Causes and consequences of fire‐induced soil water repellency

Abstract

Abstract:A wettable surface layer overlying a water-repellent layer is commonly observed following a fire on a watershed. High surface temperatures 'burn' off organic materials and create vapours that move downward in response to a temperature gradient and then condense on soil particles causing them to become water repellent. Water-repellent soils have a positive water entry pressure h p that must be exceeded or all the water will runoff. Water ponding depths h o that exceeds h p will cause infiltration, but the profile is not completely wetted. Infiltration rate and soil wetting increase as the value of h o /h p increases. The consequence is very high runoff, which also contributes to high erosion on fire-induced water-repellent soils during rain storms. Grass establishment is impaired by seeds being eroded and lack of soil water for seeds that do remain and germinate. Extrapolation of these general findings to catchment or watershed scales is difficult because of the very high temporal and spatial variabilities that occur in the field.

The effects of bushfires on hydrological processes using a paired-catchment analysis

“…The classic method of exploring fire effects on hydrological processes is to perform laboratory experiments (Aston and Gill, 1976) and field experiments on runoff (Dobrowoski et al, 1992;Robichaud and Waldrop, 1994;Cerda et al, 1995;Keller et al, 1997;Nelson et al, 1999;Morales et al, 2000;Murakami et al, 2000;Robichaud, 2000;Benavides-Solorio and MacDonald, 2001;Veenhuid, 2001) and fire-induced soil water repellency (DeBano, 2000;Scott, 2000;Letey, 2001) with rainfall simulators. However, pairedcatchment analysis becomes more appropriate when the research scale is extended from small plots to catchment scale.…”

Promoting seedling physiological performance and early establishment in degraded Mediterranean-type ecosystems

“…In deep, sandy, and hydrophobic soils such as those found in sandy plains of southwestern Australia (Roberts and Carbon 1972), soil moisture tends to occur in uneven patterns within the soil profile (Doerr et al 2000;Letey 2001). However, surfactants or wetting agents can enhance infiltration and improve water availability in hydrophobic soils (Madsen et al 2012b).…”

An Architecture for Adaptive Robust Modelling of Wildfire Behaviour under Deep Uncertainty

“…Soil hydrophobicity together with the reduced ground cover has been postulated as one of the main causes of soil erosion (SE) and runoff increasing in after-burn areas [73,74]. The reduced ground cover is also responsible of a reduced root strength affecting the soil cohesion and of a reduced leaf area evapotranspiration affecting the soil water level [74].…”