Submitted to: American Meteorological Society
Publication Type: Proceedings
Publication Acceptance Date: 10/20/2003
Publication Date: 11/20/2003
Citation: Paige, G.B., Stone, J.J., Guertin, D.P., Mcgee, R., Blumenfeld, H. 2003. Second International Wildland Fire Ecology and Fire Management Congress: Fifth Symposium on Fire and Forest Meteorology: [CD-ROM]. American Meteorology Society: The Conference Exchange. Interpretive Summary: The amounts and rates of runoff and erosion after a wildfire on semi-arid grasslands is largely unknown. Experiments are being conducted on two grassland soil vegetation complexes on the Audubon Research Ranch and the Walnut Gulch Experimental Watershed, both in southeastern Arizona, to quantify the increase in runoff and erosion after a fire and how long it takes for recovery to pre-fire conditions. Results show that immediately after the fire, runoff increased from 5 to 74% while sediment yield increased from about 400 to 2200%. Contributing to the increases were a lack of canopy cover and less ground cover, primarily litter, on the burned sites compared to unburned conditions. For the year after the fire, there was a slight increase in the amount of runoff, but a decrease in the amount of sediment yield. Although canopy cover had increased at the burned sites, it was still about 3 to 4 times lower than unburned conditions.
Technical Abstract: Rainfall simulator experiments were conducted on two semi-arid grassland Ecological Sites (ES) in June 2002 immediately following the Ryan Fire and one year later to measure and quantify post wildfire peak runoff and erosion rates. Rainfall simulator experiments were conducted at the two ESs, Loamy Upland and Limey Slopes, at two different soil moisture conditions (initial and wet) using a range of rainfall intensities between 50 and 180 mm/h. Runoff and erosion rates were measured for each rainfall intensity. The plot characteristics including surface cover, basal gap intercept and microtopography were also measured at both sites. The measured hydrologic and erosion responses from the two years of simulations on the burned sites are compared with each other and with results from similar unburned ESs. The results from the rainfall simulator experiments immediately following the Ryan fire showed an increase in the runoff ratio (runoff/rainfall) from 5 to 74% and in the sediment yield ratio (sediment yield/runoff/slope) from 399 to 2230% for the Limey Slopes and Loamy Upland ESs, respectively. The results from 2002 and 2003 showed a decrease in sediment yield, however, there was an increase in the runoff. These results indicate that there may be a decrease in the productivity of the site or a longer recovery rate than anticipated.