A BLAZE OF RED: The Fragrant Hill in the western suburb of Beijing puts on its autumn show as the city begins to feel the chill of winter (WANG XIANG)

People are donning extra layers to buttress themselves against sharpening winds. They move a bit faster, conducted by walking cadences dictated by slowly dropping temperatures. The calls of bicycle-bound hawkers selling packs of toilet paper strapped to their old conveyances as they peddle through apartment complexes penetrate deeper into still sleepy early-morning bedrooms, carried farther aloft by the cooler, thinner air.

There is a decided chill outside as Beijing once again makes its yearly transformation into a different city and throws on its winter coat. It seems no time at all—it always seems like the calendar days have been pulled off all too quickly, as if by some mischievous child playing a prank, when one dives into the memory of the recent past—since the first heat of spring loosened the city's icy joints.

Clouds of Beijing's stir-crazy denizens escaped their wintry confines then into the first warm rays of sunshine and they exploded into activities befitting the change. Plazas throughout the city, like the one in front of the exhibition center, hosted hundreds of residents who streamed out of the encircling apartment buildings to dance the tango. Over a portable amplifier, the dance leader's voice could be heard teaching movements for a new step.

"Yi, er, san, si, wu!" she called, a gleeful metronome to the dancers who moved in unison to the Argentinean music. The sky above her was sutured with half a dozen kites, all sporting the peculiar Beijing style of having brightly colored and blinking LED lights crawling up their strings and adorning their sails, creating a simulacrum of a family of airborne dragons' armored backbones. Trees and flowers along the city's medians and sidewalks celebrated, too, sprouting their warm weather costumes of verdant greens, whites and yellows that seemed to be the embodiment of Beijing's spring and summer life.

But now, that flora is doing the same as the city's human residents, but in the inverse. The trees are bedding down for the autumn by shivering off their summer clothes, sloughing off brown, crunchy leaves that once caught the organism's dinner from nourishing sun rays. The armies of street sweepers busily help the disrobing process by brushing up the organic detritus of summer with their tree-bough brooms and their metallic litter baskets. Meanwhile, the flowers and grasses begin to recede into the earth, getting ready to take shelter from the frigid conditions in the relative safety of their bulbs and roots.

It is hard to know whether it is the temperature itself or the changes in light that signal to our evolutionary brains that it is time to make preparations for benumbed seasons ahead. It is probably both, the weaker midday light and the earlier sunsets as the globe alters its tilt to accommodate the Southern Hemisphere's coming summer playing as much a role to tell us that change is come. Or perhaps it is the smells that send the alert to our cultural brains. The floral notes of the street-side fruit stands and farmer's markets is slowly being replaced by the earthiness of roasting chestnuts and boiling sugar in which kebabs of fruit are dipped. Those smells remind us that the warmth we generate among family and friends in fall and winter replaces all we remember of the warmth that is free in spring and summer.

The eight-day National Day holiday seems to have been the period on the end of the sentence that is summer and Beijing instinctively mimics the flowers that are bedding down. It is a process whereby warming bowls of Beijing noodles gain favor over cooling plates of cucumber and tomato salad. The bars and restaurants at Houhai, Nanluogu Xiang and Sanlitun are all quiet, to the chagrin of food and beverage entrepreneurs across the city, and the talk at the little expat watering holes is like a script brought out for a reading at this time every year.

"Supposed to be cold tonight," one says over a Harbin beer.

"Uh-huh," another responds. "Guess that's it for summer and rooftop-terrace cocktails."

"Yep," the first says.

"Time for one more courtyard dinner before its unmanageable?" a woman offers in a lovely, lilting British accent.

"Absolutely," the second says. "And maybe another round of chuan'er at that sidewalk Xinjiang place at the end of the street."

Outside one such bar, the thinning crowds of Chinese and foreign pedestrians serve as a thermometer for those having their drinks and quiet conversation inside, which in the warmer months would naturally elevate to anything but the adjective quiet. What once were slowly strolling window shoppers sporting airy summer dresses, T-shirts, open-toed shoes, wagging tongues and swiveling heads looking at the newest fashions on display, are now the marching and bundled figures with heads down who are just searching for somewhere warm to take shelter. All of Beijing draws inward for its long winter slumber.

The writer is an American living in Beijing