Abstract
Land degradation is one of the worldwide threats to the ecosystem, thereby reducing its capacity to provide the adequate ecosystem services. Sub-Saharan Africa is known as one of the most threatened regions by land degradation due to both the change and/or variability in the climate conditions and human activities. The impact of both climate and land use changes on land degradation was assessed in Nasarawa State, Nigeria. The focal points of this study were to assess how the climatic condition and land use changed in the study area and to appraise their impacts on land degradation, especially soil erosion by water. Temperature and rainfall data were collected for a time period of 34 years for two meteorological stations of Nasarawa State (Doma station representing the South and Kokona station representing the North. Rainfall and temperature patterns and trends were assessed using Standardized Precipitation Index, Thermal Anomaly Index, Innovative Trend Analysis, CUSUM test, and Sen and Man-Kendall rank test. For the climatic analyses, the software EXCEL 2013, XLSTAT 2015, SPSS 20.0 and MATLAB programming tools were used. Landsat satellite images of the years 1986, 1999 and 2015 were classified using maximum likelihood to produce LULC maps for 1986, 1999 and 2015 coupled with change detection in ENVI 5.1 and ArcGIS 10.0. Revised Universal soil Loss equation (RUSLE) model was used to model soil erosion for the periods 1981 and 2014 and soil erosion change trend and actuality were assessed based on multi-criteria rules methods with the help of ArcGIS 10.0, 3DEM, Global mapper and EXCEL 2013 analysis tools. The conservation priorities were then identified based on the erosion actuality and change trend. The mean temperature is increasing at the rate of 0.034°C/year (0.047°C/year in the South and 0.021°C/year in the North), the same significant increasing trend was observed in the minimum temperature at the rate of 0.098°C/year and 0.066°C/year in the South and North respectively. Only the maximum temperature did not change significantly in the study area. The rainfall equally increased at the rate of 6.39mm/year and 2.3mm/year in the South and North respectively. Land use/cover changed significantly from 1986 to 2015 and savannah shrub was the most depleted land cover (from a coverage of 78% of the landmass in 1986 to 53% in 2015) followed by savannah woodland (from 6% to 0.64%). However, agricultural land increased from 7.5% to 17%, settlements from 6.5% to 15% and degraded land or bare soil from 0.86% to 8%.The change in land use/cover pattern and climate conditions significantly impacted 27.47% of the total landmass of the study area with 15.45% and 12.02% observing improvement and deterioration status respectively. Thus, the soil erosion status improved in overall for the past 34 years. However, all the local government areas experienced some degree of deterioration of soil. About 99% of the total area need implantation of soil conservation strategies and 2% need an urgent intervention to prevent the area from the occurrence of disastrous erosion. Nasarawa, Keana, Karu, Akwanga, Lafia and Wamba are the regions of great concern for the degrading status of their land. It was concluded that changes in land use/cover and climate conditions contributed to the degradation of land (especially soil erosion by water) in Nasarawa State. Finally, implementation of sustainable land use management and mainstreaming erosion control practices in agricultural policy of the State were the major recommendations drawn up from the study.