RECONSTRUCTION OF HISTORICAL DROUGHTS IN LAKE BIWA AREA USING HISTORICAL DAILY WEATHER RECORDS

Abstract

Daily weather records of old diaries are useful for investigating hydrological environment in historical days. In this paper, we collected daily weather records from 8 old diaries of 18-20^th centuries in Lake Biwa area and attempted to use them for evaluating the intensity of historical droughts in Lake Biwa area. Annual maximum duration of continuous no-rainy days and annual minimum PI (Precipitation Index) for 30, 60, 90 days, which is calculated by summing up the number of rainy days for 30, 60, 90 days with the weights of ‘small rain:rain:heavy rain=1:2:5, ’ were calculated for each diary, and the intensity of some serious drought were quantitatively evaluated.