Floods Across the United States: Trends of the Last Century
Hirsch, R.M. and Ryberg, K.R. 2012. Has the magnitude of floods across the USA changed with global CO2 levels? Hydrological Sciences Journal 57: 10.1080/02626667.2011.621895.
Working with the global mean carbon dioxide concentration (GMCO2) and a streamflow data set that consisted of long-term (85- to 127-year) annual flood series from 200 streamgauges that had been deployed by the U.S. Geological Survey in basins with little or no reservoir storage or urban development (less than 150 persons per square kilometer in AD 2000) throughout the coterminous United States - which they divided into four large regions - Hirsch and Ryberg employed a stationary bootstrapping technique to determine if the patterns of the statistical associations between the two parameters were significantly different from what would be expected under the null hypothesis that flood magnitudes are independent of GMCO2. In doing so, the two researchers report that "in none of the four regions defined in this study is there strong statistical evidence for flood magnitudes increasing with increasing GMCO2." In fact, they say that one region, the southwest, showed a statistically significant negative relationship between GMCO2 and flood magnitudes.
In discussing the meaning of their findings, Hirsch and Ryberg state that "it may be that the greenhouse forcing is not yet sufficiently large to produce changes in flood behavior that rise above the 'noise' in the flood-producing processes." On the other hand, it could mean that the "anticipated hydrological impacts" envisioned by the IPCC and others are simply incorrect.
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