Measuring changes in water availability after fire with satellite data

Photo Credit

Forest Service photo

After fire, trees use less water, leaving more to flow downstream, for a while. (Decker Creek near Atlanta Idaho after the 2000 Trail Creek Fire)

After wildfires, forests use less water, and the amount of water flowing downstream from them increases. Measuring this change has been challenging, and even opportunistic measurements using existing stream gauges have proven relatively uncertain. Careful use of satellite-based evapotranspiration estimates, however, are proving more reliable, informative, and precise than traditional paired watershed analyses.

This approach provides the most reliable method to measure changes in water yield after wildfire, and it is much less expensive than traditional stream gauge based approaches, as it does not require pre-building a dense stream gauge network in hopes of capturing a fire and a nearby area that is undisturbed before and after a fire for a period of years.

This is a subject for which model estimates have been published, and here researchers have had the capacity to measure results objectively and with known and reasonable uncertainty for the first time.

This is the first application of a robust method to calculate water yield change from satellite data. Previous methods have not used controls, just the raw satellite-based estimates, which are known to be both biased and uncertain. By providing methods for determining control units and summarizing estimates across multiple controls, Forest Service researchers offer a rigorous and precise method for determining post-fire - or other disturbance - water yield changes.