Climate Change Human impacts

Stressing out about water stress

Kari St.Laurent

Article: Schlosser et al. 2014. “The future of global water stress: An integrated assessment,” Earth’s Future. DOI:10.1002/2014EF000238

 

What is Water Stress?

The annual runoff in millimeters per year as simulated by this study’s model for the years 1981-2000. Runoff is the excess water caused by processes such as rain and melting snow. Think of it as the “streams” of water you see after a huge downpour. The lower the runoff (red), the more likely a region will undergo water stress.
Figure 1: The annual runoff in millimeters per year as simulated by this study’s model for the years 1981-2000. Runoff is the excess water caused by processes such as rain and melting snow. Think of it as the “streams” of water you see after a huge downpour. The lower the runoff (red), the more likely a region will undergo water stress.

Water is one of the most important, if not the most important, resources on Earth. Every living creature requires water for its basic survival. According to the 2006 United Nations Human Development Report, 1.2 billion people are currently living in regions where water is considered scarce. That is nearly 20% of the global population!

Image a time when it was really hot outside and an ice cold glass of water really hit the spot. Now consider all the other things we depend on water for: we use water to grow our food, quench the thirst of livestock, bathe ourselves to prevent disease – humans depend on water not only as a beverage, but as an integral part of our existence.

Global population in 2010 and project population growth for the year 2050.
Table 1: Global population in 2010 and project population growth for the year 2050.

Water stress, loosely speaking, is when the demand for water is greater than its availability. The International Group of Funding Agencies for Environmental Change Research has identified the dire need to learn how environmental change will affect global water stress so that the proper political action can be set in motion before more of the people suffer from water scarcity. A critical part of this initiative is to better understand how climate change, in addition to socioeconomic growth, will affect water stress.

Adding socioeconomic growth to water availability predictions makes perfect sense: as the population increases, the need for water also increases. By 2050, the global population will increase by 33%. Water stress predictions must include population growth in addition to climate change to more accurately understand how water stress will change by region.

The Model

Schematic of the model used.
Schematic of the model used.

Schlosser et al. used the MIT Integrated Global Systems Model (IGSM) embedded with a Water Resource System (WRS) in order to assess how both climate change and socioeconomic growth will affect global water stress in the year 2050 (Figure 2). The IGSM includes an Emission Prediction and Policy Analysis that includes socioeconomic parameters such as population growth. The global system is divided into 282 sub-regions based on major water basins.

The 282 sub-regions that the model assesses for water stress.
The 282 sub-regions that the model assesses for water stress.

The model was run under 4 conditions in order to determine what factors will have the greatest effect on water stress: baseline (no changes), effects from socioeconomic growth (assumes the climate stays the same), effects from climate change (assumes no population growth), and the combined effects of both climate change and socioeconomic growth.

The Findings

 The model simulations predict that water stress will greatly increase in 2050 and that socioeconomic growth has a larger effect on global water stress than climate change alone, especially in developing countries. This study predicts that an additional 1.8 billion people, or an increase of 53%, will be living in regions with high water stress. About 80% of those 1.8 billion people are expected to live in developing counties.

The change in water stress from the year 2010 to the predicted water stress in 2050 taking only climate change into effect. Red indicates an increase in water stress is likely to occur over the next 40 years.
The change in water stress from the year 2010 to the predicted water stress in 2050 taking only climate change into effect. Red indicates that water stress is likely to increase over the next 40 years.

For comparison, projected water stress under a dry climate change-only scenario (no economic or population growth) predicted that 2.8% of the population will be subjected to high water stress (compared to the 53%). Water stress effected by climate change will mostly influence developed counties, such as the United States and parts of Europe.

The % change in non-irrigation water demand taking both climate change and socioeconomic change into consideration.
The % change in non-irrigation water demand taking both climate change and socioeconomic change into consideration.

With climate change and socioeconomic growth combined, approximately 5 billion of the 2050 global population of 9.7 billion people will live under moderate water stress. Once again, currently developing countries are under the most risk for increased water stress, with the African continent under the high risk potential (Figure 7). Even scarier, 3 billion people could be living in regions with overly exploited water resources.

Significance

 The goal of the study was to predict regions susceptible to increased water stress in order to promote better water management. This study calls on future researchers to look at these high risk, developing regions at a higher resolution. Climate change and population increases are unavoidable. Hopefully these model predictions will provide decision-makers with strategic insight for water policy and risk management.

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