Marcelo Fragoso

Wind Risk Assessment in Urban Environments: The Case of Falling Trees During Windstorm Events in Lisbon

Planting trees brings many benefits to the urban environment (Fabiao 1996; Jim and Liu 1997; Nilsson et al. 2000; Saebe et al. 2003; Soares and Castel-Branco 2007). Trees have a moderating effect on the urban microclimate and improve the physical, biological and chemical aspects of the urban environment, namely by reducing the urban ‘heat island’ effect (Alcoforado 1992), by acting as a barrier against strong wind channelling (Lopes 2003), by protecting urban surfaces from direct sunlight (McPherson and Muchnick 2005), by capturing air pollutants and dust in urban areas (Freer-Smith et al. 2004) and by increasing the biodiversity, providing habitat for birds and small mammals (Clergeau 1996).

Damaging flood severity assessment in Northern Portugal over more than 150 years (1865–2016)

Floods are a major natural hazard, with vast implications over a wide range of socio-economic activities. A harmonized post-flood classification is critical for a better understanding of this hazard, by providing homogeneous flood catalogues for future research on triggering mechanisms. We apply a flood severity index (FSI) to damaging floods in Northern Portugal over a 152-year period (1865–2016) and identify the most critical areas to flood occurrences. The index is a damage-based post-event assessment tool, which includes five categories ranging from minor flooding (1) to catastrophic flooding (5). FSI is applied to a historical damaging flood database with 2318 occurrences. In Northern Portugal, serious floods (3) are the most frequent typology, while catastrophic floods are typically river floods occurring in the Douro basin. Overall, damaging flood occurrences are favoured by the positive phase of the East Atlantic pattern and by the negative phase of the North Atlantic Oscillation. Furthermore, the north-western areas reveal higher concentrations of damaging flood occurrences, mainly due to higher population density, higher precipitation values and more flood plain areas. In particular, 48% of all occurrences are concentrated in the Porto Metropolitan Area, mainly the Porto city centre and nearby riverside areas of the Douro River. High-population density and heavily urbanized areas lead to greater exposure to flood risk, whereas the most peripheral municipalities, with large agricultural/forested areas, show much lower numbers of damaging floods. FSI is tool to communicate the magnitude of the flood risk and is, therefore, of foremost relevance to civil protection and risk management.

Recent and future changes of precipitation extremes in mainland Portugal

Recent and future changes in precipitation extremes over Portugal were studied. Trends in selected precipitation indices were calculated on a seasonal scale for the period of 1950–2003. Considering the same indices, this study also assessed possible changes under future climatic conditions (2046–2065). Furthermore, trends and projections for the future were evaluated using a single/unified index of extreme precipitation susceptibility (EPSI). The results revealed statistically significant drying trends in spring, mainly in northern and central Portugal, while weak wetting trends were detected in autumn. The EPSI trends also depicted a decrease of extreme precipitation in spring over central Portugal and a slight increase in autumn over northern Portugal and nearby Lisbon. On the other hand, climate change projections revealed a decrease in precipitation, mainly over northwestern Portugal, whereas the contribution of extreme precipitation to total precipitation is expected to increase, mostly in southern Portugal. The maximum number of consecutive dry days (CDD) is also projected to increase throughout Portugal. EPSI showed enhanced susceptibility for most Portuguese municipalities, which may be associated with increased vulnerability to flash floods. Climate change projections by municipality for both EPSI and CDD are an important decision support tool for civil protection and for risk management in Portugal.