Post-Fire Near-Surface Runoff From Small-Scale Rainfall Simulations, Santa Cruz Mountains

The influence of environmental variables on the runoff response to a fire is poorly understood. Small-scale rainfall simulation was used to study the factors impacting near-surface runoff following the Lockheed Fire, which occurred on August 12, 2009. A variable speed rainfall simulator was used to rain on 15 different test plots at an average rate of 50mmh-1. Variables of burn severity, time following the fire, soil parent material, vegetation type, and presence of a duff layer were all analyzed using the ratio of runoff to rainfall. The difference in-between burned sites and similar control sites were 19±6%. Only sites with a high burn severity had a significantly different runoff than the control sites (p=.027). The sites burned at high severity had runoff to rainfall ratios that decreased an average of 39% between the original simulation three months after the fire and the second simulation ten months later. The knobcone pine and manzanita vegetation grouping, which also corresponded to a mudstone soil parent material, produced both the highest average runoff to rainfall ratios (52%) and had the highest variability after a fire. A confidence interval showed anywhere between -12% and 63% increase in runoff to rainfall ratio of the knobcone pine and manzanita vegetation grouping after a fire compared to 2% to 27% for redwood and Douglas fir dominated vegetation. Very high runoff rates following a fire were correlated to near surface water movement almost exclusively along the top 2 cm of mineral soil. The trends observed within this data should help to support and guide further research on post-fire runoff