UAS to Observe the Cooling Effect of Urban Parks in Paris during PANAME 2023

Urban heat islands amplify the health risks of heat waves for its residents and tourists alike as well as stress the city’s economy and infrastructure. To this end, a major field campaign (PAris region urbaN Atmospheric observations and models for Multidisciplinary rEsearch, PANAME2023) took place in July 2023 to study the local meteorology of the Paris metropolitan area with a particular focus on the identifying spatial and temporal variability within an urban heat island. This campaign, co-led by the National Center for Meteorological Research (CNRM), ultimately aims to improve numerical weather forecasts within urban environments, which are experiencing increasingly frequent and more intense heat waves because of climate change. Understanding the role of urban parks and surrounding infrastructure within an urban heat island is essential for adapting urban environments to climatic projections of extreme heat.

In this context, the CNRM conducted the PANAME2023 campaign using an observational network consisting of surface, airborne and mobile stations dispersed throughout the Paris metropolitan region. One aspect of the PANAME2023 campaign deployed lightweight multicopter UAS to conduct vertical profiles of thermodynamic parameters (temperature, relative humidity, wind strength and direction) at nine park and urban sites. Vertical profiles were conducted up to 120 meters above the surface every 30 minutes from 18:00 to 22:00 local time; and two vertical profiles were conducted simultaneously during the measurement period, often at park-urban pairs, to quantify the difference in the evolution of the surface layer between a park and a neighboring urban environment. More than 300 meteorological profiles were conducted during PANAME2023.

The instrument payload has been validated and measurement precision quantified for each meteorological parameter (± 0.1 ^oC, ± 1.5% RH, and < 1.0 m/s). In addition to profiles of park-urban pairs, intercomparisons between UAS were conducted simultaneously at the same site to validate the observation strategy. The results from PANAME2023 show the frequent establishment of a surface boundary layer up to ca. 40 m such that urban parks cool up to 3 ^oC more than neighboring urban environments. In addition, the relative importance of local cooling within the park versus cooling on a city-wide level is defined by regional scale meteorology. The size of the urban park appears to be of secondary importance.