Warming Not Making Floods Worse, Study Finds

Published October 25, 2011

There is no increase in the magnitude of flooding events in the United States during the past century as atmospheric carbon dioxide levels have risen, scientists with the U.S. Geological Survey report in the peer-reviewed Hydrological Sciences Journal. Indeed, flooding in the southwestern United States has actually become less frequent and severe, according to the scientists.

The authors examined 200 long-term (85–127 years of record) streamgauges in the United States. Summarizing their results, the authors explain, “The coterminous US is divided into four large regions and stationary bootstrapping is used to evaluate if the patterns of these statistical associations are significantly different from what would be expected under the null hypothesis that flood magnitudes are independent of GMCO2  [atmospheric carbon dioxide concentrations]. In none of the four regions defined in this study is there strong statistical evidence for flood magnitudes increasing with increasing GMCO2. One region, the southwest, showed a statistically significant negative relationship between GMCO2 and flood magnitudes.”

“[E]xcept for the decreased flood magnitudes observed in the SW [southwestern United States] there is no strong empirical evidence in any of the other 3 regions for increases or decreases in flood magnitudes in the face of the 32% increase in GMCO2 that has taken place over the study period,” the authors observed.