Fire weather risk assessment under climate change using a dynamical downscaling approach

Results from general circulation models suggest that the increase of forest fire activity at the global scale will be one of the impacts of climate change. As attention shifts to regional climate further spatial resolution is needed to handle the forcings and circulations that occur at smaller scales. One of the available techniques to assess the impact of climate change on fire activity at the regional scale is the dynamical downscaling between global climate models and regional models. In the present work, the impact of climate change on fire danger at the regional scale was examined by means of dynamical downscaling between a general circulation model (MUGCM) and a regional meteorological model (MM5). A Southern European country, Portugal, was selected as case-study since general circulation models predict significant surface air temperature increases over Southern and Mediterranean Europe. Present and future climates, centred in 1990 and 2050, respectively, were obtained using daily data previously simulated by MUGCM. Climate change signals on temperature and precipitation derived from the MUGCM ensemble simulations were analysed using spatial averages over the Iberian Peninsula and cluster analysis applied over Portugal. For the Iberian Peninsula, a positive trend for temperature for all seasons, with higher variability for the winter months, was obtained. Over Portugal, for the future climate, the average winter temperature is expected to be higher. Precipitation increases are simulated for the end of autumn/beginning of winter, and negative changes are expected for the end of winter/beginning of spring and beginning of summer. The cluster analysis revealed important temporal changes on the meteorological variables which may be relevant for fire management planning, namely a longer fire season over Portugal is expected. The spatial refinement of the projected climate change impacts on the fire weather risk over Portugal was performed through numerical downscaling between MUGCM and MM5. The MM5 outputs, at 10 km resolution, were used to estimate the Canadian Fire Weather Index (FWI) System components. Results show higher FWI values in the beginning of summer for the 2050 scenario. An increase of the maximum values of the Drought Code (DC) in the inner part of Portugal was also detected. An increase in the total area burned is anticipated, with the consequent increase of pollutants emissions.