12 August 2006

A Break In The Heat

Posted by Dan Satterfield

Well, we finally broke the heat wave. Many areas had some heavy rains over the last 48 hours as well, so that should make the farmers happy.

I have a tree in the yard that’s about 3 years old. It was almost dead from lack of water. After a good heavy rain Thursday night, it had perked back up nicely! I had been kicking myself for not noticing it, but the rains came just in time!

The damage may be done for many of the farmers in these parts. Several counties in the area are now classified as in severe drought now.

It might seem easy to classify a drought – just look at rainfall and perhaps temperatures, right?

It’s not that simple though.

Do you classify drought conditions based on rainfall for the past 30 days, or 60. What abut 90-180 days? Even rainfall over 6 months ago can impact crops. Some crops need more rain than others and some crops can handle a dry spell better than others.

You see it’s not really that easy!

There are several different drought classification methods in place. Each with their attributes and deficiencies.

One of the older ones is the Palmer Index. There are actually several different versions of it, but the main index is a long term index. The Palmer index will not change much for our area, in spite of getting 1-2 inches of rain late last week.

Below is the Palmer Index for July 2006:

Palmer July 06

There is a newer more experimental index that has been developed by the USDA and NOAA. This index reacts a bit more quickly to drought busting rains.


The link at the bottom of the image will take you the drought monitor web site where you can read more about how the chart is made.

One final note. The temperature is vitally important in a drought. In the winter, the air and ground are cold, and there is little evaporation from the soil. Just the opposite in the warm season. Evaporation rates are very high and plants are green. The high rate of photosynthesis and transpiration also uses up the soil water quickly.

This means that an inch of rain in January, will keep the soil wet much longer than even 2-3 inches of rain in early August.

It looks like we will go back to a fairly dry pattern next week (But not as hot!). The warm weather, and green plants will suck that moisture out of the ground quickly, and the soil will be bone dry again in just a few days!