SIMULATING THE EFFECTS OF LAND USE LAND COVER CHANGE ON HYDROMETEOROLOGICAL PARAMETERS OVER WEST AFRICA

Abstract

Land Use Land Cover (LULC) in Sub-Sahara Africa has undergone rapid transformation in the last century. So comprehending the impact of land use land cover change and its interaction with the atmosphere by means of modeling, and its impact on some hydrometeorological variables is an interesting area both for present and future research. The land use land cover change (LULCC) over West Africa was analysed using the Moderate Resolution Imaging Spectroradiomater (MODIS) MCD12Q1 land use land cover data. The Weather Research and Forecasting (WRF) model was used to examine the effect of Land Surface Model (LSM) options of WRF model on temperature, precipitation and dew point temperature (DPT) in West Africa (WA). Eight simulations were performed using the Noah, Noah-multi-physics (Noah-MP), Community Land Model version 4 (CLM4) and Noah-MP LSM with a ground water option, all with same and other physics combinations. In order to assess the impacts of LULCC on some hydrometeorological parameters over WA, series of WRF simulations were carried out with 2001 and 2016 land use data, and 6 LULC scenarios which includes Built-up (Bu), Partial Deforest I (PDI), Partial Deforest II (PDII), Partial Afforest (PA), Total Afforest (TA) and Total Deforest (TD) were generated. The WRF-hydrological (WRF-Hydro) model was used to simulate the LULC change impact on streamflow over Sokoto Rima River Basin (SRRB) and 3 Forecast Points (FP) (Sokoto, Goronyo and Bakolori) were analysed. Analysis of the LULCC over West Africa (WA) between 2001 and 2016 revealed that there was a general decrease in all forest parameters and a steady increase in built up lands over the period of study. Results show that the LSMs performed differently for different variables in different land-surface conditions. However, Noah-MP was the overall best performing LSM for all the variables in all season, while Noah performed least. The differences in the simulations could be attributed to the differences in vegetation representation, soil column depth, number of soil layers and other processes in the LSMs. Experiment with 2001 and 2016 land use data revealed that WRF model is sensitive to changes in the land cover parameters. The integration of updated MODIS land use data into WRF model showed improvement in its outputs. Result also shows that for the entire area (10W, 10E, 5N, 15N), Bu scenario decreased DPT, evapotranspiration (ET) and precipitation, but increased 2m temperatures (T2m) and Sensible heat (SH). PDII and PDI scenario increased DPT, T2m, and decreases SH, ET, and Pr, while PA scenario slightly increases DPT, ET, Pr, SH and caused a decrease in T2m. TA scenario increased DPT, ET, Pr, but decreased T2m, and SH while TD decreased DPT, ET, but increases T2m, SH, and Pr. For all the FPs in the SRRB, Bu scenario caused the highest increase in streamflow, while TA scenario shows the highest decrease. The deforestation scenario generally led to an increase in streamflow, while the afforestation scenario led to a decrease. Higher streamflow occurs as a result of increased agricultural lands and decreased forest areas within the basin. The study has shown that land cover has changed over the years, and that the adverse effects of LULCC to the extreme will be increased temperature and discomfort as well as flooding as streamflow increases. The combination of Remote Sensing, GIS, WRF and WRF-hydro model provides a useful technique in assessing the impact of LULC on catchment hydrology. This is essential in selecting and developing feasible catchment management options that will promote sustainable utilization of land and water resources.