Drought Disrupts Fall Foliage

Fall is the northeastern United States’ time to shine: Leaf peepers from around the world flock to New England to enjoy the changing colors of autumn. The tourism fall foliage brings is a major industry in the region, but its success depends on the weather. A few rainy or foggy days could obviously wash out visitors’ weekend plans, but more importantly, long-term weather—like months of below-normal rainfall—can have a big impact on how much color shows up in the trees.

The amount of rain that falls in the months leading up to autumn plays a major role in determining how vivid the yellows, oranges, and reds are come fall. Leaves appear green because of chlorophyll, a pigment involved in photosynthesis—the process that allows plants to turn sunlight into the energy they need to survive. As the nights grow longer and days grow cooler, chlorophyll production in tree leaves slows to a halt. Once dying leaves stop producing chlorophyll, they change back to their “true” colors, showing us the color we would see if they didn’t have chlorophyll.

The U.S. Drought Monitor’s analysis for the northeastern United States on October 18, 2016. Image credit: Eric Luebehusen, U.S. Department of Agriculture

 
Normally, this process occurs in late September and early October in the far northern reaches of the United States, and slowly creeps south through Thanksgiving. But drought disrupts the changing of the leaves.

Trees can withstand a short-term lack of water, but when a tree goes without water for too long, it will gear up to survive the drought. To do so, trees start shutting down chlorophyll production early and cutting off water to the leaves in order to conserve water for the tree itself. As the leaves start to dry out and die of thirst, the lack of chlorophyll mutes their colors before they fall off. In a normal situation, the leaf is still getting water as chlorophyll production slows, and so survives long enough to lose its green pigment and revert to its original color. This is why many drought-stricken areas don’t see their usual fall foliage.

Unfortunately, parts of the Northeast are in a serious drought this year. This past summer tied for the third-warmest summer on record in the Northeast states, with the region as a whole measuring an average daily temperature of 69.3°F—that's 2.7°F above average. The weather patterns that caused the near-record warmth this summer also limited the amount of rain that fell over the region. For example, Boston, Massachusetts, typically sees a little more than 10 inches of rain during the summer months. This summer, the monitor at the city’s airport only recorded 3.92 inches of rain, the lowest summer rainfall on record since the weather station began operating in 1936. It’s a similar story across nearby parts of New England.

Fall colors show up in satellite imagery of interior parts of the Northeast on October 11, 2016. Image credit: SSEC/ODIS Today

 
In the days leading up to the traditional peak in fall colors across the Northeast, the U.S. Drought Monitor—a weekly analysis of drought conditions across the United States—shows that as of October 18, nearly 53 percent of the Northeastern region is experiencing some level of drought. Almost 26 percent of the drought is bad enough to be considered “severe,” and 5 percent of the Northeast is in an “extreme” drought, the second-highest category on the dryness scale.

At least the good news for folks whose livelihoods rely on tourists gawking at trees is that the very worst of the drought is near the coast, while the best colors typically appear in the deciduous and densely forested areas farther inland. Daily satellite imagery provided by MODIS Today shows that fall colors are still in full bloom across interior parts of the region. While they’re not as vivid as they would be in a more normal year, the trees will still be a sight to see for the next couple of weeks.