Water cycle 2.

In the previous post you could read about where the Earth’s water resources can be found and how much time water spends in the spheres. Now, you can find out which natural interactions are responsible for water movement between the different spheres.

The Water Cycle

Source: https://www.usgs.gov/special-topic/water-science-school/science/fundamentals-water-cycle?qt-science_center_objects=0#qt-science_center_objects

Water cycle is generated by energy arriving from the Sun. On the extensive free surface of seas and oceans water easily starts to evaporate and get into the atmosphere due to solar radiation. We can see the same process on a smaller scale on the surface of lakes and rivers or ice and snow caps. Not only the physical evaporation but also plants can transport water (mostly shallow groundwater, infiltrating rainwater) to the atmosphere. This is called transpiration.

When the air becomes saturated by vapour, water condenses and cloud formation starts. This is usually caused by the uprise and cooling of humid air masses. Clouds lead to precipitation when water migrates to the lithosphere or hydrosphere. It can have several forms like rain, downpour, thunderstorm, snowfall, hail.

When it lands on the ground surface, a part of rainwater infiltrates through the unsaturated zone and reaches the groundwater level. Groundwater flows slowly in the lithosphere and gets into rivers, lakes, lagoons, or directly into the oceans. The other part of rainwater doesn’t reach the groundwater level but it can take part in the following three processes:

1. It can move horizontally along an aquitard in the unsaturated zone and come to the surface again. This is called interflow.
2. Rainwater can flow down as surface runoff as well, if the precipitation intensity exceeds the infiltration capacity. Runoff water and rainwater can also reach rivers and be transported to seas and oceans.
3. However, rainwater can land on plants or artificial objects like rooftops or roads. Here, water can’t infiltrate so most of it evaporates and returns back to the atmosphere. This temporary process of water cycle is called interception.

As we can see, groundwater is an important part of the water cycle that we tend to forget sometimes. During a construction or city planning, we must count on increasing interception and decreasing groundwater level. Similar consequences can be expected in case of afforestation due to increasing transpiration, or a pond because of the more intensive evaporation of groundwater. Irrigation or groundwater pumping can modify groundwater flow systems and change the water balance of recharge and discharge areas.

Climate change has an impact on the water cycle as well. In Hungary, increasing average temperatures, increasing evapotranspiration, and more extreme weather conditions (drought, flash flood, intensive thunderstorm) are predicted.