Summer rains in a drought-plagued state
How much does a monsoon season relieve drought?
Since moving to New Mexico four months ago, I have taken up a strange new hobby. I call it "puddle peeping." It's cheap and easy. Any weirdo can do it: First, I make mental note of depressions in the patchy asphalt outside of my apartment. After it rains, I check on them periodically to see how long the puddles that form in them last. There's a good one next to the Zumba studio across the street that I watch from the window near my desk. As I type this, it's supporting a puddle about three feet wide. Amazing! I thought when I saw it. So far as I know, it didn't rain here this morning, last night, or anytime yesterday. That puddle, my friends, has persisted for more than 24 hours.
Before you write me off as someone you'd never want to have a beer with, in my defense, long-lasting puddles are rare natural phenomena in arid New Mexico, especially on sun-baked asphalt in the summer. Evaporation is such a powerful force here that sidewalks are often dry less than an hour after it rains. The first time I noticed a puddle in that spot across the street last for more than a day, it gave me a small thrill. Now, though, the puddle's novelty is starting to wane. Since at least July, it's materialized a couple of times a week. The puddle has become a feature of the neighborhood nearly as reliable as the four chihuahuas down the street who do their best to terrify my much larger mutt every time we pass their fence.
This monsoon season has been generous to New Mexico, with blessedly above average precipitation falling over most of the state since mid-June (see first map to the right). In early August, one of the more dramatic storms unleashed nearly 3 inches of rain on downtown Albuquerque, turning Central Avenue into a rushing river, and making my neighborhood puddle look pitiful by comparison.
Arizona hasn't been nearly as wet, but the rains have made a decent showing there, too (see second map to the right).
The monsoons have, undoubtedly, given the residents of drought-plagued New Mexico and Arizona some measure of emotional relief. But how much real drought relief have they delivered?
The quick answer: Some, but not enough. And, it depends, on where you are and what drought impacts you're worried about.
"The tricky thing about summer precipitation and drought," says Mike Crimmins, a climatologist at the University of Arizona, "is that drought is contextual. It depends on who you're talking to what the impact is." To feed their cows, ranchers in the Southwest, for instance, depend heavily on grasses that grow during the warm season with the help of the monsoons. When the rains don't materialize, they immediately feel the impact. When the monsoons do produce, it can give ranchers a big boost.
If you are, instead, an irrigator, an urban water user, or a fish, who depends on water stored in reservoirs or healthy streamflows, summer rain provides more marginal drought relief. Winter storms are often giant walls of precipitation that shed moisture over large areas. Monsoon rains, on the other hand, are spotty and inconsistent. I've had deluges at my apartment while, a couple miles away, my parents' house has stayed completely dry, and vice versa. From a distance, in New Mexico's wide open spaces, one can often see exactly where a rain begins and ends. Monsoons also "happen in a season when evapotranspiration is so high," says Crimmins, "that it very rarely turns into deep soil recharge, and very rarely ends up in streamflow in any meaningful way. It's hot, and it's very high intensity, localized rain."
Andrew Church, a meteorologist with the National Weather Service in Albuquerque agrees. Some areas in central New Mexico that were classified as being in severe or extreme drought at the start of this year, are now considered only "abnormally dry" or in "moderate drought" by the U.S. Drought Monitor, a significant improvement. But if this winter is as snow-free as last winter was, they'll likely quickly sink right back into those deeper states of drought. With the monsoons, explains Church, "you don’t get the overall basin wide recharge as you would with above-average snowfall, which is a gradual melting and a gradual recharge that takes place over several months." And even with the gangbuster monsoon season, he says, "most locations in the state are still 8 to 12 inches below the average (for overall precipitation) since January of 2010. So there’s still a lot of catch-up to do." Adds Crimmins: "We need to have a good monsoon season, followed by a good winter, followed by good monsoons. The winters have been so bad that you could have good monsoons, followed by terrible winters, and still see trees die and streamflows down."
It takes a lot more water to fill a reservoir or stream than a puddle. Still, I plan to admire the beauty of every piddling puddle to come this summer. For each accumulation of water, however small, this arid-state dweller is grateful.
Cally Carswell is a High Country News contributing editor. She is based in Santa Fe, New Mexico. Follow @callycarswell.