Representing Urban Vegetation in Weather and Climate Models

Over half of the world's population now live in urban areas, and some have grown or will soon grow so large that the term Megacity has been coined. It is therefore increasingly important that we understand and predict the microclimate of urban areas and their impact on larger-scale meteorology. Even though the complexity of urban areas presents a unique challenge, we have come a long way in understanding in the last 20 or so years and now have a solid theoretical understanding of phenomena such as the urban heat island. However, a recent inter-comparison study of various models showed that we still have a major gap in our understanding surrounding the flux of water vapour (and the energy associated with it) from the surface and hence its contribution to the exchange of energy between the surface and the atmosphere.

The research will seek to extend the representation of this exchange of energy in the Met Office's weather and climate model to incorporate at least some aspects of urban vegetation in a physically sound and consistent way. In particular use will be made of data from wind-tunnel experiments and elsewhere to develop simple representations of urban and sub-urban gardens, street level trees, anthropogenic moisture from vehicles, buildings and people. An application of this will be an assessment of the effectiveness of green roof technologies in ameliorating the urban heat island. Model developments will be applied to the London area and compared with available data from field measurements (ACTUAL, CLearflo), as well as being compared with results from the recent urban inter-comparison project.

PhD research commenced January 2014 at the University of Reading (UoR) under the supervision of Professor Peter Clark (UoR), Professor Janet Barlow (UoR) and Dr. Maggie Hendry (Met Office, Exeter).

High Density Measurements within the Urban Environment

The Birmingham Urban Climate Lab (BUCL) was established in 2011 at the University of Birmingham with the aim of making the city of Birmingham a world leading testbed for urban climate research.

The initial focus of the BUCL team is the NERC (Natural Environment Research Council) funded HiTemp (High density Temperature measurements within the urban environment) project. The aim of the project is to deploy a demonstration near real-time network of sensors to observe urban climate processes (e.g. Urban Heat Island) using existing communications infrastructure, while promoting best practice in the siting and collection of metadata.  

Across Birmingham three nested networks will be deployed
  • Network 1 - 150 wireless air temperature sensors in schools across the city.
  • Network 2 - 100 wireless air temperature sensors in a dense array across the city centre.
  • Network 3 - 25 Automatic Weather Stations (AWS) across and on the edge of the city.
The temperature sensor deployed across the network is the Aginova Sentinel Micro (ASM) wireless temperature sensor with probe which transmits its data back to a central server in near real-time using existing Wi-Fi networks. The sensor was developed in conjunction with Aginova specifically for the project along with a bespoke radiation shield to reduce sensor error due to radiation and weathering. 

The AWSs will be deployed across the city (approximately 3 km between stations) to provide additional observations to complement the wireless temperature sensor network while providing data for further urban climate studies. Variables observed include air temperature, relative humidity, air pressure, wind speed, wind direction, precipitation and solar radiation. The AWSs are self-sufficient with power provided by solar panels and communications using GPRS via mobile phone networks.   

Our project partners on HiTemp are Birmingham City Council, Amey, Campbell Scientific Ltd. and Aginova Inc. I will continue to be an associate of the Birmingham Urban Climate Lab (BUCL) through the duration of the project.