Wildfires can occur during drought conditions when the land and vegetation have dried out.
Why do I care? Wildfires can spread easily during periods of dry and warm conditions. This can lead to the loss of farmland and forests and to the destruction of crops and ecosystems.
I should already be familiar with: Drought, Humidity, El Niño, La Niña
Drought conditions sometimes develop after a period of above average amounts of rainfall over an extended area. When this happens, the wet conditions have encouraged more plants and trees to grow and to gain nutrients. These new plants and shallow-rooted trees are the first to start to wilt when dry conditions begin. If the dry conditions persist, a drought can develop, leading to conditions favorable for wildfires as all the excess dried-out vegetation provides ample fuel for the fires.
Figure A. 1998 Florida wildfires. (Image from Florida Department of Ag and Consumer Services.
Wildfires will ignite very easily under such dry conditions and can spread quickly. Lightning can be a good starter of wildfires, especially under such dry conditions. Careless use of camping or trash-burning fires and even tossed cigarettes can also start fires. Local fires can be seen in the United States almost every year when the lands start to dry out, particularly in Florida or California in the middle of spring. Under drought conditions, not enough precipitation falls to relieve the land from drought and wildfires get out of hand. In these areas, burn bans will be put into effect in an effort to stop the wildfires from developing and easily spreading. In many areas across the Southeast US, controlled burning efforts are used as a precaution to try to contain wildfires if they do happen to start up randomly. With controlled burning efforts, the short brush in the forest is burned up to eliminate the fuel source for the fires. This helps contain any fires that do develop and keep them away from settled areas.
During El Niño events, the southeastern United States usually remains wet and colder during the winter months. Though El Niño conditions vary in each episode, the increase in the average amount of rainfall allows for underbrush to grow in forests. This could allow for the easy development of wildfires across broad areas if and when conditions are right and the land dries out.
La Niña tends to worsen drought conditions in the United States. During La Niña events, the southeastern US and the southern plains remain warm and dry during the winter months. Communities in the Southeast are often happy to welcome the warmer weather during the winter season because frosts and freezes will be less likely, although the warmer weather can cause problems in the Midwest for crops like winter wheat, due to more frequent freeze-thaw cycles in these years in the colder climates. If an area in the Southeast is already under drought conditions, La Niña can only worsen these conditions. Without adequate precipitation during the winter months, the land will dry up even more. This can also enhance the likelihood of wildfires throughout the southeast US (and other states). Such a condition occurred in 1998 in Florida. The picture above shows areas in red where fires burned from June to August 1998 in Florida.
The Southeast was wet and warm at the beginning of 1998. Usually during El Niño events, the winter months are wet and cold. This wet and warm weather allowed plants and underbrush to grow in the forests. However, a La Niña event developed in late spring. Florida in particular remained hot and dry throughout the late spring; this dried out the newly grown underbrush in the forests. The hot and dry conditions led to the development of large numbers of wildfires across Florida’s coast. The circumstances for wildfires only worsened throughout the summer with the ground simmering in the hot and dry conditions. This led to the drought across the state of Florida with the below average amount of rainfall which continued throughout the rest of the year, damaging many hundreds of acres of farmland and forests.
Figure B. Drought cartoon.
Similar conditions occur in California almost every year. California usually has a wet and mild winter with a dry and warm summer. Wildfires can start easily under warm and dry conditions with low relative humidity. Wildfires get easily out of control in California because of the type of trees in the forest accompanied by conditions of low relative humidity and warm air. These fires are able to spread easily with minimal water vapor in the air. Strong winds also help with the spread of wildfires throughout California. These winds “carry” the wildfires swiftly through the forest and the fires spread quickly. These California fires damage a lot of farmland every year as well as forests that are a natural habitat for animals.
Want to learn more?
Effects of Drought, Heat Waves, Effects of Climate Change on the Southeast