Analysis of Observed Rainfall and Flooding near the Schultz Fire Scar from 2010-2013: Trends and Implications for Hydrologic Warnings and Decision Support

Four years of precipitation and property impact data have been utilized to document the change in the hydrologic response of the Schultz fire scar from 2010 to 2013. The Schultz fire burned approximately 61 km² of forested land on the east slopes of the San Francisco Peaks north of Flagstaff, Arizona from 20-30 June 2010. Flood waters flowing off the fire scar have caused significant impacts and damage to homes and property in the residential areas downstream of the fire over the past four years. A network of rain gauges was installed in and around the Schultz fire scar, and data collected over the past four convective seasons (July – September) have been available to forecasters at the Flagstaff National Weather Service (NWS) forecast office in near-real-time to support warning operations. Observed rainfall from this gauge network, as well as reports of flooding in residential neighborhoods gathered from multiple sources, have been analyzed for each of the last four convective seasons to associate observed rainfall amounts with the hydrologic response.

The hydrologic response of the Schultz fire scar has evolved considerably with time. Given the rapidly changing impact potential, providing useful decision support to people affected by flooding from the Schultz fire scar has been a challenge for forecasters. The first heavy rainfalls over the Schultz scar in 2010 produced destructive flooding, with numerous homes and roads damaged by debris flows. Progressively less damage occurred in 2011 and 2012. In 2012, flood mitigation efforts (levees and channels for carrying water through downstream neighborhoods) commenced. In 2013, one of the wettest convective seasons on record impacted northern Arizona. More than 50 cm of rain fell over portions of the Schultz fire scar. Very heavy rainfall events occurred both over and around the Schultz scar in 2013, providing a good base to compare burn and non-burn responses, and those parts of the impact area which saw some flood mitigation.

The evolution of the flood response on the Schultz fire scar will be detailed in this presentation. Evolution of decision support services will also be addressed, including the challenges in providing forecast support for an area undergoing rapid changes in impacts.