Evaluation of Future Changes of Precipitation, Evapotranspiration and Runoff Discharge due to Global Warming

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The global warming phenomenon has become of major interest in recent years. The objective of this study is to cvaluate the effects of the global warming on precipitation, evapotranspiration, runoff discharge, and develope nume-rical analysis methods useful for establishment of reservoir operating policies for drought.Taking account of monthly air temperature, nonstationary time-series models for long-term fluctuation of rainfall characteristics : the occurrance number and rainfall amount of one storm cluster. A streamflow sequence is considered as a filtered point process whose input is a daily raifall sequence. As a pulse-response function for a filtered point process, a tank model, called the model of 3-tanks with a parallel tank is developed. Thus, a streamflow sequence and its cumulants arc able to be derived from a daily rainfall sequence. By using the transition probability matrix of reservoir storage, the first passage probability of drought storage and the probability distribution of the first passage time for a reservoir to the drought state are formulated and demonstrated for actual reservoirs.As in forested watersheds interception evaporation is related to the flood alleviation function of forests, and both of interception and transpiration are closely related to the drought alleviation function of forests, a method of sepa-rately estimating daily interception evaporation and transpiration from annual evapotranspiration is proposed, and some runoff simulations are performed to evaluate the effects of changes of temperature related to interception and transpiration, precipitation, and forest on runoff discharge.