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Advanced Taiwan Ocean Prediction System

Tseng, Tsu-Lun - ALL News | 2020-05-25 | Count:66


Title: Supporting Water Resources Outlooks with Short-Term Climate Forecasting - Experiences and Challenges


Having an annual rainfall of 2,500 mm/yr in Taiwan, water resource management is still a challenging issue to our society due to significant spatial and temporal rainfall variabilities, insufficient reservoir capacity, and great agricultural water demand. Predictions of drought onset with sufficient lead time is difficult and very critical to the implementation of proper measures before sufficient rainfalls. The 2015 drought in northern Taiwan was mainly caused by less typhoon rainfalls in 2014 and insufficient spring rainfalls in 2015 which both were significantly lower than climatology records. Restriction on water supply with no water for 2 days in a week was employed in April and finally back to normal supplies until the hit of Plum rainfall in May. In this presentation, seasonal forecast products of the Central Weather Bureau (CWB) for 2015 Plum season was applied to exam their skills to support water resource predictions of the Shishmen Reservoir. The CWB seasonal forecast products provide outlooks of monthly precipitation and temperature as percentage likelihoods (i.e., probabilities and categories forecasting) with lead time of 3 months in 1-month moving windows. A Weather Generator (WGEN) was applied to generate multimembers of daily precipitation and temperature to drive the Generalized Watershed Loading Functions (GWLF) for reservoir inflow predictions. A System Dynamics Model was then employed to simulate water allocations of the regional water supply system mainly supported by the Shihmen Reservoir. Precipitation forecasts showed better forecasting skills in May, but overestimate in June causing larger estimation of inflows. Since drought is caused by persistent low rainfall lasting for several months, like the case in 2015, great improvements of seasonal climate forecast skills are needed to enhance confidence to water sectors. On the water resource management perspective, it is too conservative to rely on current reservoir capacity and climatology information to the decision making of reservoir operations. Seasonal outlooks certainly should be involved in reservoir operations subject to improved forecasting skills to be demonstrated.

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