Trend analysis of extreme climate indices in coastal Semarang using ETCCDI and Mann–Kendall Test (1995–2024)

Abstrak

This study analyzes trends in seven ETCCDI extreme climate indices at the Tanjung Emas Maritime Meteorological Station, coastal Semarang, Indonesia, over 1995–2024. Daily rainfall, minimum temperature, and maximum temperature records underwent quality control (RClimdex) and homogeneity testing (RHtestsV4). The Mann–Kendall test assessed trend significance and Sen's slope quantified trend magnitude, applied to the full 30-year period and two 15-year sub-periods (1995–2009 and 2010–2024). Among precipitation indices, total annual rainfall (PRCPTOT) and maximum 1-day rainfall (RX1day) showed significant increasing trends, with Sen's slopes of +16.53 mm/year and +2.09 mm/year, respectively. Consecutive dry and wet day indices showed no significant trends. Among temperature indices, warm night frequency (TN90p) and warm day frequency (TX90p) increased significantly at +0.50 and +0.54 days/year, respectively, while the diurnal temperature range showed no significant change. Sub-period analysis revealed acceleration of TX90p in 2010–2024 (Sen's slope = +1.19 days/year), indicating intensifying daytime warming in the more recent period. No precipitation index reached significance within either sub-period, suggesting that rainfall trends accumulate over decadal rather than sub-decadal timescales. These results provide quantitative evidence of strengthening warming signals and increasing rainfall intensity in coastal Semarang, with implications for flood risk management and climate adaptation planning.