Climate models can be useful for helping us prepare for the future, but they can also be useful even if they get something wrong. If something unexpected happens, it points to an interesting problem to investigate. This is something noticed by Zhang and colleagues who found that some trees seem to lose their leaves unusually early, even accounting for temperature. Rainfall might be a factor, but they found that places with the same total rainfall still had differing times for leaf drop. This is a problem worth solving, because when leaves fall, they’re no longer gathering carbon dioxide from the atmosphere, which affects the climate.
As with many things, rainfall is a matter of timing. Zhang and colleagues found that trees tend to lose their leaves earlier, when rain becomes less frequent. This is the case across many plants. The change in the spacing between showers creates twin challenges for plants. The air becomes drier, increasing the pull of water through the plant. But the soil also becomes drier between showers, making it harder to get water in.
Faced with drier soil and air, the plants react by managing their water use, adapting to drought. They shut the pores in their leaves to reduce water loss. However, closing the holes in their leaves mean they also draw less carbon dioxide in. That means they can’t photosynthesise as much, and what use is a leaf that doesn’t photosynthesise? A leaf that can’t efficiently produce energy becomes a resource drain, so this may explain why the shutdown starts sooner.
The findings are the result of a two-pronged approach to the problem. At scale, Zhang et al analysed satellite photos of the Northern Hemisphere over 40 years. This was correlated with data from 52 ground monitoring stations that measure plant activity directly. The team then used statistical techniques to pull apart the effects of rainfall frequency from other factors, like temperature.
Scientists know temperature changes due to climate change are changing growing seasons, and they know that rainfall has a major influence on plant behaviours, but previous studies tended to focus on total rainfall rather than rainfall frequency. This means there is room to improve climate models. When tested against real-world observations, nearly half of the model predictions got the relationship between rainfall patterns and leaf timing wrong.
Zhang and colleagues’ findings show why some regions show unexpected patterns of earlier leaf loss despite having the same total rainfall as others. Future models should include plants, not as passive users of water, but rather as active managers, to better reflect the relationship between plants and rainfall.
Zhang, X., Wang, X., Zohner, C.M., Peñuelas, J., Li, Y., Wu, X., Zhang, Y., Liu, H., Shen, P., Jia, X., Liu, W., Tian, D., Pradhan, P., Fandohan, A.B., Peng, D., & Wu, C. (2025). Declining precipitation frequency may drive earlier leaf senescence by intensifying drought stress and enhancing drought acclimation. Nature Communications, 16:910. https://doi.org/10.1038/s41467-025-56159-4
