Comparison of Evapotranspiration Following Fire in a Primary Amazonian Forest Based on MOD16 Data

Forest fires are ocurring in great number throughout the Amazon region, affecting the natural cycle of vegetation and ecosystem structure. They also can cause changes in the local and regional climate, and specifically in the surface energy flux patterns. The effects of fire on forest water cycling are not well understood, especially due to the difficulty of obtaining surface flux measurements in fire-affected areas with high temporal and spatial resolution. The present study aimed to evaluate, based on MODIS global evapotranspiration data (MOD16), the temporal behaviour of evapotranspiration in a primary Amazonian forest area affected by fire on September 12th, 2010 in the municipality of Cumaru do Norte, state of Para, Brazil. The forest area was mapped using a TM/Landsat 5 image acquired during the time of fire burning. The analysis of MOD16 data from the month before and from a month after the fire indicated a 27% decrease in evapotranspiration. The average value of evapotranspiration for the 3 years pre-fire was 1436.0 mm yr-1. After the significant decrease was verified immediately post-fire, evapotranspiration values increased at an average annual rate of 20%. The highest increase rate (58%) was verified one year after the fire. The average value of evapotranspiration 3 years post-fire was 1382.6 mm yr-1, which is quite close to that average value verified prior to burning. Therefore we conclude that 3 years was enough time for this forest area to recover its original state in terms of water vapor fluxes. Regarding this result, it is important to note that a high severity fire can alter the canopy characteristcs more strongly than a low severity fire, which means that distinct disturbance regimes will affect the evapotranspiration fluxes after the fire in forested areas quite differently.