The Very Definition Of Drought

Houseboats on the shrinking Lake Oroville reservoir in California last month. Many have now been removed from the lake. Patrick T. Fallon/Agence France-Presse — Getty Images

We knew a bit about almonds being very thirsty trees, but when you see the trees being uprooted, it becomes even more real. The questions surrounding drought are too much for a short article, so thanks to one of our favored science writers, Henry Fountain, for keeping this focused:

The Western Drought Is Bad. Here’s What You Should Know About It.

Answers to questions about the current situation in California and the Western half of the United States.

Almond trees are removed from an orchard in Snelling, Calif. Farmers are making plans to plant less water-intensive crops because of the drought. Justin Sullivan/Getty Images

Much of the Western half of the United States is in the grip of a severe drought of historic proportions. Conditions are especially bad in California and the Southwest, but the drought extends into the Pacific Northwest, much of the Intermountain West, and even the Northern Plains.

Drought emergencies have been declared. Farmers and ranchers are suffering. States are facing water cutbacks. Large wildfires are burning earlier than usual. And there appears to be little relief in sight.

There are no precise parameters that define a drought, but it is generally understood to mean a period of abnormally dry weather that goes on for long enough to have an impact on water supplies, farming, livestock operations, energy production and other activities.

A drought usually starts with less-than-normal precipitation (and what is normal varies from region to region). If the dryness persists, river flows and reservoir and groundwater levels start to decline. Warm temperatures have an impact, too, causing winter snowpack to melt faster, which can affect the availability of water throughout the year. Excessive heat also causes more evaporation from soils and vegetation, which can lead to crop failures and increases the risk of severe wildfires.

Experts with the United States Drought Monitor, a collaboration of several federal agencies and the University of Nebraska-Lincoln, assess the severity of drought in a given area, ranking it from moderate to exceptional. They take many factors into account, including precipitation totals, snowpack, stream flows and soil moisture measurements, and use images from remote-sensing satellites to assess the health of vegetation.

It’s very bad, both in terms of the size of the affected area and the severity. The latest map from the drought monitor shows that all or nearly all of California, Oregon, Nevada, Arizona, New Mexico, Utah and North Dakota are in drought, and in large areas of those states conditions are “severe” or “exceptional.” Colorado, Idaho, Washington, Montana, South Dakota and southwestern Texas are also affected.

But maps tell only part of the story. The drought is having enormous effects throughout the West, where the demand for water has increased greatly over decades as the population has grown…

Read the whole article here.

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