For the Instructor

These student materials complement the Water Science and Society Instructor Materials. If you would like your students to have access to the student materials, we suggest you either point them at the Student Version which omits the framing pages with information designed for faculty (and this box). Or you can download these pages in several formats that you can include in your course website or local Learning Managment System. Learn more about using, modifying, and sharing InTeGrate teaching materials.

The Value of Water

Does water have value?

Water is essential to life – both as a basic human need for survival, and as an "ingredient" in almost everything we do, from food production, to manufacturing, to power generation. As we will explore in more detail in Module 2 next week, precipitation and evaporation – and thus water availability – are unevenly distributed around the globe (Figure 1). This also varies seasonally. Figure 1 shows the average global distribution of precipitation for January; to see an animation over the course of the year, check this out:

There are obviously some areas of the world that are wetter than others, and these patterns are persistent throughout the year (i.e. the deserts of the American southwest, Northern Africa, and western Australia are perennially dry; whereas equatorial central America, Africa, and Indonesia are wet). This uneven distribution of water resources lies at the root of many topics we'll cover in this course, because it is a primary driver of human activity, ranging from population dynamics to types and locations of particular industries, to power generation, to politics. For example, take a look at the maps in Figures 1 and 2. Are there areas of the world that are persistently wetter or drier than others?

Activate Your Learning

1. List 3 areas/regions that are persistently dry based on the animated map shown above.

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2. List 3 areas/regions that are persistently wet.

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3. Inspect the freshwater availability map shown in Figure 2. Provide 2 examples of areas of water scarcity that "map" to areas where precipitation is low.

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4. Identify 2 areas that are characterized by low precipitation, but apparently are not faced with severe water scarcity. Provide a hypothesis as to why you think this is the case.

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As we'll see in Module 2, water is transported around the Earth by the hydrologic cycle, in which solar energy drives evaporation of water from the oceans and land surface. This water condenses in the atmosphere to form clouds and eventually to fall as precipitation. Much of that precipitation flows as surface water in rivers and streams. Some of it also infiltrates or percolates into the soil and rock, and becomes groundwater. Surface water constitutes the primary source of water for human activity – it is relatively clean, easy to obtain and move, and constantly replenished (barring prolonged dry periods; as we will discuss in Modules 4 and 8-9). Groundwater constitutes another important source of water for human activity. Although the total volume of groundwater held in fractures and pore spaces in the subsurface is large, it is replenished and flows under natural conditions far more slowly than surface water. Additional energy is required to extract groundwater, because it must be pumped from the subsurface, in some cases hundreds of feet or more. For these reasons, groundwater is generally a secondary source of water, in cases where surface water is not readily available or cannot fully meet demand.

Food for Thought

List at least 2 problems or issues (these can be political, economic, health-related, etc...) that might arise from the unequal geographic distribution of water resources.

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