Rainfall variability study in Kalimantan as an impact of climate change and El Nino

Abstract

The patterns of climate change and El Nino were studied to obtain the characteristics of rainfall variability in Kalimantan. The pattern of climate change is analyzed in ten-year periods (decades of 1986-1995, 1996-2005, and 2006-2015). The analyses carried out include climatology averages, the amount of annual rainfall, climatological patterns of high rainfall (Percentile 95), shifts to the lowest monthly rainfall, and shifting to the dry season. The frequency of rainfall that occurred in the Below Normal (BN) category was calculated using the average method and standard deviation. Annual variability analysis was correlated with El Nino by calculating the average composite frequency of BN category occurrences in El Nino intensity (weak, medium, and strong). The analysis was undertaken between the correlation of rainfall and the Nino Index of 3.4 to obtain the relationship of sea surface temperatures in the central Pacific and rainfall in Kalimantan. The results showed that the Kalimantan region's atmosphere got wetter in the last three decades in the annual rainfall patterned area and drier in the annual rainfall patterned area. This is indicated by the average climatological rainfall, which experienced an increase in rainfall in the third decade, a decrease in the frequency of occurrence BN rainfall, increased rainfall (95th percentile) in areas with annual rainfall patterns and vice versa (semi-annual). The lowest and foremost rainfall shifts occur in semi-annual rainfall patterns compared to normal and do not occur in annual rainfall patterns. The influence of El Nino has a weak to medium effect in annual and semi-annual rainfall patterns. The correlation between rainfall and the Nino index is 3.4 with r (0.33-0.66). The nature of rainfall is BN at weak, moderate, and strong intensity with a frequency of BN events between low (<33%) to medium (33-66%).