단일 저수량 인자 기반 수문학적 가뭄 임계치의 정량적 산정: 화천댐과 소양강댐을 대상으로

초록

Drought is categorized into meteorological, agricultural, and hydrological types, and is assessed by evaluating current water resource conditions relative to historical records using key variables for each sector. For drought assessment, the Standardized Precipitation Index (SPI) and the Standardized Reservoir Storage Index (SRSI)—which statistically normalize single variables such as precipitation and reservoir storage—are widely utilized. Conversely, in practical field operations, the Percent of Normal (PN), an intuitive ratio compared to average years, is primarily used. Such discrepancies in evaluation methods can lead to confusion when determining drought conditions and establishing response stages. This study proposes a methodology for the inverse calculation of a single-variable-based drought index into quantitative reservoir storage and provides a comparative analysis with indices used in practice. For hydrological drought assessment, the SRSI, which possesses statistical rigor, was applied. Quantitative reservoir storage volumes and ratios corresponding to drought thresholds were derived using the Inverse Gamma Cumulative Distribution Function (I-GCDF). In particular, this study analyzed the characteristics of the gamma distribution parameters for the Hwacheon and Soyanggang Dams to compare and analyze the seasonal sensitivity differences in critical storage rates based on dam operational purposes and scales. The results indicated that the quantified critical storage rates based on the drought index generally exceeded the current agricultural drought warning criteria (PN 70%). However, the findings also confirmed the necessity for a cautious approach due to significant numerical gaps (more than 10-20%) compared to practical standards. By providing a quantitative link between standardized drought indices and field operational indicators, this study seeks to improve the interpretability of drought analysis. The proposed quantitative thresholds are expected to support more objective and practical drought determination and decision-making, contributing to the establishment of future dam operation guidelines and systematic water resource management.

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