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Why can droughts and unusual cold spells matter for vegetation even when climate averages remain the same?

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World map with continents shaded in colors representing climate zones, from warm reds and yellows near the equator to cool blues and whites at the poles. — Climate Even in our warming world, there will be some chilly evenings.

Even when long-term climate averages remain stable, vegetation is highly sensitive to interannual and decadal climate variability because biological systems respond to the timing and intensity of specific weather events rather than just statistical means.1

Droughts and unusual cold spells disrupt the critical balance between precipitation and the water requirements of plants. Drought occurs when evaporation and transpiration exceed available moisture for an extended period, leading to water deficits that can cause crop failure and long-term damage to soil moisture levels. Even in climates with sufficient annual rainfall, "invisible droughts" can occur during hot periods when high temperatures accelerate water loss, causing plants to suffer despite frequent showers.23

Because plants have specific developmental windows, extreme weather events—such as a sudden cold snap or a multiyear dry spell—can devastate vegetation that is otherwise well-adapted to the region's average conditions. These fluctuations create significant challenges for agriculture, as they can induce social and economic dislocation even when the overall climate appears unchanged over time.12