The influences of ENSO and IOD on rainfall variability over the

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Chapter 3 CLIMATE HISTORY AND FUTURES

IN BANDAR LAMPUNG

3.1 Extreme Climate and Weather Events

3.1.1 The influences of ENSO and IOD on rainfall variability over the

Bandar Lampung Extreme climate events in Indonesia are strongly related to large-scale climate phenomena such as El Nino-Southern Oscillation ENSO and Indian Ocean Dipole IOD e.g. Boer Faqih 2004; Faqih 2004; Haylock McBride 2001; Hendon 2003; Kirono et al. 1999; Saji et al. 1999. This study analyze their impact on rainfall variability over Bandar Lampung. The relationships of both phenomena with seasonal rainfall over the city are shown in Table 3.1. It is shown that the correlations of both ENSO and IOD indices with rainfall are significant during dry seasons JJA and transition period SON. This suggests some possibilities of prolonged dry seasons and delays on monsoon onsets impacting the region during warm ENSO episodes El Nino. In addition, the El Nino impact will be stronger if accompanied by positive IOD event. Table 3.1 Correlations between seasonal rainfall over Bandar Lampung with DMI and Nino3.4 SST anomaly This study suggests that the seasonal rainfall during both seasons is more affected by the variability of IOD than ENSO. These are indicated by larger correlation results between rainfall and DMI. Stronger influence of IOD than ENSO to the rainfall variability in Bandar Lampung is due to its location along in the Sumatera Island. Several studies have indicated the low influence of ENSO on rainfall over Sumatra. Of particular reasons of this weak relationship is due to mountainous landscape on the west side of Sumatra dominating the local influence, as well as due to the cross- equatorial flow affecting rainfall variability in this region that is different from ENSO connected circulation Chang et al. 2004. On the other hands, other studies found strong effect of IOD on rainfall variability in the western Indonesia including Sumatra e.g. Saji et al. 1999. Although the correlation between rainfall and ENSO indices Nino 3.4 SSTa is lower than IOD, for a certain condition, the impact of ENSO could be considerable on rainfall variability in Lampung. This, for example, can be seen in 1996, where the La Nina event caused significant increase on rainfall amount over the region. This is associated to increased probability of floods over the region. On the other hand, the El Nino occurrence during 1982-83, 91-92 and 97-98 contributed to less rainfall over the region, associated with droughts. Figure 3.1:.S

3.1.2 Extreme wind