Active zones detection of sea surface temperature for drought events in East Nusa Tenggara Indonesia using bootstrap

El-nino is a global phenomenon that causes the rainfall in Indonesia to decrease significantly and is one of the factors which causes drought. Drought is a natural event and can be defined as the condition of water supply deficiency which lasts for a long period until the rainy season arrives. East Nusa Tenggara is known as one of the most drought-striken provinces in Indonesia. The standardized precipitation index (SPI) is a method to characterize drought events, and this paper used it as the basis of determining drought events in East Nusa Tenggara. Furthermore, composite maps of sea surface temperature (SST) showing the active regions associated with drought in East Nusa Tenggara are identified by bootstrap method. In order to overcome the bias of the mean maps, this research developed anomaly maps. The maps indicate that the North part of West Nusa Tenggara and Bali show significantly low level of sea surface temperature on one to two months prior to the occurrence of the event. The regions around Kalimantan and Sulawesi have been detected as active zones as well in particular of a month before drought happens.