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Mr. FaganNATURE HAPPENINGS - August 2002

 

How's The Weather?
by Damian Fagan

“How’s the weather?” In the land of census taking and statistical barrages, this is the most commonly asked question during a conversation of people between the ages of 8 and 108. In fact, this age span closely resembles this year’s temperature range.

Piled onto the discussion of temperature, this year we add the words drought and fire. This year, the total rainfall has not exceeded the amount that leaks from your bathroom faucet. For those of you with tight plumbing - know how you leave the tap on when you brush your teeth? Now imagine yearly precipitation.

Average annual rainfall in the Moab area ranges between seven and nine inches. Twelve inches a year and the place starts to resemble a temperate rainforest. Five inches a year and you’d better make up the guest room because the wildlife will be moving into town. Recently, a friend described how she was watering her garden and a young gopher snake slithered over and started to drink directly from the hose!
But, let’s put things into perspective. The geologic layers that surround Moab are exposed slices of time, representing millions of years. Historical geologists have sorted out the components of these layers - sands, silt, clays, organic matter, fossils, etc., and woven these constituents into a snapshot of the past. Some years back, when the Wingate Sandstone was being laid down, this place resembled the Sahara Desert, so perhaps this year’s rainfall should be taken in stride.

Just because it hasn’t seriously rained since February that doesn’t mean that all the plants are dying or that the streams are totally dry. The streams are almost totally dry and, though plants have adapted to dry conditions, there is a leaf-fall going on that is reminiscent of an autumn day. Even the cacti, those warehouses of moisture, seem gaunt and withdrawn and are dropping their outer pads like pre-Christmas hints.

According to one weather website, total precipitation for the year, to July 20th, is around 0.17". Of course, it rained the next day and probably doubled that total. Average total precipitation for that time frame is 3.45", meaning we are around 5% of average. Now that’s dry. Of course, if you moved the rain gauge a mile away, that number could change dramatically. Or if we get a couple of really hard August rains, say ¾ of an inch each time, we would jump to 33% of average.

Depending on whom you talk with, the word drought arises fairly often. Drought is defined as “abnormally dry weather within a geographic region where some rain might usually be expected.” I think we qualify under that general statement. The argument that this is the first year of a drought just doesn’t seem to carry water (pun intended). The past several years have also been dry, but it really depends on the index that used to define drought.

There is the Palmer Drought Severity Index (PDSI) and the Standard Precipitation Index (SPI), two commonly used indices that are the Standard and Poor (S&P) of the weather market. Measurements of precipitation, air temperature, and soil moisture are collected and analyzed against historical data. The SPI is a flexible measurement looking at different time scales, since drought may be short-term or occur seasonally.

However one defines drought, we have to agree that the discussion of the weather is a daily phenomenon. And with the wildfires raging across the west, fire is added into that discussion. Though there is considerable disagreement about the causes of these fires, one has to agree that the dry conditions influence the severity and magnitude of some of these wildfires. So it is no surprise to me when I hear the local meteorologists describing the current weather conditions as “hot, dry and burning up.”

 

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