The Science Behind The Flood

Adith Velavan ’19
EE
 Contributor

On September 25th, Trumbull experienced flash flooding and over seven inches of rain, the second most in the state, resulting in excessive damage in town. The high school was closed for three days, entire streets and areas were closed, and the fire department responded to 80 calls, rescuing 45 people, according to Assistant Fire Chief Alex Rauso. He went on to describe how the wet roads and ground could no longer hold any more water, and that the torrential downpour filled the storm drains, eventually overflowing and flooding the Town, four to six feet in areas.

Trumbull was hit with a weather event termed a flash flood. A flash flood is categorized as such when it occurs within six hours, in a mostly low lying area, and is often predated by a storm or other rain related event. While these floods can occur in a variety of situations and geography ranging from poorly absorbing soil to volcanoes that cause the melting of glaciers, all of these flash floods are predicated on the fact that they occurred within a short period of time.

Most people learn about rain as a simple process, and in terms of the weather cycle. Water evaporates, condenses, and then precipitates. Much of the evaporation, however, occurs in large bodies of water, which arise as a result of runoff. Due to the hill and valley topography, of Trumbull, the rain pooled in the lower areas of the town, acting as watersheds, and creating flash floods. Moreover, the amount of rain that fell in the short period of time was increased by a scientific process called coalescence, which is when rain droplets join together, as a result of a cold front, to form larger amounts, thereby allowing a greater amount of rain to fall in a shorter period of time.

Mr. Heher, the new AP Environmental Science teacher, also described how the porosity and permeability of soils can contribute to a flood.  He explains that, “we took soil…and covered it with asphalt…and with all the roads… the water now collects and starts running,” describing water pooling and running as a result of a lack of soil absorption. While Trumbull has a decent absorption level as it is composed of soil, clay, and sand, at the time of the flood, the soil was over permeated as a result of a very wet summer. The asphalt covering much of Trumbull only caused further poor absorption of water. In addition to these direct effects, there are other certain larger weather patterns that had an effect on this flood’s formation.

The weather has transformed in the past decade. Scientists attribute an increase in extreme weather, and excess rain, due to greater evaporation since the planet is warmer as a result of global warming.

Further continental and atmospheric conditions exacerbated this trend. 2018 is the transition year between the La Nina and El Nino jetstreams, air currents in the atmosphere. Many jetstreams exists at different latitudes, and can flow in a variety of paths. The heat from the sun, movement of water, and rotation of the Earth all affect the flow of these jetstreams. Formally known as the El Nino Southern Oscillation, this jet stream is the main cause for much of the extreme weather, and rain in the Northeast recently. It works by pushing colder air towards this area, allowing storms to form and move faster to the Northeast, and resulting in increased weather events.

As a result, just prior to our event, the eastern United States was hit with Hurricane Florence which brought rain along the eastern coast. In turn this storm also brought a cold front, which pushed the warm air in the area to rise, cool, condense, and then to precipitate as rain, giving us double the amount of rain.

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