It’s Time To Update How The Water Cycle Is Taught In K-12 Schools

I was sitting in a meeting yesterday watching extremely high rainfall rates from an unnamed tropical system passing through Georgia. As the rain hit the parking lot, some of it rushed to drains while portions of it pooled on the surface. Ironically, the meeting itself was for a National Science Foundation (NSF)-funded project addressing the emerging role of urban streams. In that moment, I realized that the processes being observed were not indicative of the water cycle likely being taught in many K-12 schools. Let me explain.

Most schools probably teach some version of the water cycle in the graphic above. For example, the NGSS Standard:​ ​(MS-ESS2.C-4)​ states: “Water continually cycles among land, ocean, and atmosphere via transpiration, evaporation, condensation and crystallization, and precipitation, as well as downhill flows on land.” In the atmospheric part of the water cycle, the typical components include some reference to evaporation, condensation, and precipitation. Once on the land surface, water can flow on (runoff) or through (groundwater) the ground, seep into the ground (infiltration and percolation), or be used by vegetation (uptake and transpiration). The explanation usually culminates with water finding its way back to the oceans where evaporation starts the process again. By the way, evaporation does not just happen at the oceans though the graphic above seems to suggest that too.

Ok, Dr. Shepherd what are some ways that the water cycle lessons are flawed or incomplete? Something is usually missing in typical water cycle graphics like the examples above from U.S. Geological Survey (USGS) and NASA. What is it? If you guessed urbanization, you are correct. Urbanization and associated impervious surfaces like parking lots and roadways fundamentally alter aspects of the water cycle. Over half to the world population resides in cities and that number is expected to grow in the coming years. Yet, we are still teaching kids about a “water cycle” that may not be completely representative of where they live.

Urban impervious surfaces have at least two important impacts on the water cycle. It prevents infiltration of water into soils and causes an increase in runoff into streams, creeks, rivers, and such. I often say that “floods” are not caused only by what falls from the sky. As the USGS website points out, “As watersheds are urbanized, much of the vegetation is replaced by impervious surfaces, thus reducing the area where infiltration to groundwater can occur. Thus, more stormwater runoff occurs – runoff that must be collected by extensive drainage systems that combine curbs, storm sewers, and ditches to carry stormwater runoff directly to streams.” Because water gets to the streams or rivers more rapidly, they can rise and flow with greater vigor. This leads to flooding. Rhett Jackson is a hydrologist at the University of Georgia and led the NSF urban streams meeting. Jackson once said in a press release,”Because the water in streams comes from the whole landscape, everything we see on the land has some effect on streams.” While he was referring to sediment and water quality in high elevation streams, it certainly applies to urbanization and flooding too. By the way, I said “at least” at the start of this paragraph because some of my research has revealed an “urban rainfall effect” too, but we will save that for future articles.

By the way, there are other ways that the “urban water cycle” differs from the natural water cycle. In cities, the water cycle also consists of stormwater, wastewater, treated water, and water piped into (and out of) homes, businesses, and other buildings. The City of Rochester, Minnesota website has an excellent discussion and diagram of a typical urban water cycle system.

Another way that K-12 water cycle lessons need to be updated is to account for climate change. Climate scientists have long warned that changing climate would cause an acceleration of the water (hydrological) cycle. For example, studies show that climate warming is speeding up the evaporation processes, particularly in the oceans. A University of San Diego press release describing a 2010 study said, “As water warms, it evaporates faster and escapes into the atmosphere. The atmosphere cannot hold water for long and releases it as rain and snow.” This leads to changes in salinity in the oceans and rainfall patterns. Precipitation intensity rates have generally increased as the climate system warms. An EPA website states, “In recent years, a larger percentage of precipitation has come in the form of intense single-day events. Nine of the top 10 years for extreme one-day precipitation events have occurred since 1996.” As a reminder, total amount of precipitation for an area may not change, but studies show that it falls in more intense, episodic events.

I know that some educators and school systems consider aspects of the things mentioned herein. At the aforementioned NSF meeting, a colleague mentioned how simply pouring a cup of water on the outdoor basketball court and the baseball field, respectively, is a great illustration for kids on the “urban” vs “natural” water cycle. The Earth system is changing and how we teach about it has to adjust also.

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