A study suggests that reductions in plant water loss under rising atmospheric carbon dioxide (CO2) may result in lower future drought stress than predicted by current metrics. Plants open leaf pores to absorb CO2, but the process results in a simultaneous loss of water into the atmosphere. Researchers have hypothesized that increasing atmospheric CO2 levels may reduce plant water loss in relation to carbon uptake, potentially resulting in increased soil moisture and drought curtailment. To predict how future shifts in transpiration might alter drought stress, Abigail Swann and colleagues compared drought stress predictions from the Palmer Drought Severity Index, which does not incorporate the effect of CO2 on transpiration, with a drought index that accounts for CO2-forced transpiration changes. The Palmer Drought Severity Index predicts that drought stress will likely increase across more than 70% of global land area in the future, but this value drops to 37% for the drought index with CO2-forced transpiration shifts. Both metrics indicate that drought stress is likely to increase across southern North America, northeastern South America, and southern Europe—regions with decreasing precipitation. However, the index with CO2-forced transpiration shifts suggests that drought stress is likely to decrease in temperate Asia and central Africa. According to the authors, drought indices that account for plant physiological responses to atmospheric CO2could reduce uncertainties in drought estimates and improve forecasts for agriculture, water resources, and wildfire risk. - Read at PNAS.org
Article #16-04581: “Plant responses to increasing CO2 reduce estimates of climate impacts on drought severity,” by Abigail L.S. Swann, Forrest M. Hoffman, Charles D. Koven, and James T. Randerson.