Friday, July 13, 2012

Monsoon Season and the Drought

Across the country we have been facing severe droughts, the severity of which have not been seen for over two decades.  Here in the Sonoran Desert we also have been experiencing a severe drought which has recently been relieved, at least temporarily, by the beginning of monsoon season rainfall.  Drought in the desert is sort of an odd thing.  In comparison with other regions drought is a constant pattern in deserts and actually makes a desert a desert.  What else would define a desert a part from lack of rainfall?   Every year most deserts will go through a period of time where no precipitation falls at all.  In the Sonoran Desert that almost always is late April through June.  The Mojave and Great Basin Deserts go almost all summer without any rain at all.  These differing rainfall patterns are actually part of the reason we have different types of desert.  While drought, or lack of moisture may constantly be a problem in the desert, some years are worse than others.  This year for example has been pretty extreme.  Late winter and early spring rains where next to nothing.  This meant higher temperatures due to the lower humidity causing things to dry out even more.  By the time early July hit the desert around Phoenix had only about half an inch of rain for the year!  This is way less than the typical three to four inches of rain received during the first six months of the year.  Fortunately, on July fourth we received a major rainfall which hopefully began to break this dry spell.  More rain fell on most of the desert than had fallen in the previous six months combined.

Normally, late winter and early spring rainfall helps sustain the desert until monsoon season.  This year however, the lack of rain has taken its toll on nature.  Normally, Palo Verde and Ironwood trees are able to maintain their leaves through June and July.  While it isn't that unusual for Palo Verdes to loose all their leaves it isn't typical in this part of the Sonoran Desert, but this year only a handful of trees held onto their leaves.  Ironwoods very rarely loose their leaves but this year the drought caused the majority of leaves to fall off of the trees.  This also resulted in extremely poor seed production.  The story is the same for nearly all the other plants in the desert also.  As a direct result, many desert birds and animals will also be harmed by the lack of food productivity as well as the lack of water.  Earlier this year I noted extremely poor Wolfberry production which likely had a negative effect on birds.

On July fourth however, three quarters to one inch of rain fell breaking this trend.  Since then we have had two other rainfall adding up to at most half an inch.  This immediately relieved drought conditions, causing a rapid bounce back of the plants.  Within a week the Ironwoods had greened up and added leaves.  Palo Verdes also have sprouted leaves along with Wolfberries.  Cacti also have plumped up as they soak in the extra moisture.  Everything seems to have awaken with the rain, clouds, and slightly cooler temperatures.  So hopefully this early monsoon rain continues.  At least part of the reason for the lack of rain earlier this year was the presence of La Nina conditions in the Pacific Ocean.  In June however La Nina broke and we seem to be trending towards an El Nino to start up in the next several months.  Often this means greater rainfall during the winter months, but only time will tell.

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