Abstract The south-eastern Nigeria as other parts of the tropics have been experiencing diverse levels of soil erosion for decades. An enquiry of the physical and anthropogenic drivers of soil erosion can provide a better insight into the proximate and underlying processes of occurrence of soil erosion. In this study, we employed the basin approach to investigate the nexus between geomorphometry and the socio-physical drivers of gully erosion development in the sedimentary Anambra basin. Multi-sourced remotely sensed and geospatial data were fit to multinomial regression to simulate probability maps of gully development. The laws of basin geomorphometry were also tested on linearity, shape, topographic and dimensionless metrics using digital surface model (DSM) data. Proximity to existing gully, soil, stream order, vegetation index, rainfall, flow direction, curvature and slope were found to be statistically significant to gully development across all models. The result of the study also showed that Anambra is a 7th-order basin: bifurcating averagely at 1.55; with elongation index, circularity ratio, relative relief, sinuosity index, drainage density, and mean peak flow of 3.42, 0.05, 0.21, 0.96, 0.54 km/km2 and 2,916 respectively. This suggests a synergised gully formation process such that the fluvio-dynamics and surficial factors of the basin contribute to gully development. This study thus provides decision-support mechanism for basin management such that the progressive occurrence of sheet erosion can be identified and managed prior to advancing to a fully blown gully. It also provides database for environmental engineering-oriented basin management such that disaster risk can be curtailed while ensuring safe and secured environment for the populace.

Abstract It has been debated globally that the COVID-19 lockdown had significantly diminished the emission levels of anthropogenic greenhouse gases (GHGs). However, different countries possess different footprints of GHGs emission. In regions with inconsistent air quality observation, spaceborne sensors can provide synoptic assessment of air quality with time-based environmental decision making. In this study, we utilised satellite data to quantify the temporal dynamics of carbon monoxide (CO) and nitrogen dioxide (NO2) between the pre-lockdown (January–March 2020), lockdown (April–July 2020) and post-lockdown (August–September 2020) periods in Nigeria. Periodic TROPOspheric Monitoring Instrument (TROPOMI) datasets were acquired from the Google Earth Engine Sentinel-5 Explorer and the Copernicus Open Access Hub. The Population-Weighted Mean Concentration (PWEC) of CO and NO2 was computed using raster-based population data and place-based air quality estimates. The associated economic correlates were computed using data mined from TROPOMI and available health records of Nigeria. Satellite data analysis showed that aggregate CO reduced by 35.1% (25.32⋅105 tons) and 9.06% (6.54⋅105 tons) and NO2 plummeted by 32.81% (22,500 tons) and 11.63% (5,360 tons) during the lockdown and post-lockdown periods across the 36 States of the country. While mobility rate dwindled substantially, mortality rate savings from the exposure to damaging effects of the GHGs were roughly $ 14 million (CO) and $10 million (NO2). The fluxes in CO and NO2 suggest that anthropogenic interference in air quality accounting can aid the understanding of the convoluted human–nature relationships for sustainable environmental management.