How the diminishing daylight in Mid-Missouri will trigger the start of fall foliage
If you've been out in the evening recently, you have probably noticed that we have been losing daylight quickly. Over the past couple of weeks, the entire state of Missouri has experienced its last 8 PM sunset in a long time, and sunsets are only getting earlier.
As of August 28th, the sun will be setting at 7:45 PM in Columbia, but only one week later, on September 4th, the sun will be setting 11 minutes earlier. Only 3 weeks after that, on September 25th, the sun will already be setting at 7 PM, giving us only 12 hours of daylight.
This loss of daylight and the seasons we experience are all caused by the Earth's tilt. The Earth is tilted on its axis at 23.5 degrees, and as it orbits the Sun, this tilt leads to different portions of the Earth receiving the most direct incoming solar radiation.
During the summer solstice, the most direct solar radiation is received by the Northern Hemisphere, and the Sun is at its highest angle in the sky.
As we approach the autumnal equinox and the winter solstice, the angle of the Sun in the sky begins to lower, all because the Southern Hemisphere is beginning to receive the most direct radiation.
The main focus with this lowering angle may be lower temperatures to go along with it, but the angle of the Sun also plays a major role in fall foliage emerging.
This is because chlorophyll, or the green pigment in the leaves of trees and plants, traps the incoming sunlight. This creates food for plants and trees during the growing season. When the sun angle begins to lower, transitioning from summer to fall, the intensity of the sunlight decreases.
This decrease causes cells to form at the base of the leaf and stop carrying fluids. As these fluids stop, the sugars and food begin to be trapped. This results in new color pigments being produced prior to the leaves falling.
Change in temperature throughout the seasons still plays a large role in the emergence of fall foliage, but it impacts the foliage in a different way. With abnormally warm days, more clouds, and warm nights leading up to and through the change in color results in more muted colors during the peak. As for more seasonably warm days, more sunshine, and cool, crisp nights, the result will be more vibrant colors.
Another factor that helps determine the timing of when this color change occurs is moisture and rainfall. With too little rainfall or drought stress, the dry conditions strain the trees, so in order to preserve themselves, the change in color actually occurs earlier, often also leading to more muted conditions.
The most ideal conditions would be enough rain during the spring and summer seasons to help the trees stay hydrated enough to produce enough sugars for brighter colors to occur. It's typically okay if a slightly drier early autumn is experienced, so long as sunshine persists and widespread drought does not take over.
