5:15 PM - 6:45 PM
[HGM03-P13] Sediment discharge and its determinants in the burnt area of wildfire: The case of Osaki Peninsula, Iwate
Keywords:Wildfire, Sediment discharge, Airborne Laser Scanning data
The frequency and magnitude of wildfires are increasing due to changes in climate and land use and are predicted to increase further in the future. Wildfires affect a wide variety of geomorphic, hydrologic, and ecological processes. Fire causes changes in surface conditions such as reduction in plant canopy, increase in soil water repellency, loss of surface cover, and consumption of soil organic matter. These changes affect hydrologic and geomorphologic processes such as increased surface flow and accelerated surface erosion. As a result, wildfires have been shown to increase sediment discharge. Although various factors have been shown to affect sediment discharge after wildfires, there is no quantitative studies that examined factors have a relatively large influence on sediment discharge. Therefore, the purpose of this study was to estimate the amount of sediment discharge after a fire and to clarify the factors that determine the amount of sediment discharge based on field surveys and analysis of ALS (Airborne Laser Scanning) data provided by Geospatial Information Authority of Japan.
This study focused on a wildfire that occurred in 2017 on the Osaki Peninsula, Kamaishi, Iwate. A negative linear correlation between soil thickness and topographic curvature has been observed. We compared soil thickness in the burnt and control areas of similar topographic curvature. We measured soil thickness using a hand auger and topographic curvature using ALS data. Soil thickness in the burnt area was thinner than in the control area, indicating increased sediment discharge due to the fire. Then, the amount of sediment discharge was calculated using Digital Terrain Models created from ALS data for the pre- and post-fire periods. The results indicated 2.82 times increase in sediment discharge per m2 for 3 years after the fire, with 0.08 m in the control area and 0.22 m in the burnt area. To analyze factors that control post-fire sediment discharge, we performed a multiple regression analysis that considered fire severity, logged or unlogged, elevation, slope, topographic curvature, and aspect. Then, we compared standardized partial regression coefficients for each variable to examine that relative importance of the variables. The results showed that fire severity, logged or unlogged, and topographic curvature strongly influenced sediment discharge, particularly in logged areas with higher fire severity. Moreover, the correlation coefficient between the differences in pre- and post-fire geomorphic quantity and post-fire sediment discharge was calculated to detect changes in geomorphic quantity. The results showed a rather strong positive correlation between sediment discharge and the changes in topographic curvature. From the above, we argue that the sediment discharge increased due to changes in surface conditions from higher fire severity and logging. Furthermore, as a result of the increased sediment discharge, it is possible that sediment transport followed topographic curvature and that subduing of the mountains occurred after the fire. Thus, the overall trend of sediment movement after wildfires inferred from the analysis of the ALS data was generally consistent with predictions from diffusion equation-type models.
This study focused on a wildfire that occurred in 2017 on the Osaki Peninsula, Kamaishi, Iwate. A negative linear correlation between soil thickness and topographic curvature has been observed. We compared soil thickness in the burnt and control areas of similar topographic curvature. We measured soil thickness using a hand auger and topographic curvature using ALS data. Soil thickness in the burnt area was thinner than in the control area, indicating increased sediment discharge due to the fire. Then, the amount of sediment discharge was calculated using Digital Terrain Models created from ALS data for the pre- and post-fire periods. The results indicated 2.82 times increase in sediment discharge per m2 for 3 years after the fire, with 0.08 m in the control area and 0.22 m in the burnt area. To analyze factors that control post-fire sediment discharge, we performed a multiple regression analysis that considered fire severity, logged or unlogged, elevation, slope, topographic curvature, and aspect. Then, we compared standardized partial regression coefficients for each variable to examine that relative importance of the variables. The results showed that fire severity, logged or unlogged, and topographic curvature strongly influenced sediment discharge, particularly in logged areas with higher fire severity. Moreover, the correlation coefficient between the differences in pre- and post-fire geomorphic quantity and post-fire sediment discharge was calculated to detect changes in geomorphic quantity. The results showed a rather strong positive correlation between sediment discharge and the changes in topographic curvature. From the above, we argue that the sediment discharge increased due to changes in surface conditions from higher fire severity and logging. Furthermore, as a result of the increased sediment discharge, it is possible that sediment transport followed topographic curvature and that subduing of the mountains occurred after the fire. Thus, the overall trend of sediment movement after wildfires inferred from the analysis of the ALS data was generally consistent with predictions from diffusion equation-type models.