Friday, November 28, 2008

Monsoons I Have Known

I’ve lived in this spot since October, 1973. For a few years back then, we lived in a rather primitive manner – no clocks, no calendar, no electricity, a hand pump out in the pasture, and an outdoor fire circle behind the house where we cooked our food. Not surprisingly, I don’t have any rainfall records for that era. (Though I did write some stories that capture the flavor of the wild and wonderful time.)

It wasn’t until July, 1982 that I started keeping rainfall records, and I’ve been keeping them ever since. Twenty-eight years of records from one location is starting to become statistically significant. In that time I’ve encountered a lot of unusual weather mixed with the usual dryness.

The monsoon in this part of the Southwest lasts from June through September. On the average, March through May are the driest months of the year. During this time, the dryness and heat steadily increase. Unless the monsoon fails, in which case July can be extremely hot, June is the hottest month of the year. In a poetic turn of phrase that I’ve always appreciated, James Hastings and Raymond Turner, in their book, The Changing Mile, called the pre-monsoon part of June the “arid fore-summer.”

It’s impossible to miss the beginning of the monsoon. Whenever the relentlessly hot afternoons start to give way to afternoon thunderheads, the monsoon season has begun, even if it hasn’t started to rain yet. At least the clouds provide a bit of relief from the relentless hot sun.

Before we proceed any farther, let’s look at our typical monsoon rainfall pattern. Here’s the average summer rainfall for Las Cruces between 1959 and 2005, courtesy of the Western Regional Climate Center:

June 0.75”
July 1.42
Aug 2.12
Sept. 1.28

Total Monsoon 5.57
Total Annual 9.23

The four monsoon months account for 60% of our annual rainfall; the other eight months contribute the remaining 40%. Averages are deceptive, because summer rain is typically brief and intense. Sometimes very intense. Sometimes catastrophically intense. Consider the average August rainfall of 2.12 inches. During an intense storm, we can get this much rain in 15 minutes! Rain like this has to be experienced to be believed, and in such cases one might be inclined to say, “I’m a believer already! Please stop now!” (The Great Flood of ’06 in Radium Springs was caused by 4” of rain in half an hour.)

Since 1983, monsoon rainfall at my home has varied between 2.83 (2003) and 13.25 inches (2008). This is our total rainfall for the months of June through September. 2.83 inches of rain during the four hottest months of the year is barely enough to raise the humidity. During such a summer, it’s no wonder this area is called a desert!

This past summer was our all-time wettest monsoon, with 13.25 inches of rain. The summer of 2006, the infamous Monsoon from Hell which caused disastrous flooding in Alamogordo, El Paso, Hatch, and Radium Springs, was our second-wettest, with 11.90 inches. So it’s tempting to ask – are our summers getting wetter?

According to my records, the answer to this question is a resounding “no.” The year 2000 seems like an appropriate place to begin our historical survey. During the nine years 2000-2008, the average monsoon rainfall was 6.65 inches, a little above the average of 5.57 inches. If we ignore the wet years of 2006 and 2008, the average for 2000-2008 becomes 4.95 inches, a little below the long-term average.

But there’s more. Both 2000 and 2004 had unusually wet Junes. June 2000 had an incredible 5.74 inches of rain, compared to the June average of .75 inches. This was followed by an unusually dry July -- .66”, less than one-third of the average July rainfall. The same thing happened in 2004: the June rainfall was 4.03 inches (the second-wettest June on record), followed by a July with zero rainfall. (When we get a July with no rain whatsoever, we are looking at a severe heat wave as well as a severe drought.)

Rainfall is more than a statistic. Desert plants are totally dependent on rainfall for survival, and the timing of the rains is critical. If we have heavy rainfall in June, the desert plants are stimulated into growth, but a dry July will cause them to go dormant again. So a wet June followed by a hot, dry July is far from optimal for sustained plant growth. I’m inclined, for the purposes of this discussion, to ignore both 2000 and 2004, because of their anomalously high June rainfall, and concentrate on the remaining five summers.

What we see is a pattern of severe drought. Bear in mind that these are rainfall totals for the entire summer:

2001 4.40”
2002 3.97
2003 2.83
2005 3.12
2007 4.32

Average 3.73

Some climate scientists speculate that our future climate in the Southwest will be persistent severe drought interspersed by disastrous flooding. My rainfall records seem to support this hypothesis.

Another interesting fact – there seems to be an inverse correlation between Texas and New Mexico rainfall. Texas has heavy rains when we have a dry summer, and Texas has a drought when we have floods. This pattern would bear watching – there’s probably a fairly simple mechanism at work here.

It’s interesting to compare the two unusually wet monsoons, 2006 and 2008, which were completely different. Here in Radium Springs, the 2006 monsoon didn’t start until July 29, which is extremely late. During the 37-day interval between July 29 and Sept. 3, we had 10.05 inches of rain -- greater than the average annual rainfall of 9.23 inches. That 37-day period would rank as our 5th wettest monsoon ever!

The 2008 monsoon was totally different. We had by far the wettest July ever, with 8.04 inches, thanks in part to Hurricane Dolly, which caused disastrous flooding in Ruidoso. (It’s interesting how many times the term “disastrous flooding” has appeared in this discussion.) August was wet as well, with 4.05 inches – our fourth-wettest August.
But 2008 didn’t have the disastrous flooding (there it is again) of 2006, except in isolated locales.

2006 was a classic “wildflower year.” As a beekeeper, I would prefer that the entire monsoon rainfall be spread evenly through the months of August and September. (An inch a week would be just fine, rain gods.) July rains allow the grass and amaranth to get a head start, making it harder for the wildflowers to compete. Since the wildflowers tend to sprout later than the grass and amaranth, it’s better for them if the rains hold off as long as possible. That way, everybody gets an equal chance. If the rains last until at least the middle of September, when temperatures begin to cool off, the wildflowers keep blooming right up until frost. Beekeepers like a long wildflower bloom.

2008, on the other hand, was a classic “amaranth year.” Some people call it pigweed. Since amaranth is wind-pollinated, it doesn’t produce nectar to attract bees... so beekeepers, like farmers, are inclined to call it a weed. The heavy July rains stimulated a heavy growth of this plant. The entire Mesilla Valley – roadsides, ditch banks, vacant lots – was covered with the thickest growth of amaranth I’ve ever seen.

It’s impossible to say what next summer will bring. This winter is shaping up to be a dry one, with a poor snowpack and not enough irrigation water for farmers next summer. But this means nothing as far as predicting next summer’s monsoon. We will recall that the 2006 “Monsoon from Hell” followed the driest winter in 100 years... but I doubt if there’s any correlation between winter and summer precipitation. I suspect, for no good reason except that we’re in a long-term drought, that we’ll be in for a dry summer next year. There’s a strong element of wishful thinking at work here -- after the 2006 monsoon, I’ve become a big fan of dry summers.


Anonymous Anonymous said...

It never rains in Spain, so why does it rain in Radium Springs?

11:31 PM  

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