Global Water Use How we use water and

Global Water Use How we use water and the state of our supplies

§ Describe how global water use has changed over time in relation to population. § Compare and contrast the major uses of water in the context of whether they are consumptive or non-consumptive. § Look at global patterns in water availability to consider how water use and demand may change in the future. Objectives

Is global water use going up faster than human population? This matters (a lot!) because we know the supply of water is finite • These two graphs are on similar scales so the slopes can be compared • Global water use data is limited (this data set is form ‘our world in data’) and goes to 2014 with a break between 2010 and 2014

Annual Per Capita global water use is going down Per capita is person and is measured in cubic meters person per year. • 550 m 3 is about a quarter of the volume of an Olympic size swimming pool. • Per capita use is declining but total use is still rising because population is growing

Very large variations in water use around the world Two major types of water use: Consumptive water use is the use of water that does not return to its source or whose quality is degraded to the degree that it can no longer serve as a usable resource. Non-consumptive water use is the use of water that is subsequently returned to surface water supplies at or near the site of its use. Definitions from A Changing Planet, Neff (Pearson)

Industrial Water Use Includes many different activities. Paper production, fossil fuel exploration, mining. Industrial water use scales with overall levels of industrial activity A large part of industrial water use is consumptive – either because the water cannot be recovered or because the water becomes contaminated. Note the scale here: National level use goes up to about 320 billion m 3

Agricultural water use Irrigation of crops. Uses both groundwater and surface water. Virtually all irrigation is consumptive. Crops take water up from the soil and release it into the atmosphere (through leaves). The water isn’t destroyed – it becomes atmospheric water vapor. But it is lost from the site/region. Note the scale here (700 billion m 3) This Photo by Unknown Author is licensed under CC BY-ND

Municipal water use What you actually use each day Inside the house the use is mostly non-consumptive use because the water is often returned to rivers. Outside the house (irrigation of landscapes) is consumptive water use. US is very high but there have been major changes in recent years. Note the Scale here (80 billion m 3 max). This is typically about 10 -20% of total national water use.

Water is very unevenly distributed around the world. US is 8844 m 3 Some regions have ample resources for the future. Some regions are very close to the limits of additional use. Additional population growth or additional agricultural industrial development will put pressure on freshwater resources especially in the regions on the bottom of this graph or in places like the Western US that are very dry. Remember that per capita global water use is around 550 m 3 per year

US freshwater resources estimated at ~8800 M 3 person yet we have droughts like this in September 2020. The problem with relying on surface water is that it varies so much from year to year.

Many countries already are facing water limitation/stress. This will get more severe in the future Population growth Climate change We can reduce stress with water use efficiency (especially in agriculture) Changes in what we do with water

Massive variation in the water demand of different crops! PAGE 12

Summary § Per capita water use increased up to about 1980 and then has declined (up to 2014). Total global water use is still rising. § Globally agriculture is the biggest use of water followed by industry, followed by municipal uses. Most agriculture and industry use is consumptive, municipal use is less consumptive. § Water is unevenly distributed around the world. Some regions are in much better shape than others. Year to year variations are very important and often matter as much or more than average availability.