Wet Years, Dry Years

Reblogged from WUWT

Guest Post by Willis Eschenbach

I keep reading all kinds of claims that the slight warming we’ve been experiencing over the last century has already led to an increase in droughts. A few years ago there were a couple of very dry years here in California, and the alarmists were claiming that “global warming” had put us into “permanent drought”.

Of course, the rains returned. This season we’re at about 120% of normal … it’s called “weather”.

In any case, I thought I’d take a look at the severity of droughts in the US over the last century. I always like to take a look at the longest dataset I can find. In this case, I got the data from NOAA’s CLIMDIV dataset. Figure 1 shows the monthly variations from 1895 to the present. Note that I’ve inverted the Y-axis on the graph, so higher on the graph is dryer, and down near the bottom is wetter.

Figure 1. Monthly Palmer Drought Severity Index for the continental US, 1895-2019. Above the dashed line is dryer, below the line is wetter.

We can see a few interesting things in this graph. As you might expect, the worst droughts were in the 1930s, the time of the “Dust Bowl”. There were also droughts in the 1950s, although somewhat smaller and shorter.

Then for about thirty years, from 1970 to 2000, times were generally wetter … followed by drier times up to 2010, and wetter times since then.

Next, overall there is a very slight and not statistically significant linear trend toward a bit more wetness.

Finally, it’s worth noting that if our data had started in say 1930, it would have a statistically significant trend toward wetter times … which shows that even 80 years of data may give a very different answer than we get from the 125 years of data shown above. This is why I use the longest dataset available.

In any case, according to NOAA, there’s been no increase in either droughts or wet periods in the US since 1895 …

And meanwhile, here on the northern California coast, it’s Christmas Eve, and a gentle rain has just begun falling … best of the season to everyone.

About Russ Steele

Freelance writer and climate change blogger. Russ spent twenty years in the Air Force as a navigator specializing in electronics warfare and digital systems. After his service he was employed for sixteen years as concept developer for TRW, an aerospace and automotive company, and then was CEO of a non-profit Internet provider for 18 months. Russ's articles have appeared in Comstock's Business, Capitol Journal, Trailer Life, Monitoring Times, and Idaho Magazine.
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