Expected impacts of climate change on live fuel moisture content in Mediterranean shrub species

According to recent projections on future climate, an increase in risk of summer droughts in both Central and Southern Europe is expected. The most pronounced warming is likely to take place in the Mediterranean area in summer when the highest temperatures occur. In addition, annual precipitation and the annual number of rainy days are very likely to decrease in most of the Mediterranean Basin.

More prolonged drought seasons induced by climatic changes are likely to influence general flammability characteristics of fuel, affecting load distribution in vegetation strata, floristic composition, and live and dead fuel ratio. In addition, variations in precipitation and mean temperature could directly affect the fuel water status, and consequently flammability, and length of critical periods of high ignition danger for Mediterranean ecosystems.

Mediterranean shrub species are an important component of both Mediterranean vegetation communities and understorey vegetation. They also constitute the surface fuels primarily responsible for the ignition and the spread of wildland fires in Mediterranean forests. Although fire spread and behaviour are dependent on several factors, the water content of live fuel plays a crucial role in determining wildland fire danger, especially in the Mediterranean shrubland, where live fuel is often the main component of the available fuel which catches fire. Several studies have proved the relation between live fuel moisture content (FMC) and flammability and have verified the relations between live FMC and actual fire occurrence.

Considering the observed climatic variations and foreseen future scenarios, an evaluation of the impact of these variations on fire danger seems essential. Therefore, the main aims of this work are i) to identify useful tools to determine possible impacts of expected climate change on fuel status in Mediterranean shrublands, and ii) to predict the potential impacts of climate change on the length of fire danger season due to live fuel status.

The study was carried out in Sardinia (Italy). Moisture content of live fuel was determined periodically during five years on four shrub species (Cistus monspeliensis L., Juniperus phoenicea L, Pistacia lentiscus L., and Rosmarinus officinalis L.). Meteorological variables were also recorded. Data sets were used to determine the accuracy of meteorological drought codes in estimating live fuel moisture patterns in Mediterranean areas. Threshold values of codes for estimating the starting and ending dates of high ignition danger periods were estimated by percentile and logistic analysis. Finally, a methodology to identify the length of critical periods of high ignitability risk in maquis ecosystems was proposed.

Potential climate change impact on length of ignition danger season in Mediterranean Basin shrublands was determined using the meteorological code values and future climate scenarios at a local scale derived from an advanced high resolution Regional Climate Model. Starting and ending dates of danger season were calculated for the period May-October using data from the Regional Climate Model (1961 - 1990: baseline; 2071 – 2100 A1B scenario). Changes in length of fire danger season due to live fuel water content were finally analysed.

Results suggest that future climate projections could determine changes in fuel moisture dynamics and affect the duration of the danger fire season causing a delay in the ending dates of high ignition danger periods.