Ironshore’s recent executive seminar for broker partners in California featured a discussion by meteorologist Jan Null. Null has been a meteorologist for over 45 years, 24 of those as a lead forecaster at the National Weather Service. He is a Certified Consulting Meteorologist with extensive experience as an expert witness and in preparing meteorological and climate data for litigation, insurance and research specializing in fire weather forecasting and forensic meteorology. He is also a Lecturer and Adjunct Professor of Meteorology, Department of Meteorology and Climate Science, San Jose State University. Below is an overview of Null's discussion.
Understanding Fire Weather forecasting requires knowledge of weather, climate and the factors that cause and sustain wildland fires. Climate is weather history telling you what you can expect vs weather which is what you actually get.
What sparks Wildland Fires?
There are 2 major causes of fires. Lighting and People.
- Lightning - caused fires that burned over 31% of acres burned from 2008-2018.
People create conditions in addition to urbanization and deforestation that spark fires. Major causes include:
- Power lines
- Controlled burns that get out of control
CA fire season
Because of the variety of factors that create wildland fires, wet or dry conditions leading up to the local fire season can result in fires:
- A wet season creates more growth, so there is more fuel to sustain a fire
- A dry season dries out the existing fuel, so it burns quickly and more easily.
Fire Hazard Zones
Californians can find fire hazard severity zone information using these maps issued by Cal Fire.
The current maps show the probability of wildfire in a given area by assessing vegetation, fire history and topography, since steeper slopes have higher fire risk. The hazard is ranked in three categories: moderate, high and very high. There are also two other categories: "non-wildland, non-urban" and "urban unzoned."
Red Flag Warnings
Red Flag Warning decision trees take into consideration the major factors that cause a fire.
- Are fuel conditions critical?
- Drought conditions are considered
- Fuel moisture levels are estimated
- What is the relative humidity?
- For every 20% increase in air temperature, relative humidity drops by 50%
- Is there lightning activity?
- Dry lightning vs accompanied by rain
- What are the wind conditions?
- Sustained or gust of wind
- Wind speed
- Predicted duration of wind conditions
Local fire meteorologists issue Fire Weather Watches and Red Flag Warnings based on local criteria and seasonality. If all criteria for a red flag warning are not met, local agencies may issue a Fire Watch for 48-72 hours.
Fires and Flooding
Before a fire there is a lot of natural litter on the forest floor. As that burns, resins and other compounds coat the soil creating a water repellant surface similar to a parking lot. After the fire, this water repellant soil is also covered with ash and burnt topsoil. Subsequent heavy rains cannot be absorbed by the ground and create massive debris flows. In steep mountain areas this increased runoff causes heavy erosion.
This occurred with devastating effect in Montecito, CA after a heavy 15-30 minute storm dropped <1 inch of rain. The resulting debris flow destroyed or damaged 435 homes and 23 businesses and 23 people were killed or missing.
From Jan Null’s presentation
Wildland Fires and Climate change
Over the past 30 years as global average temperatures have risen, forests are drier for longer periods of time, seasonal snow melts occur earlier, and the fire season has extended from 5 months to 7 months.
Scientists project a 1-degree Celsius increase in Global average temperature which will result in an increase in acres burned anywhere from 73% to 656% in areas of the western US.
From Jan Null’s presentation
From January 1 to October 4, 2019 there were 41,074 wildfires compared with 47,853 wildfires in the same period in 2018, according to the National Interagency Fire Center. About 4.4 million acres were burned in the 2019 period, compared with 7.7 million acres in 2018.
Losses from wildfires added up to $5.1 billion over the past 10 years.
(1) Adjusted for inflation by Munich Re based on the Consumer Price Index.
Source: © 2019 Munich Re, NatCatSERVICE.
Understanding the conditions that lead to catastrophic wildfires and how they spread provide a key context to developing resiliency plans to protect your home and business as well as ensuring financial protection by having adequate insurance.