Extreme Weather Events as a Result of Climatic Change

Testimony of Heather S. Cooley to the
United States Congress
Select Committee on Energy Independence and Global Warming

For the Hearing on Global Warming Effects on Extreme Weather
July 10, 2008

My testimony today addresses the rising risk of extreme weather-related events as a result of climatic changes and their impact on water resources, with a focus on the western United States. In the short time available, let me provide a summary overview. I have submitted more detailed supplementary materials for your review.

The United States already faces growing pressures on existing water resources due to increases in population, industrial and agricultural water demand, and rapid development in semi-arid and arid regions. Based on a sizable and growing body of scientific analysis, it now seems highly likely that climate change will vastly increase those pressures. Of special concern is an expected increased risk of extreme events, such as floods, droughts, and heat waves. I will address what we can expect, and what policymakers and the public should begin to do to reduce the risks to life and property that we now expect.

Floods and droughts are among the most common and damaging of all natural hazards and much of the existing water infrastructure in the United States was built to lessen these hazards. Since 1903, floods have killed an average of 93 people annually in the United States, but single extreme events can kill hundreds or even thousands. Droughts also can lead to illnesses and deaths, but are more closely associated with economic damages. Direct economic losses from floods and droughts are high, averaging US$11.5 billion annually in direct losses; again, individual extreme events can be much higher. Hurricane Katrina, for example, is estimated to have led to direct economic losses of $100 billion to $150 billion, of which about 30% is attributed to flood losses. If indirect damages and losses associated with floods and droughts, such as loss of business and personal income, reductions in property value, etc., are included, these estimates would increase substantially.

Floods and droughts have dominated headlines in papers across the United States in recent months. Floods along the Mississippi River and its tributaries have devastated communities throughout the Midwest. Drought conditions are prevailing across large parts of the United States. As of July 2008, moderate-to-exceptionally severe droughts are affecting 35% of the western U.S.; 40% of the South; 17% of the High Plains; and 59% of the Southeast. Overall, nearly 30% of the contiguous U.S. is suffering moderate– to-exceptional drought. In California alone, drought conditions have spawned nearly 2000 fires since late June in what may turn out to be one of the worst fire seasons on record.

Floods and droughts are, of course, a natural part of the climate system. Growing and convincing scientific evidence, however, indicates that increases in greenhouse gases are causing large, systemic change to our climate with implications for the intensity and frequency of hydrologic extremes, i.e., floods and droughts. While scientists are reluctant to attribute individual events like those experienced in 2008 specifically to climate change, long-term records and trends increasingly suggest that we are essentially “loading the dice” and increasing the probability that these types of events will increase in frequency and intensity. […]