A new method to identify and explain sources of precipitation modification, illustrated for the western Netherlands

Urban areas can influence local precipitation patterns and amounts. Although earlier studies have focused on the magnitude of precipitation modification by cities, this study develops a method to identify the source areas of precipitation. We illustrate this for the western part of the Netherlands for 2017–2023. Precipitation anomalies are located using radar‐derived precipitation data and traced back to their source areas by following the motion of the precipitation for each rainfall event. Using machine‐learning techniques, the influence of hypothesized causes—urban heat, surface roughness, air pollution, and their interactions—on precipitation anomalies is evaluated. We find that urban and industrial areas generally enhance downwind precipitation, while large rural areas weaken it. Nearly 30% of the study area frequently generates enhanced precipitation downwind, with an average increase of 16.1% of the total precipitation. The identified source areas of precipitation modification are consistent across different seasons. We also find that surface roughness and concentrations (used as a proxy for air pollution) show a positive correlation with precipitation anomalies. Air pollution appears the most influential predictor of precipitation anomalies in this study, followed by the interaction between air pollution and urban heat, and then surface roughness. Compound effects show a lower contribution than individual variables. This methodology provides a novel perspective on precipitation modification, offering a foundation to refine assumptions about source locations and improve understanding of the mechanisms driving the effect.