Understanding the characteristics of the UHI is of considerable importance due to the rises in urban population (table S1).
Different locations experience a range of identified WCs and have very different structures.
For reasons similar to those discussed above, the diurnal evolution of the UHI can differ significantly with location.
The diurnal cycle, combined with the WC, provides us with the opportunity to examine when anthropogenic activity has the largest influence on the environment. There is a range of postulated causes of urban heat (Oke 1982).
The presence and/or strength of WCs in urban areas are related to the driving forces for the anthropogenic use of energy.
These include population, character of industrial activity, patterns and intensity of vehicular traffic, typical synoptic patterns (and implications for, e.g., ventilation), physical geography of the city, proximity of the city to large water bodies and their direction in relation to the prevailing winds, frequency of inversions (and their implications for convection and for trapping of heat) and typical rain-producing mechanisms of the area.