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<p>Early winter (October-December; OND) precipitation is critical for Pakistan’s water resources, agriculture and socio-economic stability, yet the large-scale drivers and physical mechanism driving its interannual variability remains poorly understood. Using in-situ observations and ERA5 reanalysis for 1981–2023, we have investigated the dominant mode of early winter precipitation variability over Pakistan and its associated atmospheric teleconnections. The leading Empirical Orthogonal Function (EOF1) explains approximately 60% of the total variance, with the maximum interannual variability centered over northern Pakistan, including the Upper Indus Basin. A Pakistan Precipitation Index (PRI) is developed over this core precipitation region. Regression analysis demonstrates that positive PRI anomalies are associated with anomalous upper-level divergence over central-eastern equatorial Pacific and western Indian Ocean, compensated by convergence over Maritime Continent. A quasi-stationary Rossby wave train excites from tropical pacific and propagates eastward along the subtropical westerly jet into Eurasia producing an anomalous upper-level trough over southwest Asia including Pakistan. This favors enhanced ascent and cyclonic circulation anomalies along with moisture transport from western Indian Ocean and Bay of Bengal, resulting in above normal precipitation over Pakistan. The PRI is significantly correlated (<i>r</i> = 0.5) with the warm central-eastern equatorial Sea Surface Temperature (SST) anomalies (i.e., Niño3.4 index), indicating the El Niño-Southern Oscillation (ENSO) as a dominant mode of early winter precipitation variability. During El Niño, the warm SST anomalies in central-eastern equatorial Pacific enhance upper-level divergence, excite stationary Rossby wave and shift the subtropical westerly jet southward. At same time, the enhanced moisture transport and wave activity from the western Indian Ocean, favors convergence over Pakistan. In contrast, La Niña produces the opposite response. This shows ENSO along with the Indian Ocean strongly influences Pakistan precipitation variability in early winter. These findings provide valuable basis for seasonal prediction and support water resource management, agriculture and climate resilient planning across Pakistan.</p>

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Early winter precipitation variability over Pakistan and associated ENSO teleconnections

  • 期刊论文

  • 发表日期：

    2026年7月14日

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  • Romesa Najeeb,
  • Irfan Ur Rashid,
  • Rehan Ahmed,
  • Muhammad Adnan Abid,
  • Elham Ghasemifar,
  • Ibrahim Alsafari

摘要

Early winter (October-December; OND) precipitation is critical for Pakistan’s water resources, agriculture and socio-economic stability, yet the large-scale drivers and physical mechanism driving its interannual variability remains poorly understood. Using in-situ observations and ERA5 reanalysis for 1981–2023, we have investigated the dominant mode of early winter precipitation variability over Pakistan and its associated atmospheric teleconnections. The leading Empirical Orthogonal Function (EOF1) explains approximately 60% of the total variance, with the maximum interannual variability centered over northern Pakistan, including the Upper Indus Basin. A Pakistan Precipitation Index (PRI) is developed over this core precipitation region. Regression analysis demonstrates that positive PRI anomalies are associated with anomalous upper-level divergence over central-eastern equatorial Pacific and western Indian Ocean, compensated by convergence over Maritime Continent. A quasi-stationary Rossby wave train excites from tropical pacific and propagates eastward along the subtropical westerly jet into Eurasia producing an anomalous upper-level trough over southwest Asia including Pakistan. This favors enhanced ascent and cyclonic circulation anomalies along with moisture transport from western Indian Ocean and Bay of Bengal, resulting in above normal precipitation over Pakistan. The PRI is significantly correlated (r = 0.5) with the warm central-eastern equatorial Sea Surface Temperature (SST) anomalies (i.e., Niño3.4 index), indicating the El Niño-Southern Oscillation (ENSO) as a dominant mode of early winter precipitation variability. During El Niño, the warm SST anomalies in central-eastern equatorial Pacific enhance upper-level divergence, excite stationary Rossby wave and shift the subtropical westerly jet southward. At same time, the enhanced moisture transport and wave activity from the western Indian Ocean, favors convergence over Pakistan. In contrast, La Niña produces the opposite response. This shows ENSO along with the Indian Ocean strongly influences Pakistan precipitation variability in early winter. These findings provide valuable basis for seasonal prediction and support water resource management, agriculture and climate resilient planning across Pakistan.