Summary:

The Urban Model (CLMU) in the Community Land Model (CLM)

The urban parameterization in CLM (CLMU) allows for the simulation of the urban environment within a climate model, particularly the temperature in urban areas. The urban land unit is based on the "urban canyon" concept, with up to three urban land units per grid cell representing different density classes.

Key features of the CLMU:

1. Representation of urban surfaces (roofs, walls, canyon floor) and their interactions through a bulk air mass in the urban canopy layer.
2. Radiation parameterizations to account for trapping of solar and longwave radiation in the urban canyon.
3. A building energy model that simulates heat transfer through building components, HVAC systems, and waste heat.
4. Simulation of hydrology (e.g., runoff) on urban surfaces.
5. Coupling with the atmospheric model to provide and receive relevant fluxes.

Datasets and updates:

- Global urban extent and properties were developed by Jackson et al. (2010).
- An optional updated urban properties dataset and scenario tool are available (Oleson and Feddema, 2018).
- Key changes from CLM4.0 to CLM5.0 include a more sophisticated building energy model and dynamic control of the maximum building temperature.
- A module for calculating heat stress indices has also been added.

The CLMU allows for the study of how climate change affects the urban heat island and potential mitigation strategies through urban planning and design.