Paper 3 · June 2023 · Settlement and Urban Geography
Fig. 5.1 shows temperature in City X as roughly concentric closed isotherms falling outward from a hot central core, with the isotherms bending outward along the line of the river. What is this pattern, and why is the core hottest?
AA frontal inversion: warm air riding up over a wedge of denser cold air is at its thickest above the centre of the built up area, so the trapped layer beneath it is warmest there and cools away towards the edges.
BA katabatic effect: cold dense air drains off the surrounding higher ground at night and ponds at the city margins, leaving the centre relatively warm.
CA rain shadow effect: the built up area lies in the lee of high ground, so descending air warms adiabatically over the city centre.
DAn urban heat island: dense hard surfaces absorb and slowly release solar radiation, evapotranspiration is minimal, anthropogenic heat is added and street canyons trap outgoing longwave radiation.
Explanation
Concentric isotherms falling outward from a built up core is the classic urban heat island. Concrete, brick, tarmac and steel have high thermal capacity and release stored heat slowly; there is little vegetation or open water, so almost no energy goes into evapotranspiration; vehicles, industry and air conditioning add heat directly; and deep street canyons reduce the sky view factor so outgoing longwave radiation is repeatedly reflected back.
Derived from ZIMSEC Advanced Level Geography 6037/3 Paper 3 Practical Test, June 2023 session, Q5