Projected Shifts in Rainfall Intensity-Duration-Frequency Curves under Climate Change Scenarios in Lampung, Indonesia

Abstract

This study develops non-stationary Intensity–Duration–Frequency (IDF) curves for Lampung Province, Indonesia, using bias-corrected CMIP6 rainfall projections from the ACCESS-ESM1-5 model under SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5 (2015–2060). Quantile mapping was applied to daily rainfall observations (2012–2014) to reduce model bias. Post-correction performance improved substantially, with Nash–Sutcliffe Efficiency increasing to 0.87–0.97 and Kling–Gupta Efficiency reaching 0.93–0.98 across stations. Trend analysis indicates significant annual rainfall declines under high-emission scenarios (up to –12.77 mm/year, p < 0.01). Despite declining annual totals, short-duration extremes intensify markedly. For a 5-year return period, 1-hour rainfall intensity increases from 19 mm/hour (historical lowland baseline) to ~183 mm/hour under SSP5-8.5. At the 25-year return period, 1-hour intensities in high-elevation zones rise from 125 to 210 mm/hour (≈68% increase). In contrast, 24-hour intensities show comparatively moderate changes. Elevation-stratified analysis reveals stronger relative amplification in lowland regions, while highlands maintain the highest absolute intensities due to orographic enhancement. These findings demonstrate substantial upward shifts in future IDF curves and highlight limitations of stationary design assumptions for hydrological infrastructure in tropical regions.