Flood Flows and Climate Variability and Change in the US, an Exploration of the Literature, Theory, and Long-term Flood Records

Much of the recent literature about the relationship of greenhouse-gas induced warming and extreme precipitation has indicated that extreme events, in many parts of the U.S. and globally, have become more common over time. Further, global climate models predict that extreme precipitation events will become more common as greenhouse gas concentrations rise. Logic would suggest that flood flows would have increased in recent decades in response to increases in the frequency of extreme precipitation. Research to date, however, is highly equivocal on the question of increasing flood magnitudes (as distinct from economic flood damages which have shown a strong increase). Emergency preparedness and mitigation of flood damages in the future should be based on a strong scientific foundation of understanding of the reasons for the changes to date (if any) and the likely drivers of change in the future. Some of the drivers of change are undoubtedly related to land use and water management strategies. The question of a climate driver also needs exploration: including analysis of historical relationships between flood flows and greenhouse gas concentrations, as well as relationships to various indices of ocean conditions that are known to be major drivers of the hydro-climatic system at multi- year to multi-decadal time scales. Additionally, climate models need to be critically evaluated in terms of their current usefulness for estimating flood behavior at various basin scales and in various climatic zones. This study will review the literature and theory behind this issue and explore a small number of the very longest U.S. flood records to search for trends and possible relationships between flood magnitude and climate forcing.