Impacts of reservoir operations on multi-scale correlations between hydrological drought and meteorological drought

Although numerous studies have investigated the relationships between hydrological drought (HD) and meteorological drought (MD) in different regions, few studies have examined the influence of reservoir operations during drought periods on such relationships, particularly at multiple time scales. This study presents a useful framework to examine the influences of reservoir operation rules during drought periods on the multi-scale correlations between HD and MD. Two standardized drought indices (Standardized Streamflow Index (SSI) and Standardized Precipitation Index (SPI)) with different timescales (1, 3, 6, 12, and 24 months) were used to compare the pre-reservoir and post-reservoir periods. Also, a simple algorithm was proposed to examine the difference value (Dvalue) between the inflow and outflow under different reservoir operation rules and it was used to evaluate the impacts of the reservoir operation rules during the drought on the correlation of the HD and MD. Monthly streamflow and precipitation records from 1960 to 2015 and monthly inflow and outflow records of a large reservoir (Xinfengjiang reservoir) during 1974-2009 in the basin of the Dongjiang River in south China were used to demonstrate the applicability of the analysis methodology. The results indicate that (1) the reservoir operations during the post-reservoir period (1974-2015) exerted a significant influence (positive impact) on the evolution of the short-term (1 and 3 months) HD by reducing the drought duration and alleviating its magnitude and altered the linear correlation between the HD and MD compared to the pre-reservoir period (1960-1972). However, the effects on the long-term (e.g., 12 and 24 months) HD and its correlation with the MD were not apparent. (2) The impacts of the reservoir operation under the drought condition on the relationship between the HD and MD were clearly different from those under normal rules. This study provides additional information for policy-makers to regarding reservoir management during a drought.