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Extensive, longstanding dry and wet episodes are one of the most frequent climatic extreme events in the Iberian Peninsula. Here, we present a method for ranking regional extremes of persistent, widespread drought and wet events, considering different time scales. The method is based on the multiscalar Standardized Precipitation Evapotranspiration Index (SPEI) gridded dataset for the Iberian Peninsula. SPEI was computed using the Climatic Research Unit (CRU) between 1901 and 2016 using a log-logistic probability distribution function. The Potential Evapotranspiration (PET) was computed through the Penmann-Monteith equation. The ranking classification method is based on the evaluation of the magnitude of an event, which is obtained after considering both the area affected respectively by the dryness or wetness - defined by SPEI values over a certain threshold - and its intensity in each grid point. A sensitivity analysis on the impact of different thresholds to define dry and wet events is performed. A comprehensive dataset of rankings of the most extreme, prolonged, widespread dry and wet periods in the Iberian Peninsula is presented, for aggregated time scales of 6, 12, 18 and 24 months. Results show that in the Iberian Peninsula there is not a region more prone to the occurrence of any of these long-term (dry and/or wet) most extreme events. [ABSTRACT FROM AUTHOR]

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In the context of sustainable agricultural management, drought monitoring plays a crucial role assessing the vulnerability of agriculture to drought occurrence. Drought events are very frequent in the Iberian Peninsula (and in Portugal in particular) and an increase of frequency of these extreme events are expected in a very near future. Therefore, the quantitative assessment of the natural ecosystems vulnerability to drought is still very challenging, mainly due to the difficulties of having a common definition of vulnerability. Consequently, several methods have been proposed to assess agricultural vulnerability. In this work, a principal component analysis (PCA) was performed based on the components which characterize the Exposure, Sensitivity and Adaptative Capacity of the agricultural system to drought events with the aim of generating maps of vulnerability of agriculture to drought in Portugal. Several datasets were used to describe these components, namely drought indicators, vegetation indexes and soil characterization variables. A comparison between the PCA-based method and a subjective non-automatic categorical method using the same indicators was performed. Results show that both methods identify Minho and Alentejo as regions of low and extreme vulnerability, respectively. The results are very similar between the two methods, with small differences on certain vulnerability class. However, the PCA method has some advantages over the categorical method, namely the ability to identify the sign of the indicators, not having to use the indicator-component subjective relationship, nor calculating weights. Furthermore, the PCA method is fully statistical and presents results according to a prior knowledge of the region and the data used. [ABSTRACT FROM AUTHOR]

Atmospheric fronts are fundamental features of the weather variability in the mid‐latitudes and are frequently associated with high‐impact weather events such as hail, wind gusts or precipitation. A method to link precipitation with synoptic‐scale fronts on sub‐daily timescales is developed based on ERA‐Interim data (1979–2016). A case study, a climatology and a trend analysis are presented and discussed. Spatially, an optimal attribution radius is identified based on a random sampling technique. The method is demonstrated using a past weather event that occurred over western Europe. Annual and seasonal cycles are presented and confirm, in agreement with previous studies, that frontal precipitation accounts for a large fraction of all precipitation (up to 80%) in the mid‐latitudes, especially during autumn and winter. Finally, a negative trend in frontal precipitation is identified, mostly affecting the Gulf Stream region. Cold fronts drive most of the observed trends in this region and the trend pattern suggests a polewards displacement of the zone of enhanced precipitation. A method is presented to relate, in time and space, precipitation to mid‐latitudes synoptic‐scale fronts using 6‐hourly ERA‐Interim data, distinguishing warm and cold fronts (a). The method is validated using a case study occurred over the North Atlantic and European sector (b). Annual and seasonal climatological means for precipitation assigned to fronts are analysed (c). A trend analysis for the period 1979–2016 suggests a statistically significant decrease of precipitation south of the Gulf Stream SST zone, mostly driven by cold fronts. [ABSTRACT FROM AUTHOR]

In this work, the impacts of drought events on vegetation activity in the period 1998-2014 were analysed, on an area located in southeastern Europe, using the Standardized Precipitation Evaporation Index (SPEI) at several time scales, and the Normalized Difference Vegetation Index (NDVI), as obtained by SPOT/VEGETATION. A correlation analysis between monthly NDVI and SPEI was performed, as well as the assessment of the simultaneous occurrence of drought events and low vegetation activity. The analysis was performed from April to October, corresponding to the months showing the highest vegetation activity. The impacts of drought were assessed in the entire period, but also on the drought event in 2000/2001, which was the driest in this area since 1961. The results show the area with positive correlation between the two indices reaches 77% in July on agricultural land, and its impacts are seen from May to October, pointing to a high vulnerability to drought. Forests seems to be less sensitive to drought, although being more influenced by drought mostly on July and August. However, negative correlations were also observed in June at high altitudes pointing to a positive effect of dryness on the vegetation activity. This feature changed in July, possibly as a result of the increasing temperature coupled to the decrease in precipitation that leads to a water stress situation. The drought event in 2000 provoked a generalized decrease in vegetation activity, and 71% of the area showed a decrease on at least four months between April and October. Almost 60% (20%) of the studied area presents a concordance of anomalous low vegetation activity and dry conditions of at least 50% (80%) on the month of August, whereas the Carpathian Mountains generally present a lower value of concordance than the remaining area. [ABSTRACT FROM AUTHOR]

Future climate scenarios point to an increase in the frequency of extreme droughts events, even in humid biomes. Throughout the 21st century, large areas of the Amazon basin experienced the most severe droughts ever recorded with special emphasis on the 2005 and 2010 events due to their severity and extent. Currently, there is an increased demand to understand the geographic extent and seasonal variability of climate variables during drought events, especially with respect to the social and environmental impacts. In this study, we aim to compare the observed climate conditions during the drought episodes of 2005, 2010 and 2015. We perform a detailed assessment of the measured precipitation, land‐surface temperature (LST) and solar radiation anomalies. We provide evidence that the anomalous precipitation deficit during 2015 exceeded the amplitude and spatial extent of the previous events, affecting more than 80% of Amazon basin, particularly the eastern portion. The pronounced lack of rainfall availability during late spring and early summer, coincident with radiation and temperature surpluses during these years are significant and notable. Changed meteorological spatial patterns were observed, with precipitation and radiation being the most prominent parameters in 2005, whereas precipitation and LST were most relevant in 2010. Understanding the behaviour and interactions of pertinent meteorological variables, as well as identifying similar or divergent patterns over the region during distinct extreme events, is essential for the improvement of our knowledge of Amazon forest vulnerability to climate fluctuation changes. [ABSTRACT FROM AUTHOR]

According to the ice-core record, atmospheric CO2 growth rate (plateau) stalled during the 1940s, in spite of maintained anthropogenic emissions from fossil fuel burning and land-use change. Bastos et al. (2016) have shown that the state-of-the-art reconstructions of CO2 sources and sinks do not allow closing the global CO2 budget during this period. Their study indicates that even considering an enhancement of the ocean sink, still a gap sink of 0.4-1.5 PgC.yr-1 in terrestrial ecosystems is needed to explain the CO2 stabilization. They hypothesised that (i) the major socioeconomic and demographic disruptions during World War II (WWII) may have led to massive land-abandonment, resulting in an additional sink from regrowing natural vegetation which is not accounted for in most reconstructions and/or (ii) the warming registered at the same time, especially in the high-latitudes, might have led to increased vegetation growth and an enhancement of the natural sink. Here, we test the different contributions of these two factors in the Former Soviet Union (FSU), motivated by several reasons. On the one hand, the territory of the FSU encompasses 15% of the terrestrial surface, 20% of the global soil organic carbon pool and is responsible for a considerable fraction of the present-day terrestrial CO2 sink. On the other hand, heavy economic and demographic losses have been registered in FSU during WWII, together with likely decrease in farmland due to occupation, destruction of infrastructure and shortages of manpower. Here we present a newly compiled dataset of annual agricultural area in FSU, which better matches other socioeconomic indicators and reports a decrease in cropland of ca. 62 Mha between 1940-1943. We use an updated version of the land-surface model ORCHIDEE, ORCHIDEE-MICT, which is specifically developed to better represent high-latitude processes to simulate the carbon fluxes in terrestrial ecosystems over the 20th century. Using our new cropland dataset, we test the different contributions of the land-use change and the decadal warming reported in the 1940s to explain the plateau. As reference, we compare our results with the gap sink estimated by the group of land-surface models in Bastos et al. (2016): 0.7 PgC/yr. We find that the massive cropland decrease between 1940-1943, even if short-termed, could result in an additional decadal sink of 0.04-0.07 PgC/yr, i.e. 6-10% of the gap sink required to explain the plateau. The ORCHIDEE-MICT simulations also indicate a very strong enhancement of the terrestrial sink by 0.4 PgC/yr, explaining about 60% of the gap sink from the TRENDYv4 models. This enhancement is mainly explained by tree-growth in high-latitudes coincident with strongest warming sustained over the 1940-1949 decade, which is not captured by any of the other land-surface models. Even if land-abandonment during WWII might contribute to a relatively small fraction of the sink required to explain the plateau, it is still non-negligible, especially since such events have likely been registered in other regions. The vegetation growth in high-latitudes simulated by ORCHIDEE-MICT and absent in other models appears to be supported by tree-ring records, highlighting the relevance of improving the representation of high-latitude hydrological and soil processes in order to better capture decadal variability in the terrestrial CO2 sink. [ABSTRACT FROM AUTHOR]

This work focuses on the spatial and temporal variability of burnt area ( BA) in the entire Iberian Peninsula ( IP) and on the construction of statistical models to reproduce the inter-annual variability. A novel common dataset was assembled for the whole IP by merging the registered BA from 66 administrative regions of both Portugal and Spain. We applied a cluster analysis to identify larger regions with similar fire regimes and results point to the existence of four clusters (Northwestern, Northern, Southwestern and Eastern) whose spatial patterns and seasonal fire regimes are shown to be related with constraining factors such as topography, vegetation cover and climate conditions. The relationship between BA at monthly time scale with both long-term climatic pre-conditions and short-term synoptic forcing was assessed using correlation and regression analysis based on: (1) temperature and precipitation from 2 to 7 months in advance to fire peak season, (2) synoptic weather patterns derived from 11 distinct Weather Types Classifications ( WTC). Different relations were obtained for each IP region with a relevant link being identified between BA and short-term synoptic forcing for all clusters, while the relation with long-term climatic preconditioning was relevant for all but one cluster. Stepwise regression models based on the best climatic and synoptic circulation predictors were developed with cross-validation to avoid over fitting. The performance of the models varies within IP regions, though models exclusively based on WTC tend to better reproduce the annual BA time series than those merely based on pre-conditioning climatic information. Nevertheless, the use of both synoptic and climatic predictors provides the best results, particularly for the two western clusters, with Pearson correlation coefficient values higher than 0.7. Finally, it is shown that typical synoptic configurations that favour high values of BA correspond to dry and warm wind flows associated with anti-cyclonic regimes. [ABSTRACT FROM AUTHOR]

Copyright of Silva Lusitana is the property of Unidade de Investigacao de Silvicultura e Productos Florestais and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Vegetation trends in Portugal point to a generalized greening in this territory in the period 1982-2012, in agreement with global greening patterns. Nonetheless, vegetation dynamics may be altered by natural hazards, such as fires and droughts, and also by human activities like land management and land use change. The identification of trend shifts allows to better understand their impacts on vegetation, as well as the recovery after these disturbances.A recently developed a high-resolution (1.1km) spatial dataset of the Normalized Difference Vegetation Index (NDVI) for Portugal spanning the period from 1981 to 2015 is used in the present work. NDVI was derived from the Advanced Very High Resolution Radiometer (AVHRR) sensor on board of the NOAA satellites. Land cover and land cover change are identified using CORINE Land Cover maps. Trends are assessed on seasonally adjusted NDVI time series. Results show at least one breakpoint in the NDVI time series over the study area. Moreover, the majority of the breakpoints separate segments of increasing trend, indicating the recovery of the vegetation after the disturbance. In particular, the extreme drought event of 2005 is pointed out as one main cause of the vegetation shifts occurring, namely in central and southern Portugal, highlighting that water availability plays a major role in vegetation activity in these areas. Additionally, the 2005 fire season presents the second highest value of burned area during the study period, and it is also responsible for a significant number of vegetation shifts. Vegetation behaviour and recovery over the areas affected by drought and/or fires are analysed. Land cover change is also a likely driver of vegetation shifts, since they are both identified on a pixel level on some regions.Acknowledgements: This work was partially supported by national funds through FCT (Fundação para a Ciência e Tecnologia, Portugal) under Project IMDROFLOOD WaterJPI/0004/2014) and the research grant attributed to Ana Russo (SFRH/BPD/99757/2014). [ABSTRACT FROM AUTHOR]

Extreme hot events are increasing in frequency and intensity worldwide, whit special emphasis on the high number of events which occurred during the last decade. Europe was particularly affected by unprecedented mega heat waves during the last decades, namely the events that have struck Western Europe in 2003 and Eastern Europe in 2010. Despite their intense impacts, heatwaves are usually of short duration, lasting in the order of a few days to a few weeks. Therefore, monitoring and assessment strategies of extreme hot events is imperative to further investigate their link with atmospheric conditions, especially within the framework of future warming scenarios and risk assessment.The year of 2018 was reported as an unusually hot year, with record breaking temperatures in many parts of Europe during spring and summer, which were associated to severe and unusual wildfires and significant crop losses in central and northern Europe.In this study we analyse the temperature extremes over Europe and their vegetation impacts during 2018 using Land Surface Temperature (LST) and Fraction Vegetation Cover (FVC) retrieved from SEVIRI/Meteosat available through LSA-SAF (http://lsa-saf.eumetsat.int). LST monthly means and anomalies were computed, considering the diurnal cycle of reprocessed Land Surface Temperature (LST), for the period between 2004-2015 with the LST CDR and for 2016 to present with the operational LST dataset. Monthly means and anomalies were also computed using FVC. ECMWF ERA-Interim skin temperature was also used for the period from 1980 to 2018 and monthly means and anomalies were computed for the extended period and for a sub-period simultaneous with LST dataset.The results exhibit strong spatial patterns of monthly LST anomalies during spring and summer of 2018 over central and north Europe. Over a particularly large region, breaking LST records with respect to last 15 years, persist for more than 4 months. ECMWF ERA-Interim skin temperatures corroborate the exceptional heat extremes observed over central and northern Europe during 2018, highlighting the ability and usefulness of the LST-CDR for climate variability and extremes assessment.Acknowledgements: This study was performed within the framework of the LSA-SAF, co-funded by EUMETSAT. This work was partially supported by national funds through FCT (Fundação para a Ciência e a Tecnologia, Portugal) under project IMPECAF (PTDC/CTA-CLI/28902/2017). Ana Russo thanks FCT for grants SFRH/BPD/99757/2014. [ABSTRACT FROM AUTHOR]

Better understand the combined effects of drought and heat extremes in the onset of the following fire season becomes relevant, in particular in ecosystems where vegetation activity is limited by water availability. High temperatures are not the driven factor of fire activity in low productive ecosystems, whereas in high productivity ecosystems (where available biomass for fire is high) fire is more sensitive to warm conditions. These results stress the role of fuel availability in fire occurrence and severity on the Iberian Peninsula. The aim of this work is to assess the relation with dry matter productivity and vegetation status with fire occurrences, fire severity and fire danger in Portugal. In this context, Dry Matter Productivity (DMP), disseminated by Copernicus Global Land Service (CGLS) at 1km spatial resolution since 1999 is used. DMP represents the overall growth rate or dry biomass increase of the vegetation and is directly related to ecosystem Net Primary Productivity (NPP). Additionally, annual NPP fields from MOD17A3 C5 dataset and Net Photosynthesis (PsN) monthly fields from MOD17A2 dataset, both at 1km resolution from 2000-2018 are used. Monthly Psd and decadal DMP anomaly fields, as the departure from the corresponding long-term median in the study period were computed, as well as the cumulated biomass as obtained using PsN and DMP (monthly and decadal anomalies of cumulated biomass: PsN and DMP). The relationship between vegetation dynamics (as obtained by monthly and decadal NDVI, EVI and GEMI anomaly fields) and biomass accumulation (PsN and DMP) with fire occurrence and fire severity is obtained, taking in account the soil water availability during pre-fire season. Obtained results highlighted the high amount of cumulated biomass observed before the Megafire events of June and October of 2017 and August of 2018 in Portugal. The proposed methodology allows to provide estimates of fuel state in order to mitigate the impacts of high biomass availability on fire severity and danger.Acknowledgements: This study was performed within the framework of the LSA-SAF, co-funded by EUMETSAT. This work was partially supported by national funds through FCT (Fundação para a Ciência e a Tecnologia, Portugal) under project MDROFLOOD (WaterJPI/0004/2014). [ABSTRACT FROM AUTHOR]

This work aims at characterizing the exceptional drought that affected Madeira Archipelago (Portugal) during the 2011–2012 hydrological year while including some major impacts but also the main atmospheric circulation mechanism behind the event. Precipitation records from six meteorological stations are used to assess the extreme drought episode by means of a decile classification. The assessment of the drought duration and severity is further corroborated by the Standardized Precipitation Index (SPI) computed for the 3, 6, 12 and 24 months’ time scales which confirmed that the 2012 drought event was one of the events with higher drought intensity at all scales, being classified as extreme at the 6-month time sale (SPI6 < −1.65) from December 2011 until May 2012 on the majority of the meteorological stations analysed. Long-term precipitation data available since 1865 for the station of Funchal confirm the exceptional dryness of this episode, particularly during the winter season (December to March) corresponding to the driest winter in 150 years. Vegetation activity is assessed through anomalies of NDVI (Normalized Difference Vegetation Index), confirming several large sectors of Madeira under vegetative stress. The southern sector of Madeira Island suffered up to seven months (out of nine) of extremely negative anomalies. From an operational point of view, obtained results reveal the ability of the developed methodology to monitor vegetation stress and droughts in Madeira. The extreme dryness of the Island favoured an unusually intense summer fire season of 2012 (between June and September) in Madeira being the year with highest number of fires in the last decade (with robust data). Furthermore, the main fire hotspots of the 2012 fire season are mostly coincident with the areas affected by drought. The large-scale atmospheric circulation responsible for the setting and intensification of the drought is evaluated using reanalysis data. An extensive high pressure anomaly (maximum above 12 hPa in December) persisted over the North Atlantic during the extended winter months (October to April), centred between the Azores Islands and the UK. This feature is in agreement with a positive NAO index (2.25 in December), a negative EA index (−1.76 in January and −1.73 in February) and compatible with enhanced north-easterly trade winds over the region. As a consequence of this uncharacteristic dynamics there was a deficit of moisture availability over the region as evaluated by the vertically integrated horizontal water vapour transport with a negative anomaly up to −120 kg m −1 s −1 . [ABSTRACT FROM AUTHOR]

The increase in frequency, severity, and duration of droughts poses as a serious issue to the management of forests in the Iberian Peninsula, with particular emphasis on the decline of forest growth and forest dieback. Hence, the adoption of adaptation and mitigation measures in forest ecosystems that are more vulnerable to drought is a pressing matter that needs to be addressed in the near future. This work aims at identifying the regions in the Iberian Peninsula where forest exhibit high vulnerability to drought conditions. To accomplish that, a vulnerability map is produced by considering three pillar components: exposure, sensitivity, and adaptive capacity to drought. Exposure is estimated based on the multi-scalar drought index Standardized Precipitation-Evapotranspiration Index (SPEI) and aridity, while the remotely sensed Vegetation Health Index (VHI) and mean forested cover are used to assess the regions' sensitivity to drought. Finally, elevation, water table depth, fire radiative energy, and annual solar irradiation are compiled as indicators to assess adaptive capacity. Principal component analysis was then applied to the three pillar components to identify the areas more vulnerable to drought. This approach allows for the identification of forested areas vulnerable to drought in terms of vulnerability classes automatically determined. Forests presented very high vulnerability in eastern Spain, and central Portugal. Within the most vulnerable vegetation communities, mosaic tree and shrub types revealed to be extremely vulnerable to droughts in the Iberian Peninsula, followed by needle-leaved forests (in Central Portugal, and Northeast Iberia). This work highlights the regions and primary vegetation communities to which the effort of adapting and mitigating drought consequences should be utterly enforced by the responsible authorities. [ABSTRACT FROM AUTHOR]