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Importance of a Good Precipitation Year on Drought

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Rex Trulove's image for:
"Importance of a Good Precipitation Year on Drought"
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Few people enjoy a drought, but they do happen. Sometimes they can linger for years. Many people may be puzzled why a good water year can reverse the effects of several years of drought. The answer is both interesting and enlightening.

Drought cause

It is a common misconception that drought is caused by a year when precipitation levels are way below normal. However, this is only a portion of the reason drought happens. Quite often, a major culprit is man. Even when people try to conserve water, the number of people in an area can seriously deplete the amount of water that is available, especially if the amount of precipitation is small or below average. In this way, man works in concert to create drought conditions, and this is something that many people don't fully understand.

Water sources

Some towns and cities draw their water directly from lakes and reservoirs. Some use catchments that gather precipitation. Still others tap water directly out of the ground. In each case, the water is coming from an aquifer. In general, an aquifer is a source of ground water, above or below the ground. 

As an aquifer is drawn down, by human activity or by the action of plants and animals, less water is available for use. If the aquifer isn't replenished, a drought is created. The longer conditions go, before there is sufficient moisture to replenish the aquifer, the worse the drought becomes.

Aquifer configuration

Most aquifers are primarily under the earth. The water is trapped between layers of rock that the moisture can't easily flow through. Though the gap between the two isn't usually very deep from top to bottom, it can be spread over hundreds of square miles. The amount of water it can hold when it is full is tremendous. Lakes are an example of aquifers where the top layer of rock, near the surface, is missing, so nothing is preventing the water from laying on the surface. This can make matters worse, due to evaporation.

Aquifer replenishing

The rock that is above and below an aquifer isn't totally impervious. Water can seep in and it can drain out, normally. This means that rain and snow melt can add to the pocket of water, and plants and animals can draw out of it. Otherwise, it wouldn't be a source of ground water. The aquifer is thus replenished by precipitation, primarily.

Progressive drought

If the layer of rocks are, for example, 20 feet apart, but the aquifer holds 100 million gallons of water, as more water is used but less is put back, the level can and often does drop, foot by foot. Each foot it drops means that there are 5 million gallons less in the strata. If the drought continues for 5 years, and the water level drops a foot each year, counting all incoming water, that is a net loss of 25 million gallons of water, or a quarter of the aquifer.

Good water year

In a year where rain and snowfall are abundant, the water sinks in and starts to fill up the aquifer. It may sound like a loss of 25 million gallons of water might take years to make up, but that isn't the case. If the underground water supply, in non-drought years, gets extra water, the excess runs off, finding its way to rivers and streams and ultimately to the ocean. This is similar to a glass that is totally full of water, when an attempt is made to add more.

After the cavity has been partly emptied, though, there is room to hold the water. Even a light rainfall can start the process. A good water year, then, means that the aquifer can fill back up. Even if lakes and reservoirs still seem low, the water that is underground is 'topped off', as it were. Subsequent precipitation fills the lakes and reservoirs. 

The amount of water involved sounds vast, however a good water year can end a drought by refilling the aquifers. This takes a lot less time that people might think. It doesn't mean that it still isn't a good idea to conserve water, but a good water year can turn the tables on a years-long drought.

More about this author: Rex Trulove

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