Fresh Ideas: Changes in rainfall

Last week I heard Sao Paulo in Brazil is suffering from a seemingly unexplainable drought because the rains expected during the wet season never materialized and the precipitation for 2014 — at one-third of normal — is the lowest on record for it.

Its largest reservoir is down to 7.1 percent of its capacity, and by July it may be completely dry. This reservoir serves 6.5 million people, and if filled to capacity would last only 220 days without additional inflow. Thus far, reservoirs have been the “solution,” but now there’s talk of conservation and building canals. Explanation for this drought only mentions deforestation which has resulted in rain-induced mudslides.

Deforestation is a likely contributor, but as with everything on this Earth, there are many causes, all of which are intertwined. For instance, the Sahelian monsoon, named after the Sahel region in Africa, began weakening in the 1960s, and the Sahel which had always had marginal rainfall to begin with became a new drier climate — a desert. People thought overgrazing and an ever-growing population was at fault, but climatologists at the National Center for Atmospheric Research in Colorado determined in 2003 rising sea-surface temperatures in the Indian Ocean (which resulted from an accumulation of greenhouse gases) caused the Sahelian monsoon to weaken.

Curiously enough, “global dimming,” a phenomenon that cuts down the amount of sunlight reaching Earth’s surface, causes a cooling of the oceans around Europe, which also weakened the Sahelian monsoon. And global dimming itself is in large part due to particles spewed out into the air by coal-fired power plants, automobiles, and factories, which of course also result in greenhouse gases.

Perth, situated on the coast of southwestern Australia, on the Indian Ocean, experienced reliable winter rainfall for the first 146 years of European habitation — that is, until 1975 when rainfall began decreasing. Today the region gets 15 percent less rain than it did formerly, but this loss has had a profound effect because summer rain has increased.

Summer rain is more erratic so farmers don’t plant crops, then letting the rain soak down into the water table where it meets salt. This salt has been blowing in from the Indian Ocean for millions of years and it has formed on the average between 150 to 250 pounds of salt under every square yard of land in that region. Salt which used to stay crystalline because it was used up by the former native vegetation, now has become absorbed into the soil and caused dead vegetation and brooks and streams to become salty drains. Farmers have gone bankrupt and roads, railways, houses and airfields are damp and salty.

From 1975 until 2000 Perth drew on its nearby underground reservoir but since rain failed to replenish the water consumed. By 2005 the city’s water experts predicted depletion if continued and plans were made to build a desalination plant. This still only supplies about 15 percent of the city’s water.

The American West has not been as dry as it is now since 700 years ago. In the last 50 years there has been a decline in the average amount of snow, but what makes it worse is the southwest has warmed by 1.4 degrees fahrenheit so snowpack melts earlier and runoff occurs three weeks earlier than in 1948. We can “blame” the warming of the Pacific Ocean which has caused the jet stream to push northward, thus taking the moisture we used to get with it.

Nothing about rainfall is simple, but there is one common denominator: those pesky greenhouse gases that create warming oceans.

Ursula Carlson, Ph.D., is professor emerita at Western Nevada College and credits Tim Flannery’s “The Weather Makers” with the facts and data.


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