This study investigates the impact of land use and land cover (LULC) changes on surface water quality in the Chao Phraya River Basin, focusing on the Metropolitan Waterworks Authority's (MWA) Samlae intake—Bangkok's primary raw water source. LULC classifications from 2007 to 2021 were performed within a 2.5 km buffer zone along the riverbanks and projected to 2025 and 2030 using a Cellular Automata–Artificial Neural Network (CA–ANN) model integrated with QGIS. The results show substantial urban expansion in downstream provinces, particularly near CP.05, where built-up areas increased by over 7% and agricultural land declined by up to 10.7%. Forecasts suggest urban land at CP.05 will exceed 30% by 2030. A Water Quality Index (WQI) was developed using eight parameters, including DO, BOD, NH₃–N, salinity, chlorophyll-a, and coliforms. Seasonal WQI analysis from 2014 to 2022 revealed a consistent decline during dry seasons at CP.05, with values dropping from 64.48 to 56.61, and projected to reach 54.75 by 2030. A Pearson correlation of –0.57 confirms that increased urban land is strongly associated with WQI deterioration. A key contribution of this research is developing a real-time WQI evaluation model, which enables MWA to assess raw water suitability at Samlae instantly, provided upstream parameter inputs are available. This capability enhances intake operation planning and emergency response. The integrated LULC-WQI forecasting framework also supports long-term resilience and land use policy for water resource protection.
Kraikriangsri et al. (Mon,) studied this question.