Long-term rainfall seasonality trends and abrupt shifts in the Northeast Indian Province of Manipur

This study assessed spatiotemporal changes in rainfall seasonality in Manipur, a hilly state in northeast India, using long-term (1901–2022) gridded rainfall data (0.25° × 0.25° resolution). Three indices—the Seasonality Index (SI), Individual Seasonality Index (SIi), and Replicability Index (RI)—were used to characterize rainfall patterns. Trends, magnitudes, and abrupt shifts in SIi were analysed using the non-parametric Mann–Kendall (MK) test, Sen’s slope (Qmed), and sequential Mann–Kendall (seqMK) test. The results revealed significant rainfall variability, with pronounced seasonal and spatial variations observed across the state. The winter and post-monsoon seasons exhibited the highest variability (CV > 100%), while the monsoon season displayed lower variability (CV 20–45%) due to orographic effects and monsoonal winds. Manipur’s rainfall regime is classified as ‘seasonal’, with SI values ranging from 0.60 to 0.79. Trend analysis showed that 57.57% (19/33) of grid points exhibit increasing SIi trends, especially in northern and southern districts, while 30.3% show decreasing trends, mainly in central areas. Trend magnitudes are small (Qmed: − 0.00003 to 0.00089/year). Moreover, the SeqMK analysis reveals multiple abrupt change points, mostly occurring after 1973 and intensifying after 2000, indicating increased variability in rainfall seasonality likely driven by climate and land use changes. Areas around Imphal, Churachandpur, and Ukhrul show mixed or intensified trends, whereas Thoubal and Senapati appear more stable. The observed changes in rainfall seasonality may have significant implications for water resources, patterns of hydrological hazards, and the socioeconomic stability of the state.