Effects of Land Cover Change and Climate Variability on the Hydrological Balance of the Kulpawn Basin, Ghana

Technical Summary: Effects of Land Cover Change and Climate Variability on the Hydrological Balance of the Kulpawn Basin, Ghana

Problem Statement
The Kulpawn River Basin (KRB), a critical sub-basin of the White Volta in Ghana, faces escalating hydrological challenges driven by the dual pressures of Land Use and Land Cover (LULC) changes and climate variability. The region, characterized by a single rainfall regime and prolonged dry seasons, is heavily reliant on rain-fed agriculture and natural resources. However, rapid urbanization, agricultural expansion, deforestation, illegal artisanal mining, and fuelwood extraction have degraded the basin's vegetative cover. While previous studies have examined climate variability or LULC changes in isolation within the broader White Volta Basin, there remains a significant gap in understanding their combined, cumulative effects on the hydrological processes of the Kulpawn Basin. This lack of integrated analysis hinders the development of targeted water resource management strategies, leaving the basin vulnerable to reduced water availability, increased flooding, and diminished ecosystem resilience.

Methodology
The study employed an integrated approach combining remote sensing, machine learning, and hydrological modeling to assess changes from 1995 to 2023.

• LULC Classification: Landsat satellite imagery (TM, ETM+, and OLI) from 1995, 2005, 2015, and 2023 was processed using the Random Forest (RF) algorithm in R software. Five LULC classes were identified: dense savannah forest, light savannah forest, agricultural lands, built-up areas, and water bodies. Accuracy was validated using Overall Accuracy (OA) and Kappa coefficients.
• Hydrological Modeling: The Soil and Water Assessment Tool (SWAT) was utilized to simulate hydro-climatic conditions. The model was calibrated and validated using observed streamflow data (1992–2012) via the Sequential Uncertainty Fitting (SUFI-2) algorithm within SWAT-CUP. Performance was evaluated using the Nash-Sutcliffe Efficiency (NSE), Coefficient of Determination ($R^2$), and Kling-Gupta Efficiency (KGE).
• Climate Analysis: Climate data were sourced from the Ghana Meteorological Agency and satellite products (CHIRPS, NASA POWER). Future climate projections were derived from six Global Climate Models (GCMs) under two Shared Socioeconomic Pathways (SSP1-2.6 and SSP5-8.5) from the CMIP6 project.
• Scenario Assessment: The study simulated hydrological components (precipitation, evapotranspiration, surface runoff, groundwater flow, water yield, etc.) under different LULC scenarios (1995, 2005, 2015, 2023) and climate scenarios to isolate and quantify the impacts of land cover changes and climate variability.

Key Results

• LULC Dynamics: Significant land cover transitions were observed between 1995 and 2023. Dense savannah forest decreased by 28.34%, converting primarily into light savannah forest (20.83%) and agricultural land (3.22%). Built-up areas expanded by 29.80% annually, while agricultural lands increased by 9.35% annually. Conversely, water bodies declined by approximately 13.78% over the study period.
• Hydrological Impacts: The shift in LULC correlated with distinct changes in the water balance:
  • Precipitation: Decreased by 2.14% (from 2691 mm to 2633.25 mm).
  • Evapotranspiration (ET): Declined by 4.91% due to reduced vegetative cover.
  • Surface Runoff (SurfQ): Increased by 7.78%, attributed to reduced infiltration rates caused by urbanization and vegetation loss.
  • Water Yield (WYLD): Showed a significant decline of 14.5%, indicating reduced overall water availability.
  • Groundwater and Percolation: Lateral flow decreased by 1.8%, and percolation declined by 4.87%, suggesting reduced groundwater recharge capacity.
• Climate Trends: Under the high-emission SSP5-8.5 scenario, the basin experienced a 12.48% increase in temperature and a 3.47% decrease in precipitation from 1995 to 2023. The study established a strong positive correlation between LULC changes and hydro-climatic variables, indicating that land cover alterations significantly influence local rainfall and temperature patterns.
• Seasonal Variability: The impact of LULC changes was most pronounced during the wet season (May–October), where surface runoff increased dramatically, while the dry season (November–April) exhibited severe water deficits and reduced baseflow contributions.

Significance and Contributions
This study provides a critical integrated assessment of how anthropogenic land cover changes and climate variability jointly drive hydrological degradation in the Kulpawn Basin. By establishing a strong correlation between LULC transitions and hydro-climatic variables, the research highlights that the decline in water yield and the increase in surface runoff are not solely climate-driven but are exacerbated by unsustainable land management practices. The findings underscore that the conversion of dense savannah forests to built-up areas and agricultural lands has compromised the basin's natural buffering capacity, leading to heightened risks of flash floods in the wet season and water scarcity in the dry season.

Recommendations and Policy Implications
Based on these findings, the authors advocate for integrated management strategies to enhance the basin's hydrological resilience. Key recommendations include:

• Implementing and enforcing spatial land use plans to prevent encroachment into sensitive ecological zones.
• Promoting climate-smart agricultural practices, such as agroforestry, cover cropping, and minimum tillage, to conserve soil moisture and reduce erosion.
• Prioritizing community-based reforestation and afforestation programs using native species to restore vegetative cover.
• Establishing basin-level stakeholder platforms involving the Environmental Protection Authority, Water Resources Commission, and local communities to foster collaborative governance.
• Developing long-term monitoring systems using remote sensing and hydrological models to track LULC changes and hydrological responses.

The study concludes that without sustainable land and water use planning, the availability of water in the Kulpawn Basin will continue to deteriorate, with severe consequences for food security, livelihoods, and ecosystem services in the region.