As I shared in a previous post, Vapor Pressure Deficit (VPD) is an index that translates into plant stress.  The darker the color in these images, the more stressed the dry environment is putting on vegetation.  The more stressed, the more potential to burn.  While these levels vary from day to day, overall VPD levels have been on the rise in recent years.

Utilizing VPD to better characterize the fire environment is new to many of us. It describes fuel conditions in ways similar to fuel moisture and ERCs. Because it is an absolute value, it will better reflect the impacts from climate change. I am updating this again fairly regularly during August and September 2023 to help build reference points and improve an understanding of trends relative to this metric and the fire behavior we see.

Vapor Pressure Deficit Labor Day 2020
Vapor Pressure Deficit values from 5pm PDT on 9/7/2020, Labor Day of that year, compared to the same time for 8/26/2023. The darker the color, the higher the VPD value, which means more stressed vegetation.

*Map times are UTC, 7 hrs ahead of Pacific Time in the US. These maps are showing 5pm on the date prior to the image heading.