Agricultural Drought in Indonesia - Monitoring and Predicting Agricultural Drought: A Global Study - page 332

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Fig ure 26.1 Climatology of seasonal rainfall (updated, based on Boerema, 1938, and ASEAN
Secretariat, 1982).

Line
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0.3
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Norm
PgEn

la te withdrawal of the monsoon result in a lengthy wet season, while the
late onset and the early withdrawal entail a relatively short rainy season
and a longer dry season.
The dry season ranges between 5 and 35 dekads (one dekad equals 10
days). Most of the area in the eastern part of Indonesia has relatively longer
dry seasons. The longest and driest periods are found in central and east-
ern Lombok (30-35 dekads). The second longest dry season (26 dekads)
occurs in Lombok North, and the third one (25 dekads) occurs in eastern
Sumba, Flores, Pasuruan-Probolinggo, East Java and Subang, Indramayu,
and West Java. The length of the dry season in most of East Java is between
15 and 25 dekads. The shortest periods are found in western and central
Java and along the eastern coast of Sumatra. Rainfall during the dry season
ranges from 250 to 500 mm in most areas of the archipelago. However, in
some parts around the northern coast of West Java, the southern coast of
East Java, central and northern Lampung, Sumbawa, West Lombok, the
northern part of East Timor, and the northern and southern coasts of Irian
Jaya, the rainfall amounts are between 500 and 750 mm.

[332

Im pact of El Niño/Southern Oscillation on Rainfall Variability

Indonesia is a tropical country influenced by the Indian and Pacific oceans.
Rainfall variability is affected by at least five factors (Tjasyono, 1997):
meridional circulation (Hadley), zonal circulation (Walker), monsoon ac-
tivity, local effects (topography), and tropical cyclones. These five factors
work simultaneously throughout the year, but in certain conditions, one
factor might become more dominant than others. Table 26.1 shows that
all but six drought events were associated with El Niño during the 1844-
1998 period. Many studies imply that droughts in Indonesia were mostly
associated with El Niño events (Braak, 1919; Berlage, 1927; Nicholls,