In 2015, the world experienced the strongest El Niño year on record, and forest fires tore through homes, businesses and lives in many parts of the world – one of which was California. That year 150,000 acres burned in the state, costing over USD $1 billion in insurance claims. This past year, 2017, the numbers were even worse and an inglorious new record was set. According to the most recent estimates, which are still coming in, 8400 buildings were destroyed in Northern California’s wine country alone, a total of 1,381,000 acres were burned statewide, and some estimates suggest that the total cost of the fires will be about $180 billion USD, or 8 percent of the states’ GDP.
These fires also often occur in or near areas with high population densities, devastating hundreds of thousands of lives through their effects. These effects include loss of life from smoke inhalation, razed homes, shuttered businesses, closed schools, disrupted local economies, and millions of dollars of lost property. And, in a sort of negative feedback loop, these fires also reduce the ability of forests to sequester carbon. Large, high severity fires kill hundreds of thousands of acres of trees that would normally take carbon out of the atmosphere, acting as carbon sinks and natural filters for pollution. High intensity fires can also impact vital soil components, such as mycorrhizae, seedbeds and nutrient-rich humus layers, as well as reduce the water holding capacity of soils. Forest fires therefore worsen the degree to which our climate is changing, in more ways than one.
The ecosystems of California have experienced lightning- and human-caused wildfires for millennia. Prior to 1800, it is estimated that an average of 4,400,000 acres of California would burn per year; many of those fires burned over days to months during the summer and fall. Western dry forests are by nature dependent upon fire; before Europeans settled in or near these forests, fires burned naturally on a multi-annual cycle, keeping fuel loads low, restricting the bulk of wildfires to smaller areas and heat levels, and protecting the older trees and overall forest resilience. But, since the beginning of the 20th century, fire has been excluded from many ecosystems because forest managers were actively suppressing it. Earlier in the 20th century, we thought this was the best way to save lives and property. However, science is now showing us that this practice has now resulted in excess fuel – meaning that there are now intense wildfires in many areas that formerly experienced frequent, but low-severity, fires.
In California, SIG was recently working on this challenge in partnership with CALFIRE and the Desert Research Institute (DRI). Together they have developed an updated map of California’s wildfire risk distributions for the California Public Utilities Commission. The SIG team used a weather forecasting model to produce 10 years of weather data for all of California, which was overlaid on a gridded map and calibrated with local historical weather readings from around the state. Using this enormous dataset, the researchers then ran models of over 100 million possible fire ignitions and statistically estimated where the top two percent of the worst fire weather conditions would be. With this info they developed two-kilometer resolution maps showing the areas of greatest fire risk across the state, helping them predict and direct future fire risk mitigation efforts towards where they are most needed.