Climate Change Daily Earth Science Hydrosphere Repost

Water stress on a hotter planet

Around the globe, up to half of the human population faces water scarcity at some point during the year. Recent studies predict that the number of people experiencing prolonged water stress could double by 2050. This change would increase the number of people under stress by an additional 190 to 380 million, relative to 2010. But the final number depends on actions taken, or not taken, by world governments to mitigate global warming.

Water stress is a measure of demand versus availability and occurs when the demand for water exceeds the availability. Since water stress is a demand-driven measure, it is valuable for long-range planning to predict where problems may occur. Insight into developing problems allows governments and regulators to manage long-term change.   


Geography plays a definitive role in water stress calculations. River systems like the Indus (Pakistan) or Colorado (USA) provide critical water supplies to large populations. People living in the headwater or upstream portions of these rivers are ‘first-users’ of the available water. If demand in the upstream area of a river basin increases, less water passes downstream, therefore creating a fresh water deficit. 

State, national and international treaties and agreements often regulate water use within a basin to ensure an equitable distribution of available water resources. But as populations increase and water demand soars, these agreements will come under pressure. Available water supplies are finite, and when total demand exceeds supply, then winners and losers must be picked. Unfortunately, the losers become part of the 190 to 380 million additional people coming under water stress by 2050. 

The largest predicted increases in water stress occur across North Africa, the Middle East, South Asia, and Central Asia. But North America is not immune to this problem, and much of the American West faces water stress from rising demand and shrinking supply. 

Megadroughts and increasing populations

The American West has been in a prolonged drought for the past two decades. The effects of this drought extend to surface water supplies like the Colorado River and groundwater resources like the Ogallala aquifer. Water from both sources is critical to agricultural and municipal water supplies. However, outdated regulatory practices and aging water-use agreements are inadequate for meeting the increased need.

 The Colorado River provides water for some 40 million people, and it also provides irrigation for 5.5 million acres of farmland. Six major cities (Denver, Salt Lake City, Las Vegas, Phoenix, Los Angeles, and San Diego) depend on the Colorado River. Also, this river supports about $1 trillion of economic activity each year.

But the demands on this river now exceed its annual flow capacity. From 1999 – 2004, Lakes Powell and Mead on the Colorado River (two of the largest reservoirs in the USA) lost half their water. Lake Mead is currently only 40 percent full. Water flow in the Colorado River has declined by 20 percent compared to the last century. So, water stress is inevitable for some areas of the Colorado River basin.

One-sixth of the world’s grain production, and America’s breadbasket, depend on groundwater from the Ogallala Aquifer. But water doesn’t magically appear in an aquifer. The aquifer must continually be recharged from surface water. Unfortunately, the rate of recharge for the Ogallala Aquifer groundwater is slower than the rate of water withdrawal. In western Kansas, aquifer water volumes are down by 60 percent from original levels.

The recharge problem for the Ogallala Aquifer is related to not enough rainfall replacing withdrawals by municipalities and commercial enterprises. Current models predict a dryer, more arid future for the High Plains. So, the gap in accounting between deposits and withdrawals will grow larger, adding to water stress in the American West.


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

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

Sinking ground – Water in the American West (Source: ArcheanWeb) –  Also:


380 million people could face ‘water stress’ by 2050, climate experts warn (By Daisy Dunne; World Economic Forum) –  Also:

Water stress (Source: European Environmental Agency) – Also:

Future transboundary water stress and its drivers under climate change: a global study (By Hafsa Ahmed Munia, Joseph H. A. Guillaume, Yoshihide Wada,Ted Veldkamp, Vili Virkki, Matti Kummu; AGU – Earth’s Future) –  Also:

Feature Image: Dry river (Modified) – By John Nguru Kamau – Own work, CC BY-SA 4.0,  

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.