Divergent drivers of runoff changes in the Indus eastern tributaries: Insights from attribution analysis based on the Budyko framework

Abstract

Study region The eastern tributaries of the Indus River Basin: Chenab, Jhelum, Ravi, and Sutlej. Study focus Using discharge records from the Water and Power Development Authority, Pakistan and climatic data from reanalysis datasets, this study constructs long-term, up-to-date hydro-climatic time series spanning 1951–2024 for the eastern Indus tributaries. After identifying the abrupt change years, the observed runoff changes between the pre-change and post-change periods are then attributed to climatic and residual non-climatic drivers based on a Fu-type Budyko framework. New hydrological insights for the region The observed runoff declines are evident at all tributaries during 1951–2024, which could be explained by contrasting drivers. Climatic factors are found to dominate the runoff declines at the western sub-basins. In Chenab, the decline is almost entirely driven by climatic factors. Jhelum shows a positive residual effect that partly offsets the climate-induced runoff decline. Precipitation dominates the climatic signal, explaining ∼43–97% of the absolute runoff change, while reference evapotranspiration only contributes a small share. In contrast, non-climatic drivers play a more important role at the eastern sub-basins. The relatively large non-climatic contributions in Ravi and Sutlej (∼47% and 55%) are consistent with intensive regulation, diversions, and consumptive use in these tributaries. These findings highlight that effective water management policy must differentiate between climate-sensitive and human regulation-intensive sub-basins for sustainable water governance in transboundary river basin systems.