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<p>The Bilate River Basin in Ethiopia faces recurrent hydrometeorological drought; yet, no continuous 1990–2024 multi-index assessment exists. Using the Soil and Water Assessment Tool (SWAT)-based hydrological reconstruction, this study generated continuous monthly streamflow for Bilate-Alaba Kulito and Bilate-Tena and quantified drought dynamics using the Standardized Precipitation Index (SPI), the Standardized Precipitation-Evapotranspiration Index (SPEI), the Standardized Streamflow Index (SSI), and the Standardized Runoff Index (SRI) at 1-, 3-, 6-, and 12-month scales. We calculated index thresholds to evaluate both the duration and severity of drought events. The SWAT model performed acceptably (NSE = 0.75–0.82, R² = 0.82–0.88), enabling gap-filling for missing periods (4 years at Kulito; 18 years at Tena). For 3-month indices, meteorological drought (index &lt; 0) occurred in ~ 44% (SPI) and ~ 50% (SPEI) of months, with moderate-to-extreme drought in ~ 14% and ~ 17%, respectively. SPEI’s higher detection rate reflects warming-induced evaporative demand. Hydrological drought occurred in 48% of months, with maximum event durations of 5 months. The strongest propagation from meteorological to hydrological drought occurred at 6–12 months. Trend analysis showed mostly non-significant changes (<i>p</i> &gt; 0.05) for SPI and SSI, while SPEI showed consistent intensification (0.08–0.13 index units/decade) but without uniform statistical significance. Coupling multi-index diagnostics with model-based reconstruction provides basin-level evidence for early drought warning and climate-risk-informed water management.</p>

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Multi-index drought trend analysis in the Bilate River Basin, Ethiopia (1990–2024) using SWAT-hydrological reconstruction

  • 期刊论文

  • 发表日期：

    2026年7月14日

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  • Kebede Ganole,
  • Mihret Dananto,
  • Alemayehu Muluneh

摘要

The Bilate River Basin in Ethiopia faces recurrent hydrometeorological drought; yet, no continuous 1990–2024 multi-index assessment exists. Using the Soil and Water Assessment Tool (SWAT)-based hydrological reconstruction, this study generated continuous monthly streamflow for Bilate-Alaba Kulito and Bilate-Tena and quantified drought dynamics using the Standardized Precipitation Index (SPI), the Standardized Precipitation-Evapotranspiration Index (SPEI), the Standardized Streamflow Index (SSI), and the Standardized Runoff Index (SRI) at 1-, 3-, 6-, and 12-month scales. We calculated index thresholds to evaluate both the duration and severity of drought events. The SWAT model performed acceptably (NSE = 0.75–0.82, R² = 0.82–0.88), enabling gap-filling for missing periods (4 years at Kulito; 18 years at Tena). For 3-month indices, meteorological drought (index < 0) occurred in ~ 44% (SPI) and ~ 50% (SPEI) of months, with moderate-to-extreme drought in ~ 14% and ~ 17%, respectively. SPEI’s higher detection rate reflects warming-induced evaporative demand. Hydrological drought occurred in 48% of months, with maximum event durations of 5 months. The strongest propagation from meteorological to hydrological drought occurred at 6–12 months. Trend analysis showed mostly non-significant changes (p > 0.05) for SPI and SSI, while SPEI showed consistent intensification (0.08–0.13 index units/decade) but without uniform statistical significance. Coupling multi-index diagnostics with model-based reconstruction provides basin-level evidence for early drought warning and climate-risk-informed water management.