Abstract
Imbalances within the hydrological system, such as irregular rainfall distribution, can trigger hydrometeorological disasters, particularly floods. This study aims to determine the correlation between rainfall indices and flood occurrences in the Jangkok River, employing a statistical approach to elucidate the relationship between two variables. The rainfall index method used is the Standardized Precipitation Index (SPI), a statistical measure that calculates rainfall deviation from the long-term mean over specific timescales. Meanwhile, the flood index is analyzed using the Standardized Streamflow Index (SSI), which assesses wet or dry conditions of an area based on river discharge data. This research examines the relationship between monthly SPI-1 and monthly SSI-1 using Pearson correlation method. The results show correlation coefficient (r) of 0.405 between the SPI-1 rainfall index and the SSI-1 flood index. This indicates a moderate positive relationship, meaning that increase in the rainfall index tends to be followed by increase in the streamflow (flood) index. Consequently, the SSI flood index can be explained by 16% of SPI rainfall index, while the remaining 84% is influenced by other factors. In other words, 16% of flood events at the study site directly influenced by rainfall, whereas majority driven by other factors affecting hydrological.