Integrated Assessment of Climate‐Driven Shifts on Spatio‐Temporal Variation of Hydrological Components and Terrestrial Water Storage of a River Basin Using Regional Scale Model and <scp>GRACE</scp> Datasets

ABSTRACT River basin scale integrated assessment of climate‐driven shifts in the spatio‐temporal variability of key hydrological components, such as rainfall, streamflow, evapotranspiration (ET), baseflow, and terrestrial water storage change (TWSC), is critical for effective water resources management. In India, the Godavari River Basin (GRB), the second largest and predominantly rainfed basin, exhibits strong heterogeneity in hydro‐geomorphology and has faced recurrent droughts and floods, underscoring the need to quantify recent basin‐scale hydrological changes. Here we simulated gridded water‐budget components (rainfall, ET, runoff, and baseflow) using the Variable Infiltration Capacity (VIC) model for 1981–2024 and assessed TWSC using GRACE datasets. The VIC model was calibrated and validated at three gauging stations (Ashti, Tekra, and Polavaram), representing upper, middle, and lower basin conditions, to capture the spatial variability in parameters and responses. Decadal analyses relative to a baseline (1981–1994) show Decade 1 (1995–2004) was drier, while Decade 2 (2005–2014) and Decade 3 (2015–2024) were wetter, with Decade 3 the wettest. Spatial patterns show higher variability and patchier responses in Decade 1, transitioning toward a more coherent basin‐wide signal in Decade 3, consistent with strengthened hydroclimatic forcing. Correlation‐shift matrices across decades indicate ET moderately modulates runoff and baseflow, highlighting the role of land–atmosphere fluxes in controlling the hydrological partitioning and low‐flow generation. For 2002–2022, we combined observed precipitation with VIC‐derived ET, GLEAM ET, and runoff to estimate TWSC and evaluated it against GRACE‐derived TWSC. VIC and GRACE TWSC agree closely at annual and monthly scales, with robust seasonal cycles and consistent interannual drought–flood signatures. The storage anomalies track rainfall anomalies, indicating precipitation as the dominant driver of storage variability. The distributed assessment provides actionable insights for localised water management and decision support, and VIC‐derived TWSC can serve as a proxy for water availability during periods with the missing GRACE data observations. The methodological framework presented here is transferable to other hydro‐climatically similar basins.