IMPACT OF LAND USE AND LAND COVER CHANGES ON GROUNDWATER RECHARGE USING GIS-BASED WETSPASS MODEL (CASE STUDY OF WABI TOGDHEER CATCHMENT, SOMALILAND)

Abstract

The significant alteration of land use and land cover (LULC) poses serious challenges to groundwater recharge, threatening water resources and ecosystem sustainability in the Burao Catchment. This thesis investigates these impacts to evaluate how LULC changes have affected the spatial and temporal distribution of groundwater recharge over the past two decades. To achieve this, the spatially distributed quasi-state WetSpass-M model was employed to simulate groundwater recharge. Satellite images were classified into four distinct types (rangelands, bare lands, vegetation and urban areas) using the maximum likelihood algorithm in ArcMap 10.8, achieving an overall accuracy of 95%, validated through comprehensive confusion matrices, stratified random sampling, and field verification. In addition to the LULC maps, several other important data inputs were used. Precipitation, temperature, wind speed, PET, soil, dem and slope maps were used. The model was run twice by keeping all the inputs the same except the LULC which its impact on the results is evaluated. The model demonstrated strong reliability, indicated by RMSE and NSE values of 0.91 and 0.85 during calibration, and 0.87 and 0.83 during validation, respectively. The results revealed a significant decline in annual groundwater recharge from 105 mm in 2002 to 90 mm in 2022, correlating with a decrease in bare lands and increases in vegetation and urban areas. The analysis has also shown that over 84% of the annual total recharge is received during the wet seasons, namely spring (Gu) and autumn (Dayr), while about 13% is received during summer (Hagaa) and very small amount is received in winter (Jilal). Recharge estimates of the groundwater reveal spatial variation over the study area. Rangelands are the dominant land use type and contribute the most recharge to groundwater. While bare lands and vegetated areas in the upper part of the catchment add significant amounts of recharge to the groundwater. The study found that the invasion of the Prosopis Juliflora and restoration of bare lands negatively affect the groundwater recharge of the catchment. To cope with the reduction of groundwater recharge and unsustainable water abstraction the study recommends to employ effective land use planning strategies. To maintain sustainable usage of groundwater resources, it is essential to adopt land use practices that enhance groundwater recharge and minimize environmental degradation. Implementing these practices will ensure the availability of groundwater for future generations and maintain theThe significant alteration of land use and land cover (LULC) poses serious challenges to groundwater recharge, threatening water resources and ecosystem sustainability in the Burao Catchment. This thesis investigates these impacts to evaluate how LULC changes have affected the spatial and temporal distribution of groundwater recharge over the past two decades. To achieve this, the spatially distributed quasi-state WetSpass-M model was employed to simulate groundwater recharge. Satellite images were classified into four distinct types (rangelands, bare lands, vegetation and urban areas) using the maximum likelihood algorithm in ArcMap 10.8, achieving an overall accuracy of 95%, validated through comprehensive confusion matrices, stratified random sampling, and field verification. In addition to the LULC maps, several other important data inputs were used. Precipitation, temperature, wind speed, PET, soil, dem and slope maps were used. The model was run twice by keeping all the inputs the same except the LULC which its impact on the results is evaluated. The model demonstrated strong reliability, indicated by RMSE and NSE values of 0.91 and 0.85 during calibration, and 0.87 and 0.83 during validation, respectively. The results revealed a significant decline in annual groundwater recharge from 105 mm in 2002 to 90 mm in 2022, correlating with a decrease in bare lands and increases in vegetation and urban areas. The analysis has also shown that over 84% of the annual total recharge is received during the wet seasons, namely spring (Gu) and autumn (Dayr), while about 13% is received during summer (Hagaa) and very small amount is received in winter (Jilal). Recharge estimates of the groundwater reveal spatial variation over the study area. Rangelands are the dominant land use type and contribute the most recharge to groundwater. While bare lands and vegetated areas in the upper part of the catchment add significant amounts of recharge to the groundwater. The study found that the invasion of the Prosopis Juliflora and restoration of bare lands negatively affect the groundwater recharge of the catchment. To cope with the reduction of groundwater recharge and unsustainable water abstraction the study recommends to employ effective land use planning strategies. To maintain sustainable usage of groundwater resources, it is essential to adopt land use practices that enhance groundwater recharge and minimize environmental degradation. Implementing these health of the ecosystem. practices will ensure the availability of groundwater for future generations and maintain the