# Uncovering Vegetation Changes in the Urban-Rural Interface through Semi-Automatic Methods
###### Abstract  
Forest fires are considered by Portuguese civil protection as one of the most serious natural disasters due to their frequency and extent. To address the problem, the Fire Forest Defense System establishes the implementation of fuel management bands to aid firefighting. The aim of this study was to develop a model capable of identifying vegetation removal in the urban-rural interface defined by law for fuel management actions. The model uses normalised difference vegetation index (NDVI) of Sentinel-2 images time series and is based on the Welch \(t\)-test to find statistically significant differences between (i) the value of the NDVI in the pixel; (ii) the mean of the NDVI in the pixels of the same land cover type in a radius of 500 m; and (iii) their difference. The model identifies a change when the \(t\)-test points for a significant difference of the NDVI value in the 'pixel' as compared to the 'difference' but not the'mean'. We use a moving window limited to 60 days before and after the analysed date to reduce the phenological variations of vegetation. The model was applied in five municipalities of Portugal and the results are promising to identify the places where the management of fuel bands was not carried out. This indicates which model could be used to assist in the verification of the annual management of the fuel bands defined in the law. S 20221229412229412229412  
demographic and social changes in rural areas have been drivers of land abandonment which in turn influences land use/cover and fuel management [11; 12; 13]. To mitigate and reduce the problem of forest fires, a legal apparatus that establish plans to better fight and prevent the spread of fires. Decree-of-Law 124/2006 of 28 June 2006 implements the Forest Defence System Against Fires (_Sistema de Defresa da Floresta Contra Incradio_--SDFCI). Article 13 defines the networks of fuel management bands around strategic locations where the total or partial removal of existing biomass should be carried out each year between September and May. Fuel management bands aim to reduce the effects of fire and protect communication routes, infrastructure, and social facilities, built-up areas, and forest stands, as well as to isolate potential fire ignition points. According to Article 15, agglomerations into or adjacent to forests, campsites, and industrial activities must have a minimum width of 100 metres of fuel management band. As for buildings bordering forests, bushes, or natural pastures, the minimum width becomes 50 metres. The criteria for fuel management are available in the annex to the Decree-Law. Generally, in the tree stratum the canopies must maintain a minimum distance of 4 metres, varying with the tree species. Moreover, the trees shall be ploughed at least 4 metres from the height of the ground, the shrub stratum should not exceed 50 centimetres height and the grassland stratum cannot exceed 20 centimetres. Around buildings, the treetop must be located at least 5 metres away to avoid its projection over the roof of the building. Fuel management and planning in general requires detecting vegetation changes in a regular basis, meaning that supporting information is always updated. However, the most detailed official Portuguese land use/cover data (_Carta de l'uso e Coupacao do Solo_--COS) is not released in a yearly basis, which implies that the urban-rural interface map is often outdated. Thus, the justification of this research links to this problem as the central objective is to create a model capable of identifying the removal of vegetation around urban areas, namely in the fuel bands around population clusters, and that can support the updating of urban-rural interfaces in periods when a new version of COS is still not available. Previous works on vegetation change mapping based on satellite images identify two main approaches: (i) detection of the change from image to image; and (ii) time series-based change detection [14].