SPATIO-TEMPORAL VARIABILITY AND CLIMATIC DRIVERS OF HARMATTAN DUST OVER NORTHEAST NIGERIA USING MERRA-2 REANALYSIS

Abstract

Harmattan dust significantly affects air quality, visibility, public health, and regional climate across Northeast Nigeria; however, its long-term variability and climatic controls remain insufficiently quantified. This study investigates the spatio-temporal variability and climatic drivers of Harmattan dust over Northeast Nigeria from 1980 to 2025. Aerosol Optical Depth (AOD) at 550 nm was used as a proxy for atmospheric dust concentration. AOD data were obtained from NASA’s MERRA-2 reanalysis and MODIS aerosol products; similarly, wind speed data were sourced from ERA5 reanalysis, and rainfall and temperature data were derived from the Climate Research Unit (CRU) dataset. An Inter-Tropical Discontinuity (ITD) index was computed from reanalysis pressure and wind fields. Seasonal (December–February) averages were extracted to represent peak Harmattan conditions. Descriptive statistics, spatial mapping, Mann–Kendall trend analysis, Pearson correlation, and multiple linear regression were employed to assess variability and climatic relationships. Results reveal a persistent north–south AOD gradient, with the highest dust concentrations in Yobe and northern Borno States. AOD increased significantly between 1980 and 1995, stabilized between 1995 and 2010, and declined moderately after 2010. Wind speed emerged as the dominant driver (r = 0.71, p < 0.001), followed by ITD displacement, while rainfall showed a strong negative relationship (r = -0.63). Atmospheric circulation dynamics are the primary control of Harmattan dust intensity, as confirmed by the regression model's 68% contribution to AOD variability.  Strengthening early warning systems, improving regional climate monitoring, and integrating dust forecasting into environmental policy are recommended to mitigate impacts.