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Drought Impacts Post-Wildfire Flooding and Debris Flow Hazard: A sign of the times in the Southwestern U.S.

NOAA’s National Integrated Drought Information System (NIDIS) released a flyer introducing a project that examines the role of drought on post-wildfire flooding and debris flow hazards. The release is particularly timely in that the drought-stricken Southwestern U.S. is ablaze with hundreds of wildfires, some of record size and impact (Figure 1. Inciweb wildfire map 21 Aug 2020).

Inciweb map showing summer 2020 wildfires

This multi-agency team, led by Dr.s Benjamin Hatchett (Desert Research Institute Atmospheric Science) and Luke McGuire (UArizona Geosciences) is investigating how drought influences the post-wildfire environment, especially in the short-term (< 5 years post-fire). Some questions being addressed are:

•    How long after a wildfire are debris-flows likely to form (Figure 2 below)?
•    How ca drought magnify post-fire flooding and debris-flows by impeding vegetation recovery?
•    What  tools are available to assess the influence of drought on post-wildfire geologic hazards?

From McGuire & Hatchett flyer: 'A conceptual diagram of debris-flow likelihood (solid blue line) and vegetation cover (solid green line) following a fire (vertical red dashed line'.

According to Phil Pearthree, Arizona State Geologist and Director of the AZGS, "Arizona and the rest of the Southwest have been experiencing overall drought conditions for the past 20 years. Large and recurring wildfires that are a product of this drought have substantially changed watershed vegetation and runoff potential. Understanding these changes is critical to accurately assessing the potential for flooding and debris flows in the wake of wildfires."

Along the same research avenue, Ann Youberg (AZGS Research Scientist) is collaborating with Luke and his UArizona grad students to monitor the onset of post-wildfire debris flows in southeastern Arizona and western New Mexico. For a brief description of their research, see ‘After a wildfire, how intense does rainfall need to be to cause a debris flow?’.

National Integrated Drought Information System   for a U.S. government source on nationwide drought.