Temperature Differences Between Rooftop and Urban Canyon Sensors: Diurnal Dynamics, Drivers, and Implications

Area of Science:

• Climatology
• Urban Meteorology
• Environmental Science

Background:

• Urban heat island effects are complex within the urban canopy layer (UCL).
• Discrepancies exist between rooftop and urban canyon temperature measurements.
• World Meteorological Organization (WMO) guidance favors urban canyon monitoring over rooftop observations.

Purpose of the Study:

• To quantify temperature differences between rooftop and urban canyon locations within the UCL.
• To identify factors influencing these temperature variations.
• To assess the representativeness of rooftop sensor data for urban climate studies.

Main Methods:

• Deployment of two temperature sensors: one on a rooftop and one within an urban canyon.
• Continuous temperature data collection over a diurnal cycle.
• Analysis of temperature differences in relation to solar radiation and wind speed under clear-sky conditions.

Main Results:

• A significant diurnal cycle in temperature difference was observed.
• Urban canyons were warmer than rooftops, with a peak difference exceeding 1°C between 12:00 and 16:00 local time.
• Daytime warming in canyons was primarily driven by solar radiation and, secondarily, by wind speed under clear skies.

Conclusions:

• Rooftop temperature measurements may not accurately represent conditions within the urban canopy layer.
• Sensor location significantly impacts urban temperature data, particularly during daytime under clear skies.
• Findings have implications for citizen science urban monitoring initiatives and WMO guidelines.