Where Has All The Rainfall Gone?
Last updated 5/15/2018 at 11:21am
You probably noticed we haven't had much rain in Borrego this season. In the 2016 – 17 season, we had nine inches of rain, 50 percent above our average six inches. In this, the 2017 – 18 season, measured at the State Park rain gauge, we've had, wait for it, 1.01 inches!
On a single day, Jan. 9, 94 percent of that fell between midnight and 9 p.m. A few drops of water were felt during late morning April 19, but they were wind-bourne off the San Ysidro mountain tops and barely measured on the gauges.
So what does that mean, both for our aquifer and our Peninsular bighorn sheep?
The vast bulk of our aquifer recharge (estimated by the U.S. Geological Survey at 5,700 acre-feet per year and used for benchmark purposes for our Groundwater Sustainability Plan) derives from mountain stream runoff, and most of that from Coyote Canyon.
Rain falling in Borrego Springs is not nearly as important to aquifer recharge as rain in the mountains. It's estimated that rain from the skies directly to the ground in the Valley (exclusive of storm runoff from the canyons) is all but completely consumed by evapo-transpiration (water uptake by vegetation root systems and released from leaves into the air). Rain that does percolate down takes 30 – 50 years to reach the upper water table, now several hundred feet or more below the surface in places.
This coming July, it will be interesting to see water quality results in light of this season's dry conditions.
To conclude, we still need a lot more local research so as not to rely solely on informed guesswork and loose correlations, but rather get our facts right on what's actually happening.
In nature, everything counts, including rainfall, soil moisture, fault zones, and sheep. We hope for minimal impact this year in regard to our lack of rainfall's effects on the spring lamb count (and the overall bighorn population), and we can only look to the skies for more rain whenever we can get it.
Thanks go out to John Peterson, Mark Jorgensen, and Sicco Rood for their valuable input.
Full story in the May 3 issue of the Borrego Sun.