On the definition of urban heat island intensity: the 'rural' reference

One of the fundamental objectives of many studies on urban heat islands (UHI) involves establishing their intensity on determined nights or, if there is a sufficiently high number of observations, their maximum intensity and average intensity can also be ascertained. Regardless of the methodology employed, whether it refers to differences between two fixed observatories, one urban and another peripheral or non-urban, mobile urban transects or remote sensing, in the end it is a question of providing a value of thermal differences between contrasted points or sectors, one urban and another that could be termed non-urban