Estimation method for obtaining estimation results of meteorological quantities in a specified area during a specified future period, including steps of: provisionally creating a meteorological time-series model from historical data of the meteorological quantities observed in the specified area; adjusting parameters of the created time-series model on the basis of long-range weather forecast data for wider area, which contains future meteorological tendency relative to normal years, to adjust the created time-series model; and conducting simulation using the adjusted time-series model to obtain the estimation results.