Elsevier

CATENA

Volume 19, Issues 3–4, June–August 1992, Pages 345-361
CATENA

The effects of fire and water repellency on infiltration and runoff under Mediterranean type forest

https://doi.org/10.1016/0341-8162(92)90008-YGet rights and content

Abstract

An investigation is being made into the relationship between forest fire and hillslope hydrology in the Selva region of Catalonia over a three year period at sites with a known fire history. The major sites are on granite, granodiorite or on sediments derived from these rocks at locations between Santa Christina d'Aro and Santa Coloma de Farnes. It appears that there is a general relationship between the type of organic profile found in a forest and the impact of fire in terms of loss of organic matter, soil erosion hillslope hydrology and on the regeneration of the forest.

This paper summarises the results of about 150 rainfall simulation experiments and presents an overview of work carried out so far. A major conclusion is that runoff processes are discontinuous and spatially structured due mainly to the effects of water repellency.

As a result of surface properties (macropores, hydrophobic behaviour and swelling), four types of infiltration curve can be recognised. At many locations infiltration increases with time during the early part of an experiment, reaches a maximum value after about 30 minutes therupon subsequently decreasing. This type of relationship can not be modelled with standard infiltration equations. Illustrations are given of sections through both burnt and unburnt soils to show how the hydrophobic effect influences water penetration. It can be seen that infiltration patterns are similar for both burnt and unburnt soils and that micropores filled with organic matter are very important in conducting water through a water repellent surface layer. The hydrophobic layer traps water in the BC horizon and prevents evaporation and loss by upwards capillary movement. Although the hydrophobic effects mean that small areas sometimes have a high runoff coefficient, on larger areas there are many macropores and shrubs, beneath which the soil is permeable, and these trap runoff generated on the water repellent areas.

The main effect of fire is to illiminate the storage of water in the organic horizons (several cm). At first infiltration rates remain high but later these decrease as there is a reduction in porosity. The sites having a moder type profile have better water retention properties, more organic matter that survives the fire and a faster rate of vegetation recovery. Sites with a mor type profile can be degraded and erode if they are subject to disturbance.

The study provides another example of how, on seemingly uniform slopes, hydrological processes are structured by interactions with vegetation. The patterns produced by these interactions survive the effects of fire.

References (13)

There are more references available in the full text version of this article.

Cited by (0)

View full text