Writing prompt Grade 8 Science
Why Port Aubrey Gets Rain and Sennick Valley Does Not
A grade 8 science explanatory writing prompt on prevailing winds, a coastal current, and a mountain range that leave two fictional towns with very different supplies.
Objectives
- Students will explain how unequal heating of Earth and its rotation produce the prevailing winds at a given latitude.
- Students will trace a water molecule from ocean evaporation to rainfall on a coastal slope and runoff back to the sea.
- Students will connect a region's rainfall pattern to the water supply choices its towns face.
Vocabulary
- Evaporation
- Evaporation happens when liquid water, often warmed by the sun, turns into an invisible gas called water vapor that rises into the air. It is how water leaves oceans, lakes, and puddles.
- Condensation
- Condensation is when water vapor in the air cools down and turns back into tiny liquid water droplets. It is how clouds form and why a cold glass gets wet on the outside on a warm day.
- Aquifer
- An aquifer is an underground layer of rock, sand, or gravel that holds water in the tiny spaces between its grains. Wells reach down into aquifers to bring water up to the surface.
Also: prevailing wind, rain shadow, water reuse
Teacher overview
Two towns can sit less than a hundred miles apart and still receive rainfall so different that they build entirely different water systems. The explanation runs from the sun through the wind belts to a single mountain range, and it is a good test of whether students can hold several causes in order. This prompt gives students a fictional pair of towns and asks for an explanatory essay rather than an argument, so the scoring rewards accurate sequence and clear cause-and-effect language. The essay ends by connecting the climate explanation to what each town has to do to get water.
Prompt
Background
Port Aubrey is a fictional coastal town. Sennick Valley is a fictional inland town about 90 miles east of it. Between them stands the Zephyr Range, a line of peaks rising to about 7,000 feet. Both towns are at the same latitude, and both were founded in the same decade.
Their weather is not the same. Port Aubrey records about 52 inches of rain in an average year in this scenario. Sennick Valley records about 11 inches.
Here is what scientists know about the region.
The sun heats the Earth unevenly. Sunlight strikes near the equator almost straight on, while it arrives at a low angle near the poles. That difference in heating makes air rise in some latitude bands and sink in others. As the Earth rotates, those rising and sinking bands are bent into belts of steady wind. At the latitude of these two towns, the steady wind blows from west to east. Winds like this are called prevailing winds.
West of Port Aubrey lies open ocean. A cold ocean current runs along that coast, part of the global circulation that carries heat from the tropics toward the poles. Air moving east across that wide stretch of ocean picks up water vapor by evaporation, which the sun powers.
When that moist air reaches the Zephyr Range, it has nowhere to go but up. Air cools as it rises. Cool air holds less water vapor than warm air, so the vapor condenses into droplets, clouds form, and rain falls on the western slopes. By the time the air crosses the crest and sinks into Sennick Valley, most of its moisture is gone, and sinking air warms as it descends. The dry belt on the far side of a range is called a rain shadow.
The two towns get their water in different ways. Port Aubrey collects runoff in two reservoirs on the western slope. Gravity moves that water down to the town, and the treatment plant is small because the streams run clear. Sennick Valley has no reliable stream, so it pumps groundwater from an aquifer that refills slowly. The Sennick Valley board is now studying whether to treat and reuse the town's wastewater to stretch the supply.
Your task
Write an explanatory essay for your school newsletter titled "Why the Rain Stops at the Zephyr Range." Explain, in order, why Port Aubrey receives so much more rain than Sennick Valley. Begin with the sun and the prevailing winds, continue with evaporation over the ocean, and finish with what happens to the air as it crosses the range. Then explain what those rainfall totals mean for how each town gets its water. Use the vocabulary from the background, and do not take a side about what Sennick Valley should do.
Planning Organizer
Complete every row before drafting. Each row becomes one paragraph or one clear set of sentences.
| Part of the essay | What you write here |
|---|---|
| Main idea | One sentence naming what the essay explains. |
| Step 1: the sun | How uneven heating and Earth's rotation create prevailing winds here. |
| Step 2: the ocean | How evaporation over the ocean puts water vapor into the moving air. |
| Step 3: the climb | What happens to the air, its temperature, and its vapor as it rises over the range. |
| Step 4: the far side | Why the air reaching Sennick Valley is dry, and what sinking air does. |
| What it means for Port Aubrey | How the town collects and treats its water, and why gravity matters. |
| What it means for Sennick Valley | Where the town's water comes from and what it is studying now. |
| Closing | One or two sentences tying the rainfall difference to the supply difference. |
From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.
Exemplar & Rubric
Exemplar response
Port Aubrey and Sennick Valley sit about 90 miles apart at the same latitude, yet one gets about 52 inches of rain a year and the other gets about 11. The reason is a chain of causes that starts with the sun and ends at the crest of the Zephyr Range.
The chain begins with uneven heating. Sunlight hits the Earth almost straight on near the equator and at a low angle near the poles, so some latitude bands warm much more than others. Warm air rises and cooler air sinks, and the rotation of the Earth bends those movements into belts of steady wind. At the latitude of these two towns, the prevailing wind blows from west to east. That single fact decides which town is upwind.
The next step happens over water. West of Port Aubrey there is open ocean with a cold current running along the coast. Energy from the sun evaporates water from the ocean surface, and the moving air carries the vapor east. By the time the air reaches the coast it is loaded with water it picked up at sea.
The third step is the climb. The Zephyr Range rises to about 7,000 feet, and moving air cannot go through a mountain, so it goes over. Rising air expands and cools, and cool air holds less water vapor than warm air. The extra vapor condenses into droplets, which build into clouds and fall as rain on the western slopes. That is why Port Aubrey is wet.
The last step is the descent. Air that crosses the crest has already dropped most of its moisture. As it sinks into Sennick Valley it warms again, which lets it hold more vapor rather than release it. Dry sinking air produces the belt called a rain shadow, and Sennick Valley sits inside it.
These four steps explain the two water systems. Port Aubrey stores runoff behind two reservoirs on the wet slope and lets gravity carry the water down to town, and its treatment plant stays small because clear mountain streams need little cleaning. Sennick Valley has no dependable stream, so it pumps groundwater from an aquifer that refills slowly, and the town board is studying whether to treat and reuse its wastewater to stretch that supply.
The same water cycle serves both towns. Because the air crossing the Zephyr Range drops most of its rain on the western side, Port Aubrey can rely on reservoirs fed by runoff, while Sennick Valley has to depend on a slowly refilling aquifer.
Rubric
| Criterion | 1 Emerging | 2 Developing | 3 Proficient | 4 Advanced |
|---|---|---|---|---|
| Focus and main idea | The essay states no main idea. | A main idea appears but drifts. | A clear main idea opens the essay and holds through it. | A clear main idea opens and closes the essay and frames every step. |
| Scientific accuracy | Two or more steps are missing or wrong. | The steps appear but one is out of order or inaccurate. | All four steps appear, in order and accurately. | All four steps are accurate, in order, and each is linked to the next by a stated cause. |
| Supply connection | The essay does not reach the water systems. | One town's supply is described. | Both towns' supplies are described and tied to rainfall. | Both are described, tied to rainfall, and the role of gravity or slow recharge is explained. |
| Vocabulary and conventions | Key terms are absent or misused. | Some terms are used correctly. | Terms such as evaporation, condensation, and rain shadow are used correctly. | Terms are used correctly and precisely, with transitions that mark each step in the sequence. |
Differentiation
Support
Give these students the organizer with the four science steps already numbered and a word bank containing evaporation, condensation, prevailing wind, rain shadow, and aquifer. Allow a labeled cross-section drawing of the range with arrows for the wind, submitted alongside a three-paragraph essay rather than a full one.
Extension
Ask these students to add a section explaining what would change if the prevailing wind at this latitude blew from east to west instead. They should predict which town would be wetter, name the evidence in the background that supports their prediction, and explain what would happen to Port Aubrey's reservoirs.
ELL supports
Pre-teach "prevailing," "evaporation," "condensation," "rain shadow," and "aquifer" with a large cross-section diagram of the ocean, the range, and the two towns, kept posted during drafting. Provide transition frames for each step: "First, the sun ___," "Next, the air ___," "As the air rises, ___," and "On the other side of the range, ___."
Extensions
Students look up the average yearly rainfall for two real towns on opposite sides of a mountain range in their own region and compare the difference with the fictional one in this prompt. They then write one paragraph on whether the same four-step explanation fits the real pair, and what additional information they would need to be sure.