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<p>This study assesses how future climate change will reshape meteorological and hydrological droughts in the Nakanbé River Basin upstream of Wayen (NRUW), Burkina Faso, a strategic basin hosting major reservoirs critical for urban water supply and agriculture amid growing water security challenges. Because non-stationary hydroclimatic conditions complicate traditional drought projections, we use relative standardized drought indices (rSPI for precipitation, rSPEI for precipitation-evapotranspiration balance, rSSI for streamflow) referenced to a fixed 1981–2014 baseline, enabling consistent comparisons across changing climates. Bias-corrected and downscaled NEX-GDDP-CMIP6 projections from 27 global climate models are analysed under SSP2-4.5 and SSP5-8.5 scenarios for two horizons: 2036–2065 and 2071–2100. A multivariate bias correction scheme is applied to preserve inter-variable dependencies among precipitation, temperature, and potential evapotranspiration. Basin-scale hydrological drought is derived using the GR2M rainfall-runoff model, calibrated and validated over 1979–2020 (Kling-Gupta Efficiency = 0.82 in calibration / 0.87 in validation). Projections are further grouped into “dry” (high evaporative demand) and “wet” (moderate precipitation gains) trajectories to capture uncertainty. Results reveal robust warming across ensembles (+ 1.5 to + 4.5&#xa0;°C basin-mean by 2071–2100), driving potential evapotranspiration (PET) increases of 9–18%, similar to uncertainty in precipitation increase (8–14%). Under SSP5-8.5, meteorological and hydrological drought duration extends by 1–2 months, severity intensifies by 15–25% (<i>p</i> &lt; 0.05 versus baseline), and extreme event frequency (≥ 90th percentile) increases twofold by 2100. Dry-trajectory models amplify these trends through elevated atmospheric demand, while wet trajectories offer partial mitigation but fail to avert overall aridification. Key uncertainties in these projections stem from inter-model spread and assumptions in PET estimation. Drought intensification emerges consistently from rising evaporative demand, tightening the basin water balance. By applying relative standardized drought indices, this study provides a robust, transferable framework for non-stationary drought assessment and delivers actionable insights for adaptive reservoir operations, drought early-warning systems and risk management in Burkina Faso and the wider Sahel region.</p> Graphical Abstract <p></p> <p>This graphical abstract synthesizes the methodological framework and key findings of the study, with emphasis on relative standardized drought indices and ecohydrological model trajectories. CMIP6 projections from 27 global climate models, combined with observational data, are first bias-corrected and used to simulate historical and future hydroclimatic conditions in the Nakanbé River Basin upstream of Wayen (NRUW), Burkina Faso, under SSP2-4.5 and SSP5-8.5 scenarios for two future horizons (2036–2065 and 2071–2100), relative to a historical baseline (1981–2014). A calibrated and validated GR2M hydrological model (KGE = 0.82–0.87) is used to derive streamflow, enabling computation of three relative standardized drought indices (rSPI, rSPEI, rSSI). The graphic highlights the separation between baseline and future states and illustrates the classification of climate model projections into “<i>dry</i>” and “<i>wet</i>” trajectories. Despite moderate rainfall increases, strong warming and rising evaporative demand drive longer, more intense, and more frequent droughts, with dry trajectories converging toward higher water stress and wet trajectories only partially offsetting long-term aridification. The framework underscores the need for adaptive reservoir management and drought-resilient water planning.</p>

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Assessing the Future of Droughts Using Relative Standardized Indices: Insights from the Nakanbé River Basin, West Africa

  • 期刊论文

  • 发表日期：

    2026年2月17日

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  • Tazen Fowé,
  • Roland Yonaba,
  • Lawani Adjadi Mounirou,
  • Elias Nkiaka,
  • Harouna Karambiri

摘要

This study assesses how future climate change will reshape meteorological and hydrological droughts in the Nakanbé River Basin upstream of Wayen (NRUW), Burkina Faso, a strategic basin hosting major reservoirs critical for urban water supply and agriculture amid growing water security challenges. Because non-stationary hydroclimatic conditions complicate traditional drought projections, we use relative standardized drought indices (rSPI for precipitation, rSPEI for precipitation-evapotranspiration balance, rSSI for streamflow) referenced to a fixed 1981–2014 baseline, enabling consistent comparisons across changing climates. Bias-corrected and downscaled NEX-GDDP-CMIP6 projections from 27 global climate models are analysed under SSP2-4.5 and SSP5-8.5 scenarios for two horizons: 2036–2065 and 2071–2100. A multivariate bias correction scheme is applied to preserve inter-variable dependencies among precipitation, temperature, and potential evapotranspiration. Basin-scale hydrological drought is derived using the GR2M rainfall-runoff model, calibrated and validated over 1979–2020 (Kling-Gupta Efficiency = 0.82 in calibration / 0.87 in validation). Projections are further grouped into “dry” (high evaporative demand) and “wet” (moderate precipitation gains) trajectories to capture uncertainty. Results reveal robust warming across ensembles (+ 1.5 to + 4.5 °C basin-mean by 2071–2100), driving potential evapotranspiration (PET) increases of 9–18%, similar to uncertainty in precipitation increase (8–14%). Under SSP5-8.5, meteorological and hydrological drought duration extends by 1–2 months, severity intensifies by 15–25% (p < 0.05 versus baseline), and extreme event frequency (≥ 90th percentile) increases twofold by 2100. Dry-trajectory models amplify these trends through elevated atmospheric demand, while wet trajectories offer partial mitigation but fail to avert overall aridification. Key uncertainties in these projections stem from inter-model spread and assumptions in PET estimation. Drought intensification emerges consistently from rising evaporative demand, tightening the basin water balance. By applying relative standardized drought indices, this study provides a robust, transferable framework for non-stationary drought assessment and delivers actionable insights for adaptive reservoir operations, drought early-warning systems and risk management in Burkina Faso and the wider Sahel region.

Graphical Abstract

This graphical abstract synthesizes the methodological framework and key findings of the study, with emphasis on relative standardized drought indices and ecohydrological model trajectories. CMIP6 projections from 27 global climate models, combined with observational data, are first bias-corrected and used to simulate historical and future hydroclimatic conditions in the Nakanbé River Basin upstream of Wayen (NRUW), Burkina Faso, under SSP2-4.5 and SSP5-8.5 scenarios for two future horizons (2036–2065 and 2071–2100), relative to a historical baseline (1981–2014). A calibrated and validated GR2M hydrological model (KGE = 0.82–0.87) is used to derive streamflow, enabling computation of three relative standardized drought indices (rSPI, rSPEI, rSSI). The graphic highlights the separation between baseline and future states and illustrates the classification of climate model projections into “dry” and “wet” trajectories. Despite moderate rainfall increases, strong warming and rising evaporative demand drive longer, more intense, and more frequent droughts, with dry trajectories converging toward higher water stress and wet trajectories only partially offsetting long-term aridification. The framework underscores the need for adaptive reservoir management and drought-resilient water planning.