Influence of wildland fire on surface runoff from a hillslope

Abstract

Surface runoff from three adjacent hillslope plots, unbumt or subjected to light or moderate prescribed burns, was monitored over a four-year period. Al1 plots initially bore Ulex scmb. In the fust year, runoff from the unburnt plot was about 3.5% of rainfail, while that from the bumt plots was between 5.2 and 6.6% of rainfail. Runoff from the burnt plots graduaily dropped over the study penod, and we estimate that preburn values are reattained within four to five years (corresponding to the time required for re-establishment of the vegetation cover). The water repellency of the soil was not appreciably increased by either light or moderate bums, indicating that wildfire-induced increases in runoff in this region are due largely to reduced interception as a result of the destruction of vegetation. Finaily, although buming caused clear relative increases in mnoff, the absolute increases were small (2 - 3% of rainfall), suggesting that wildfire-induced increases in runoff are unlikely to have major effects on the flow regimes of receiving nvers. The estimated postfire increases in infiltration, on the other hand, were much more marked, and it is possible that wildfire-induced increases in subsurface flow have important effects on watershed hydrology.