Assessing the Impact of Climate Change on Forest Fire Weather Index Using Downscaled Climate Model Data

In recent years, fire activity at high latitudes has reached unprecedented levels, driven in part by global warming, which increases fire danger. Climate projections of fire risk rely on indices like the Canadian Forest Fire Weather Index (FWI), which are often derived from coarse-resolution climate models. Thus, there is the need for finer-scale fire weather projections to enable more effective planning and resource allocation as wildfire threats grow. High-resolution climate projections can be achieved through various methods, including dynamical and statistical downscaling, each potentially yielding different estimates of FWI and its future changes. We calculated the FWI based on HCLIM - Nordic Convection Permitting Climate Projections (NorCP) over Fennoscandia. The simulations include 12 x 12 km resolution models using HCLIM-ALADIN and convection-permitting simulation at 3 x 3 km resolution with HCLIM-AROME, covering both historical and future periods under the RCP8.5 scenario. Results were compared against FWI estimates from other climate datasets, such as CORDEX and statistically downscaled NASA Earth Exchange Global Daily Downscaled Projections (NEX-GDDP).

As expected, all the simulations indicate that the annual and summer mean FWI indices will increase significantly in warmer future climates, along with an increase in days with moderate and high fire weather risk. However, the magnitude of the risk depends heavily on the climate dataset used. For instance, HCLIM-AROME simulations generally show higher FWI values in the historical period even when compared to the future projections of HCLIM-ALADIN, due to generally lower summer precipitation in the former model. Additionally, there are notable regional disparities between the HCLIM simulations, with the highest FWI values observed in coastal areas of southern Finland and Sweden. According to the HCLIM-AROME simulations under the RCP8.5 scenario, these regions experience a moderate fire risk (FWI > 11) on roughly one out of three summer days, whereas HCLIM-ALADIN simulations indicate an average of 7–20 days per summer with such risk. There are also differences in the magnitude and regional distribution of FWIs calculated from HCLIM, NEX-GDDP, and CORDEX simulations. However, all future FWI predictions consistently indicate that, without effective mitigation of global warming, conditions for forest fires will worsen in the future.