ◽  
S. P. Harrison ◽  
H. Wang ◽  
M. Simard ◽  
...  
Keyword(s):  
Primary Production ◽  
Seasonal Cycle ◽  
Fire Regime ◽  
Net Primary Production ◽  
Annual Variability ◽  
Benchmark System ◽  
Vegetation Models ◽  
Global Vegetation ◽  
The Impact ◽  
Benchmarking System

Abstract. We present a benchmark system for global vegetation models. This system provides a quantitative evaluation of multiple simulated vegetation properties, including primary production; seasonal net ecosystem production; vegetation cover; composition and height; fire regime; and runoff. The benchmarks are derived from remotely sensed gridded datasets and site-based observations. The datasets allow comparisons of annual average conditions and seasonal and inter-annual variability, and they allow the impact of spatial and temporal biases in means and variability to be assessed separately. Specifically designed metrics quantify model performance for each process, and are compared to scores based on the temporal or spatial mean value of the observations and a "random" model produced by bootstrap resampling of the observations. The benchmark system is applied to three models: a simple light-use efficiency and water-balance model (the Simple Diagnostic Biosphere Model: SDBM), the Lund-Potsdam-Jena (LPJ) and Land Processes and eXchanges (LPX) dynamic global vegetation models (DGVMs). In general, the SDBM performs better than either of the DGVMs. It reproduces independent measurements of net primary production (NPP) but underestimates the amplitude of the observed CO2 seasonal cycle. The two DGVMs show little difference for most benchmarks (including the inter-annual variability in the growth rate and seasonal cycle of atmospheric CO2), but LPX represents burnt fraction demonstrably more accurately. Benchmarking also identified several weaknesses common to both DGVMs. The benchmarking system provides a quantitative approach for evaluating how adequately processes are represented in a model, identifying errors and biases, tracking improvements in performance through model development, and discriminating among models. Adoption of such a system would do much to improve confidence in terrestrial model predictions of climate change impacts and feedbacks.

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