The period during the months of March, April, May, and the month September, October, November is called the First and Second Transition Monsoon respectively. The strength of the winds is generally weak and their direction is highly variable.
During the northwest monsoon the winds bring quite heavy rain to the archipelago, especially to its western part. During the southeast monsoon this area experience dry period. In the eastern part of the archipelago the difference of the amount of rain received during the wet and dry period is net as large as in the western part.
Beside the seasonal and annual variation of wind and rain, the archipelago also experiences the inter-annual variation of climate, namely the El Nino and La Nina. During El Nino the country experiences long period of drought with high economical, agricultural and health consequences to the country. During La Nina, the reverse occurrs namely the large amount of rain that causes floods in cities and other areas. The floods also cause damages to houses and infrastructures such as roads, schools, dams etc.
El Nino
El Nino is a natural phenomenon that occurrs in average every other four years. It is an interaction between ocean and atmosphere that very much disturb the meteorological condition in many countries including the Indonesian archipelago.
When El Nino occurrs, Indonesia always experience long drought with multiple adverse consequences. According to the record of the Southern Oscillation Index, there have been about 16 El Nino occurred during the 20th Century. The severe ones are the El Nino of 1982-83 and 1997-98.
The impact of El Nino is primarily occurrs in the agricultural sectors. It causes drought in large areas of various farm lands, plantations and aquacultures. The drought in turn causes crop failures of rice, corn, vegetables, fruits, potatoes, coming from farming; soy bean, palm oil, coffee, cacao, latex, tea, timber, coming from plantations; shrimps, fishes, crabs, oisters etc., coming from aquaculture.
The drought further causes drop in freshwater amount in rivers and lakes, which in turn causes problem in transportation, communication and freshwater supply for industry, household and irrigation.
Several rivers in Kalimantan, Sumatra, and other islands are used as media of transportation and communication of people and goods between towns and villages. El Nino causes these activities disturbed with great economical losses.
Low irrigation water causes additional problem to agricultural sector. But the most affected is the production of electricity that is dependent on the hydrological power. Low electricity supply causes other problem to industries and households; operation of factories are affected, resulting in low production capacity. Living activity and laisures are disturbed. Low clean water supply to households may causes health problem to the population.
