The impacts of post-wildfire on streamflow and sediment dynamic in Mae Chaem River Basin

Prangtip Triritthiwittaya*, Chaiwat Ekkawatpanit*, Duangrudee Kositgittiwong and Amnat Chidthaisong

<p style="text-align:justify;"><strong>Abstract: </strong>The Mae Chaem River Basin experienced frequent wildfires, particularly during the dry season (January to April), with the
majority occurring in reserved forest areas. These wildfires' impact is generally classified by severity, disrupted vegetation, soil
properties, and hydrological regimes. This study aims to evaluate streamflow and sediment dynamics changes from 2014 to 2018
using the Soil and Water Assessment Tool (SWAT), comparing pre-fire and post-fire scenarios. The results from the Difference
Normalized Burn Ratio (dNBR) showed that low severity burn areas, comprising 20-67% of the total burned area, led to an
escalation of peak discharge and sediment flow during the rainy season (May to September). The study found that the total runoff
increased by 3% after the fire, which indicates a potential for more severe flooding. The average annual baseflow increased at the
basin scale but fluctuated at the subbasin scale. The influence of wildfires on sediment transport exhibited a heightened magnitude
compared to water yield. The sediment outflow from the watershed increased by approximately 15% based on the post-fire model.
This increase was found to be related to precipitation intensity and the proportion of the burned area. Furthermore, sediment
degradation and deposition were found to shift towards subbasins, with 25% of burned areas becoming more susceptible to
combustion.
</p><p><strong>Keywords:</strong> Burned area, sediment dynamic, streamflow, SWAT, wildfire.</p>