Delft Measures: Citizen Science for Urban Climate Research

The Citizen-Science programme ‘Delft Measures’ has been running for several years in the city of Delft, the Netherlands. Within this programme, interested citizens can apply to receive a low- cost Alecto WS5500 weather station, to measure local meteorological parameters in their own garden. Currently there are over 45 of these citizen-science weather stations spread across neighbourhoods in Delft, capturing the variability of different urban microclimates, with a specific focus on rainfall observations.However, the scientific quality of the specific citizen weather stations (Alecto) has never been tested, and from previous work we know that rigorous quality assurance is necessary in order to get meaningful weather data. Thus we have installed 8 Alecto stations in The Green Village outdoors urban climate field lab at the TU Delft. Stations have been explicitly installed in ways that a citizen might do: slightly tilted; next to a wall (simulating the limited open garden space of a Dutch residence); on top of a shed; as well as free-standing. These different measurement setups, combined with a row of reference stations, allow us to investigate the bias in rainfall observations caused by less-than-ideal station installation, as well as systematic errors related to the tipping bucket mechanism and sensor drifts. Results show a general overestimation of the Alecto compared to reference stations and radar observations, and a discernible negative bias caused by sheltering effects of plants and, to a lesser extent by walls.The value of the Citizen Science approach is in the regular contact with the Citizen Scientists, providing valuable feedback and local knowledge that a crowdsourcing-focused approach would not yield, which was of great use in correcting faulty data. Such a two-way process with a long-term group of dedicated Citizen Scientists has shown great potential to improve the usability of crowdsourced data for urban hydrometeorological applications.