Statistical Downscaling for the Projection of the Keetch Byram Drought Index in the Barito Basin

Abstract

Over the last few decades, prolonged drought in Indonesia has led to a catastrophic wildfire hazard, including on Kalimantan Island. The Barito River basin is one of the major river basins on the island, located in South and Central Kalimantan Provinces. According to The Indonesian National Board for Disaster Management (BNPB), the drought hazard index in the southern part of Kalimantan is mostly at the medium to high-risk level. In terms of Integrated Water Resources (IWRM), more detailed drought risk analysis needs to be conducted at the river basin level, so that drought adaptation and mitigation strategies can be integrated into long-term river basin management plans. In this study, a drought projection of the Barito River basin was simulated by using the Coupled Model Intercomparison Project 5 (CMIP5). A coarse grid of CMIP5 data was statistically downscaled to a smaller grid over the basin area. Data from climatology observation stations and Climate Forecast System Reanalysis (CFSR) were used to calibrate the bias correction function of the CMIP5 data. This function for rainfall data was developed based on the rainfall probability curve, while the bias correction function for temperature data was developed based on the elevation-temperature relation. The bias-corrected rainfall and temperature data were used as input for the Keetch-Byram Drought Index (KBDI) analysis. The study shows that the potential for drought hazard may increase in the future. Drought projection in the Barito basin for 2050 using KBDI shows that the potential areas with medium and high drought risk may cover around 50% and 2%, respectively, or about 35,000km2 and 1,400km2. The occurrence of wildfires also has a strong correlation with the drought index. A comparison between 1998 and 2015 fire hotspot data shows that most hotspots were located in areas in the medium and high drought risk categories. The study shows the importance of climate change impact analysis to prevent more catastrophic hazards in the future, especially in the Barito River basin, Kalimantan Island.