Human consumption of water and interaction with the water cycle both contribute to water stress in a complex dynamic that has resulted in environmental damage and risks to human security.
- Humans are directly disrupting the hydrologic cycle in the way they use water through the unsustainable use of freshwater, pollution of water at all stages of the cycle, and manipulations of water flows.
- Disruptions in the hydrologic cycle are resulting from climate change. This climate change, or global warming, is thought to be caused by human-driven carbon dioxide emissions.
- A disrupted cycle means that we can no longer predict as accurately where water will be, in what form, and in what quantities. We depend on our knowledge of how the hydrologic cycle has worked over time, but climate change undermines the reliability of this information in forecasting future weather patterns and freshwater flows.
In this section...
How Humans Directly Disrupt the Water Cycle
Below are some of the ways in which humans directly disrupt the water cycle:
- Pollution that harms the quality of water in all its three forms: liquid, gas, and solid. When it finally ends up as freshwater, its quality is often compromised.
- Depletion of aquifers (underground water) by over-extraction and drilling for freshwater. Many aquifers are recharged by annual rainfall and melting of the snow pack, but humans are using water of aquifers faster than it can be replenished. This means there is less water available annually in these previously abundant underground lakes. It also means that water is harder to access because water tables fall (i.e., you have to go deeper and deeper to get it). Flows to rivers and lakes, and even back to the ocean, can also be affected by low water tables.
- Damming of rivers and streams that impedes water flow and harms fish and other marine life. Water that is trapped in lakes doesn’t move through the recycling process as efficiently.
- Urbanization that has replaced porous soils with concrete, removed trees and plants that control water-runoff, and stressed water supplies by concentrating human activity. That many of these cities are coastal and built on wetlands and marshes only further damages ecosystems that help the movement of water through the cycle.
How Humans Indirectly Disrupt the Water Cycle: Climate Chage
Below are some of the effects of climate change:
- Global warming melts the environment’s natural water banks – glaciers, ice caps, and snow pack. At higher temperatures, water moves more quickly from its solid to liquid form. In the short-term, this can cause floods as rivers and streams swell from fast-melting snow and ice. In the long-term, it is like spending your savings from a bank; it takes a long time to replenish what is withdrawn.
- Melting snow changes the composition of the oceans. Oceans depend on a fragile balance of fresh and seawater, cold and warm water. Disruptions affect marine life and ecosystems vital for the health of the oceans and thus the health of the hydrologic cycle. These changes to the ocean’s composition also affect currents and weather patterns and can lead to increased volatility in the form of tropical storms and other extreme climate events.
- Glacial melt is expected to contribute to rises in sea levels as well, as more volume in the ocean from melted snow and ice pushes water up and over existing sea-land boundaries. This destroys fragile river delta areas as freshwater is overwhelmed by sea water.
- Climate change has resulted in warmer temperatures in many bodies of water. Warmer water, whether in oceans or lakes and streams, evaporates faster than cooler water, speeding up the hydrologic cycle. This can result in the disappearance of freshwater before it can be used. Rivers and lakes can run dry even before they make it to the ocean, effectively taking water out of circulation in this part of the cycle.
- Weather pattern disruptions brought on by climate change mean that precipitation (rain or snow) patterns change, with resulting desertification and drought in some areas, floods in others. Both mean that water is not efficiently returned to the cycle after it falls from the sky. In a flood, the ground as well as surface lakes and rivers cannot absorb all the water that falls in a short period of time, and therefore precious rainfall is wasted as the run-off flows quickly back to the ocean. In droughts, the ground becomes so hard that when it does rain, the moisture is poorly absorbed, with the same result.
Next: Water and the Environment: The World's Oceans