The BBC, citing a study in Nature, informs us that climate change models have underestimated the risk of flooding. High atmospheric carbon dioxide levels mean plants suck less water out of the soil. Wetter soil means faster soil saturation in heavy rains, hence more serious flooding.
From the BBC:
Researchers say efforts to calculate flooding risk from climate change do not take into account the effect carbon dioxide (CO2) has on vegetation.
Higher atmospheric levels of this greenhouse gas reduce the ability of plants to suck water out of the ground and “breathe” out the excess.
Plants expel excess water through tiny pores, or stomata, in their leaves.
Their reduced ability to release water back into the atmosphere will result in the ground becoming saturated….
The higher the level of atmospheric CO2, the more the pores tighten up or open for short periods.
As a result, less water passes through the plant and into the air in the form of evaporation. In turn, this means that more water stays on the land, eventually running off into rivers when the soil becomes saturated.
The upside is that wetter soil should reduce the severity of droughts, but with higher temperatures, it’s not clear whether that effect is net positive.