The present invention provides methods for water conservation with irrigation controllers based upon the ambient temperature and extraterrestrial radiation of a particular geographical area. It receives a preliminary irrigation schedule from the operator and computes a water budget ratio by comparing current local geo-environmental data with stored local geo-environmental data, then modifying the preliminary irrigation schedule based upon that ratio. The present invention utilizes fewer variables, is less complex, and is much easier to install and maintain than the current evapotranspiration-based controllers.