Evaluating drought index using NDDI method on toposequence of the Western Lawu Mountain, Karanganyar Regency, Indonesia

Global climate change can potentially impact the agricultural sector through La Nina and El Niño phenomena such as increasing drought risk. Karanganyar Regency, Central Java, is categorized as an area with high drought vulnerability. This study aims to identify the level of drought using the Normalized Difference Drought Index (NDDI) method and analyze the influence of land characteristics on the drought index in the toposequence of the western slope of Mount Lawu. The study was conducted from August 2024 to March 2025 using an exploratory descriptive survey approach. Sampling points were determined through purposive sampling based on land map units in 4 zones of toposequence. The NDDI method utilizes the vegetation index (NDVI) and the wetness index (NDWI). The results show that severe drought occurs in areas with a topography of 200–400 masl and moderate drought occurs at 600–1000 masl with drought index values of 0.25 and 0.21 – 0.23, respectively. Statistical test results indicate that topography, slope gradient, and precipitation have a significant influence on the drought index. The highest drought index occurs in areas with a 0–15% slope and precipitation of 1,292.40 mm/year. The 5-year trend indicates that the drought index increases at the beginning of the dry season, which spans from July to August, and then decreases as the dry season comes to a close in September to November.