Where have all the colors gone?
Last summer we had, technically speaking, a series of heat waves. Experientially, however, the summer was more like one long heat wave, interspersed here and there by a day or two below the ninety-degree mark. As the heat persisted, I know that I wasn’t alone in longing for the cool, crisp days of fall.
At last, after an exceptionally warm start to the month, we’re finally there, enjoying seasonable days and windows-open, cool nights. Unfortunately, those hot, dry days of summer and a summer-like September will probably translate into less brilliancy in fall foliage. We’ve already seen leaves turning brown and dropping from trees. Will they all go directly from green to dead, without putting on the colorful display we’re used to?
The change in leaf color is a product of shorter days and cooler nights. But what about the actual color? How can you know if the foliage in any given year will be more or less brilliant than usual?
You probably remember the basics from science class: chlorophyll, which gives leaves their green color, is predominant during the warm, growing months. As the weather cools, trees shut down their food manufacturing system. Chlorophyll decreases, letting the other colors already present in the leaves show up.
I love this easy-to-understand explanation from meteorologist Jake Reed (WHNT 19, in Atlanta, Georgia). He says that it takes “a succession of warm, sunny days and cool, crisp but not freezing nights . . . to bring about the most spectacular color displays. During these days, lots of sugars are produced in the leaf but the cool nights and the gradual closing of veins going into the leaf prevent these sugars from moving out.
“These conditions — lots of sugar and lots of light — spur production of the brilliant anthocyanin pigments, which tint reds, purples, and crimson. The amount of moisture in the soil also affects autumn colors.
“A warm period during fall will also lower the intensity of
autumn colors. A warm wet spring, favorable summer weather, and warm sunny fall days with cool nights should produce the most brilliant autumn colors.” (http://whnt. com/2016/09/15/how-willthe-ongoing-drought-affect-fall-foliage/)
So, how “favorable” was our summer weather? Let’s take a look at the rainfall over the past several months. The second half of summer wasn’t just hot, it was also dry. In our area, the average rainfall for July, August, and September is roughly twelve inches. At present, we’re nearly thirty percent short of that mark.
While that may not sound too drastic, the entire
month of August registered just 0.94 inch on my rain gauge. We don’t typically expect a lot of rain in late summer, but this was dramatically less than usual. My records show 3.13 inches in August 2015, 4.67 inches in August 2014, and 6.21 inches in August 2013. The scant inch we saw in August this year — the sum of five precipitation events — was barely enough to settle the dust; it certainly couldn’t penetrate down to tree roots.
Rain is coming this week. In fact, it may be raining as you read this. Will it be enough to boost leaf color? We will have to wait and see.
Note: Did you know that you can find monthly rainfall data for Chester County online? Volunteers in twenty-one municipalities collect and
report the precipitation each month, which is compiled and archived by the Chester County Water Resources Authority. Their online records go back to 2000. I’m one of the volunteers, showing up on the chart as Station 106, East Pikeland Township.