Surface and groundwater dynamics in the sedimentary plains of the Western Pampas (Argentina)

Sedimentary plains with extremely flat topography, such as the Pampas in Argentina, often display flooding–drought cycles. Changes in water table depth and surface water coverage affect natural and cultivated vegetation, wildlife, and people. Here, we describe groundwater dynamics and water-body expansion in a 10-year flooding cycle in the valuable agricultural lands of Western Pampas. We analysed water-table depth, surface water coverage, and rainfall from 1996 to 2005 covering 3⁄428 000 km2. We characterized the dynamics of water storage based on groundwater observations and remote sensing estimates of the coverage (LANDSAT) and elevation (ENVISAT) of water bodies as well as water storage anomalies captured by the gravity recovery and climate experiment (GRACE). Surface water coverage fluctuated from 3 to 28% and groundwater levels displayed a 3⁄42Ð5 m change. Regional water storage raised by 3⁄4800 mm with 63% of this water accretion accounted by groundwater. Ground and surface water dynamics were closely coupled but this link differed between lowlands and highlands and depending on whether the system was at the gaining or retraction stage. This asymmetrical behaviour was likely caused by shifts in regional connectivity. Regional surface C groundwater storage compared well with water storage anomalies obtained from GRACE, suggesting that this tool may represent a methodological shortcut to estimate water storage changes. The tight connection between ground and surface water, and the relatively slow process of cumulative water accretion and coalescence of water bodies that precedes flood events offer the opportunity of developing warning systems that could help land managers to adapt to climate changes. Copyright  2010 John Wiley & Sons, Ltd.