Why Are We Concerned About
Drought?
Although
the major droughts of the 20th century, the 1930s Dust Bowl and
the 1950s droughts, had the most severe impact on the central
U.S., droughts occur all across North America. Florida suffered
from the 1998 drought along with the states of Oklahoma and Texas.
Extensive drought-induced fires burned over 475,000 acres in
Florida and cost $500M in damages. In the same year, Canada suffered
its fifth-highest fire occurrence season in 25 years. Starting
in 1998, three years of record low rainfall plagued northern
Mexico. 1998 was declared the worst drought in 70 years. It became
worse as 1999 spring rainfalls were 93% below normal. The government
of Mexico declared five northern states disaster zones in 1999,
and nine in 2000. The
U.S. West Coast experienced a six-year drought in the late 1980s
and early 1990s, causing Californians to take aggressive water
conservation measures. Even the typically humid northeastern
U.S. experienced a 5-year drought in the 1960s that drained reservoirs
in New York City down to 25% of capacity. In fact, almost every
year, some region of the North America experiences drought.
Drought is a natural hazard that cumulatively has affected more people in North America than any other natural hazard (Riebsame et al. 1991). The cost of losses due to drought in the United States averages $6-8 billion every year, but range as high as $39 billion for the three year drought of 1987-1989, which was the most costly natural disaster documented in U.S. history. Continuing uncertainty in drought prediction contributes to crop insurance payouts of over $175 million per year in western Canada.
Beyond the monetary costs, the impacts of drought on society, the economy, and the natural environment are tremendous. Although measures such as development of irrigation systems, financial aid programs and interbasin water transfers have been undertaken to mitigate the impacts of drought in recent decades, some regions of the U.S. are becoming more vulnerable to the impacts of drought.
Although irrigation has made
it possible to grow crops on land that was once considered barren,
this practice has led to a reliance on ground water and surface
storage in reservoirs. Increasing demands on water have resulted
in the depletion of ground water reserves in many areas, which
can make the removal of additional water uneconomical if not
impossible, especially during a drought. In many urban areas
of the semi-arid and arid western U.S., population growth, expansion
into marginal areas, and the subsequent development is overtaxing
water supplies and heightening vulnerability to drought. Along
with this increased vulnerability, concern exists because some
research suggests that drought in the future may be amplified
in certain areas due to changes in climate variability and extremes
resulting from global
warming.
Scientists have much to learn about the characteristics of drought and the conditions that lead to the persistence of drought. Although some progress has been made, (for instance, droughts that are related to El Niño and the Southern Oscillation (ENSO) are now more predictable on a seasonal scale), scientists still cannot predict longer, multi-year droughts.
The two major droughts of the 20th century, the 1930s Dust Bowl drought and the 1950s drought, lasted five to seven years and covered large areas of the continental U.S. Complete scientific understanding of how and why these two drought episodes occurred remains elusive. From a societal perspective, the important question is, how unusual are these events? Most instrumental records (from thermometers and rain gauges) are only about 100 years long, so they are too short to answer this question. However, paleoclimatic proxy data are a valuable tool to investigate this question by providing a longer context within which to evaluate the reoccurrence of these major droughts over hundreds to thousands of years.
For more complete information on the impacts of drought in North America, see the National Drought Commission report titled "Preparing for Drought in the 21st Century"
On to... 20th Century Drought