Environmental Issues

According to the U.S. Geological Survey, the water cycle comprises sixteen major components. They are water storage in oceans, evaporation, sublimation, evapotranspiration, water in atmosphere, condensation, precipitation, water storage in ice and snow, snowmelt runoff to streams, surface runoff, stream flow, fresh water storage, infiltration, groundwater storage and discharge and springs (2009).
   
Water cycle describes how water molecules move from the earths surface into the atmosphere and back again. Oceans account for 96.5  of the earths water supply and 90 of evaporated water (USGS, 2009 Graham, Parkinson  Chanine, 2010). Evaporation is the transformation of liquid water into gas or water vapor. Sublimation, that is, conversion of ice and snow directly into water vapor without turning to liquid first, accounts for a small portion of evaporated water (USGS, 2009). The remaining moisture comes from plant transpiration, release of water through the small pore or stomata on leaves, and evaporation from soil, collectively known as evapotranspiration. Volcanic magma containing water through volcanic emissions also contributes to atmospheric moisture. After entering the lower atmosphere water vapor moves to higher atmosphere and cools down. It condenses into cloud droplets which then grow into precipitation such as rain, sleet, snow, and hail (Graham, Parkinson  Chanine, 2010).
   
Some of precipitated water re-evaporates. Precipitation in the form of snow is partly stored in ice caps and glaciers. During warmer periods, some snow packs melt and water flows as snowmelt over land and enters streams (USGS, 2010). Some water infiltrates into the ground and can be found as groundwater in zones of aeration and saturation in the soil (Graham, Parkinson  Chanine, 2010). Part of the groundwater returns to water bodies as groundwater discharge. Some water is also stored as freshwater in lakes. The rest of the water runs off into streams and rivers and stream flow directs most of it to oceans and other bodies of water, initiating the cycle afresh (Graham, Parkinson  Chanine, 2010). The amount of water in storage far exceeds the amount of water participating in the water cycle (USGS, 2009). Despite this, 49,500 cubic kilometers of water is annually cycled through the atmosphere (Graham, Parkinson  Chanine, 2010).
 
Water cycle is also known as hydrologic cycle and the same is being impacted by climate change (Geerts, 2010). Increased greenhouse gas emission and atmospheric concentration raise temperature difference between surface water and the atmosphere. This intensifies evaporation process along with other aspects of the water cycle (Geerts, 2010). Research studies indicate that global warming is the result of increased night temperatures, which can lead to greater cloudiness and humidity at night and higher evaporative cooling during day time (Geerts, 2010). Rise in water vapors atmospheric concentration due to global warming facilitates greater precipitation by storms and increase precipitation in general. Further, rain patterns have been modified, increasing the severity of droughts in some regions while hiking flood threats in others. Empirical observations show that global warming results in heavier rainfall rather than more frequent or longer duration rainfall (Geerts, 2010). Agriculture has been greatly impacted as a consequence of the same. Storm intensity associated with Northern Hemispheres atmospheric fronts has also risen (Geerts, 2010). Since humans intercept water at different stages of the cycle, it is in the interest of human race to counter human-induced changes to water cycle.