PAST: Rising Temperatures, Decreasing Precipitation, and Wildfires in Los Angeles County

2/16/2020

Average annual temperatures in Los Angeles County from 1895 to 2020. Source: NOAA Climate at a Glance.

Climate changes and the local environment:

Within the past century, the average temperature in Los Angeles County has increased by 3˚C. The number of days with a maximum temperature above 90˚ F has increased steadily over the past 20 years and is projected to continue rising. In addition to warmer average temperatures, Los Angeles County has experienced a decrease in precipitation during the fall and winter seasons. Increasing temperatures and decreasing levels of precipitation have increased the County’s risk for more severe droughts, as well as wildfires.

Average precipitation during the months of October to April in Los Angeles County from 1895 to 2020. Source: NOAA Climate at a Glance.

Los Angeles County receives the majority of its annual rainfall during the late fall through early spring, then experiences a dry season during the summer months. The amount of winter season precipitation Los Angeles experiences has decreased over the past century, and this decline is predicted to continue. This reduction in rainfall means that there is less moisture in the soil at the beginning of the summer, which is the County’s dry season. The water evaporates from the soil and plants during the summer, and less winter precipitation ultimately leaves the vegetation drier earlier in the year.

Drought severity in Los Angeles County from 2000 to 2020. Darker colors represent more severe droughts. Source: United States Drought Monitor.

In addition to lower levels of rainfall, rising temperatures are reinforcing dryer and hotter summers in Los Angeles County. Higher annual temperatures lead to earlier snowpack melting, meaning that the winter season is shorter, there is less moisture in the soil during the dry season, and that the dry season is even longer. Warming temperatures also speed up evaporation, thus drying out the soil and parching the trees and vegetation.

Drier and hotter summers have increased Los Angeles County’s drought risk, and by 2050 California’s risk of summertime drought is expected to almost triple. California’s dry and hot summers have always made the state more vulnerable to wildfires; however, rising temperatures and lower levels of precipitation have made the fire seasons longer and more severe. Los Angeles County’s fire season has already lengthened by approximately 75 days, and will likely increase in the future as well.

With a longer and wetter winter season, Los Angeles County’s vegetation would soak up moisture which could help prevent summertime wildfires. This moisture dried out slowly through the summer season until it could be replenished the following fall. However, because the summer season has grown longer and hotter, and fall and winter rainfalls have decreased, flammable tinder has accumulated to high levels. Moreover, fire suppression over the last several decades has only added to the dangerous levels of tinder that has been available, and will continue to be available, to burn.

How we know:

These reconstructions are based on two easy to use tools that are freely accessible online: the National Oceanic and Atmospheric Administration (NOAA) Climate at a Glance tool and National Drought Mitigation Center's United States Drought Monitor.

NOAA's Climate at a Glance tool uses data collected at weather stations and stored in NOAA's U.S. Climate Divisions database. This data is used to generate graphs about temperature, precipitation, and droughts, with the ability to look at global, national, and local averages.

The Drought Monitor produces maps of drought conditions across the United States and publishes them weekly. The tool combines climate, soil, and water data with reports from 350 experts across the country. This generates an assessment of current drought conditions nationally, with the ability to look at data for individual states or counties.

Human consequences:

Warmer average temperatures, dryer seasons, and changing seasonal time frames have increased the number of wildfires in Los Angeles County, as well as in the intensity of the flames. Of the 20 largest fires to ever occur in California, two of them occurred in the last 10 years in Los Angeles County: the Thomas Fire in 2017 and the Station Fire in 2009. Over the past 50 years, summertime forest fires in the state have increased in size by approximately 800%, and 11.2 million residents in California currently live in areas with elevated risk for wildfires.

Residents of Los Angeles County have already experienced the severe impacts of these wildfires. Wildfires release toxic smoke into the air, leaving dangerous air quality conditions, ash, and debris in their wake. Additionally, as wildfires rapidly spread, citizens can be forced to evacuate and in the worst situations, can lose their properties and homes to the fires. In 2018, the worst year of California wildfires on record, fires destroyed over 24,000 homes and buildings in the state.

This increased risk of fire damage to residents’ homes has increased economic inequality in Los Angeles County, as wealth significantly enhances one’s possible response to wildfires. As early as 2005, wealthy individuals have been able to sign up for Private Fire Protection Services, typically at a high cost. While most individuals affected by fires were forced to flee their homes, wealthy individuals were able to wait out wildfires in luxury hotels while private firefighters worked to defend their properties from impending flames.

This disparity was evident during the most recent Thomas Fire in 2017, when farm-owners left their properties to seek safety and returned to find their crops — and ultimately their livelihoods — destroyed. At the same time, many wealthy celebrities returned to their mansions on the beach, next-door to the farmers, with their properties untouched by the flames.

Some climate activists have begun to refer to this emerging phenomenon as an impending “disaster apartheid.” As climate change continues to exacerbate wildfires and natural disasters become more frequent, there is a worry that a divide will form between “common” middle- and lower-class individuals and the wealthy elite. Los Angeles County will need to work especially hard in the near future to ensure that wealth does not drive a further wedge between its residents in the face of climate change.