El-nino effect on reservoir volumetric (A case study of the Batujai Dam on the island of Lombok)

El-Nino has been occurred from 1952 to 2016 with the types of weak, medium, strong and very strong. The event of El-Nino has significant impact on all aspects of economy, social, industry and agriculture. There is a decrease in the quantity of water resources such as in the reservoir where the reservoir inflow becomes very small and the water outflow becomes high. At the event of very strong El-Nino is occurred some of the reservoirs will dry. The aim of the research is to investigate the deficit capacity of the reservoir in the event of El-Nino. The data analyzed in this article were the volume of the half-month reservoir, especially in the event of El-Nino events. The analysis of frequency deficit probability was using Weibull probability and Log Pearson Type III distribution. The results show significant decrease in reservoir water volume over a very long-time period. The reservoir volume never reached maximum water level and persists for almost one year. The deficit of reservoir volumes reached was 16,01x10 6 m 3 , 18.64x10 6 m 3 , and 21,07x10 3 m 3 for weak, moderate, and very strong El-Nino, respectively.