Drought and Salinity Intrusion in the Lower Chao Phraya River: Variability Analysis and Modeling Mitigation Approaches

Abstract. Saltwater intrusion in the Lower Chao Phraya River (LCPYR) is a significant national concern for Thailand, requiring a thorough understanding and a development of effective prediction systems for current and future management. This study investigates the key drivers influencing saltwater intrusion in the LCPYR. Cross-wavelet analysis was applied to examine the interactions between tidal forces, drought conditions represented by the standardized discharge index (SDI) and standardized precipitation index (SPI), and salinity levels. Numerical simulations are used to explore the covariation among these drivers further. The results show that hydrological drought, particularly indicated by the SDI, plays a major role in driving the sub-annual to annual variability of saltwater intrusion, while extreme events are largely governed by sea-level oscillations, underscoring the importance of non-tidal sea levels. Local precipitation, as reflected by the SPI, strongly influences salinity levels, at times weakening the usual correlation between salinity and hydrological drought. The numerical model demonstrates high accuracy in simulating both hydrodynamic and salinity behaviors, validating the cross-wavelet analysis and offering a reliable approach for modeling salinity in this complex estuarine system. These findings offer essential insights to guide management strategies and the development of prediction tools for the LCPYR and surrounding regions.