Soil drought anomalies in MODIS GPP of a Mediterranean broadleaved evergreen forest

The Moderate Resolution Imaging Spectroradiometer (MODIS) yields global operational estimates of terrestrial gross primary production (GPP). In this study, we compared MOD17A2 GPP with tower eddy flux-based estimates of GPP from 2001 to 2010 over an evergreen broad-leaf Mediterranean forest in Southern France with a significant summer drought period. The MOD17A2 GPP shows seasonal variations that are inconsistent with the tower GPP, with close-to-accurate winter estimates and significant discrepancies for summer estimates which are the least accurate. The analysis indicated that the MOD17A2 GPP has high bias relative to tower GPP during severe summer drought which we hypothesized caused by soil water limitation. Our investigation showed that there was a significant correlation (R-2 = 0.77, p < 0.0001) between the relative soil water content and the relative error of MOD17A2 GPP. Therefore, the relationship between the error and the measured relative soil water content could explain anomalies in MOD17A2 GPP. The results of this study indicate that careful consideration of the water conditions input to the MOD17A2 GPP algorithm on remote sensing is required in order to provide accurate predictions of GPP. Still, continued efforts are necessary to ascertain the most appropriate index, which characterizes soil water limitation in water-limited environments using remote sensing

Evaluation of the LSA-SAF gross primary production product derived from SEVIRI/MSG data (MGPP)

The objective of this study is to describe a completely new 10-day gross primary production (GPP) product (MGPP LSA-411) based on data from the geostationary SEVIRI/MSG satellite within the LSA SAF (Land Surface Analysis SAF) as part of the SAF (Satellite Application Facility) network of EUMETSAT. The methodology relies on the Monteith approach. It considers that GPP is proportional to the absorbed photosynthetically active radiation APAR and the proportionality factor is known as the light use efficiency ε. A parameterization of this factor is proposed as the product of a εmax, corresponding to the canopy functioning under optimal conditions, and a coefficient quantifying the reduction of photosynthesis as a consequence of water stress. A three years data record (2015–2017) was used in an assessment against site-level eddy covariance (EC) tower GPP estimates and against other Earth Observation (EO) based GPP products. The site-level comparison indicated that the MGPP product performed better than the other EO based GPP products with 48% of the observations being below the optimal accuracy (absolute error < 1.0 g m−2 day−1) and 75% of these data being below the user requirement threshold (absolute error < 3.0 g m−2 day−1). The largest discrepancies between the MGPP product and the other GPP products were found for forests whereas small differences were observed for the other land cover types. The integration of this GPP product with the ensemble of LSA-SAF MSG products is conducive to meet user needs for a better understanding of ecosystem processes and for improved understanding of anthropogenic impact on ecosystem services.The objective of this study is to describe a completely new 10-day gross primary production (GPP) product (MGPP LSA-411) based on data from the geostationary SEVIRI/MSG satellite within the LSA SAF (Land Surface Analysis SAF) as part of the SAF (Satellite Application Facility) network of EUMETSAT. The methodology relies on the Monteith approach. It considers that GPP is proportional to the absorbed photosynthetically active radiation APAR and the proportionality factor is known as the light use efficiency epsilon. A parameterization of this factor is proposed as the product of a epsilon(max), corresponding to the canopy functioning under optimal conditions, and a coefficient quantifying the reduction of photosynthesis as a consequence of water stress. A three years data record (2015-2017) was used in an assessment against site-level eddy covariance (EC) tower GPP estimates and against other Earth Observation (EO) based GPP products. The site-level comparison indicated that the MGPP product performed better than the other EO based GPP products with 48% of the observations being below the optimal accuracy (absolute error <1.0 g m(-2) day(-1)) and 75% of these data being below the user requirement threshold (absolute error <3.0 g m(-2) day(-1)). The largest discrepancies between the MGPP product and the other GPP products were found for forests whereas small differences were observed for the other land cover types. The integration of this GPP product with the ensemble of LSA-SAF MSG products is conducive to meet user needs for a better understanding of ecosystem processes and for improved understanding of anthropogenic impact on ecosystem services.Peer reviewe

Review of the use of remote sensing for monitoring wildfire risk conditions to support fire risk assessment in protected areas

Fire risk assessment is one of the most important components in the management of fire that offers the framework for monitoring fire risk conditions. Whilst monitoring fire risk conditions commonly revolved around field data, Remote Sensing (RS) plays key role in quantifying and monitoring fire risk indicators. This study presents a review of remote sensing data and techniques for fire risk monitoring and assessment with a particular emphasis on its implications for wildfire risk mapping in protected areas. Firstly, we concentrate on RS derived variables employed to monitor fire risk conditions for fire risk assessment. Thereafter, an evaluation of the prominent RS platforms such as Broadband, Hyperspectral and Active sensors that have been utilized for wildfire risk assessment. Furthermore, we demonstrate the effectiveness in obtaining information that has operational use or immediate potentials for operational application in protected areas (PAs). RS techniques that involve extraction of landscape information from imagery were summarised. The review concludes that in practice, fire risk assessment that consider all variables/indicators that influence fire risk is impossible to establish, however it is imperative to incorporate indicators or variables of very high heterogeneous and “multi-sensoral or multivariate fire risk index approach for fire risk assessment in PA.Keywords: Protected Areas, Fire Risk conditions; Remote Sensing, Wildfire risk assessmen

Drought resistance across California ecosystems: Evaluating changes in carbon dynamics using satellite imagery

Additional Supporting Information may be found online at: http://onlinelibrary.wiley.com/doi/10.1002/ecs2.1561/fullDrought is a global issue that is exacerbated by climate change and increasing anthropogenic water demands. The recent occurrence of drought in California provides an important opportunity to examine drought response across ecosystem classes (forests, shrublands, grasslands, and wetlands), which is essential to understand how climate influences ecosystem structure and function. We quantified ecosystem resistance to drought by comparing changes in satellite-derived estimates of water-use efficiency (WUE = net primary productivity [NPP]/evapotranspiration [ET]) under normal (i.e., baseline) and drought conditions (ΔWUE = WUE2014 − baseline WUE). With this method, areas with increasing WUE under drought conditions are considered more resilient than systems with declining WUE. Baseline WUE varied across California (0.08 to 3.85 g C/mm H2O) and WUE generally increased under severe drought conditions in 2014. Strong correlations between ΔWUE, precipitation, and leaf area index (LAI) indicate that ecosystems with a lower average LAI (i.e., grasslands) also had greater C-uptake rates when water was limiting and higher rates of carbon-uptake efficiency (CUE = NPP/LAI) under drought conditions. We also found that systems with a baseline WUE ≤ 0.4 exhibited a decline in WUE under drought conditions, suggesting that a baseline WUE ≤ 0.4 might be indicative of low drought resistance. Drought severity, precipitation, and WUE were identified as important drivers of shifts in ecosystem classes over the study period. These findings have important implications for understanding climate change effects on primary productivity and C sequestration across ecosystems and how this may influence ecosystem resistance in the future.The authors would like to acknowledge the excellent support provided by the Open Science for Synthesis-2014 training (supported by the National Science Foundation under Grant No. OCI-1216894) at the National Center for Ecological Analysis and Synthesis (NCEAS), a center funded by the University of California, Santa Barbara, and the State of California. The authors would like to thank OSS instructors Nancy Baron, Ben Bolker, Stephanie Hampton, Matthew Jones, Karthik Ram, Mark Schildhauer, and the participants of the OSS training. The authors would also like to thank the Goulden Lab at the University of California Irvines. A. J. Pérez-Luque acknowledges funding received by NCEAS and to MICINN (Spanish Government) for the PTA 2011-6322- I contract; D. P. Drucker acknowledges support from the USAID and the U.S. Department of State through the Sustainable Landscapes Brazil program; and M.G. Tulbure acknowledges funding from the Australian Research Council Early Career Researcher Award (DE140101608)

Selected UV Photochemical and Photobiological Impacts on Marine Ecosystems: General Characteristics and Sensitivity Analyses

In the recent years, numerous efforts have been performed in order to characterize the impacts of UVR on marine photobiology and photochemistry. The quantification of these UV-dependent processes through modelling approaches requires (i) an accurate description of UV underwater light field (ii) an adapted parameterization of the response of marine water compounds and/or organisms to spatio-temporal changes in solar radiations. The spatial and temporal variability of the absorption coefficient of the colored detrital material, which is a key element for studying undersea UV climate, has been characterized in the two basins selected for this study (the Mediterranean Sea and the Norwegian Seas) using the SeaWiFS products archive recently achieved for the period 1998-2006. Moreover, the various models currently available for the description of selected optical (CDOM photobleaching), photochemical (CO and DIC production) and photobiological (primary production inhibition) effects of UVR on marine waters have been described. Further, the general characteristics of these UV-dependent processes have been presented focusing, in particularly, on their variability along the daily, vertical and spectral dimensions. Several sensitivity analyses have been performed in order to define the relative importance of the various inputs of the spectral and depth resolved model on the final estimations. Finally, some of the straightforward models recently proposed in order to estimate some of the UV impacts at large temporal and or spatial scales have been tested and their limits of application have been discussed.JRC.H.3-Global environement monitorin

Vegetation productivity losses linked to mediterranean hot and dry events

Persistent hot and dry conditions play an important role in vegetation dynamics, being generally associated with reduced activity. In the Mediterranean region, ecosystems are adapted to such conditions. However, prolonged and intense heat and drought or the occurrence of compound hot and dry events may still have a negative impact on vegetation activity. This work aims to study how the productivity of Mediterranean vegetation is affected by hot and dry events, examining a set of severe episodes that occurred in three different regions (Iberian Peninsula, Eastern Mediterranean and Western Europe) between 2001 and 2019. The analysis relies on remote sensing products, namely Gross Primary Production from MODIS to detect and monitor vegetative stress and LST from MODIS and SM from ESA CCI to evaluate the influence of temperature and soil water availability on stressed vegetation. Of all events, the 2005 episode in the Iberian Peninsula was the most significant, affecting large sectors of low tree cover areas and crops and leading to reductions of annual plant productivity in affected vegetation of ~47 TgC/year. The obtained results highlight the influence of land-atmosphere coupling on vegetation productivity and clarified the role of warm springs on vegetation activity and soil moisture that may amplify summer temperatures. The functional recovery of affected vegetation productivity after these episodes varied across events, ranging from months to years. This work highlights the influence of hot and dry events on vegetation productivity in the Mediterranean basin and the usefulness of remote-sensing products to assess the response of different land covers to such episodes

Remote sensing and ecosystem modeling to simulate terrestrial carbon fluxes

[EN] The main goal of this thesis is the establishment of a framework to analyze the forest ecosystems in peninsular Spain in terms of their role in the carbon cycle. In particular, the carbon fluxes that they exchange with atmosphere are modeled to evaluate their potential as carbon sinks and biomass reservoirs. The assessment of gross and net carbon fluxes is performed at 1-km spatial scale and on a daily basis using two different ecosystem models, Monteith and BIOME-BGC, respectively. These models are driven by a combination of satellite and ground data, part of the latter being also employed as a complementary data source and in the validation process.[ES] El objetivo principal de esta tesis es el desarrollo de un metodología operativa para analizar las zonas forestales de la península a través de los flujos de carbono que intercambian con la atmósfera. En concreto se ha evaluado la producción primaria bruta y la producción neta, ambas escala diaria y a 1 km de resolución espacial, con la aproximación de Monteith y el modelo BIOME-BGC, utilizando datos de satélite y diversos tipos de medidas en superficie. Estas últimas se emplean también en el proceso de validación.This thesis was developed in the framework of the project RESET CLIMATE CGL2012-35831 (Remote sensing of terrestrial essential climate variables: Water stress effect on carbon flux assessment) and ESCENARIOS CGL2016-75239-R (Monitoring carbon fluxes in forest ecosystems and simulation for climate change scenarios), both from the Spanish Ministry of Economy, Industry and Competitiveness (MINECO), and co-financed by FEDER funds. The author was granted with the support of the Plan Estatal de Investigación Científica y Técnica y de Innovación 2013-2016 (pre-doctoral scholarship BES-2013-064548). The research was carried out at the Environmental Remote Sensing Group of the University of Valencia, UV-ERS (www.uv.es/uvers).Sánchez-Ruiz, S. (2019). Simulación de flujos de carbono terrestres mediante teledetección y modelización de ecosistemas. Revista de Teledetección. (53):87-91. https://doi.org/10.4995/raet.2019.11220SWORD87915

A Novel Diffuse Fraction-Based Two-Leaf Light Use Efficiency Model: An Application Quantifying Photosynthetic Seasonality Across 20 AmeriFlux Flux Tower Sites

. Diffuse radiation can increase canopy light use efficiency (LUE). This creates the need to differentiate the effects of direct and diffuse radiation when simulating terrestrial gross primary production (GPP). Here, we present a novel GPP model, the diffuse-fraction-based two-leaf model (DTEC), which includes the leaf response to direct and diffuse radiation, and treats maximum LUE for shaded leaves (εmsh defined as a power function of the diffuse fraction (Df)) and sunlit leaves (εmsu defined as a constant) separately. An Amazonian rainforest site (KM67) was used to calibrate the model by simulating the linear relationship between monthly canopy LUE and Df. This showed a positive response of forest GPP to atmospheric diffuse radiation, and suggested that diffuse radiation was more limiting than global radiation and water availability for Amazon rainforest GPP on a monthly scale. Further evaluation at 20 independent AmeriFlux sites showed that the DTEC model, when driven by monthly meteorological data and MODIS leaf area index (LAI) products, explained 70% of the variability observed in monthly flux tower GPP. This exceeded the 51% accounted for by the MODIS 17A2 big-leaf GPP product. The DTEC model’s explicit accounting for the impacts of diffuse radiation and soil water stress along with its parameterization for C4 and C3 plants was responsible for this difference. The evaluation of DTEC at Amazon rainforest sites demonstrated its potential to capture the unique seasonality of higher GPP during the diffuse radiation-dominated wet season. Our results highlight the importance of diffuse radiation in seasonal GPP simulation

Vegetation Carbon Losses Linked to Mediterranean Extreme Events

Tese de mestrado, Ciências Geofísicas (Meteorologia e Oceanografia) Universidade de Lisboa, Faculdade de Ciências, 2021A atividade dos ecossistemas terrestres é particularmente suscetível à variabilidade climática e, face às mudanças globais e regionais que têm vindo a ocorrer, tem reagido com rápidas mudanças no ciclo de vegetação natural, na produtividade das plantas e na absorção de carbono terrestre. Os eventos climáticos extremos, nomeadamente as secas, as ondas de calor e os grandes fogos associados, têm sido reconhecidos por terem um papel preponderante na alteração da dinâmica dos ecossistemas. A ocorrência de condições quentes e secas alteram a dinâmica da vegetação e perturbam severamente os regimes fotossintéticos, levando a fortes perdas de produtividade das plantas e, consequentemente, a fortes anomalias na regulação do mecanismo de absorção de carbono dos ecossistemas. Além disso, o aumento da frequência e severidade destes eventos climáticos extremos, como reportado nos recentes relatórios do IPCC, contribuirá para a intensificação das perturbações nos sistemas terrestres que absorvem carbono, desestabilizando o ciclo de carbono e contribuindo, consequentemente, para o aumento de CO2 na atmosfera. Os eventos de seca são reconhecidos, entre uma ampla gama de eventos extremos, por desempenharem um papel crucial no ciclo de carbono devido às perturbações que induzem na fotossíntese e na absorção de carbono. Por sua vez, o aumento da frequência e severidade das secas terá impactos a curto-médio prazo, mas também, a longo prazo, devido aos efeitos continuados que têm nos ecossistemas, inibindo-os de recuperar e regenerar. Dessa forma, ao longo de vários meses, a produtividade das plantas estará perturbada, podendo ter consequências desastrosas e permanentes na dinâmica vegetação. Além disso, estes eventos têm o potencial de aumentar o risco de incêndios devido à maior vulnerabilidade dos ecossistemas, elevando as perdas de produtividade das plantas, e contribuindo, geralmente, para atrasar o seu processo de regeneração durante muito tempo. A Europa, e em particular, a região do Mediterrâneo, têm sido afetadas por secas severas e grandes fogos nas últimas décadas, sendo uma região particularmente sensível a fenómenos extremos. Nos últimos anos, vários estudos têm comprovado e analisado os impactos que estes eventos têm na vegetação e o seu contributo para a diminuição do carbono armazenado nos ecossistemas da região. No entanto, vários desses estudos observaram que o acoplamento clima-vegetação, ou seja, a relação que existe entre a influência do evento climático e a resposta da vegetação não é fácil de estabelecer, tendo em conta que o efeito extremo do evento climático nem sempre gera uma resposta extrema a nível ecológico. Tendo em conta as premissas anteriores, estre trabalho propõe-se a avaliar o impacto de um conjunto de secas severas e grandes fogos, ocorridos entre 2001 e 2019, em três regiões diferentes da bacia do Mediterrâneo (Península Ibérica, Itália e Grécia, e França), pretendendo analisar a sua influência na vegetação. Será avaliada a persistência de condições secas no solo e o número de meses em que a sua normal atividade é perturbada, bem como a perturbação de cada evento extremo no balanço anual de produtividade da vegetação de cada região. Foram utilizados produtos de deteção remota para monitorizar a produtividade dos ecossistemas, nomeadamente o Gross Primary Production (GPP) e o Net Photosynthesis (PsNet), para analisar a quantidade de água no solo foi utilizado o produto ESA CCI Soil Moisture (SM) e para detetar áreas queimadas foi utilizada a área ardida do produto FIRECCI. A qualidade de todos estes produtos de deteção remota foi analisada, de modo a conhecer a sua precisão para a monitorização e a sua capacidade de capturar os efeitos dos eventos climáticos extremos nos ecossistemas na região do Mediterrâneo. A análise da quantidade de água no solo e produção primária da vegetação, para o período mencionado, permitiram identificar os eventos de seca mais severos e que tiveram maiores impactos nos ecossistemas. Recorrendo a métricas estatísticas, como a determinação, ao longo do período de análise 2001-2019, do desvio padrão médio mensal da produtividade da vegetação, foi possível a identificação das áreas mais afetadas por condições de seca prolongadas. Além disso, com base no cálculo do percentil 25 das anomalias de SM, de forma a identificar os períodos com maiores deficits de disponibilidade de água no solo, foi possível reconhecer as regiões cujos ecossistemas foram fortemente perturbados por eventos extremos. Na Península Ibérica, os episódios de 2005 e 2012 provocaram amplas alterações na atividade da vegetação. Na generalidade, em ambos os casos de estudo, as regiões mais afetadas foram o oeste e o sul da Península Ibérica. Várias áreas revelaram uma elevada falta de água no solo na primavera, que conduziu a impactos severos no estado e na atividade das plantas durante muitos meses. A severidade do evento de 2005, que levou a perdas de produtividade líquida de ~ 40 TgC/ano, conjugada com condições climáticas pouco propícias ao processo de recuperação nos meses seguintes, levaram a um pro-longamento das anomalias da produtividade na vegetação afetada. Dessa forma, houve um aumento das perdas de fotossíntese líquida durante um intervalo de tempo longo, o que afetou profundamente a dinâmica da vegetação. Na região da Itália e Grécia, os eventos de 2003, 2007 e 2012 afetaram os ecossistemas de cerca de 30-35% do território, destacando-se especialmente o ano de 2007 pela sua intensidade, devido ao efeito combinado de um evento de seca, intensas ondas de calor no verão e grandes fogos. Dada a sua grande complexidade, este evento composto levou a uma forte inibição da recuperação da vegetação afetada nos meses seguintes, amplificando as perdas anuais de produtividade até ~ 24 TgC no período entre 2007 e 2009. Apesar de menos intensos, os eventos de seca de 2003 e 2012 geraram fortes deficits de água no solo, promovendo fortes anomalias na dinâmica das plantas, principalmente nos meses de verão. Em França, o episódio de 2006 afetou mais de 25% da vegetação do território devido às condições de seca severas que perturbaram a produção dos ecossistemas durante 3 a 5 meses em diversas áreas, e induziu perdas anuais de produtividade de ~ 25 TgC/ano. A ocorrência de épocas de fogo severas está intimamente associada à disponibilidade de biomassa de combustão rápida na presença de um evento climático extremo. A conjugação desses fatores despoletou épocas de fogos catastróficas, nomeadamente em 2003 e 2017 na Península Ibérica e 2007 na Itália e Grécia, associadas a intensas ondas de calor no verão, e 2005 e 2012 na Península Ibérica e 2012 na Itália e Grécia, associadas a condições de seca muito persistentes. Em todos os casos de estudo, a vegetação demorou vários meses a conseguir recuperar a atividade fotossintética normal, mesmo quando as condições climáticas foram favoráveis, demonstrando o impacto que as épocas de fogo severas têm na dinâmica dos ecossistemas. A avaliação das perturbações na atividade fotossintética causadas por secas e grandes incêndios permitiram quantificar as perdas de produtividade da vegetação e, ainda, a avaliação do seu processo de recuperação nos meses seguintes. A resposta dos ecossistemas varia amplamente, podendo demorar meses a anos a recuperar a atividade fotossintética normal. Essa resposta depende das condições climáticas nos meses seguintes e do tipo de cobertura vegetal afetada. As perturbações induzidas na atividade da vegetação, provocadas por eventos de seca são significativamente maiores do que as provocadas por incêndios, especialmente devido à sua maior área afetada. Além disso, as secas possuem uma escala temporal muito maior, o que induz mais perturbações na produtividade das plantas durante um longo intervalo de tempo. No entanto, apesar de os fogos corresponderem a eventos de menor duração, podem inibir fortemente a vegetação de regenerar, amplificando as perdas nos ecossistemas durante vários meses.The activity of terrestrial ecosystems is particularly susceptible to the climate variability and, facing the recently global and regional changes, has been responding with rapid changes on natural vegetation cycle, plants productivity and terrestrial carbon uptake. Droughts have been broadly recognized, among a wide range of extreme events, as playing a central role on the carbon cycle. Dry permanent conditions contribute to the occurrence of high hydric stress on vegetation, generating disturbances on the regular photosynthesis, carbon uptake and regular plants mechanisms. Furthermore, they may increase the risk of fires due to the higher vulnerability of ecosystems, enhancing the losses on vegetation productivity, and inhibiting, generally, their regenera-tion process for a long time. Europe, and in particular, the Mediterranean region, has been affected by severe droughts and large fires in the last decades, being an area particularly sensitive to extreme phenomena. Therefore, this work proposes to assess the impact of a set of the severest droughts and large fires, between 2001 and 2019, over three different regions of Mediterranean basin (Iberian Peninsula, Italy and Greece, and France), attempting to analyse their influence on vegetation. It will be assessed the persistence of soil dry conditions and the number of months that the normal activity of vegetation is disturbed. Remote sense products were used to monitor the plant’s productivity, to assess the soil moisture and to detect burned areas. The analysis of soil moisture and primary production of vegetation, for the referred study period, allowed to identify the most hazardous drought events which had larger impacts on ecosystems. Over Iberian Peninsula, both 2005 and 2012 episodes caused wide disturbances on ecosystems, with large areas showing water availability deficit in soils, driving to severe impacts on vegetation and productivity losses of ~ 40 TgC/year. Throughout Italy and Greece region, the events of 2003, 2007 and 2012 affected the ecosystems of about 30-35% of the territory, being 2007 particularly intense due to the combined effect of a drought, major heatwaves and large fires. In France, the 2006 episode affected more than 25% of the vegetation of the territory and induced losses on annual productivity of ~ 25 TgC/year. In turn, the occurrence of severe fire seasons is closely associated with the availability of biomass that easily burns in the presence of an extreme climatic event, such as summer heatwaves (e.g. Iberia in 2003 and 2017, and Italy and Greece in 2007), or persistent droughts in previous months (e.g. Iberia in 2005 and 2012, and Italy and Greece in 2012). The assessment of the disturbances on photosynthetic activity caused by droughts and large fires allowed the quantification of the losses of vegetation productivity, and also, the evaluation of the recov-ery process during the following months. The ecosystems response varies widely, with vegetation may taking months to years to recover the normal activity. The disturbances on net productivity caused by droughts are significantly higher than the ones caused by large fires, especially due to their extension and their timescale, that can last from weeks to several months. However, despite fires have a shorter period of time, these events can strongly inhibit the vegetation to regenerate, amplifying the productivity losses on ecosystems during a long period