It's fall here in the Northern Hemisphere. The nights are getting longer and temperatures are getting cooler.
Trees in cool climates are preparing themselves for winter by breaking down the chlorophyll in their leaves so that the nutrients can be used in their roots and trunks. As the green-colored chlorophyll disappears, yellow pigments in the leaves are revealed. Some also start producing red pigments, likely to help the trees store up nitrogen. The result can be spectacular, with whole forests clad in fiery yellow and orange and red.
That said, as a California native, I never fully understood the New England fall color frenzy when I was living in Boston. Along with the weather forecasts the local news stations would have fall color reports., apparently so you would know where to join the zillion other leaf peepers who jam the back roads of Maine and New Hampshire in late September and early October. I'd just as soon see the forest past it's peak if it means fewer people.
Here in the southwest, the foliage has apparently just hit it's color peak. That's not really noticeable, at least where I live. Few of the native trees and shrubs here change color in the fall. Many don't even lose their leaves for the winter. Not surprising, considering that winters here are pretty mild. At higher elevations where snow is common, the forests are pine, not leafy trees.
That's not to say that there aren't plenty of colorful reminders that fall is here and winter is approaching.
Non-native trees like liquidambar (sweetgum) provide color to residential neighborhoods and parks.
Colorful apples are ripe and ready to pick - and delicious to eat.
Pyracantha berries are plentiful, much to the delight of the local birds.
The lakes are stocked with colorful fish.
Lantana and other flowers are in bloom.
Pumpkins - both real and artificial - add orange to the landscape.
And of course there are the colorful political signs, which will vanish (hopefully) after tomorrow.
Of course this coloration is due to human intervention - non-native plants and animals, man-made signs and decorations.
You have to look to the hills and skies for the true natural colors of autumn: hillsides sprouting green from the first rains of the season, blue skies, and orange sunsets.
Fall is my favorite season.
(If you are interested in my nerdy take on seasonal change, check out my post about Night and Day at Science in My Fiction)