A blue roof is a roof design that is explicitly intended to store water, typically rainfall. Blue roofs that are used for temporary rooftop storage can be classified as "active" or "passive" depending on the types of control devices used to regulate drainage of water from the roof. A number of blue roof pilot projects have been implemented around the United States. Active blue roofs for storm water detention using forecast integration were first proposed in 2008. Active blue roofs are sometimes referred to as automated roof runoff management systems.