Jeda hujan (dry spell) dan curah hujan berbasis probabilitas pada tipologi lahan kering di Lombok

Abstract

Dry    spell    and         probability    of precipitation  are very  essential  for   both  rainfed and the dry land agriculture. The parameters are important  indicators  of drought   status and  have relevance  to  crop    risk  in  dry  land  areas.  The research  objective  was  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   stations    were       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 first order, using daily rainfall data of 16 years. Probability of precipitation  was determined  using  a formula  of transformation  in order to meet the normal curve distribution  properties.  Drought-level  assessment was   carried   out  based   on  the   value   of  the standard  precipitation  index,  SPI  using   growing season rainfall data of  span 30 years. The results show,  that the dry spells    and  probability-based rainfall varied spatially  and temporally  as well as they were influenced by variation in the standard precipitation index; dry spell was longer getting to the east, while  rainfall decreased.  Dry spell was parabolic in nature; It is always longer in the early growing season (November) and at the end of the season   (April),   and  It  was  relatively   short   in between.  Dry  spell  on  SPI-negative  was  longer than that on SPI-positive. The characteristic of the growing season tends to be getting   drier, with a level  of  mild  drought  over  all.