Quantifying relations between surface runoff and aridity after wildfire: Relations between surface runoff and aridity after wildfire

Post-wildfire runoff and erosion are major concerns in fire-prone landscapes around the world, but these hydro-geomorphic responses have been found to be highly variable and difficult to predict. Some variations have been observed to be associated with landscape aridity, which in turn can influence soil hydraulic properties. However, to date there has been no attempt to systematically evaluate the apparent relations between aridity and post-wildfire runoff. In this study, five sites in a wildfire burnt area were instrumented with rainfall-runoff plots across an aridity index (AI) gradient. Surface runoff and effective rainfall were measured over 10 months to allow investigation of short- (peak runoff) and longer-term (runoff ratio) runoff characteristics over the recovery period. The results show a systematic and strong relation between aridity and post-wildfire runoff. The average runoff ratio at the driest AI site (33.6%) was two orders of magnitude higher than at the wettest AI site (0.3%). Peak runoff also increased with AI, with up to a thousand-fold difference observed during one event between the driest and wettest sites. The relation between AI, peak 15-min runoff (Q15) and peak 15-min rainfall intensity (I15) (both in mm h-1) could be quantified by the equation: Q15 = 0.1086I15 × AI 2.691 (0.65

Keywords:

• Hydrology
• Geology
• Surface runoff
• Erosion
• Debris flow
• Arid
• macropore flow
• Hydraulic conductivity

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