December 8, 2025 – During a drought, it’s not how hot or how dry it is that determines gas emissions from plants–but how quickly conditions change, according to a new study by Hebrew University of Jerusalem (HU) researchers, which may reshape the understanding of the relationship between drought, vegetation, and air pollution.

The new study—led by Dr. Eran Tas from the Institute of Environmental Sciences at HU’s Robert H. Smith Faculty of Agriculture, Food and Environment in collaboration with Prof. Alex Genther from the University of California, Irvine, and Prof. Pawel Misztal from the University of Texas at Austin—was conducted in the Beit Keshet Forest in northern Israel. It showed for the first time that the rate of change in relative humidity (ΔRH/Δt) is the most reliable indicator for the BVOCs emission rate. Until now, scientists had assumed that humidity or temperature levels were the primary factors determining the intensity of emissions from plants. 

Published in the Science of The Total Environment, the study reveals a striking phenomenon: when the weather shifts rapidly–for example, a sharp increase in humidity or a sudden drop in temperature–vegetation responds immediately by changing the rate at which it emits naturally occurring biogenic volatile organic compounds (BVOCs) into the air. On their own, these compounds are not pollutants; however, they participate in forming tropospheric ozone and fine particles–both of which affect air quality and climate change. 

The study is based on precise, high-frequency measurements of gas concentrations above vegetation using advanced instrumentation (PTR-ToF-MS), combined with meteorological analysis using climate models. 

“The forest responds in real time,” according to Dr. Eran Tas. “Drought doesn’t just dry out the soil; it changes the chemistry of the air. Our findings offer a more accurate way to simulate the effect of vegetation on the feedback between the meteorological conditions and air pollution, which becomes increasingly important under climate change, especially in dry regions like the Middle East.” 

These insights will help improve global climate and air quality prediction models, which until now have not adequately accounted for the impact of rapid weather fluctuations. 

The research was supported by the Israel Science Foundation (ISF). 

The research paper titled “The effect of meteorological conditions during drought on BVOC mixing ratios over an Eastern Mediterranean Forest” is now available in Science of The Total Environment and can be accessed here.

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