[env-trinity] West's record, computer modeling indicate prolonged droughts likely again

[Mark Dowdle - TCRCD]

Opinion:

Learning from our arid past

More droughts, less water -- our future depends on adapting to scarcity.

Los Angeles Times - 4/29/08

By Brian Fagan - emeritus professor of anthropology at UC Santa Barbara and 
the author of "The Great Warming: Climate Change and the Rise and Fall of 
Civilizations



One of the downsides to global warming is drought. About 11 million people 
in northeast Africa alone were in serious danger of starvation in 2006 as a 
result of drought. The International Institute of Tropical Agriculture in 
Nigeria estimates that about 300 million people in sub-Saharan Africa --  
nearly a third of the population -- will suffer from malnutrition because of 
intensifying drought by 2010. With continued warming and more droughts on 
the horizon, we need to learn how to better live with our natural world and 
its cycles.

Here in the Western United States, it's tree rings that tell us that cycles 
of wet and dry, warm and cool are the historical reality.

In California, the source is tree stumps in Sierra lake beds. Owens Lake 
once covered more than 115 square miles at the mouth of the Owens River. The 
mountain runoff that fed the lake varied dramatically in cycles of wet and 
dry years. In drier periods, trees grew in the still-moist soil of the 
receding lake. When the rains came, the trees drowned, leaving stumps as a 
chronicle of aridity: An epochal drought began before AD 910 and ended about 
1100; a wetter century then ensued, when rainfall was higher than in modern 
times. A second drought started before 1210 and ended 140 years later.

As for the wider West, a grid of more than 600 tree-ring sequences from 
throughout the region, compiled by a team at the Lamont-Doherty Tree Ring 
Laboratory at Columbia University, puts today's droughts in perspective. The 
centuries between AD 900 and 1253 witnessed long dry spells. After 1300, an 
abrupt change to wetter conditions lasted for 600 years, then gave way to 
today's aridity. Some people refer to a "mega-drought epoch" 1,000 years 
ago, when cool, dry La Niña conditions persisted for decades over the 
eastern Pacific and the winter jet stream stayed well north of what is now 
California.

None of today's droughts approach the intensity and duration of the medieval 
ones. The six-year California drought that began in 1987 resulted in Sierra 
Nevada runoff that was only 65% of normal. During the great medieval 
droughts, inflow to Owens Lake is estimated to have been 45% to 50% lower 
than usual.

Why did the medieval droughts persist so long? Gradually accumulating 
climatic evidence from around the world is showing that the mega-drought 
epoch experienced significant warming on a global level, similar to recent 
conditions. During the 20th century, increased Northern Hemisphere 
temperatures and unusual warming of the western Pacific and Indian oceans 
contributed to drought formation over middle latitudes.

How did people survive? A thousand years ago, California's human population 
was tiny, a scattering of hunters, gatherers and fishermen who adapted 
effortlessly to long-term drought. They tapped rare permanent water 
supplies, changed their diet and moved to higher ground. Acorns were a 
staple; so were sea fish in places such as the Santa Barbara Channel. 
Survival in some of the toughest landscapes on Earth depended on 
cooperation, intelligence about water supplies, mobility and flexibility, 
knowledge of their environment and on taking advantage of all kinds of food 
resources when they became available. Nevertheless, prolonged aridity must 
have killed thousands of people in medieval times, from the American West to 
the Saharan Sahel.

Although today's droughts are minuscule compared with the dry spells of 
1,000 years ago, the future is truly frightening. Sophisticated computer 
models by Britain's Hadley Center for Climate Prediction and Research 
predict a 3% to 18% increase in the amount of the Earth's surface that will 
be exposed to extreme drought by 2100; 40% of the world will suffer from 
severe drought, up from the current 18%; 50% will suffer from moderate 
drought. California and other Western states, at the very least, will suffer 
from severe drought. By 2025, an estimated 2.8 billion of us will live in 
arid areas like California.

Today, we harvest water on an industrial scale -- from rainfall, from rivers 
and lakes and from rapidly shrinking water tables. Many of us in California 
live off what are, effectively, looted water supplies, brought by canal from 
Owens Lake or the Colorado River or drained from aquifers.

But at best we have accommodated ourselves to nature's fickle realities. Our 
greatest asset is not necessarily our technology but our opportunism and 
endless capacity to adapt to circumstances. We must learn from the history 
of the great droughts and begin to think of ourselves as partners with, 
rather than potential masters of, the changing natural world.

Brian Fagan is emeritus professor of anthropology at UC Santa Barbara and 
the author of "The Great Warming: Climate Change and the Rise and Fall of 
Civilizations."#

http://www.latimes.com/news/opinion/commentary/la-oe-fagan29apr29,0,4871853.story