Temporal and spatial dynamics of land use and land cover changes in derived savannah hydrological basin of Enugu State, Nigeria

The combined effects of climate change and aggressive anthropogenic activities linked to urban developments have resulted in major land use and land cover (LULC) changes in eastern Nigeria. These LULC changes have grave implications for water resources and the surface hydrology. This study was aimed at specifically quantifying the extent of LULC changes and the implications for surface hydrology of the study area. The study investigated the spatiotemporal effects of LULC on the hydrology of the basin of Enugu State, Nigeria, using the Soil and Water Assessment Tool (SWAT). SWAT model has been extensively used to study watershed response to rainfall and LULC dynamics. The trend of the basin's LULC was studied over two decades. The watershed was delineated into 17 sub-basins using SRTM digital elevation model. The delineation of the watershed and the extraction of the stream network were enabled by SAGA Strahler order plug-in. The model results showed that the basin's soil composition, associated with moderately high run-off, remains somewhat static during the 20-year study period. The soil types were distributed as follows: plinthic acrisols (42.4%), ferric acrisols (11.9%) and dystric nitosols (45.7%), with Ap15-1a-1068 being the most dominant and comprising 66% sand. All soil types in the study area belong to the hydrological soil group C. The LUCL of the basin (3027.4 km(2)) comprised of rangeland (2414.57 km(2)), built-up (57.46 km(2)), cropland (541.25 km(2)), forest (11.25 km(2)) and water (0.21 km(2)). Over the two decades of interest, the basin has undergone LULC changes of - 14.71%, 21.29%, 50.62%, 98% and 0.00% in rangeland, built-up area, cropland, forest and water body, respectively. The changes led to encroachment, alterations and diversification of LULC types of the sub-basins, resulting in changes in their surface characteristics and an increase in the number of hydrologic response units (HRUs) within the sub-basins from 74 in 2001 to 97 in 2019. Out of the 17 sub-basins, the HRU increased in 12, decreased in 2 and stayed the same in 3 sub-basins. Increase in the number of HRUs is significantly higher for HRUs smaller than 100 km(2). The major trend of LULC changes is the conversion of rangeland to residential area and agricultural land due to aggressive urbanization and rising need for food production to meet the demands of increasing population. Proper legislation should be put in place to ensure that the impact of urbanization and activities of herdsmen be contained and re-aligned with the sustainable development goals.

Automated summary

The combined effects of climate change and urban development activities in eastern Nigeria have significantly impacted land use and land cover changes, with implications for water resources and surface hydrology. Using the SWAT model, this study analyzed the effects of land use/land cover changes on the hydrology of Enugu State's basin, revealing alterations in surface characteristics and an increase in hydrologic response units within sub-basins. The major trend observed was the conversion of rangeland to residential and agricultural areas due to aggressive urbanization and food production demands.