Comparison Method of Standardized Precipitation Index (SPI) and Thornthwaite Mather in Determining Drought Index in The Rondoningu Watershed, District of Probolinggo

摘要

Drought is the availability of water which is far on below water demand for necessities of domestic life, agriculture, and environment. To solve the drought, the most important attribute to be paid attention is drought index dimension, to find out the drought level before developed further drought management. This research using Standardized Precipitation Index (SPI) and Thornthwaite Mather methods. SPI method was aimed to identify the meteorological occurrence of the drought which was characterized by the lack of rainfall. Thornthwaite Mather method was used to identify agriculture drought featured by the reduction of soil humidity. The resultant drought index was then used to produce spatial distribution map using the Kriging Interpolation provided within ArcGIS Software. The result of research indicated that SPI-based drought peak at 1-month deficit period was found in January and April, and the drought had affected some districts including Krejengan, Maron, Gading, and Krucil. The result from Thornthwaite Mather method revealed that drought peak occurred in September in entire districts. The result of conformity analysis between the drought index and discharge data had shown that drought index resulted from Thornthwaite Mather method had higher accuracy than SPI method.