Urban Land Cover Effects on a Compound Heatwave and Convective Rainfall Event: A WRF Ensemble Study over Amsterdam

Extreme rainfall and urban heat events are intensifying across Europe under climate change, with compound occurrences where heatwaves are followed by convective precipitation posing particular challenges for urban flood risk and heat stress management. While the urban heat island effect and its influence on local atmospheric dynamics are well documented, the net impact of urban land cover on compound hydrometeorological extremes remains poorly understood, particularly at the convection-permitting scales needed to resolve city-scale processes.
This study aims to quantify the net effect of urban land cover on a compound hydrometeorological extreme that struck the Netherlands in July 2025: a sustained heatwave followed by a cold front-driven convective rainfall episode over the Amsterdam metropolitan region. Using the Weather Research and Forecasting (WRF) model, this is achieved by comparing simulations against a no-urban control case in which urban land cover is removed from the domain. To ensure this comparison is robust and not contingent on a single model configuration, the analysis is conducted across two dimensions of uncertainty. First, three urban landscape configurations of increasing heterogeneity are tested: the standard MODIS land use classification, a Local Climate Zone (LCZ) dataset from World Urban Database and Access Portal Tools (WUDAPT), and a high-resolution data derived from realistic 3D urban morphology, allowing the urban signal to be assessed independently of how the city is represented. Second, a physical scheme ensemble combining three turbulence treatments (YSU and MYJ planetary boundary layer schemes, and a Large Eddy Simulation approach without PBL parameterization) and three microphysics schemes (WSM6, Thompson, and Morrison double-moment) is used to constrain the sensitivity of the results to physical parameterization choices.
Model performance is evaluated against hourly observations from the KNMI station at Schiphol, covering 2 m air temperature, 10 m wind speed, specific and relative humidity, and incoming solar radiation, with precipitation evaluated against radar observations. Preliminary results from the baseline configuration show strong agreement with observed diurnal temperature cycles (R² = 0.90, RMSE = 1.85°C ), while systematic biases emerge in wind speed and near-surface humidity, and simulated convective precipitation is delayed and underestimated relative to observations.
These initial findings establish a credible baseline from which the full ensemble analysis will provide a rigorous and representation-independent estimate of how urban land cover modulates heatwave intensity, convective triggering, and precipitation distribution during compound hydrometeorological extremes.