a b s t r a c tUnderstanding the spatial patterns of wildfire ignition and spread has important implications for landscape planning for reducing fire hazard. In this paper we characterise the patterns of wildfire occurrence in 3 regions of northern Portugal, using selection ratio functions to evaluate the fire proneness of different land cover and topographic categories. For attaining this objective we characterised 1382 wildfires larger than 5 ha, which occurred in the years 1990-1991, according to land cover (10 categories), slope (5 categories) and aspect (5 categories) within which they occurred. For each fire, the use of the different land cover and topographic categories was compared with availability in a surrounding buffer. For land cover, fire proneness was much higher in shrublands, whereas agricultural areas and agro-forestry systems where less likely to burn. In terms of slope, steep slopes were more prone to fire. Differences in land cover in the different slope categories contributed to this result, although there was an overall slope effect on the fire proneness of all land cover types. In terms of aspect, only flat areas were less fire prone. Finally, there were regional variations in land cover susceptibility to fire, but these did not occur for slope or aspect. In terms of landscape planning these results suggest that the more effective fuel breaks should be implemented in areas with agricultural crops in flat slopes.

Agricultural nutrient balances have been receiving increasing attention in both historical and nutrient management research. The main objectives of this study were to further develop balance methodologies and to carry out a comprehensive assessment of the functioning and nutrient cycling of 1950s agroecosystems in Portugal. Additionally, the main implications for the history of agriculture in Portugal were discussed from the standpoint of soil fertility. We used a mass balance approach that comprises virtually all nitrogen (N), phosphorus (P) and potassium (K) inputs and outputs from cropland topsoil for average conditions in the period 1951–56. We found a consistent deficit in N, both for nationwide (−2.1 kg.ha−1.yr−1) and arable crops (−1.6 kg.ha−1.yr−1) estimates, that was rectified in the turn to the 1960 decade. P and K were, in contrast, accumulating in the soil (4.2–4.6 kg.ha−1.yr−1 and 1.0–3.0 kg.ha−1.yr−1, respectively). We observed that the 1950s is the very moment of inflection from an agriculture fertilized predominantly through reused N in biomass (livestock excretions plus marine, plant and human waste sources) to one where chemical fertilizers prevailed. It is suggested that N deficiency played an important role in this transition.

Available research has extensively examined the spatiotemporal patterns of fire-weather regime in Portugal, but a comprehensive climatology of extreme wildfires is still under development. This study calls for different strategies and scales of analysis aiming to describe the relationships between medium and low troposphere weather conditions and severe fire behaviour in mainland Portugal,

The length of the fire season has not garnered much attention within the broad field of meteorological research on fire regime change. Fire weather research on the Iberian Peninsula is no exception in this case; there is no solid understanding on fire season lengthening in Portugal, although recent decades do suggest ongoing transitions. Based on a complete record of fire occurrence and burned area between 1980 and 2018, we first searched for consistent trends in the monthly distribution of fire activity. To determine day-scale changes, an exceedance date method based on annual cumulative burned area was developed. Results show an early onset of fire activity in a range of 23–50 days and no significant extension into autumn, suggesting that existing projections of the lengthening of the fire season in Portugal over the present century have been already achieved. Fire weather results show a trend in the cumulative Daily Severity Rating (DSR), with the last two decades (2000–2018) displaying an early build-up of meteorological fire danger in late spring and early summer. The detailed spatio-temporal analysis based on the daily Fire Weather Index (FWI) shows that June stands out with the largest increase (year-round) in days per month with an FWI above 38.3, the threshold above which fire conditions make suppression uncertain. This aggravated fire weather is likely sustaining early fire activity, thus contributing to a longer critical fire season.