Evaluation of recent drought conditions by standardized precipitation index and potential evapotranspiration over Indonesia

摘要

In South Asia, an increasing population and frequent droughts have been significant factors deeply affecting water deficits in the region. In this study, recent drought conditions were evaluated by calculating the standardized precipitation index (SPI) for the period of 1991-2006, based on past data during the period from 1961 to 1990. In addition, the Thornthwaite equation was used to compute monthly potential evapotranspiration for the entire area of Indonesia. The APHRODITE data set was utilized for precipitation and temperature. Monthly rainfall data from April to September for 30 years (1961-1990) were used to obtain the gamma function for the computation of SPI values. Calculated probability of SPI for which values were - 2 during the period from 1991 to 2006 was used to evaluate recent Indonesian drought conditions. Regarding potential soil water deficits, under the very simple assumption that the root zone is 30 cm, soil porosity is 0.4, and field capacity is 80% of soil porosity, the critical threshold of soil water deficit was set as - 96 mm. Frequency of potential water deficits - 96 mm was counted during 1991-2006. The results of the SPI in Indonesia indicate that most parts of Indonesia have encountered severe and extreme drought for the period 1991-2006. Based on SPI interpretation, Borneo Island and West Papua are the islands that encountered the most extreme drought during the dry seasons. Borneo Island seems to have encountered extreme drought at the beginning and the middle of the dry seasons (April, May, and July). On the other hand, based on the Thornthwaite interpretation, Java and Bali Islands, and especially in Central Java and East Java, seem to have encountered the greatest soil water deficit at the middle and the end of the dry seasons (May, June, July, and September).