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3.2 Trends of Historical Climate in Bandar Lampung
3.2.1 Rainfall
Previous study suggested that the observed rainfall in Indonesia experienced decreasing trends after 1970s globally IPCC 2007. Nevertheless, the trends could
vary locally across different region. Here we investigate the spatial trends of rainfall in Bandar Lampung city as respectively shown in Figure 3.3. In addition, we also use
a longer rainfall data of Climate Research Unit CRU, namely CRU TS2.0 Mithcell and Jones 2005. Since the selection of different ranges of data will affect the trend
and the result of statistical test, it is crucial to analyse the long-term data in order to confirm the consistency of rainfall trend in the region especially related to climate
change studies. The CRU TS2.0 dataset has 0.5x0.5 degrees grid resolution covering global land area for a period of 1901-2002. In order to analysis the rainfall data over
Bandar Lampung, a spatially averaged data within the city 110.25E-110.51E, 7.12S- 6.95S is extracted from the datasets Figure 2.2.
Figure 3.3:.Spatial patterns of seasonal rainfall trends over Bandar Lampung .
Trend analysis for Bandar Lampung city is conducted using short observations, which is then compared with relatively long CRU TS2.0 records. The spatial patterns
of seasonal rainfall trends based on short observations are performed in Figure 3.3. It is shown that the city is experiencing downward trends at all seasons with rapid
decreases occur in MAM and JJA, while slow decreases are found during wet seasons SON and DJF. This informs that during the late 20
th
century after 1970, there is a significant decrease of rainfall during dry seasons MAM and JJA that
leads to an increase probability of drought disasters within the city. However, the
38 decreasing trend found during this short period is unlikely caused by global warming.
Instead, the trend is more likely due to the oscillations of low-frequency climate phenomenon occurred in the Pacific that is associated with more frequents El Nino
occurrences. The low-frequency oscillations in seasonal rainfall data can be seen from the filtered data using a simple moving average as shown in Figure 3.6. This
low-frequency components is possibly related to the low-frequency of Indo-Pacific climate drivers such as Interdecadal Pacific Oscillation IPO Folland et al. 1999 or
Pacific inter-Decadal Oscillation PDO Mantua Hare 2002 ; Mantua et al. 1997. This study suggest that the trends obtained from longer time periods of data as shown
in Figure 3.4 is more reliable for describing the effect of climate change in Bandar Lampung.
In Figure 3.4, we find a very rapid increase of rainfall trend during DJF and a slow increase of rainfall during MAM. In contrast, the rainfall trends during JJA and SON
show slowly decreasing trends during 20
th
century. This suggests that the wet season rainfall tend to shift into MAM season while the dry season tends to extend into SON
season. However, by referring to Figure 3.5 that describes the trends of wet days frequency in the city, the slow decreasing trends found during SON season is not
supported by the downward trend of wet days frequency. Instead, the trend of wet days frequency during SON is found to be positive. This indicates that increasing wet
days frequency is not followed by increasing rainfall intensity.
Figure 3.4:.Trends of seasonal rainfall in Bandar Lampung city 105.15E-105.34E, 5.51S-5.34S extracted from CRU TS2.0 dataset
.
Figure 3.5:.Trends 105.15E-105.34
Figure 3.6:. .Low-freq
defin
3.2.2 Temperature
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