A comparative study of SPI, PCI, PCD, and RAI methods for estimating drought in the Palu River Basin, Indonesia

Abstract

The Palu Watershed is vulnerable to extreme hydrological events, especially periods of heavy rains and prolonged dry seasons. This study aims to determine the drought index and the results of a comparison of the drought index between the Standardized Precipitation Index (SPI) and the Rainfall Anomaly Index (RAI), Rainfall Concentration Index (PCI), Rainfall Concentration Level (PCD), and Rainfall Concentration Period (PCP). The data used are monthly rainfall from Bora, Kalawara, Kulawi, Palolo, and Wuasa stations with observation periods from 1985 to 2021. The Pearson and Spearman correlation coefficients are used to determine the relationship between SPI and RAI, PCI, PCD, and PCP. RMSE and MAE are used to find out the absolute error in predictions. The results obtained show: PCI shows a uniform distribution of rainfall (76.57%) and moderately seasonal (32.43%) there is no distribution of seasonal and strongly seasonal rainfall, the dominant SPI is the normal category followed by mild and moderate drought, PCD and PCP show that rainfall is homogeneous and distributed throughout years and no rain is concentrated at any one time, Comparison of the relationship between SPI and RAI is very strong and significant compared to SPI versus PCI, SPI versus PCD and SPI versus PCP.