The collapse of the 2015-16 El Niño, one of the strongest ever recorded, has left many residents of the Golden State similarly deflated. Despite forecasts and hopes of an alleviation of California’s multi-year drought by abundant precipitation from El Niño-driven winter storms, much of the state remains stuck in the “Exceptional” category. With a drier, warmer La Niña pattern in the forecast heading into the fall and winter, not only are agricultural interests preparing for another handicapped harvest season, but a more sensational and urgent threat associated with persistent drought has unfortunately made recent international headlines – massive, devastating wildfires.
The recent fire that forced the total evacuation of Fort McMurray, Alberta, a city of more than 90,000 people, was at one point burning more than 1.246 million acres, an area about the same size as the state of Delaware. It destroyed 2,400 structures and is expected to become the costliest natural disaster in Canadian history. This weeks-long wildfire was blamed in part on an unusually dry winter and spring tied to the strong El Niño. A similar pattern associated with the record El Niño of 1997-98 caused anomalous wildfires in Indonesia, Russia, South America, and Central America. If the frequency and intensity of El Niño episodes continue to increase, a correlated uptick in drought and wildfires may also be expected.
The fire risk preceding the Fort McMurray fire across most of Alberta and neighboring Saskatchewan was judged by Environment Canada to be category five, “Extreme”, the highest of a five-level index factoring in how easy it is to ignite vegetative fuel, how difficult it might be to control a fire, and what would be the potential damage cause by a wildfire. Meteorologists at NOAA’s Storm Prediction Center likewise look for these ingredients to forecast a wildfire threat in the U.S.:
- Dry air mass (low relative humidity)
- Warm or hot air mass (greater potential for ignition)
- Strong winds (to push the fire out of control)
- Dry burning medium (low moisture content of ground vegetation)
Forecasting for these factors can be very complicated. Highly localized wind phenomena such as the Santa Ana winds in the Southwest can rapidly increase winds while lowering humidity values and raising temperatures. The mid to late summer also heralds the development of the Southwestern monsoon and the increasing risk of “dry” thunderstorms that develop relatively high up in the atmosphere over arid regions with precipitation that evaporates before it reaches the ground. Despite this lack of surface precipitation, these storms still produce cloud-to-ground lightning and high winds, bolstering the wildfire environment.
The outlook for the next few months calls for near to below normal precipitation and widespread above normal temperatures in the West, typical of a mild La Niña. As of Sunday afternoon there are eight large fires burning through parts of California, including the Erskine fire that has claimed nearly 37,000 acres, at least 150 homes, and two lives. The increasing occurence of dry thunderstorms in the new few months will provide more opportunities to spark wildfires. However, it’s important to realize that 90% of wildfires are caused by human agency – only 10% can be attributed to natural causes like lightning or volcanic lava flows. People who live in or are traveling through regions of high fire danger have to be hyperaware of the potential consequences of every carelessly discarded cigarette butt, unattended campfire, and improperly handled debris burn, heeding authorities when burn bans are in effect.