Influence of Time‐Averaging of Climate Data on Estimates of Atmospheric Vapor Pressure Deficit and Inferred Relationships With Wildfire Area in the Western United States

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Abstract Vapor pressure deficit (VPD) is a driver of evaporative demand and correlates strongly with wildfire extent in the western United States (WUS). Vapor pressure deficit is the difference between saturation vapor pressure ( e s ) and actual vapor pressure ( e a ). Because e s increases nonlinearly with temperature, calculations of time‐averaged VPD vary depending on the frequency of temperature measurements and how e a is calculated, potentially limiting our understanding of fire‐climate relationships. We calculate eight versions of monthly VPD across the WUS and assess their differences. Monthly VPDs calculated from daily data are 2%–6% higher, and more accurate, than when calculated from monthly data. Using daily maximum and minimum temperature, instead of mean, increases VPD by ∼20%, but can overestimate true values depending on how e a is calculated. These differences do not meaningfully impact correlations with annual wildfire area, however, suggesting our understanding of historical fire‐VPD relations is not very sensitive to how VPD is calculated.

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