Is the Historic Drought in the Western U.S. Now Moving East?

More people are noticing the multi-year drought in the West, but is it spreading? The following question about drought is from viewer Mike Schrammel in Stillwater, Oklahoma.

“Seems like over the last 40 years or so…arid conditions seem to be moving east. Several miles per year. Climate change or historical weather pattern movements?”

Read more stories about drought on AgWeb.

I should point out this question was received last spring before many parts of the Midwest endured some below-normal rainfall. I had my preconceptions what the answer was, but a little research muddied the waters – or dust anyway. The term arid is defined as having little or no rain but is usually connected with high temperatures as well.

I think these maps from NOAA data might help.
 

This map of the continental U.S. shows current average annual rainfall. The colors can be misleading but there is a sharp decline in the eastern Plains.  

Compare that with these series of 30-year increments of rain and temperature from NOAA. Climate scientists have fixed on 30 increments to create averages and expose trends. For precipitation the averages are actually increasing east of the Mississippi, and a smaller amount elsewhere. The largest change has been in the northern Midwest which probably contributes greatly to cropping changes and yields we have seen during my career. Now add in the same series for temperatures, which are even more dramatic.

The perception of increased aridity may come from both factors, but temperature appears to be the dominant influence.  The West is scorching with acceleration since the turn of the century. Since rainfall was not high there historically, what little more has been received is subject to rapid evaporation.

Both maps show trends going mainly one direction, not randomly changing. I think it is a result of climate change because it is exactly what a climate scientist told me would happen in my area of the central Midwest twenty years ago: longer and more frequent droughts and larger and more frequent rain events.

If it is a cycle, it is on a long enough timescale farmers cannot simply outlast the trend.