Rainfall variation and uncertainty are
believed to be related to a large scale ENSO
phenomenon that is defined as the combination of
ocean warming and the reversal of surface air
pressure, at opposite ends of the tropical Pacific
Ocean that usually occur simultaneously (Peskan,2001). In considering a number of studies and
analyses that have been carried out so far, the
general type of relationship and degree of
association between rainfall over Thailand and
ENSO is still ambiguous and cannot be pinpointed
exactly. The analyses sometimes revealed
different conclusions. For example, Xu et al.
(2004) found a strong relationship existing
between ENSO and rainfall in the Mae Klong and
Ping River Basins, while Singhrattna et al. (2005)
showed a significant relationship among those
variables during the post-1980 period. In contrast,
Otarig (2000) reported that there was no
correlation between El Nino and rainfall over
Thailand.The different results may be due to the
large spatial and temporal variation of monsoon
rains. Moreover, ENSO itself is a complex system,
comprising several dynamic natural behavioral
characteristics with tele-connections with local
rainfall in many places around the globe. Thus, it
becomes difficult to identify any single uniform
relationship between ENSO and monsoon rainfall
that holds up for different locations in Thailand.
However, further analysis and research are still
required to pursue the answers to these questions.
Therefore, this research objective was to select the
subsets of the ENSO index (MEI) and rainfall
index (SPI) with the most potential to estimate rice
water requirements during the post-rainy period
by a crop growth model and provide a decision
basis for water release scheduling at the paddy field
level in the Central Plain of Thailand.