Spatio-temporal characteristics of extreme rainfall over western Java, Indonesia, across interdecadal-to-multidecadal periods

Spatio-temporal characteristics of extreme rainfall over western Java across interdecadal-to-multidecadal periods allow assessment of the impact of various large-scale climate events on the region. In this paper, we describe these characteristics using extreme rainfall indices, based on a quality-assured daily rainfall dataset from 185 rain gauges with varying temporal coverage, ranging from 1950 to 2020. The characterisation was done by calculating Sen’s slopes of the extreme indices across three interdecadal (10–15 and 16–25 years) and multidecadal (>25 years) periods. Our study shows that the interdecadal and multidecadal periods were dominated by Sen’s slopes with no statistical significance, and likewise for their regression with elevation. Thus, there is no compelling evidence of any spatial dependency (e.g. topographical effect) of Sen’s slopes in any of the extreme indices and periods in the region despite its complex terrains and coastlines. Much steeper Sen’s slopes in interdecadal compared with multidecadal periods signal regional responses to large-scale climate internal variabilities, such as the long-term modulation of the El Niño–Southern Oscillation (ENSO). The significance of extreme rainfall in interdecadal periods is well exemplified by the decade 2001–10, which exhibits a larger number of locations with positive and significant Sen’s slopes than 1991–2000 and later decades. The positive and significant Sen’s slopes in 2001–10 may be associated with a shift towards negative phases of the Pacific Ocean climate drivers, such as La Niña events. Our study suggests that interdecadal changes in extreme rainfall over western Java indicate a key regional climate impact concern that warrants mitigation efforts.