Dryness in a Mediterranean-type climate - implications for wildfire burnt area: a case study from Mount Carmel, Israel

摘要

Wildfires are an integral component of Mediterranean ecosystems, in which the occurrence of fire has markedly increased since the 1970s, due to anthropogenic stresses and climate change. Although fires are often associated with both factors, the relationship is not straightforward; however, dryness plays a key role in fire behaviour. Commonly, dryness is calculated by analysing the intervals between rainstorms - termed dry spells. The number of dry days since last rain (DDSLR) represents an innovative approach in which various aspects such as severity, consistency and temporal uncertainty of dryness are monitored. DDSLR at the University of Haifa meteorological station was calculated at two different daily rainfall thresholds (DRT=1.0 and 5.0mm) in 1976-2013 and correlated with large wildfires (>100ha). The severity, consistency and temporal uncertainty of dryness are presented for both thresholds and for the entire year, rainy season and winter. The results show that dry periods longer than 60 days occur every year, and a dry period of at least 150 days occurs twice in 3 years. Large fires occur during long dry periods. DDSLR trend analysis indicates an elongation of the dry period at an average rate of 1 day per year. Therefore, larger areas affected by wildfires might be anticipated.