Analyze an environmental problem doing calculations

A growing population and farm water

Units 3 and 5
10 points
About 24 minutes

You can use a calculator on this question, just like on exam day.

You work through an environmental scenario using numbers: set up and solve calculations (showing your work), then explain the science and propose solutions. Several of the 10 points come from the calculations, usually one for the setup and one for the answer. On the exam: Question 3 of 3 in the 70-minute free-response section (Section II is 40% of the exam score).

The question

The country of Valtera has a crude birth rate of 42 per 1,000 people per year and a crude death rate of 17 per 1,000 people per year. Assume no immigration or emigration. Most of the country's food is grown on 200,000 hectares of irrigated farmland. Each hectare of crops needs 5,400 cubic meters (m³) of water to reach the plants' roots each year. The farms currently use flood irrigation, which is 60% efficient (60% of the water applied reaches the roots). Drip irrigation is 90% efficient.

Suggested time: 24 minutes

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Part (a)

2 points

Calculate Valtera's rate of natural increase as a percentage. Show your work.

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Part (b)

2 points

Calculate the number of years it will take for Valtera's population to double if this growth rate continues. Show your work.

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Part (c)

2 points

Calculate the volume of water that Valtera's farms would save each year by switching all 200,000 hectares from flood irrigation to drip irrigation. Show your work.

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Part (d)

1 point

Identify the stage of the demographic transition model that best describes Valtera.

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Part (e)

1 point

Explain one reason that a country's death rate typically falls before its birth rate does.

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Part (f)

1 point

Describe one environmental problem that flood irrigation can cause in farm soil.

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Part (g)

1 point

Propose one realistic policy that Valtera's government could adopt to slow its population growth.

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