More CO2 means moister soil.
There is a growing realization that more CO2 in the air means more moisture in the soil. The major cause of water loss in plants is attributable to transpiration, in which the stomata or pores on the undersides of the leaves are open to absorb CO2. With more CO2, the stomata are open for shorter periods, the leaves lose less water, and more moisture remains in the soil. Increasing soil moisture owing to CO2 fertilization has been linked to decreases in global fire, drought and heat waves.