Question

If every person on Earth consumed as much water as the average American, how might this influence the

global hydrologic cycle? Would impacts to local hydrologic cycles be different? Explain.

Assume Earths population is 7.5 billion and yearly fluxes.

Note: There is no one answer to this question, defend yours with calculations, explanations, and indicate

sources for the numbers you use. Keep track of units!

(1) Consider only American domestic water use.

(2) Consider total water use per American in the U.S. (use the most up-to-date values available)

(3) How does your answer in (b) compare to the volume of freshwater lakes on Earth? Is this

consumption significant? Freshwater lakes comprise 0.007% of water on Earth.b

Answer 1

Answer:

Here's what I get  

Explanation:

The latest data on American water consumption are from 2015, provided by the USGS (United States Geological Survey)

Data (per day):

$\begin{array}{rrr}\textbf{Use} & \textbf{Gal \mathbf{/10^{9}} } & \textbf{L \mathbf{/10^{9}} }\\\text{ Total water use}& 322.0 & 1219\\\text{Total freshwater use} & 281.0 & 1060\\\text{Total domestic use} & 42.3 & 150\\\end{array}$

Note: Individual measurements are good only to three significant figures. I used trailing zeros as padding for decimal alignment.

The US population in 2015 was 325.0 million.

(1) Daily domestic water use

$\text{US domestic use} = \dfrac{\text{150 \times 10^{9} L }}{\text{325 \times 10^{6} persons}} = \text{462 L/person}\\\\\text{World domestic use} = 7.5 \times 10^{9}\text{ persons} \times \dfrac{\text{462 L }}{\text{1 person}} = \text{3.46 \times 10^{12} L}$

(2) Daily US freshwater use

$\text{Total US use} = \dfrac{\text{1060 \times 10^{9} L }}{\text{325 \times 10^{6} persons}} = \text{3260 L/person}\\\\\text{World domestic use} = 7.5 \times 10^{9}\text{ persons} \times \dfrac{\text{3260 L }}{\text{1 person}} = \text{24.5 \times 10^{12} L}$

(3) Implications

The total volume of water on Earth is 1.386  × 10⁹ km³ (1.386 × 10²¹ L).

$\text{Volume of lake water} = 1.386 \times 10^{21} \text{ L water} \times \dfrac{\text{0.007 L lake water}}{\text{100 L water}}\\= 100 \times 10^{15}\text{ L}\\\\\dfrac{\text{Volume of lake water}}{\text{World usage}} = \dfrac{100 \times 10^{15}\text{ L}}{25 \times 10^{12}\text{ L/d}} =\text{4100 d} \approx \text{11 yr}$

Theoretically, if the world used fresh water at the same rate as the United States, the supply of fresh water would vanish in just over a decade.

Of course, this won't happen. The used water goes into rivers and into the oceans, where it evaporates and returns to the surface via the hydrologic cycle.

There will be little impact on the global hydrologic cycle.

However, the water that evaporates may return to the surface far from its source. There will be a significant impact to local hydrologic cycles as lakes and aquifers dry up because water is being used faster than it can be replenished.