Spatial Analysis of Historical and Near-Future Droughts using the SPI and SPEI Indices in the Competence Area of the Nakanbé Water Agency in Burkina Faso (1981–2050)

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Résumé

This study analyzes the spatio-temporal variability of meteorological drought in the Competence Area of the Nakanbé Water Agency (Burkina Faso) over 1981–2050. Drought conditions are characterized using the 3-month Standardized Precipitation Index (SPI-3) and the 3-month Standardized Precipitation Evapotranspiration Index (SPEI-3), with a focus on two rainy-season windows: MJJ (onset) and ASO (cessation). For the historical period, SPI-3 and SPEI-3 were computed using CHIRPS precipitation data and TerraClimate potential evapotranspiration. Results show persistent drought from the mid-1980s to the early-1990s, followed by a gradual return toward near-normal rainfall after 2004 but with marked dry years (e.g., 2006, 2015), consistent with the broader Sahelian drought legacy. SPEI-3 indicates an 1980s drought core, partial recovery, and more frequent wet anomalies after 2010, while recurrent MJJ deficits and ASO droughts highlight risks of delayed onset and early cessation. The SPEI generally highlights more severe drought than the SPI, reflecting rising temperatures and evaporative demand. Near-future (2021–2050) SPEI-3 projections were derived from MIROC6 under SSP2-4.5 and SSP5-8.5. MIROC6 was selected after benchmarking 17 NEX-GDDP-CMIP6 models against CHIRPS over the historical Nakanbé Basin, showing the best overall agreement in seasonal variability and extremes. Seasonal maps for MJJ and ASO indicate recurrent drought even under SSP2-4.5, punctuated by severe-to-extreme events. Under SSP5-8.5, extremes are earlier, more frequent, and more spatially extensive, alternating with very wet years and increasing year-to-year water-balance volatility. Overall, the combined SPI–SPEI approach proves relevant for anticipating climate-related risks and for strengthening the resilience of populations and rainfed agricultural systems to climate change in the Nakanbé Basin.

Mots-clés

Meteorological drought, Spatial analysis, Climate variability, Nakanbé, SPEI