Runoff and erosion processes after a forest fire in Mount Carmel, a Mediterranean area

Abstract

In the Mediterranean forest area of Israel, fires increase runoff and sediment yield rates relative to undisturbed forested land. The September 1989 fire covered an area of 4 km 2 in the main recreation area of Mount Carmel, a typical Mediterranean forest area. The lithology is chalk and limestone, and about 40% of the burnt area has steep slopes, exceeding 30%. Three study plots were established in burnt and unburnt areas. Plots were located on 100–300 m 2 areas with different slope exposures. Runoff and sediments were collected after each storm by a collector system. A hydrometric station was established, draining an area of 1 km 2 in the burnt zone. Rainfall was measured by two recorders and several rain gauges at the experimental sites. In the first rainfall season after the fire, runoff and sediment yield were 500 and 100,000 times higher respectively in the burnt areas. Rainfall intensity is a dominant factor in runoff and sediment yield rates. In the measured basin, total runoff in the first year was 1.6%. Revegetation recovery of the area was rapid, as shown by the results from the second season: runoff decreased by one order of magnitude, from an average of 10 mm to 1.5 mm; sediment yield decreased by two orders of magnitude, from 1200 g m −2 to 10 g m −2. The third season 1991/1992, was an exceptionally rainy year and therefore runoff and sediment yield increased, but to less than in the first year. Runoff and sediment yield are related to vegetation cover, rainfall intensity, soil properties, slope steepness and exposure and fire intensity. Logging activities after fire increase sediment yields. Through its effects on vegetation cover and soil, fire severity increases the potential for erosion.