Introduction to Environmental Science: Water Cycle and Human Use

The water or hydrologic cycle has to do with the way that “water moves through the land, ocean, and atmosphere in a continuous process”. The cycle has four major parts which allow said cycle to function and run. These parts are evaporation, transpiration, condensation and precipitation. Evaporation occurs when there is a transfer of water “molecules from a liquid to a gaseous state”. When water returns to land and water this is done through condensation which is the formation of liquid water from a gaseous state. Transpiration is when water vapor is lost as it moves “from the soil through green plants and exits through leaf pores”. Lastly, precipitation is when water is released from clouds in the form of rain, snow, sleet or even hail. It is important to note that with any scientific cycle there will be human impacts to said cycle. Categories of human impacts to the water cycle include changes to Earth’s surface, changes to Earth’s climate, atmospheric pollution, as well as, withdrawals for human use.

Changes to Earth’s surface are not limited to the loss of vegetation, taming rivers and wetlands, along with building impervious surfaces such as roads, buildings and parking lots. Loss of vegetation is bad because like with everything else, when something in a cycle is altered it has consequences for things that rely on it. Plants are kings so without them it affects the world around us in ways we wouldn’t even imagine possible. “In cleared forests and overgrazed land, plants do not intercept rainfall”. This is not good because it leads to water shifting creating runoff which we know is not a good thing. “Less infiltration leads to less groundwater recharge resulting in dry, barren, lifeless streambeds” which again is not good for the ecosystem and people dependent on the water source. As far as impervious surfaces go, they prevent infiltration and increase runoff which is not good for the ecosystem and organisms that deal with said runoff. Humans also affect the flow of surface water. This is done with the use of dams, levees, impervious surfaces, channelizing rivers, and vegetation removal. Although people use dams to “try to lower flood risks, they do cause ecological issues”. Dams keep and use surface water, but they ruin habitats surrounding them and change the flow of the river. Which is not good because then certain fish cannot swim upstream/downstream to return to the ocean which messes with the food web / food chain.

Earth’s climate is indeed warming due to the rise in greenhouse gases which also alters the water cycle. When the “climate is warmer it means that there was more evaporation from land surfaces, plants and water bodies”. While a wetter atmosphere means more frequent and heavier precipitation. Climate change also has impacts on water bodies due to warm water having greater volume. It’s important to note that a warmer ocean creates a higher sea level; along with melting glaciers turning water from ice to liquid eventually making its way into the ocean.

Not only is the Earth’s climate changing but we are seeing an increase of anthropogenic aerosols in the air. They are being seen in the form of “sulfates from sulfur dioxide in coal, carbon in soot and dust which are forming a brownish haze”.

Since aerosols promote the formation of smaller-than-normal droplets in the clouds, aerosols actually suppress rainfall where they occur in abundance, even though they encourage cloud formation. As they do so, the atmospheric cleansing that would normally clear the aerosols is suppressed, and they remain in the atmosphere longer than usual. With suppressed rainfall comes drier conditions, so more dust and smoke (and more aerosols) are the result.

Aerosols are a problem even if they are on a smaller scale compared to climate change as a whole. Due to climate change being an issue for everyone where aerosols are more local.

Withdrawal of water for human use is also a huge problem. Humans tend to overtake non-reusable resources water being included. “70 % of the water we use is used for irrigation purposes”. Furthermore, irrigation uses 80% of freshwater in the United States which is a whole lot of water. Developing countries are not as lucky to have clean fresh water for drinking; so they are forced to use contaminated water. This brings the argument in of whether bottled water is the answer for these unfortunate people. Bottle water is also harmful to the environment due to the amount of energy needed to produce and ship the water bottles; though bottled water is useful in emergency situations. It’s a catch 22, because nothing is ever going to be 100% good for the environment (sustainability) and good for humans – especially not if we keep overtaking like we currently do.

All of the human impacts are important and effect the water cycle, but the issue with climate change and human withdrawal are the two most prominent. This is because they are the two humans can do something to lessen the impacts for. We can do this by not using single use plastics as much as possible, eating local, using drip irrigation over flood irrigation. Lessening human impacts can also be achieved by creating more public policy that is put in place for fracking to try and limit this practice since it has the potential to contaminate drinking water.

Works Cited

• “Chapter 10 - Water: Hydrologic Cycle and Human Use.” Environmental Science Toward a Sustainable Future, by Richard T. Wright and Dorothy F. Boorse, Pearson, 2016, pp. 233–259.
• Williams, Jennifer. Chapter 10. October 2019, https://blackboard.stockton.edu/webapps/blackboard/content/listContent.jsp?course_id=_71899_1&content_id=_1769004_1. PowerPoint Presentation.
• “Description of the Hydrologic Cycle.” Northwest River Forecast Center (NWRFC), 22 Oct. 2002, www.nwrfc.noaa.gov/info/water_cycle/hydrology.cgi.