When land goes thirsty

When land goes thirsty – Special Report

Kim Y. Masibay

After the rainless spring of 2002 parched Arizona, a few matches sparked the largest wildfire in the state’s history. The Rodeo-Chedeski fire scorched 500,000 acres last summer, leaving ranchers like Kenny Evans of Payson, Ariz., with nothing but charred land. “It burned faster and more intense than anything I’ve seen,” he says.

Fire is a natural part of western U.S. ecosystems, clearing overgrowth to allow new plants to flourish. On average, wildfires burn 2.1 million U.S. acres each year. But from January to August 2002, fire incinerated nearly 5 million acres. Why is this year’s fire season so extreme? Drought–a period of abnormally dry weather. “Drought and fires go hand in hand,” says Douglas Le Comte at the Climate Prediction Center in Camp Springs, Md. “People and lightning cause fires–drought adds to the vulnerability.”

In a drought, one spark can ignite forest and brush so parched experts call them “dry fuel.” Humans started Rodeo-Chedeski and Colorado’s devastating Haywood fire, but most of 2002’s blazes (see map, right) began in nature’s way: with lightning, a strong electrical charge that flows from the base of a thundercloud to Earth and back.

The causes of wildfires are easier to explain than the causes of drought. Scientists point to a complex brew of factors–high temperatures, winds that steer storms away from certain regions, and low sea-surface temperatures (SSTs) in the Pacific Ocean (see diagram, right). But there’s an element of mystery involved, too. For example, says Le Comte, “the SSTs that produce a drought one year, don’t the next. That’s what makes drought so hard to forecast.”

No place was harder hit in 2002 than the Navajo Indian Reservation, which stretches 17.5 million acres across New Mexico, Arizona, and Utah. Some areas haven’t seen rain since fall 2001. “Between fire and drought it’s hard to stay here,” says Alex DiNatale, Navajo Nation hydrologist (water scientist). “We have 7,500 dry watering ponds–30,000 dead cows.”

The National Weather Service predicts normal to above-normal precipitation for Arizona this winter. But DiNatale says that won’t be enough water to replenish the wells, reservoirs, and parched earth: “A wetter-than-average winter would still leave us in a state of mild drought next year.”

THE 2002 DROUGHT: HOW IT TOOK FORM

This diagram shows how wind patterns and local weather conditions worked together to create the worst U.S. draught since 1988.

1 Normal Water Cycle

Water from rivers, lakes, soil, and plants evaporates and forms clouds. Winds can also bring rain-bearing clouds from other regions.

2 Disrupted Water Cycle

Drought is a natural, somewhat mysterious part of the climatic cycle. If soil is arid–as it is now in parts of the U.S. (see map) from years of lower than average rainfall-little or no water evaporates, no clouds or rain form, and passing sunny day soil grows drier.

3 Worsening the Drought

(A) Areas of high-pressure and low-pressure air constantly move across Earth’s surface. High-pressure areas form where cooler air presses down toward Earth. Low-pressure areas form where warm air rises.

(B) High-pressure air sometimes settles over a region, blocking winds that bring rain-bearing low-pressure systems. The lack of rainfall worsens the drought.

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