The last couple weeks have brought rain to the majority of California, but unfortunately, most of the state remains in a rainfall deficit. With the exception of the San Diego area, which is above normal, the rest of the state gets progressively drier as you move north.
Reservoirs are Full but Northern California is Still in a Deficit
The state’s largest reservoirs are located across Northern California and the Sierra Nevada Mountain range. These reservoirs are currently at or above historical averages for this time of the year, but the snow pack that feeds these stockpiles are measuring just over half of their normal levels for the season. Across the rest of the state the story is similar. San Francisco, for example, has only received about 50% of the normal rainfall for the year. April precipitation is not expected to alleviate this deficit, with most forecasts predicting a dryer than normal month. This does not bode well for some of the dryer portions of the state trying to catch up. Many areas need triple digit increases in the average rain totals to make up for the shortfall. San Jose tops this list, requiring an almost 500% increase in rainfall before the end of June, just to breakeven.
What Does This Mean for Wildfire Season?
The recent rains may help to stave off an early start to the 2020 wildfire season but may actually fuel wildfires moving forward. In areas that have experienced prolonged drought conditions, rains often lead to an explosive growth of new vegetation. Much of this vegetation growth is in the form of native and non-native grasses. Moist fuels are an ideal fire retardant, but these grasses are very susceptible to drying out after just a short period of low humidity and high temperatures.
The March storms failed to break California’s drought so the fuel moisture of this vegetation is going to be a concern as temperatures begin to rise across the state. Once dried, these “fine fuels” are easy to ignite. Something as small as an errant cigarette butt is a sufficient catalyst to spark a wildfire. When active, these wildfires can move rapidly and are prone to “spotting”. Spotting occurs when embers are blown to nearby fuels and cause multiple ignitions, making the wildfire difficult to contain.