Abstrack:
Drought is a natural disaster that threatens life and cause enormous damage. Report of the Intergovernmental Panel on Climate Change states that the world is more vulnerable to drought in the next 25 years, and climate projections indicate that this will get worse in the future. An important component of a national drought strategy is a comprehensive drought monitoring system which can give warning at the beginning and end of the drought, determine the severity, and disseminating information on various sectors, especially agriculture, public water supply, energy, and health. Such a monitoring system needs a drought index, which is a variable for assessing the effect of a drought, and defining different drought parameters, to detect and evaluate occurrence of droughts. Drought generally classified into meteorological drought, hydrological drought, agricultural drought, and socio-economic drought. Hydrological drought is related to a period with inadequate surface and subsurface water resources for established water uses of a given water resources management system. At present no hydrological index has been developed and applied in Indonesia. This paper describes the development of a hydrological drought index for Indonesia, using indicator of traditional pasten, or its modern derivative Faktor-K indicating the ratio between water supplied available and the corresponding water demand in an irrigation system. Since long time ago, early in the colonial Dutch era, farmers in Indonesia already cultivate rice in the same way as nowadays. The allocation of irrigation water for sugarcane, rice and palawija is planned and monitored using the pasten system to achieve a fair distribution. At present the farmers still practice the pasten system, and the data on water demand and supply is available on most irrigation diversions. It is expected that a hydrological drought index using the easily available data at the farmer level that have been practiced for centuries in Indonesia, can be developed and applied for drought monitoring and water allocation. Preliminary results using this pasten system with the statistical theory of run, indicate that this index is highly correlated with the occurrence of drought in the northern parts of Central Java.
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