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Earlier plant growth, linked to rising global temperatures, has been intensifying wildfires across the northern hemisphere.

Climate change has amplified the risk of wildfires聽around the world by making conditions ideal for fires to break out. 鈥淭here has been a lot of fires recently, and we continue to see that these fires are increasing year to year,鈥� says at ETH Zurich in Switzerland. They are also getting more damaging, he says.

Vegetation is also being affected by the changing climate, with warmer weather triggering many plants to grow earlier in the year than usual. Zohner and his colleagues wanted to understand whether this change is also linked to the outbreak of fires.

To assess when plants have been growing in the northern hemisphere, the researchers analysed satellite data from between 2001 and 2018 that measured the radiation emitted by plants during photosynthesis, as well as the wavelengths of light reflected by the leaves to determine how much vegetation there was. They also looked at wildfire records over the same period.

Zohner and his colleagues found that the earlier in the year that vegetation started to grow and reached peak photosynthesis, which is when they produce the most energy, the greater the number of wildfires in the region and the larger the area that was burned. They also found that earlier vegetation growth correlated with wildfires starting earlier in the year.

There are a few ways the shift in vegetation growth may be contributing to wildfires, the researchers suggest. First, earlier growth means plants are sucking water from the ground earlier in the year, leading to drier conditions that are more vulnerable to fire.

鈥淎dditionally, we find that the earlier timing caused earlier leaf senescence, when leaves drop from the trees, which provides more fuel for the fires,鈥� says team member at the Chinese Academy of Sciences.

鈥淲henever there鈥檚 a wildfire, we talk about climate change,鈥� says Zohner. 鈥淣ow there鈥檚 strong evidence that its negative effects on vegetation further enhance fires.鈥�

Whether this process might have worsened the wildfires that have hit in recent months, such as in Greece and Hawaii, isn鈥檛 known, says Wu, but data for this year is being processed.

The researchers hope that a better understanding of what is driving wildfires can help authorities prevent or manage them.