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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - GRADIENT (Understanding fire, weather and land cover interactions from long-term terrestrial observations and satellite data in a north to south transect in Europe and North Africa)

Teaser

Summary

Long-term historical time series records of fire activity (number of fires and total area burned) extending back to the late 1800s, that are very rare worldwide, were found and used within the GRADIENT project that correspond to (i) Switzerland, central Europe (1900-2014), (ii) Greece, south Europe (1897-2014), (iii) Algeria, north Africa (1870-2014) and (iv) Tunisia (1902-2015), north Africa which together with the spatial-explicit reconstruction of recent fire history from Landsat satellite images (1984-2016), gave a unique and excellent opportunity to understand fire, weather and land use/land cover (LULC) interactions in a north to south transect. The Tunisia study case was added during the implementation period of the project since in the original proposal only the first three study cases were proposed.
Differences in bio-geographical characteristics provided by the four selected study areas, located on a large geographical gradient covering two continents gave the opportunity to document the role of fire in different biomes, to explore cross-scale issues and assess how fire-weather-LULC interactions vary across different scales, especially under a climate change context. GRADIENT project consisted of three topics that correspond mainly to three different scales. The specific objectives were: (i) the identification of trends, patterns and relationships between forest fires, weather, land cover and socio-economic variables from long-term observations, (ii) the reconstruction of recent fire history and the assessment of burning patterns and fire selectivity on an annual basis from satellite images, and (iii) the exploration of post-fire vegetation dynamics and recovery for selected large fire events using time series satellite images.

Work performed

Some remarks and outcomes for the specific objective of the project are the fact that there are similarities and non-similarities among the four study area that compose the gradient from north to south. Specifically, for each one of the three objectives the main overall conclusions are (i) in principle there is a characteristic fire activity in all four study areas defined by the general pyro-environment with certain peaks occurred at specific years associated to physical and social factors. The role of precipitation is different in the gradient from the wet to dry areas. Moisture is more evident as an underlying explanation mechanism in the wet study area while temperature is more evident in the dry study areas. It was evident that there is a clear and different role of precipitation from promoting to discouraging fire activity across the north to south gradient together with the social aspects and the role of human dimension, (ii) remote sensing can be used with semi-automatic methods to reconstruct the recent fire history though certain difficulties exist especially in the North study area where cloudiness is a potential problem. The huge number of satellite images needs the development of automatic or semi-automatic techniques to avoid the time-consuming manual methods and techniques. This is a critical issue in cases where many satellite images are required, such as the spatially explicit reconstruction of recent fire history where hundreds of images might be used in the processing chain. For all study areas selective burning is evident that also depends on the available to burn landscape. Frequent fires were also observed that burn mainly grasslands and shrublands. and (iii) remote sensing either by using low resolution or medium-high resolution satellite data provides critical information of the phenology of the fire affected areas that can be used efficiently to post-fire studies. Satellite time series data need special attention because of atmospheric and other sources of radiometric problems. The consideration of the full phenological cycle of landscape enhances the interpretation power of the spectral signal. The synergy and co-processing of low spatial resolution high temporal resolution time series data (e.g. MODIS) with high spatial resolution low temporal resolution time series data (e.g. Landsat, Sentinel-2) needs further understanding. Within the GRADIENT project vegetation phenology and time series statistics proved very useful not only to study vegetation recovery in fire affected areas but also to identify the time period where the fire or fires occurred and define also the vegetation phenology before the fire. This is very useful first for integrating this concept into a burned land mapping approach and second for identifying what type of vegetation is burned.

Final results

The results and outcomes of the GRADIENT project can contribute further to the better understanding of fire, weather and land cover interactions, and therefore provides knowledge for fire and land cover management practices, especially under a climate change context. Understanding of post-fire vegetation dynamics and recovery can be useful for the mitigation of short and long-term consequences of fire occurrence. The knowledge acquired from the past can be used to understand current processes and project them to future.