Agricultural Drought in Indonesia - Monitoring and Predicting Agricultural Drought: A Global Study - page 334

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(Tjasyono, 1997). The impact of the El Ni no/Southern Oscillation (ENSO)
on rainfall is more pronounced during the dry seasons than the wet sea-
son (USDA, 1984; Las et al., 1999). Various studies on the influences of
ENSO on interannual rainfall variability in Indonesia reveal some seasonal
patterns (USDA, 1984; ADPC, 2000; Yoshino et al., 2000; Kirono and
Partridge, 2002): (1) The end of the dry season occurs later than normal
during El Niño and earlier during La Niña years, (2) the onset of the wet
season is delayed during El Niño and advanced during La Niña years, (3)
a significant reduction of dry season rainfalls could be expected during El
Niño and significant increase could be expected during La Niña years, (4)
long dry spells occur during the monsoon period, particularly in eastern
Indonesia. Observations at five locations during 1982-83 showed these
patterns (table 26.2).
An analysis of time-series rainfall data (1951-98) for Pandeglang and
Lebak (West Java) revealed that the normal onset of the dry season in this
zone could be around the first week of June (ADPC, 2000). However,
during extreme La Niña years, it could be delayed to the first week of
August. During extreme El Niño years, the onset of the dry season could
be advanced as early as mid-April. Against the normal rainfall of 379 mm
during April-September, the rainfall could be as high as 979 mm during the
La Niña years and as low as 15 mm during El Niño years (ADPC, 2000).

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M onitoring Agricultural Drought
Decrease in rainfall below normal is a drought indicator commonly used
by the Bureau of Meteorology and Geophysics (BMG), whereas the total
area affected by drought is an indicator used by the Directorate of Plant
Protection (Alimoeso et al., 2000, 2002). Remotely sensed data such as nor-
malized difference vegetation index (NDVI; chapter 5) is used by Lembaga
Penerbangan dan Antariksa Nasional (Kushardono et al., 1999; Heryanto
et al., 2002). The following sections describe how these indicators are mon-
itored and drought forecasted in Indonesia.

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D rought Monitoring and Forecasting System

The Indonesian BMG developed an operational seasonal climate prediction
scheme for Indonesia in 1993. It is a statistical-analogue scheme based on a
detailed historical analysis of rainfall data for 102 meteorological regions
across the whole country. The forecast is issued in early March for the
dry season (April-September) and in early September for the wet season
(October-March).
The seasonal forecast products are forecast of seasonal monsoon onset
dates at 10-day interval; seasonal cumulative rainfall; and monthly rainfall.
There is an ongoing forecast verification process undertaken by the BMG,
the results of which are shown in table 26.3 for the 1993-97 period. The
verification of forecasts shows a good skill in predicting the onset period