Evaluation of Near Real-Time IMERG Precipitation Estimates for Fire Weather Applications in Alaska

Large wildfire outbreaks in Alaska are common from June to August. The Canadian Forest Fire Danger Rating System (CFFDRS) is used operationally by Alaskan fire managers to produce statewide fire weather outlooks and forecast guidance near active wildfires. The CFFDRS estimates of fire potential and behavior rely heavily on meteorological observations (precipitation, temperature, wind speed, and relative humidity) from the relatively small number of in-situ stations across Alaska with precipitation being the most critical parameter.

To improve the spatial coverage of precipitation estimates across Alaska for fire weather applications, a multi-satellite precipitation algorithm was evaluated during six fire seasons (1 June – 31 August 2014-2019). Near real-time daily precipitation estimates from the Integrated Multi-Satellite Retrievals for the Global Precipitation Mission (IMERG) algorithm were verified using 322 in-situ stations across four Alaskan regions. For each region, empirical cumulative distributions of daily precipitation were obtained from stations observations during each summer, and compared to corresponding distributions of interpolated values from IMERG grid points (0.1^o x 0.1^o). The cumulative distributions obtained from IMERG exhibited wet biases relative to the observed distributions for all regions, precipitation amount ranges, and summers. A bias correction approach using regional quantile mapping was developed to mitigate for the IMERG wet bias. The bias-adjusted IMERG daily precipitation estimates were then evaluated and found to produce improved gridded IMERG precipitation estimates. This approach may help to improve situational awareness of wildfire potential across Alaska’s expansive and varying terrain, as well as be appropriate for other high-latitude regions where there are sufficient in-situ precipitation observations to correct IMERG precipitation estimates.