What's the relationship between dew point and temperature? From a Ph.D dissertation, the writer change the land surface from nature earth to urbn and built up to compare the difference involving with this land use change.    

Due to the urban heat land effect, the temperature of lower atmosphere above the surface increase, and the dew point decrease.     

Dew point is a parameter represent the absolute moisture. When the temperature increase, how to analysis the dew point increase?
There are two separate effects:


The average temperature above urban land is greater than above rural land. This could be because of the cooling effect of plants evaporating water, or because of the higher albedo of vegetation than pavement and roofing.
The absolute humidity decreases; that is, the total amount of water vapor in a given volume of air decreases, perhaps due to the capture and run-off of rainwater into storm drains, rather than evaporating.