近年來受到氣候變遷的影響，極端氣候發生次數愈加頻繁，台灣地區也面臨嚴重乾旱事件的挑戰，未來在水資源的使用及儲蓄上需格外小心注意並制定相關應對措施，才能將衝擊與損失降至最低。本研究目的為利用四項標準化指數分析乾旱傳遞的過程與水庫缺水之間的關係，本研究選用台灣南部南化水庫與甲仙攔河堰系統進行研究，首先將集水區平均雨量與水庫入流量資料及以標準營運策略獲得之水庫蓄水量、缺水量資料轉換以得到不同時間尺度之標準化指數，再透過分析乾旱特徵、相關性分析及利用copula函數求取彼此互相影響的條件機率以得到乾旱傳遞的過程。結果顯示發生氣象乾旱後間隔約2旬時間會發生水文乾旱，且在長時間尺度中發生氣象乾旱後必定會發生水文乾旱；若發生水文乾旱則只有約一半機率會發生水庫缺水，稽延時間隨時間尺度變長而縮短。相關性分析結果顯示氣象乾旱與水文乾旱最為相關，其次為水文乾旱與水庫蓄水量，而氣象乾旱與水庫缺水相關程度最低。另外，當氣象乾旱較輕微時較容易發生輕微或中度水文乾旱及水庫蓄水量變化，反之當氣象乾旱愈嚴重則愈容易發生嚴重或極度水文乾旱或水庫蓄水量變化；水文乾旱與水庫蓄水量變化間的結果也類似。

In recent years, the frequency and magnitude of extreme weather events have increased due to global climate change. Taiwan is also facing serious challenges of extreme events such as floods and droughts. The purpose of this paper is to analyze the process of drought propagation and its relationship with water shortage using four standardized indexes. The study uses the Nanhua Reservoir and Jiashian Weir System located in southern Taiwan as an example to illustrate the methodology. By transforming data such as rainfall, streamflow, reservoir storage, and water shortage into four standardized indexes, it is possible to analyze the process of drought propagation among them. The results indicate that hydrological drought occurs approximately 20 days after meteorological drought, and meteorological drought always leads to hydrological drought at longer time scales. If hydrological drought occurs, there is only about a 50% probability of reservoir water shortage, and the duration of the shortage decreases as the time scale increases. Besides, the correlation analysis shows that meteorological drought has the highest correlation with hydrological drought, followed by hydrological drought with reservoir storage, while the correlation between meteorological drought and reservoir water shortage is the lowest. Moreover, when meteorological drought is mild, there is a higher likelihood of mild or moderate hydrological drought and changes in reservoir storage. Conversely, as meteorological drought becomes more severe, there is a higher likelihood of severe or extreme hydrological drought or changes in reservoir storage. Similar results are observed between hydrological drought and changes in reservoir storage.

1. Barker, L. J., Hannaford, J., Chiverton, A., & Svensson, C. (2016). From meteorological to hydrological drought using standardised indicators. Hydrology and Earth System Sciences, 20(6), 2483-2505.
2. Cancelliere, A., & Salas, J. D. (2004). Drought length properties for periodic‐stochastic hydrologic data. Water Resources Research, 40(2).
3. Dash, S. S., Sahoo, B., & Raghuwanshi, N. S. (2019). A SWAT-Copula based approach for monitoring and assessment of drought propagation in an irrigation command. Ecological Engineering, 127, 417-430.
4. Ding, Y., Gong, X., Xing, Z., Cai, H., Zhou, Z., Zhang, D., Sun, P., & Shi, H. (2021). Attribution of meteorological, hydrological and agricultural drought propagation in different climatic regions of China. Agricultural Water Management, 255, 106996.
5. Guo, H., Bao, A., Liu, T., Ndayisaba, F., Jiang, L., Kurban, A., & De Maeyer, P. (2018). Spatial and temporal characteristics of droughts in Central Asia during 1966–2015. Science of The Total Environment, 624, 1523-1538.
6. Guo, Y., Huang, S., Huang, Q., Leng, G., Fang, W., Wang, L., & Wang, H. (2020). Propagation thresholds of meteorological drought for triggering hydrological drought at various levels. Science of The Total Environment, 712, 136502.
7. Kuwayama, Y., Thompson, A., Bernknopf, R., Zaitchik, B., & Vail, P. (2019). Estimating the impact of drought on agriculture using the US Drought Monitor. American Journal of Agricultural Economics, 101(1), 193-210.
8. Maity, R., Ramadas, M., & Govindaraju, R. S. (2013). Identification of hydrologic drought triggers from hydroclimatic predictor variables. Water Resources Research, 49(7), 4476-4492.
9. Masson-Delmotte, V., Zhai, P., Pirani, A., Connors, S. L., Péan, C., Berger, S., Caud, N., Chen, Y., Goldfarb, L., & Gomis, M. (2021). Climate change 2021: the physical science basis. Contribution of working group I to the sixth assessment report of the intergovernmental panel on climate change, 2.
10. McKee, T. B., Doesken, N. J., & Kleist, J. (1993). The relationship of drought frequency and duration to time scales. Proceedings of the 8th Conference on Applied Climatology, Boston, MA, USA.
11. Men, B., Wu, Z., Li, Y., & Liu, H. (2019). Reservoir operation policy based on joint hedging rules. Water, 11(3), 419.
12. Patel, N., Chopra, P., & Dadhwal, V. (2007). Analyzing spatial patterns of meteorological drought using standardized precipitation index. Meteorological Applications, 14(4), 329-336.
13. Peters, E., Van Lanen, H., Torfs, P., & Bier, G. (2005). Drought in groundwater—drought distribution and performance indicators. Journal of Hydrology, 306(1-4), 302-317.
14. Raje, D., & Mujumdar, P. (2010). Reservoir performance under uncertainty in hydrologic impacts of climate change. Advances in Water Resources, 33(3), 312-326.
15. Sattar, M. N., Lee, J.-Y., Shin, J.-Y., & Kim, T.-W. (2019). Probabilistic characteristics of drought propagation from meteorological to hydrological drought in South Korea. Water Resources Management, 33, 2439-2452.
16. Stagge, J. H., Kohn, I., Tallaksen, L. M., & Stahl, K. (2015a). Modeling drought impact occurrence based on meteorological drought indices in Europe. Journal of Hydrology, 530, 37-50.
17. Stagge, J. H., Tallaksen, L. M., Gudmundsson, L., Van Loon, A. F., & Stahl, K. (2015b). Candidate distributions for climatological drought indices (SPI and SPEI). International Journal of Climatology, 35(13), 4027-4040.
18. Stefan, S., Ghioca, M., Rimbu, N., & Boroneant, C. (2004). Study of meteorological and hydrological drought in southern Romania from observational data. International Journal of Climatology, 24(7), 871-881.
19. Taghian, M., Rosbjerg, D., Haghighi, A., & Madsen, H. (2014). Optimization of conventional rule curves coupled with hedging rules for reservoir operation. Journal of Water Resources Planning and Management, 140(5), 693-698.
20. Tallaksen, L. M., Hisdal, H., & Van Lanen, H. A. (2009). Space–time modelling of catchment scale drought characteristics. Journal of Hydrology, 375(3-4), 363-372.
21. Telesca, L., Lovallo, M., Lopez-Moreno, I., & Vicente-Serrano, S. (2012). Investigation of scaling properties in monthly streamflow and Standardized Streamflow Index (SSI) time series in the Ebro basin (Spain). Physica A: Statistical Mechanics and its Applications, 391(4), 1662-1678.
22. Thomas, B. F., Famiglietti, J. S., Landerer, F. W., Wiese, D. N., Molotch, N. P., & Argus, D. F. (2017). GRACE groundwater drought index: Evaluation of California Central Valley groundwater drought. Remote Sensing of Environment, 198, 384-392.
23. van Langen, S. C., Costa, A. C., Ribeiro Neto, G. G., & van Oel, P. R. (2021). Effect of a reservoir network on drought propagation in a semi-arid catchment in Brazil. Hydrological Sciences Journal, 66(10), 1567-1583.
24. Van Loon, A., & Laaha, G. (2015). Hydrological drought severity explained by climate and catchment characteristics. Journal of Hydrology, 526, 3-14.
25. Wong, G., Van Lanen, H., & Torfs, P. (2013). Probabilistic analysis of hydrological drought characteristics using meteorological drought. Hydrological Sciences Journal, 58(2), 253-270.
26. Yan, H., Wang, S. Q., Wang, J. B., Lu, H. Q., Guo, A. H., Zhu, Z. C., Myneni, R. B., & Shugart, H. H. (2016). Assessing spatiotemporal variation of drought in China and its impact on agriculture during 1982–2011 by using PDSI indices and agriculture drought survey data. Journal of Geophysical Research: Atmospheres, 121(5), 2283-2298.
27. You, J. Y., & Cai, X. (2008). Hedging rule for reservoir operations: 1. A theoretical analysis. Water Resources Research, 44(1).
28. Zhang, R., Chen, X., Zhang, Z., & Shi, P. (2015). Evolution of hydrological drought under the regulation of two reservoirs in the headwater basin of the Huaihe River, China. Stochastic Environmental Research and Risk Assessment, 29, 487-499.
29. Zhang, T., Su, X., Zhang, G., Wu, H., Wang, G., & Chu, J. (2022). Evaluation of the impacts of human activities on propagation from meteorological drought to hydrological drought in the Weihe River Basin, China. Science of The Total Environment, 819, 153030.
30. Zhou, Z., Shi, H., Fu, Q., Ding, Y., Li, T., Wang, Y., & Liu, S. (2021). Characteristics of propagation from meteorological drought to hydrological drought in the Pearl River Basin. Journal of Geophysical Research: Atmospheres, 126(4), e2020JD033959.
31. 國家災害防救科技中心，2020年夏季西太平洋副熱帶高壓偏強與東亞極端氣候事件初步分析，2020