This study was conducted to identify variability in precipitation entropy and specify the water resource zones of Iran. Precipitation data with a spatial resolution of 0.25° during the period from 01/01/1962 to 31/12/2019 were used. For the investigation of variability in precipitation entropy over Iran, two indices were applied: entropy and disorder. The results demonstrated that the maximum occurred at the Caspian coasts and the minimum observed at the southern coasts of Iran. Most areas over the country have encountered negative trends in the entropy index. The rates of the entropy index have decreased, and the mean rate of the disorder index has increased. An analysis of variability in the extension of water resource zones in terms of the entropy index demonstrated that Iran could be divided into four zones: abundant and permanent; deficient and permanent; deficient and concentrate; and abundant and concentrate. After 1998, the abundant, permanent zone in the northern, high-altitude half of the country, the abundant, concentrated zone in the southwest, and the zone with deficient and permanent precipitation in the northern half of the central parts have become less extensive, while the zone with deficient and concentrate precipitation has become more extensive toward the northern latitudes.
