Can Rain Cause More Fire?

Can rain cause more fire? It depends.

This may seem counter-intuitive. Rains put out fire. Wet vegetation doesn’t burn.

That is true. But rains during the growing season can spark a burst of plant growth in otherwise relatively barren lands. And then if dry conditions follow, you’ve got the perfect setting for fire — dry fuel, and lots of it.  

This is what’s going on in Texas. Volatility in conditions, from rains to extreme drought, can prime the land for fire. And we see similar patterns across many places in the Southwestern US.

Take Nevada in the early 2000s, highlighted in this graphic. There was a spell of drought and Nevada’s scrubby desert didn’t burn much. But then in 2005 rains came and led to a burst of vegetation growth, and sure enough, large fires followed (notice the flame is yellow, indicating the burn was low or light, that is because even with a lot of scrub vegetation it's still not a lot of fuel to sustain a really intense high fire burn).  

Meanwhile, in western Montana and in other conifer forests in the Northwest, the opposite pattern occurred. That is because those forests carry more than enough fuel for a fire, but they only burn when the trees are dried out from drought. So large, hot fires burned in 2003 (notice the large red and orange flames relative to Nevada, because a dried out conifer forest can burn really hot). By 2005, rains moistened the forest, helping to protect it from fire.  

The fire data in each state comes from Monitoring Trends in Burn Severity. Scientists from the United States Geological Service and United States Forest Service work together to analyze images derived from NASA satellites including LandSat and MODIS. These instruments provide highly detailed images of the earth from which scientists can measure the perimeter and intensity of burn events in real-time across the globe.

Here are current pictures from MODIS of the recent fires in Texas.

The complex interactions between fire, climate, and vegetation are one of the more interesting and challenging aspects of understanding how fire is changing on our landscape in response to climatic change.

Credit: Image produced by DuKode Studio for Climate Central.