During drought, dry air can stress plants more than dry soil

The finding suggests that models used to gauge the impact of drought on ecosystems should be refined to more accurately account for the role of low atmospheric humidity. It will become more important in the future, as the Earth's climate grows warmer and lower humidity has an increasing impact.

And as these humidity levels fall, plants may become less effective at removing carbon from the atmosphere, reducing their ability to offset climate change. At the same time, agricultural management strategies like irrigation, which improve soil moisture but have a smaller effect on humidity, may become less effective in the future.

https://www.sciencedaily.com/releases/2016/09/160905114521.htm