These mechanisms include an increase in area and persistence of sub-tropical high pressure cells, changes in summer monsoonal circulations, lower ocean temperatures, and the displacement of the mid latitude storm track. Low relative humidity, high temperatures, and high winds are also factors which can greatly impact a drought and its intensity. Two different types of drought definitions exist. The first, known as a conceptual definition, is put into general terms. This makes it easier for people to understand the concept of drought.
Conceptual definitions are also important in establishing drought policies.
Science-based assessments are what help determine declarations of extreme drought. This type aids in helping people understand things like the beginning, end, and severity of droughts. When the beginning of a drought is determined, the operational definitions help in specifying the degree of departure from average of precipitation over a time period. This can be done by comparing the current conditions with historical climatic data, usually over a 30-year period of data. This definition can also be used when dealing with agriculture, to tell things such as the impact the drought is having on crops an the rate of soil depletion.