Urban-PLUMBER model evaluation project: initial results

We present initial results of the Urban-PLUMBER international model evaluation project. This project assesses the performance of land surface models used in meteorological simulations of urban areas. Phase 1 included 24 models of varying complexity, from simple slab models through to multi-layer urban canopy models.

54 model output variables are requested, including primary surface energy fluxes, anthropogenic heat and moisture fluxes, soil variables, albedo, canopy and building air temperatures. This rich dataset is used to both compare model outputs with observations and to understand factors contributing to model performance.

The project involved a number of other innovations including:

• An online portal (modelevaluation.org) is used to distribute site data and accept submissions.
• Upon submission to the portal participants are provided with variable near-instant compliance checks and analyses allowing participants to make corrections if required.
• A ten-year ERA5-derived spin up which overcomes the typically short period of urban flux tower observations and allows the entire observed period to be used in analyses.
• Testing models alongside simple empirical benchmarks (e.g. out-of-sample linear regression of turbulent fluxes on shortwave radiation) to assess if input information is used effectively.

We also discuss the initial stages of Phase 2 which involves testing models at many urban sites. From the known global urban flux tower observations, following assessment, 25 are selected to capture a range of urban characteristics and climates. Surface characteristics are gathered, observations quality controlled and prepended with ten years of bias corrected ERA5 meteorological data for spinup. This new standardised urban flux tower dataset will become a valuable tool in future urban modelling projects.