Two towns, Greenfield and Stonehaven, are identical in size and population. Greenfield has a large park with trees and a lake. Stonehaven has no park — its land is covered with roads, carparks and buildings.
During a hot and dry period with no rainfall, a student predicts: "Greenfield will have higher total evaporation than Stonehaven, but Stonehaven will experience more intense rainstorms when rain eventually arrives."
Which explanation best supports BOTH parts of the student's prediction?
AGreenfield has higher evaporation because the lake surface and transpiring trees release more water vapour than hard surfaces; Stonehaven has more intense rain because its dark surfaces heat the air strongly, causing faster updrafts that force water vapour to condense rapidly into heavy rain.
BGreenfield has higher evaporation because more sunlight reaches the ground through the tree canopy; Stonehaven has more intense rain because buildings block wind, causing water droplets to combine into larger drops before falling.
CGreenfield has lower evaporation because tree shade cools the ground; Stonehaven has higher evaporation from hot roads, and this extra water vapour causes heavier rain over the city.
DGreenfield and Stonehaven have the same total evaporation because both towns receive equal solar energy; the difference in rainfall intensity is caused by the number of dust particles in Stonehaven's air acting as condensation nuclei.
Show Worked Solution
Worked Solution
Step 1: Analyse evaporation sources in each town
Evaporation requires both solar energy and liquid water. Greenfield has two major sources: (1) the large lake surface continuously evaporating, and (2) transpiration from trees releasing water vapour. Stonehaven has only small puddles and drain water — hard surfaces hold very little water. Even though Stonehaven's surfaces get hotter (no shade), there is far less water to evaporate. Therefore Greenfield has higher total water vapour output.
Step 2: Analyse why Stonehaven has more intense rain
Stonehaven's dark roads and rooftops absorb more solar energy and heat the air strongly. Hot air rises quickly in strong updrafts (convection). When this warm moist air reaches altitude, it cools rapidly and condenses into water droplets in a concentrated column, producing intense localised thunderstorms rather than steady drizzle.
Step 3: Match to option A
Option A correctly explains both halves: Greenfield's lake + transpiration = higher total evaporation. Stonehaven's strong surface heating = fast convective updrafts = intense condensation = heavy rain when moisture does arrive. This is the urban heat island effect applied to the water cycle.
Step 4: Eliminate distractors
Option B misidentifies the evaporation source and incorrectly attributes rainfall to wind blocking. Option C reverses the evaporation comparison. Option D incorrectly assumes equal evaporation from equal solar energy.
Correct answer: Greenfield has higher evaporation because the lake surface and transpiring trees release more water vapour than hard surfaces; Stonehaven has more intense rain because its dark surfaces heat the air strongly, causing faster updrafts that force water vapour to condense rapidly into heavy rain.
Want more questions like this? Superholic Lab has 10,000+ MOE-aligned questions with full worked solutions.