CLIMATE CHANGE AND FLOODPLAIN MANAGEMENT
IN THE UNITED STATES
J. ROLF OLSEN
Institute for Water Resources, U.S. Army Corps of Engineers, CEIWR-PD, Casey Building,
7701 Telegraph Road, Alexandria, VA 22315
E-mail: j.rolf.olsen@iwr01.usace.army.mil
Abstract. Federal agencies use flood frequency estimates to delineate flood risk, manage the Na-
tional Flood Insurance Program, and ensure that Federal programs are economically efficient. The
assumption behind traditional flood risk analysis is that climate is stationary, but anthropogenic cli-
mate change and better knowledge of interdecadal climate variability challenge the validity of the
assumption. This paper reviews several alternative statistical models for flood risk estimation that
do not assume climate stationarity. Some models require subjective judgement or presuppose an un-
derstanding of the causes of the underlying non-stationarity, which is problematic given our current
knowledge of the interaction of climate and floods. Although currently out of favor, hydrometeoro-
logical models have been used for engineering design as alternatives to statistical models and could be
adapted to different climate conditions. Floodplain managers should recognize the potentially greater
uncertainty in flood risk estimation due to climate change and variability and try to incorporate the
uncertainties into floodplain management decision-making and regulation.
1. Introduction
Changes in the frequency and magnitudes of floods have been repeatedly suggested
as a potential consequence of global warming. The most recent report from the
Intergovernmental Panel on Climate Change (IPCC, 2001b) states that
Flood magnitude and frequency are likely to increase in most regions, and low
flows are likely to decrease in many regions. The general direction of change in
extreme flows is broadly consistent among climate change scenarios, although
confidence in the potential magnitude of change in any catchment is low (IPCC,
2001b).
A warming of the atmosphere caused by increases in greenhouse gases may cause an
increase in heavy precipitation events (Trenberth, 1999). Increased temperatures
tend to increase evaporation, which increases the atmospheric moisture content.
More available moisture will tend to increase precipitation rates for all types of
storms. Some climatologists conclude that the enhanced storm intensity may cause
increased flooding.
Even without anthropogenic climate change, better understanding of climate
has shown that it varies over multiple time scales (NRC, 1998). Climate patterns
can exhibit slowly varying episodic behavior over decades or centuries. Nonlinear
Climatic Change (2006) 76: 407–426
DOI: 10.1007/s10584-005-9020-3
c
Springer 2006