Changing Fire Weather in Colorado: A Contrast Between Observational Data and Reanalysis Data

Recent wildfires raise the question of whether rising global temperatures have caused an increase in fire weather in Colorado, affecting how electrical utilities plan for fire weather occurrences. We use two datasets to address the question: “How has the occurrence of fire weather changed in Colorado?” Using 21 years of observed weather conditions from a meteorological tower at the National Renewable Energy Laboratory (NREL) and 83 years of ERA5 reanalysis data, we assess changing trends in Colorado fire weather. The observational data is limited in temporal extent, but it captures the exact real-world conditions at its location in complex terrain. The reanalysis data is available for an extended period of time and for the entire state, but its data is of relatively coarse spatial resolution and likely fails to capture extremes.

To quantify fire risk, we calculate the hot-dry-windy index (HDWI) which relies on winds and vapor pressure deficit. No statistically significant trend in the Hot-Dry-Windy index (HDWI) appears in the observational dataset. However, according to the reanalysis data, strong increasing trends emerge in HDWI values across all of Colorado. This apparent conflict between observational and reanalysis data suggests that reanalysis data may not be representative and more long-term observational datasets are required to assess fire risk and the resulting impact on utility operations.