Impact of fragmented urbanization on observed precipitation

Abstract Research regarding the urban impact on precipitation focuses mostly on large‐scale, isolated cities, making the conventional methodologies inapplicable to more complex urban morphologies, such as fragmented urban landscapes. This study addresses this limitation by exploring an innovative observation‐centered method, in which precipitation observations are classified according to the fraction of urban land cover in the upwind area. Precipitation indices, including precipitation frequency, mean precipitation and precipitation intensity, are compared between rural‐ and urban‐labeled observations. The analysis is performed for an extensive rain gauge network in Belgium, recording hourly or daily precipitation totals for the time period 2013–2023. Results reveal a decrease in precipitation frequency downwind of urban areas, but a substantial increase in precipitation intensity during summer. This intensity enhancement appears to be convectively driven, as indicated by its dependence on season, time of day and wind direction. A case study over Brussels further supports the presence of an urban signal for hourly precipitation and highlights the added value of hourly observations, as opposed to daily ones, for revealing the urban impact. The observation‐centered method proves effective for analyzing the impact of fragmented urban areas on downwind precipitation and could, with minor adaptations, be extended to other data sources, such as radar or lightning observations. This method allows more complex urban landscapes, previously overlooked, to be incorporated into the discussion of the urban impact on precipitation.