[A-HW24] Human- and Climate-induced variability in water cycle and (sub)surface water resources

[AHW24-P05] Quantifying Groundwater Storage Variations and its Governing Factors in the Amazon River Basin

*RONIKI ANJANEYULU¹, Abhishek Abhishek¹, Nabakishor Garai¹ (1.Indian Institute of Technology (IIT) Roorkee)

Keywords:Terrestrial water storage (TWS), Groundwater storage (GWS), GRACE, Amazon River Basin, SWOT

Amazon River Basin involves complex earth and atmospheric processes, including intense precipitation and evapotranspiration (ET), dense rainforests, vast floodplains, and complex topography spanning approximately six million km² across seven South American countries with an average annual rainfall of 2200 mm. Groundwater storage (GWS) plays a significant role in the Amazon basin hydrology, which supplies a significant quantity of water vapor to the atmosphere and freshwater discharge to the ocean. However, an up-to-date assessment of GWS variability, its governing factors, and its contribution to the overall water storage of the basin is lacking. Here, we focus on the GWS variability in the Amazon Basin from Apr-2002 to Dec-2023 and discern the governing factors using multisource data. The spatial variation of GWS across the Amazon River basin ranges from -150 to 120 mm/month and is primarily interrelated to geological properties, precipitation, and ET. The highest GWS was observed in the middle and northern regions of the Amazon basin due to high precipitation and soil permeability. In contrast, the lowest GWS can be seen in the southeast regions of the basin. The trend analysis shows an increasing trend with a slope of 0.18 mm/month (1.88±0.56 mm/year) and is statistically significant at a 95% confidence interval (P<0.05). The seasonal GWS analysis highlights that the average monthly GWS ranges from -77 to 75 mm and follows the seasonal pattern of terrestrial water storage (TWS). During the dry period, ET was supported by groundwater storage by increasing soil moisture. The stable ground evaporation and rising transpiration in the dry period underscore the critical role of shallow groundwater in sustaining ET and forest resilience, supporting about 34% of the Amazon rainforest. GWS and TWS show the peak value in May and the lowest value in November, highlighting that GWS is the major component of TWS in the basin. This study highlights the dynamic interplay between precipitation, ET, and the water distribution and variability of major constituent water storage components. Future work will include incorporating improved estimations of the surface water storage, e.g., those derived from the Surface Water and Ocean Topography (SWOT) mission, to get better insights into the GWS dynamics. The results of the current study highlight the need to understand the hydrological dynamics in the basin to inform conservation efforts and sustainable water resource management.