Joana Parente

Long-term burn severity assessment can support better pre- and post-fire management plans. In this study, the Portuguese Burn Severity Atlas was created, containing historical fires in Portugal from 1984 to 2022. As prerequisites, fire data were gathered and delimited for all years. Due to the availability of satellite images, for different years, different imageries from Landsat sensors (30 m) were applied. Exploratory analysis showed that burn severity estimates are significantly affected by the time lag between the satellite imagery acquisition and the fire date. We explicitly incorporated the effect of time lag into the degradation of burn severity estimates in the selection of the most suitable pre- and post-fire satellite images for each fire. Using Google Earth Engine, burn severity estimates were calculated for fires that were equal to or larger than 100 ha and that occurred from 1984 to 2022 with known dates (valid fires). Different indices were calculated, such as the differenced normalized burn ratio (dNBR), the relative dNBR (RdNBR), the relativized burn ratio (RBR), and a burn severity index that combines the dNBR with the enhanced vegetation index (dNBR-EVI). Overall, in Portugal, 4.85×10⁶ ha burned over the 38-year period (1984–2022), with the burned area covering 3.29×10⁶ ha being caused by valid fires (68 %). Among these, a total area of 3.18×10⁶ ha had burn severity estimates via the applied indices (97 % of valid and 66 % of all fires). Results show that Portugal has experienced, on average, “high” burn severity throughout this period, with large percentages of dNBR pixels between 0.419 and 0.66 (32 %) and >0.66 (21 %). Estimates from different burn severity indices provided a more complete representation of the burn severity impacts. This atlas can be accessed at https://doi.org/10.5281/zenodo.12773611 (Jahanianfard et al., 2025) and can be used by researchers to have a better understanding of historical fires and their corresponding impacts on vegetation cover, air, soil, and water quality, as well as to identify the most influential environmental and climatic drivers of burn severity.

Wildfires have been known as one of the most disturbing phenomena in Portugal during last decades with increasing frequency, annual number of ignition and affected area. However, the extent of wildfire-induced changes on soil and vegetation, or burn severity, of these historical wildfires is unclear. To contribute to a better knowledge of post-fire impacts, this study presents a long-term burn severity atlas of historical wildfires in Portugal from 1984 to 2022 using satellite data.Burn perimeters and start/end dates for large wildfires (>=100ha) were gathered and necessary corrections were manually applied on them. Due to the availability of satellite images, different imagery from Landsat sensors were used for different years: Landsat-5 (TM) for 1984 to 2011, Landsat-7 (ETM+) for 2002, and Landsat8 (OLI) for 2013 to 2022. The time lag between wildfire occurrence and satellite image acquisition dates was quantified and used to determine the suitability of each satellite image to estimate burn severity. Then, using Google Earth Engine API (JavaScript) and through a semi-automated process, the burn severity of each wildfire was calculated via difference normalized burn ratio (dNBR) derived indices (dNBR, relative dNBR (RdNBR), Relativized Burn Ratio (RBR), dNBR – Enhanced Vegetation index (dNBR-EVI)). These maps were created by the application of a pair of pre- and post-fire images with the highest suitability values.The analysis performed on the time lag quantification showed a decrease in dNBR accuracy with the increase of both pre- and post-fire time lags. Over 3.7 million ha of land burned in Portugal from 1984 to 2022 in all vegetation types, around 3.2 million were associated with wildfires equal or larger than 100ha with known start and end dates (86.2%). Among these wildfires, 3.1 million ha had dNBR estimates (83.72% of all wildfires and 97.05% of wildfires>=100ha).To the best of our knowledge, a long-term burn severity atlas has never been developed for an entire European country before. Another noteworthy advancement provided by this atlas is that the imageries from Landsat family of sensors were utilized for development of burn severity maps, offering the resolution of 30m over the manually corrected historical wildfire data (perimeters, locations, and dates). Also, a semi-automated process has been provided, equipped with the capacity to develop burn severity atlas for historical wildfires of any other region in the world with the prerequisite of wildfire data. Such datasets can be used by both scientific and management communities to improve current knowledge on post-fire impacts and develop better pre- and post-fire management plans to mitigate wildfire impacts. Moreover, this multidecadal burn severity dataset can be used by other research communities in the fields related to water, soil, and air quality which are potentially at risk due to wildfire occurrences.AcknowledgementsWe acknowledge CESAM by the Portuguese Foundation for Science and Technology FCT/MCTES (UIDP/50017/2020+UIDB/50017/2020+LA/P/0094/2020). D. Jahanianfard is supported by the Portuguese Foundation for Science and Technology (FCT-Fundação para a Ciência e Tecnologia) with a PhD grant reference (2021.08094.BD). O. Gonzalez-Pelayo further acknowledges FCT for the funding of FRISCO (PCIF/MPG/0044/2018) and SOILCOMBAT (PTDC/EAM-AMB/0474/2020) projects.

Long-term burn severity assessment can support better pre- and post-fire management plans. In this study, Portuguese Burn Severity Atlas was created containing historical fires in Portugal from 1984 to 2022. As prerequisites, fire data were gathered and delimited for all years. Due to the availability of satellite images, for different years, different imagery from Landsat sensors (30 m) were applied. Exploratory analysis showed that burn severity estimates are significantly affected by the time lag between the satellite imagery acquisition and the fire date. We explicitly incorporated the effect of time lag in the degradation of burn severity estimates in the selection of the most suitable pre- and post-fire satellite images for each fire. Using Google Earth Engine, burn severity estimates were calculated for fires equal to or larger than 500 ha between 1984 and 2000 and larger than 100 ha for fires from 2001 to 2022 with known start and end dates (valid fires). Different indices were calculated, such as the differenced Normalized Burn Ratio (dNBR), relative dNBR (RdNBR), Relativized Burn Ratio (RBR), and a burn severity index that combines dNBR with enhanced vegetation index (dNBR-EVI). Overall, in Portugal, 4.92 M ha burned over the 38-year period (1984–2022), from which 3.19 million ha were caused by valid fires (64.8 %). Among these, a total area of 3.11 million ha had burn severity estimates via the applied indices (97 % of valid and 63 % of all fires). Results show that Portugal has experienced, on average, “high” burn severity throughout this period, with large percentages of dNBR pixels between 0.419 and 0.66 (29 %) and > 0.66 (20 %). Estimates from different burn severity indices provided a more complete representation of the burn severity impacts. Via the analysis of only three fires throughout the study period, the dNBR-EVI showed potential in differentiating the “unburned” and “regrowth” burn severity while RBR was more prone to signal saturation, i.e., inability to show “high” and “very high” burn severity. However, more in-depth research is needed to fully confirm these properties. This atlas can be accessed at https://doi.org/10.5281/zenodo.12773611 (Jahanianfard et al., 2024) and be used by researchers to have a better understanding of historical fires, their corresponding impacts on vegetation cover, air, soil, and water quality, and identification of the most influential environmental and climatical drivers of burn severity.

Wildfires are uncontrolled and unwanted fires that usually occur in forested/rural areas and burn forests, agricultural areas, and wildlands. Land abandonment, with the consequent growth of the rural–urban interface, increases the exposure and vulnerability of fire-prone regions around the World. In the last two decades, Europe experienced a high number of wildfires causing large burnt areas mainly concentrated in the Mediterranean Basin. This high fire incidence seems to be the result of human activities including land use/land cover changes, but also of climate variability and change. In the present study, we analyse the current situation in Portugal, which is the European country with the highest total number of wildfires and the second-highest total burnt area. The spatial and temporal variability of the wildfires within the country is very heterogeneous, due to the human and biophysical drivers. In this regard, four main aspects are considered and discussed: (1) the spatial and temporal distribution of wildfires in mainland Portugal; (2) the main human and biophysical fire drivers; (3) socioeconomic impacts; and (4) the main strategies for fire risk mapping and management. The main results indicate high spatial heterogeneity of the fire incidence, with higher fire activity in the northern region than the southern region, mainly promoted by a higher irregular topography and significantly different types of climate and land use/land cover characteristics. We highlight how fire incidence is strongly dependent on many biophysical and human factors/drivers and the direct and indirect socioeconomic impacts of wildfires. Methodologies and indexes developed by Portuguese authorities to map fire risk and assess fire danger are described. The elements discussed in this chapter result from research and lessons learned in recent years on the fire regime in Portugal and Europe. These findings can contribute to improving forest, landscape, and fire management, in Mediterranean European countries which share similar characteristics.

Over the last decades, the establishment of new fast‐growing forest plantations has been prospering. Although the European continent has the lowest share worldwide of forest plantations out of its total forest area, the Portuguese reality contrasts this. Since the last century, eucalypt plantations have increased widely in Portugal, and nowadays, it represents 36% of the total country's forests. Consequently, the soils of these plantations are commonly targeted with intensive soil mobilization by heavy machinery before planting, which in the case of sloped areas, frequently results in bench terracing. This study aims to quantify the widespread bench terracing implementation over the last 20 years in the Caramulo Mountains in north central Portugal. To do so, an analysis of satellite imagery was performed with Google Earth Pro, which allowed determining the coverage of forest areas where new terraces have been implemented, and their respective temporal dynamics. These results were then compared with additional spatiotemporal databases on land cover, topography, and bedrock, in order to understand the drivers of terrace implementation. Till date, 15% of the forest area in the mountains of Caramulo is under terraces, and over the last 20 years, the construction rate of new terraced land decreased in time, from 4% between 2000 and 2004 to 2% between 2015 and 2019. Among the two bedrock types existent in the area, terracing was found nearly exclusive over schist bedrock type (97%), while few areas were implemented over granites (3%). Their distribution was found limited above 30° of slope angle while 39% were found implemented below 15° of slope angle, conflicting with literature recommendations. Terracing was also found to be a driver of land cover change in 12% of the newly constructed terraces, whereas 8% were constructed over previous pine plantations and 4% on shrublands. This study allowed identifying several knowledge gaps associated with terracing implementation. Therefore, the authors of this work suggest a multidisciplinary approach when planning new terraces for a better assessment of the benefits and impacts of such land management practices.

Wildfires play a fundamental role in Land Use/Land Cover (LULC) change dynamics by burning vegetation in forested and rural areas and by affecting human infrastructures. Conversely, LULC can disturb fire regime by altering vegetation cover, conditioning subsequent transitions, and acting on fuel loads and continuity. Though there is an evident mutual influence between wildfires and LULC changes, a rigorous quantification of their reciprocal effects in Europe has never been performed before. To fill this gap, in the present study we developed a methodology allowing the evaluation of different indicators for the quantitative assessment and a better understanding of the transitions among LULC classes and Burnt Areas (BA) that occurred in Europe within the last two decades (2000 – 2020).Our analyses revealed that the two LULC classes which had experienced major changes were Forests (44%), and Scrubs and/or herbaceous vegetation associations (32%). As a general trend, within the five European Mediterranean Countries more prone to wildfires (Portugal, Spain, France, Italy, and Greece) we found a decrease in the classes Forests and Arable land, and an increase in Scrubs and/or herbaceous vegetation associations, suggesting the impact of wildfires in shaping the natural and rural landscape. This assumption was better evaluated and confirmed by the following analyses, performed at both the European and national levels. Results showed that most of the BA have occurred in Forests (42% for the entire Europe), with a predominance in Coniferous forests; the subsequent transitions from BA were generally to Transitional woodland/shrub or again to BA. This last indicates a high frequency of wildfires in a given area, while the first transition can be partially due to the regeneration/recolonization of the vegetation after a wildfire event. Outcomes for the single countries followed almost the same trend.Overall, our results confirm the existence of a strong relationship between wildfires and LULC changes in Europe, which have been quantified in the present study. These findings are in line with previous research and provide a deep insight into the process at the global and local levels, paving the way for further analyses on fire intensity and frequency with coupled environmental elements of land cover and climate changes.

Wildfires in the Mediterranean basin, especially in Portugal, have increased in extent and frequency over the last few years. One of the many impacts of wildfires on humans and ecosystems is on the water quality of surface waters. Ashes and increased erosion rates might elevate the influx of nutrients, sediments, or other water quality-related components, possibly affecting the water supply. This study has three main objectives. (1) Identifying post-fire water contamination events in over 60 Portuguese reservoirs, through changepoint analysis of historical time series for (2) Testing the relationship between post-fire water contamination events with fire-, watershed-, reservoir-, and climatic drivers through logistic regression using generalized additive models. (3) The modelling and evaluation of post-fire water supply contamination risks in Portugal, using a deterministic approach. Results showed increases in TSS in 13.6% of all wildfires. Most changes fell into the unusually large fire seasons of 2003-2005 and 2017, while the most significant impacts could be seen in southern reservoirs after 2005. Fire size was identified as the main driver of post-fire water contamination, while reservoir and climate-related characteristics like water levels also played a significant role in TSS. Increased levels of suspended sediments were identified as a potential threat to the water supply, especially when large wildfires coincide with drought-induced low reservoir water levels. The modelling of past water contamination episodes shows a similar spatial distribution as the structural fire risk in Portugal, identifying the centre (and southern) regions as the most affected areas. This study may support numerous case and modelling studies and inform water managers about possible future threats.

The models currently used to predict post-fire soil erosion risks are limited by high data demands and long computation times. An alternative is to map the potential hydrological and sediment connectivity using indices to express the general properties of the landscape under evaluation and map the possible connectivity between the different parts of a catchment.In this study, we aim to answer the question: Do these alternative approaches identify post-fire sediment mobilization hotspots? To achieve this, we assess the spatial variability distribution of the location of soil erosion hotspots using the Index of Connectivity (IC), Revised Universal Soil Loss Equation (RUSLE model) and the Sediment Export (SE) and compare it to the simulation results of a more complex Landscape Evolution Model (LAPSUS model). Additionally, we evaluate statistical measures of association between the four tools. Furthermore, IC, RUSLE model and SE are used due to their simplistic representation of erosion and ease of application, and the LAPSUS model is used as the best representation of erosion and sediment transport in the study area.Our results show that the three tools (IC, RUSLE model and SE) tested in this study are suitable for identifying sediment mobilization hotspots, i.e., areas where the erosion rates are above the 90th percentile, in recently burnt areas, and differences between their performance are minor. These findings can be considered for post-fire and water contamination risk management, especially for fast prioritization of areas needing emergency post-fire intervention.

Wildfires are key drivers of land use/land cover (LULC) dynamics by burning vegetation and affecting human infrastructure. On the contrary, LULC changes (LULCCs) may affect the fire regime by influencing vegetation type, burnable areas, fuel loads and continuity. This study investigates the relationship between LULCC and wildfires. We developed a methodology based on different indicators, which allowed us to quantitatively assess and better understand the transitions between LULC classes and burnt area (BA) in Europe in the last two decades (2000–2019). The assessment was performed for the entire European continent and, independently, for each of the five European countries most affected by wildfires: Portugal, Spain, France, Italy and Greece. The main results are the following: (i) LULCC analysis revealed a net loss in forests and arable land and a net gain in shrubs; (ii) most of the BA occurred in forests (42% for the whole of Europe), especially in coniferous forests; (iii) transitions from BA generally were to transitional woodland/shrub or, again, to BA. Overall, our results confirm the existence of a strong relationship between wildfires and LULCCs in Europe, which was quantified in the present study. These findings are of paramount importance in fire and environmental system management and ecology.

Background: The models currently used to predict post-fire soil erosion risks are limited by high data demands and long computation times. An alternative is to map the potential hydrological and sediment connectivity using indices to express the general properties of the burnt landscape. Aims: In this study, we aimed to answer the question: Do these tools identify post-fire sediment mobilisation hotspots? Methods: To achieve this, we assessed the spatial variability distribution of the location of soil erosion hotspots using the Index of Connectivity, Revised Universal Soil Loss Equation and the Sediment Export, and compared it with the simulation results of a more complex Landscape Evolution Model (LAPSUS model). Additionally, we evaluated statistical measures of association between the four tools. Key results: The three tools tested in this study are suitable for identifying sediment mobilisation hotspots, where the erosion rates are above the 95th percentile, and differences between their performance are small. Conclusions: The results indicate that these tools help locate extreme erosion locations in recently burnt areas. Implications: These results can be considered for post-fire and water contamination risk management, especially for fast prioritisation of areas needing emergency post-fire intervention.