Entropy-Based Characterization of Drought and Climate Change Amplification in the Jhelum River Basin, Pakistan (1981–2024)

The Jhelum River Basin supplies water, food, and energy to millions downstream of Mangla Dam in Pakistan, yet its drought regime under accelerating climate change remains insufficiently characterized. This study integrates Shannon-entropy-based rainfall variability analysis with SPI, SPEI, and SRI drought indices across 209 grid cells (0.125° resolution) using CHIRPS, ERA5-Land, and GLDAS-2.1 datasets for 1981–2024. Four novel findings emerge: (i) post-monsoon rainfall dominates inter-annual variability with a post-monsoon/monsoon entropy ratio of 3.36 (Mann–Whitney p=7.66×10−70); (ii) 52.15% of the basin is drought-vulnerable, concentrated counter-intuitively in the mid-basin (61.0%) and upper-basin (59.6%) rather than the lower basin (26.9%); (iii) an eastern rain-shadow belt is identified (drying ratio 2.6); and (iv) a statistically significant negative SPEI–SPI gap trend (-0.0083 yr−1, Hamed–Rao p=7.33×10−5) with a Pettitt-identified breakpoint at November 1998 (p=6.81×10−51) provides direct evidence of warming-driven drought amplification. Findings inform Mangla reservoir operations and Pakistan’s national drought-monitoring framework.