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<p>This study evaluates how climate warming alters drought diagnostics by comparing precipitation- and PET-based drought indices over Pakistan (1950–2024). The Standardized Precipitation Index (SPI), Standardized Precipitation Evapotranspiration Index (SPEI), and standardized Reconnaissance Drought Index (RDIst) are evaluated across accumulation timescales of 3, 6, 12, and 24 months using a common climatological baseline (1991–2020). Results show that long-term precipitation anomalies exhibit weak and insignificant trends, whereas temperature and atmospheric evaporative demand display pronounced non-stationarity. Consequently, PET-aware indices consistently identify higher drought occurrence and broader spatial extent than precipitation-only SPI across all timescales. Moderate drought remains the most frequent class nationwide; however, SPEI and RDIst detect substantially larger areas of severe and persistent drought, particularly at longer accumulation periods. Spatial trend analyses further reveal strong index dependence in inferred drying patterns. Although national mean drought series remain highly correlated, SPI systematically under-detects drought months relative to PET-aware diagnostics, with false-negative rates exceeding 30% in many regions. These findings highlight the risk of underestimating drought exposure in water-scarce regions when precipitation-only metrics are used for monitoring and planning.</p>

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Climate-driven divergence in meteorological drought diagnostics: a comparative analysis of SPI, SPEI, and RDI over Pakistan (1950–2024)

  • 期刊论文

  • 发表日期：

    2026年4月22日

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  • Usama Bin Anjum,
  • Hong Fan

摘要

This study evaluates how climate warming alters drought diagnostics by comparing precipitation- and PET-based drought indices over Pakistan (1950–2024). The Standardized Precipitation Index (SPI), Standardized Precipitation Evapotranspiration Index (SPEI), and standardized Reconnaissance Drought Index (RDIst) are evaluated across accumulation timescales of 3, 6, 12, and 24 months using a common climatological baseline (1991–2020). Results show that long-term precipitation anomalies exhibit weak and insignificant trends, whereas temperature and atmospheric evaporative demand display pronounced non-stationarity. Consequently, PET-aware indices consistently identify higher drought occurrence and broader spatial extent than precipitation-only SPI across all timescales. Moderate drought remains the most frequent class nationwide; however, SPEI and RDIst detect substantially larger areas of severe and persistent drought, particularly at longer accumulation periods. Spatial trend analyses further reveal strong index dependence in inferred drying patterns. Although national mean drought series remain highly correlated, SPI systematically under-detects drought months relative to PET-aware diagnostics, with false-negative rates exceeding 30% in many regions. These findings highlight the risk of underestimating drought exposure in water-scarce regions when precipitation-only metrics are used for monitoring and planning.