The interaction of rivers and urban form in mitigating the Urban Heat Island effect: A UK case study

TLDR

The Urban Heat Island effect raises city‑centre temperatures, and increased surface porosity and surface water—including urban rivers—can mitigate this through evaporation. This study examines how small urban rivers and the surrounding urban form influence UHI mitigation. The authors conducted a field survey of a Sheffield river during spring and summer to assess cooling effects. Cooling above the river rose with ambient temperature, peaking at over 1.5 °C in spring but falling in summer as river water warmed, while seasonal factors, solar radiation, wind, humidity, and bank form also modulated the effect.

Abstract

The Urban Heat Island (UHI) effect already produces elevated temperatures in city centres therefore urban design has a key role to pay in reducing the UHI to create safe and pleasant places in which to live and work. Increased surface porosity and bodies of surface water have a role to play in increasing potential cooling through evaporation. Urban rivers may, therefore, have a place in reducing the UHI. This paper investigates the effectiveness that small urban rivers may have in reducing the UHI effect and also examines the role that the urban form on the banks of a river can play in propagating or reducing this potential cooling. The results from a field survey during spring and summer are presented for a river in Sheffield, UK. The level of cooling is related to the ambient air temperature, increasing at higher temperatures. However, there are also seasonal dependencies and relationships linked to the river water temperature, incident solar radiation, wind speed and relative humidity. A mean level of daytime cooling of over 1.5 °C was found above the river in spring, but this was reduced in summer when the river water temperature was warmer. The urban form on the river bank influenced the levels of cooling felt away from the river bank.