利用跨尺度天氣預報決定解除限水時間—以民國100年石門水庫為例

乾旱時期限水措施往往需要等到水情已經足夠明朗後才解除。然而，根據歷史天氣紀錄，多數情境具備提早解除限水的條件。以民國100 年石門水庫限水為例，本研究利用月、季天氣預報與氣候平均預測，並考慮不同天氣預報命中率下，探討解除限水的時刻，以及決策時機。歷史資料顯示，民國100 年石門水庫的限水停止約到六月底。以100 年實際入流量推算，約可於第十四旬（五月上旬）解除限水。本研究顯示，當季預報命中率為100%時，採用完美短期氣候預報資訊最早可於三月上旬決定五月中旬時解除限水。然而當季預報命中率下降至60%時，非完美短期氣候預報資訊顯示，在四月中下旬時，即可推測可望於五月中旬時解除限水。依實際CWB目前月、季長期天預報能能力所假設的降雨預報情境下，仍具有提早解除限水的潛力，在本研究案例中約可提早1 個月解除限水。

Usually, water rationing against drought period is terminated after a significant amount of rainfall in the watershed of reservoirs. However, based on the historical weather records, it seems that the rationing can be terminated earlier. In this study, we employed the CWB monthly weather outlook, CWB seasonal weather outlook, and climatological weather forecast to determine the time of terminating water rationing for different hit-rates of weather forecasts. We used Shimen reservoir and the drought event in 2011, phase 1 water rationing had executed from March 1 to June 30, as our case study. Based on the reservoir inflow records in 2011, the rationing can be terminated as early as the middle May (14th ten-day). According to the weather outlooks (seasonal rainfall outlook) with the accuracy of 100%, we make decision in the early March, that the normally supply can start from middle May. With the accuracy of seasonal rainfall outlook of 60%, in the middle and late April, the termination of rationing in middle May can be estimated. Based the weather forecasts with current forecast system in Taiwan, the water can be supplied normally 1 month ahead.