Warming without Detectable Drying in the Bouaké Area, Côte d’Ivoire (1985–2024)
Ange Emmanuella Yao
Equipe de la Géographie Physique et Environnement de l’Institut de Géographie Tropicale, (UFR –SHS), Université Félix Houphouët-Boigny, 01 BPV 34 Abidjan, Côte d’Ivoire.
Kouadio Christophe N’da
Equipe de la Géographie Physique et Environnement de l’Institut de Géographie Tropicale, (UFR –SHS), Université Félix Houphouët-Boigny, 01 BPV 34 Abidjan, Côte d’Ivoire.
Aka Jacques Adon *
Equipe de la Physique pour l’Environnement, Laboratoire de Physique Fondamentale et Appliquée, Université Nangui Abrogoua, Abidjan 02 BP 801, Côte d’Ivoire.
*Author to whom correspondence should be addressed.
Abstract
Long, homogeneous station records are scarce in central Côte d’Ivoire, where the Bouaké area lies in the forest–savanna transition zone. We assess 1985–2024 changes in temperature, precipitation, relative humidity, dry-air days and wind at three localities in the Bouaké area (Bouaké, Béoumi, Sakassou) using CHIRPS rainfall, ERA5 temperature and wind, and MERRA-2 relative humidity (two distinct grid cells). Trends were tested with an autocorrelation-corrected Mann–Kendall test, cross-checked using pre-whitening, with adjustment for 28 tests using the false discovery rate; results were reported with Theil–Sen slopes, serial-dependence-adjusted confidence intervals and minimum detectable trends. Warming was detected; drying was not detectable. Annual mean ERA5 temperature rose by 0.25 °C per decade at the three highly correlated localities (r = 0.98–0.99; 95% confidence intervals 0.15–0.33) and by 0.26–0.28 °C per decade in the November–April dry season; at Bouaké, the 2015–2024 mean exceeded the 1985–1994 mean by 0.66 °C. An incomplete GHCN-Daily station record agrees in direction but cannot confirm the magnitude. No monotonic trend was detected in annual or dry-season precipitation, relative humidity, dry-air days or daily-mean wind-vector magnitude; at Bouaké, confidence intervals span about −4% to +5% of the mean per decade for annual rainfall and −0.6 to +2.3 percentage points per decade for dry-season relative humidity. The 12-month Standardized Precipitation Index computed in December (SPI-12, summarising January–December rainfall), which identified 1992, 1997, 2005, 2015 and 2020 as drought years at Bouaké, was weakly associated, without statistical significance with dry-air days in the overlapping dry season (Spearman rank correlation −0.27, p = 0.096, n = 39), a test of limited power. Model-conditional minimum detectable trends (from Gaussian AR(1) simulations; about 45–65 mm per decade for annual rainfall) define which changes these series could have revealed; non-detection does not demonstrate the absence of drying.
Keywords: Climate warming, trend detectability, precipitation, relative humidity, standardized precipitation index, ERA5, detection limits, Côte d’Ivoire