With reference to the diagram above, describe and comment on the precipitation in the urban environment (7 marks).

From the figure, the effect of the urban hear island on precipitation is demonstrated as the temperature is highest in the centre and most built up areas, at a peak of approximately 3.5⁰C compared to the cooler rural areas between 0-1⁰C. Consequently, due to the warmer temperatures in the city centre caused by the release of heat from buildings, for example, a low-pressure system develops, which therefore means increased precipitation. This means that the warm air begins to rise, as described in the figure. Therefore, when this warmer air meets with the cooler air above, it cools, condenses and forms clouds, which area positioned over the city centre and is evidence of convectional rainfall. This means that precipitation is generally higher in urban areas, as they have a microclimate, compared to rural areas. This is also exacerbated by the fact that due to the high-rise buildings in the city centre, the air is forced upwards and this vertical movement of air is typically more turbulent, contributing to the rising of the warmer air and formation of a low-pressure system. Furthermore, due to the high levels of industry in the city centre, there also tends to be higher levels of precipitation. This is because particles such as PM10s are released by factories, which allows for the hygroscopic condensation of water vapour around a nucleus. This means that due to the effect of industry in urban areas, more precipitation can develop as the water vapour can grow in size around nuclei of particulates.