Hail the Autumnal Equinox!

It’s official: Summer is over. Oh, I know. Lots of folks thought it was already over, once the kids went back to school, or once Labor Day passed. But officially, Summer ends and Fall begins today, September 21.

This date is known as the Autumnal Equinox, one of only two days all year when the length of daylight is exactly the same as the length of night. The other day is the Vernal Equinox, on March 21. Each of these days have attracted great attention from our ancestors because of this unique feature. Nowadays, folks don’t seem to pay so much attention to such cosmic events. More is the pity.

Sadly, the amount of daylight is diminishing rapidly now, and the length of days will continue to diminish until the Winter Solstice comes on December 21. It also means that things will be cooling off.

What this means to water folks is that our customers should be using less water. The main reason for the decline in demand is irrigation. Shorter, cooler days mean that plants will need less water. And there are two factors behind this.

First, less sunlight means less growth for photosynthetic organisms like plants. Less carbon dioxide will be taken from the atmosphere by plants — terrestrial and aquatic. I would expect to see carbon dioxide levels rise world wide — at least in the Northern Hemisphere — due to this decrease in activity. I wonder what our climatologists will have to say on this issue.

But less plant activity means that the plants will require less water. Every carbon dioxide molecule that is converted into chemical energy during photosynthesis will require one water molecule for the conversion. So, less sunlight means less photosynthesis, and less photosynthesis means the plant will consume less water.

During the Fall, evaporation rates are low, due to lower air temperatures and less sunlight. This will also reduce the amount of water required for irrigation. So make sure to use the Equinox as a time to reset your sprinkler timers.

In most climates, Autumn means great Fall foliage, such as in today’s photo. In Southern California, it means the onset of fire season instead! We will experience some extremely dry weather periods as the Santa Ana winds come upon us. This poses a challenge to homeowners struggling with their landscaping, and for fire fighters watching for the next big blaze.

But it also poses a huge challenge to water folks. Rapid changes in demand mean that treatment plants will be experiencing frequent flow rate changes. Reservoirs will be too full or too empty, as customers fluctuate their flows. Water quality changes in raw water reservoirs may require frequent changes in chemical dosages. Change is the theme of the season.

And those fire fighters are far more effective when they have something coming out of their hoses! For them to do their jobs, we need to do ours — especially now, during the challenging weeks following the Autmnal Equinox.

I will be “on assignment” the next couple of days. If all goes as planned, I’ll be back with you on Friday.

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