JEDA HUJAN (DRY SPELL) DAN CURAH HUJAN BERBASIS PROBABILITAS PADA TIPOLOGI LAHAN KERING DI LOMBOK

Abstract

Dry spells and the probability of precipitation are very essential for  both rainfed and dry land agriculture. The parameters are important indicators of drought  status and have relevance to crop  risk in dry land areas. The research objective is to determine duration of dry spells and probability-based rainfall in the area of climate types D and E at southern Lombok. Descriptive research was conducted in 2014 by collecting daily rainfall data from 13 rainfall stations. The station are  assigned as purposive sampling to represent the southern part of Lombok area. Conditional upon the nature of the incident rainy day or day without rain  was analyzed using Markov chain model of level one, using daily rainfall data of 16 years. Probability of precipitation was determined using the formula of transformation in order to meet the normal curve distribution properties. Drought-level assessment carried out based on the value of the standard precipitation index (Standard Precipitation Index, SPI) using growing season rainfall data of   span 30 years. The results show, that the dry spells   and probability-based rainfall varies spatially and temporally as well as influenced by variations in standard precipitation index; dry sells was longer getting to the east, and rainfall decreased. Dry spell   is parabolic; always longer in the early (November) and the end of the growing season (April), and relatively short in between. Dry spell on SPI-negative was longer than the SPI-positive. The nature of the growing season tends to a dry nature, with level of mild drought