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Climate change and surface water

Climate change alters the distribution of surface water on planet earth. Some changes in distribution are the result of geography, but human needs drive other changes. Emerging signs of those changes are evident in places like the Indus valley where declining glacial ice reserves impact the annual water supply to the Indus River, thus affecting 120 million people. 

On a planet where 71% of the surface is water, there is surprisingly little water actually available to support terrestrial life. Approximately 97.5% of all the water on the planet’s surface is saline, and most of the remaining 2.5% of the freshwater resides in glaciers and ice sheets. The amount of usable water available to humans is a mere 0.3% of the total water supplies. Of the 0.3% available for human use, the bulk of this water resides below the earth’s surface as groundwater.

How this available water is distributed has historically been a function of climatic, hydrologic, and geologic conditions. Human ingenuity changed that equation, and now, through massive engineering projects, the Colorado River is drained dry, so Los Angeles has water. In other areas of the globe, agriculture can flourish in the deserts.

An estimate of the world’s water budget from the National Ground Water Association is:

  • Ocean water: 97.2 percent
  • Glaciers and other ice: 2.15 percent
  • Groundwater: 0.61 percent
  • Freshwater lakes: 0.009 percent
  • Inland seas: 0.008 percent
  • Soil Moisture: 0.005 percent
  • Atmosphere: 0.001 percent
  • Rivers: 0.0001 percent.
  • Other: 0.0169 percent

Steady incremental usage

For 5000 years, human civilizations developed by occupying areas with predictable annual water cycles. Predictability is essential for agricultural planning and meeting the water needs of towns and villages. So, without water supply predictability, civilizations flounder.

Egypt developed one of the most advanced civilizations in the ancient world based on the predictability of the Nile River. The culture arose in a desert sliced in two by a thin strip of water, the Nile river. The river brought a steady supply of needed water to the empire. Additionally, the annual flood cycle dumped organic-rich silts on the farmer’s fields, thus providing the necessary nutrient replacement to maintain a healthy, sustainable agricultural system.

Humans use water in incremental amounts. An annual rainfall of 24 inches a year can sustain a fixed population size unless the entire 24 inches fall over just several days, and then no rains fall for the rest of the year. So an effective water supply requires a requisite volume of water delivered in incremental amounts throughout the year.

Earth’s water towers

An incremental supply of water is the intrinsic value of the world’s water towers (freshwater locked in high mountain glaciers and ice). The water from periods of heavy precipitation collects as ice, then the ice gradually melts and releases water throughout the year. So excessive melting of the world’s mountain water towers is an area of concern for many people as global temperatures rise. 

High mountain ice, locked in glaciers, serves as a storage tank for freshwater and a stabilizer for critical river flow. During dry seasons the ice melts and forms a steady base-level flow for major rivers. The ice evens out the river flow over the year. Without the glacial ice, rivers receive their annual allotment of precipitation as rain only and go into flood stage in the wet season. During the rest of the year, the rivers shrivel and suffer drought.

The Indus river is one of the world’s most important river systems relying on water towers. Meltwaters from glaciers of the Karakoram, Hindu Kush and Himalayan ranges feed this river.  The river then flows across the dry Indus plains, where it provides life to over 120 million people. But the glaciers now melt faster than ice accumulates. This melting is because the average annual temperature increases in the high Himalayas are twice as high as the average global temperature rise. Therefore, the future of these water towers is under threat.

Other vulnerabilities to climate change

A warming atmosphere creates two primary effects. The first of these effects is increased evaporation because of higher temperatures. This extra evaporation then further exacerbates conditions in already dry areas.  The second effect is larger volumes of water available for precipitation when it does rain. Since the physics of water vapor dictates that warmer air holds more moisture, a warmer planet creates more drought-deluge cycles.

California provides a great example of drought-deluge cycles. The State’s dry seasons now last longer and have higher average temperatures. This amplified drying of the environment sets the stage for more frequent wildfires. But the rains still come in the wet season, and intense winter storms then dump excessive amounts of water onto landscapes with no vegetation left to hold the soil in place. Gravity operates independent of climate change, and when the soils are water-saturated, and the slopes are steep enough, mudslides then occur, devastating some urban communities.

Climate change will affect surface water distribution. Early attention to developing surface water supply problems is better than waiting until a crisis arises. However, effective planning solutions require appropriate government policy.  Effective government policy only comes through the ballot box.


The world’s water towers (Source: ArcheanWeb) – Also:

Climate change at the margins (Source: ArcheanWeb) –  Also:

The Colorado River is running dry (Source: ArcheanWeb) – Also:

Hot and dry in the Western USA, a megadrought in progress (Source: ArcheanWeb) – Also:

Ogallala Aquifer groundwater, sustaining life (Source: ArcheanWeb) – Also:

Wildfires and Mudslides (Source: ArcheanWeb) – Also:


How Much Water is There on Earth? (USGS) – Also:

Information on Earth’s Water (By Kimberly Mullen; NGWA) – Also:

THE IMPACT OF CLIMATE CHANGE ON WATER RESOURCES (By Climate & Environment) (Modified) – Also:

Feature Image: That’s What This Desert Needs- a Lake! (By  cogdogblog) (Modified) –!_(15016748476).jpg   –   This file is licensed under the Creative Commons Attribution 2.0 Generic license. –

William House
William is an earth scientist and writer with an interest in providing the science "backstory" for breaking environmental, earth science, and climate change news.