Seite - 579 - in Book of Full Papers - Symposium Hydro Engineering

[7] Shafer, B.A., and Dezman, L.E. (1982). Development of a surface water supply index (SWSI) to assess the severity of drought conditions in snowpack runoff areas. Proceedings of the Western Snow Conference, Fort Collins, CO, 50, 164-175. [8] Vicente-Serrano, S.M., Beguería, S., and López-Moreno, J.I. (2010). A multiscalar drought index sensitive to global warming: the standardized precipitation evapotranspiration index. Journal of Climate, 23 (7), 1696-1718. [9] Mason I. (1982). A model for assessment of weather forecasts. Australian Meteorological Magazine, 30, 291-303. [10] Kim, G. and Lee, J. (2011). Evaluation of drought indices using the drought records. Journal of Korea Water Resources Association, 44 (8), 639-652 [11] Bae, D.H., Son, K.H., and Kim H.A. (2013). Derivation and evaluation of drought threshold level considering hydro-meteorological data on South Korea, Journal of Korea Water Resources Association, 46 (3), 287-299. [12] Yoo, J.Y., Song, H.Y., Kim, T.-W., and Ahn, J,-H. (2013). Evaluation of short- term drought using daily standardized precipitation index and ROC analysis. Journal of the Korean Society of Civil Engineers, 33 (5), 1851-1860. SUMMARY This study developed Dam Inflow Drought Index (DIDI) for Chungju Dam in Korea and evaluated the usability of the DIDI by comparing with Surface Water Supply Index (SWSI) and Standardized Precipitation Index (SPI). DIDI is calculated by the cumulative difference between the critical inflow and the observed inflow. The critical inflow means the essential inflow keeping the water supply criteria of the dam. Considering the limit of dam capacity, the upper limit of the cumulative difference has to be determined, and the threshold is estimated by performing Receiver Operating Characteristics (ROC) analysis. The Optimal threshold is determined by a value that represents maximum ROC score. The maximum ROC score of the DIDI was 0.93, and the threshold at this point was 630 ×106 m3. The maximum ROC score of the DIDI was 0.21 higher than it of SWSI and 0.33, 0.22, 0.16, and 0.17 greater than it of SPI(3), SPI(6), SPI(9), and SPI(12), respectively. DIDI showed much better performance in monitoring dam droughts than SWSI and short-term and long-term SPI. The DIDI is useful for monitoring the dam inflow drought, and its application could help mitigate drought damages. 579