A comprehensive assessment of water storage dynamics and hydroclimatic extremes in the Chao Phraya River Basin during 2002-2020

A holistic assessment of the hydroclimatic extremes, which have caused tremendous environmental, societal, and economic losses globally, is imperative for the highly vulnerable Chao Phraya River Basin. In this study, the water storage dynamics and extremes in the basin during 2002-2020 were quantified, for the first time, using GRACE (Follow-On) based terrestrial water storage anomaly (TWSA) with the help of a novel artificial neural network-based model for the data gap filling. TWSA showed a linear trend of -1.12 +/- 0.05 cm yr(-1) (equivalent to a volumetric trend of -1.79 +/- 0.08 km(3) yr(-1)) in the basin, and segregation of the constituent components of TWS revealed that the groundwater storage is a significant contributor (45%) to TWS with a linear trend of -0.51 +/- 0.06 cm yr(-1) (-0.82 +/- 0.10 km(3) yr(-1)) followed by surface water storage (i,e., cumulative of the water storage in the reservoirs, flood inundation, and rivers) (36%) and soil moisture storage (19%). The hydroclimatic extremes detected in TWSA are primarily triggered by the variations in precipitation during the monsoon season (May to October) and further amplified by the subsequent water storage and abstraction. TWSA attained a maximum of 42.86 cm in October 2011 during severe floods of 2011 (similar to 95% increase in net precipitation during 2010 and 2011) and a minimum of -31.81 cm during the drought of May 2020 (similar to 82% decrease in net precipitation during 2019 and 2020). All other flood and drought events in some years, e.g., 2006, 2010, 2015, 2016, are also well recorded in TWSA, albeit with a lag time of up to a maximum of two months from precipitation. Further, the basin's increasing potential of severe drought, as assessed by the effective water-storagebased novel drought potential index (DPI), underscored the need for multifaceted water management essentially focused on the demand side rather than the supply side in the basin. The proposed framework can be utilized for policymaking for adequate and equitable water allocation, developing the early warning systems for the droughts and floods, and employing the optimal adaptation measures in the Chao Phraya River Basin and other data-scarce river basins globally.