Characteristics and return period of hydrological drought base on reservoir capacity reliability: Case study of Mamak Dam in Sumbawa Island, West Nusa Tenggara, Indonesia

The analysis of hydrological drought indices by using the reservoir will obtain an actual and real drought indefinite and have a clear physical meaning. In this research, we use daily data of the water level of reservoir, inflow and outflow. The research method used to obtain the hydrological drought index (HDI) is the water balance method in the reservoir. Based on selected distribution, for the estimation of drought in a certain return period using the log Pearson type III. The results showed that the extreme drought on Sumbawa Island took place on average for 265 days with a maximum deficit of 35,378 × 10³ m³ from the effective storage. The hydrological drought index (HDI) ranges from -1.31 to -0.01 with very severe drought criteria to weak drought. The hydrologic drought in the return period of 1, 2, 5, 10, 25, 50, 100 and 200 years, i.e., respectively -0.01, -0.54, -0.90, -1.04 and -1.12.