伴隨系統的降水現象是導致台灣地區極端降雨事件的來源之一，但同時也是重要的水資源。在過去的研究中顯示，不同季節的鋒面系統與大尺度環境的變化與多重時間尺度的氣候振盪相關。這也代表在氣候變遷情境下，多重時空尺度之大氣環境條件改變也對於台灣地區的梅雨鋒面系統有所影響。本研究將利用長期之氣候分析資料與客觀分析技術，回溯台灣長期鋒面系統之變化。並使用CMIP5/CMIP6模式推估資料集，分析各種氣候變遷情境下台灣地區鋒面系統發生頻率的變化。同時利用分析的結果，針對各種氣候變遷情境下台灣地區伴隨鋒面系統降雨進行氣候推估。本計劃前兩年執行期間已經完成歷史鋒面系統分析，客觀分析工具建置等工作外。第三年的計畫是針對CMIP6模式大氣環境特徵之群聚分析與跨模式鋒面辨識模型的實驗測試。透過分析不同氣候推估模式之現在、近未來與遠未來的鋒面事件頻率變化，我們可以注意到各模式間對於各季節的鋒面影響頻率變化有所差異，模式間對於鋒面系統的變化並沒有一致的共識。各模式間變化較為一致的是春天的鋒面系統的影響頻率變化，不管在近未來或遠未來都是下降的趨勢。另外一個值得注意的部分是大部分的模式顯示，在遠未來的秋季鋒面系統影響頻率有所增加。在氣候變遷情境下的鋒面降雨強度推估上，我們注意到模式間的鋒面降雨強度變化差異較大，這與先前在群聚分析的結果一致。整體來說，透過氣候推估資料可預期近未來與鋒面系統相關的累積降雨有減少的現象，但在遠未來則呈現大幅增加的現象。
Frontal precipitation is one of the important water resources in Taiwan. However, this type of precipitation is also the major cause of extreme rainfall and induces natural disasters. Previous studies show that front systems from different seasons correlate with large-scale environmental variations and multi-scale climate oscillations. This correlation also implies that the change of the large-scale environmental variations can influence frontal systems frequency or properties in Taiwan under climate change scenarios. In this study, we will use long-term climate numerical reanalysis/hindcast data and objective analyzing tools to reinvestigate the change of the long-term front system in Taiwan. Furthermore, we will apply the CMIP5/CMIP6 simulations used for climate projection in IPCC Assessment Report (AR5/AR6). The final goal is to use those data to analyze the frequency of the front system in Taiwan under different climate change scenarios. This project will be divided into three years. We already developed suitable tools to identify the front systems by re-analyzing data and also marked the historical dates of the front system and established the objective analyzing tools in the first year. In the project's second year, the cluster analysis of the atmospheric environment characteristics of the CMIP6 model and the experimental test of the cross-model front identification model. By analyzing the historical run, near-future, and far-future frequency changes of frontal systems in different climate model projections, we can notice differences in the frequency changes of frontal impact between different models in each season. The changes in the frontal system frequency between models are also not consistent. The relatively constant opinion of the frontal frequency in the Spring season shows decressing trends in the near future or the far future. Another noteworthy thing is that most models show an increase in the frequency of frontal system impacts in the far future in the autumnal season. In estimating frontal precipitation intensity under climate change scenarios, we noticed that the variation of frontal rainfall intensity varies significantly between models, which is consistent with the previous results in the cluster analysis. Generally, a decrease in the cumulative rainfall associated with frontal systems can be expected in the near future. Still, a substantial increase in frontal rainfall in the far future can be expected from climate estimates. Generally, a decrease in the cumulative rainfall associated with frontal systems can be expected in the near future. Still, a substantial increase in frontal rainfall in the far future can be expected from climate estimates.
