Station-Based Characterization of Seasonal Drought across Burkina Faso’s Climatic Zones: Insights from SPI-3 and SPEI-3 (1981-2021)

Abstract

This study characterizes seasonal drought variability at nine synoptic stations spanning Burkina Faso’s climatic zones over 1981-2021, using the Standardized Precipitation Index (SPI-3) and the Standardized Precipitation Evapotranspiration Index (SPEI-3) computed at nine synoptic stations representative of the country’s three climatic zones—Sahelian, Sudano-Sahelian, and Sudanian. A multi-indicator approach combining non-parametric trend analysis (Hamed-Rao modified Mann-Kendall test, Sen’s slope) and structural change point detection (Pettitt test) is applied to two intra-seasonal windows: the early rainy season (MJJ: May-June-July) and the late rainy season (ASO: August-September-October). Results reveal three structurally distinct hydroclimatic phases. The period 1981-1990 was dominated by severe and extreme droughts, spatially coherent across all zones and concentrated in the Sahelian sector. A partial rainfall recovery emerged from 1991 onward, consistent with the documented Sahelian re-greening, with significant structural change points clustering in two windows: 1997 and 2007-2009. However, SPEI-3 systematically detects higher moderate and severe drought frequencies than SPI-3 after 2000, revealing an intensification of evapotranspiration-driven water stress decoupled from precipitation trends—particularly in the Sudano-Sahelian zone and at the late-season scale. SPI-3 retains superior sensitivity for extreme drought detection, driven by catastrophic rainfall deficits, while SPEI-3 better captures chronic, low-intensity stress with direct implications for rainfed agriculture. The early season (MJJ) constitutes the primary locus of monsoon onset vulnerability, while the late season (ASO) experiences increasing thermal amplification of drought, particularly in the Sudanian zone. These findings underscore the diagnostic necessity of jointly using SPI-3 and SPEI-3 for drought monitoring in semi-arid West Africa, and provide a spatially differentiated evidence base for climate adaptation strategies in a country where over 80% of the population depends on rainfed agriculture.