Drivers of a New Hydrological Scenario in the Chaco-Pampas Breadbasket: The Role of Climate and Vegetation Trends

Simón Alsina; Esteban G. Jobbágy; Marcelo D. Nosetto

doi:10.18172/cig.6782

Authors

Simón Alsina Instituto de Matemática Aplicada San Luis (UNSL & CONICET) https://orcid.org/0009-0006-4867-8912
Esteban G. Jobbágy Universidad Nacional de Entre Ríos
Marcelo D. Nosetto Instituto de Matemática Aplicada San Luis (UNSL & CONICET) https://orcid.org/0000-0002-9428-490X

DOI:

https://doi.org/10.18172/cig.6782

Keywords:

NDVI, groundwater, land-use change, water-table, GIMMS

Abstract

The Chaco-Pampas plain in Argentina, a key region for global food production, is experiencing a hydrological shift marked by increasing water surpluses. These surpluses are evident in rising water-table levels, increased flooding, expanded wetland and saline areas, and the formation of new rivers, all of which threaten productive systems. To investigate the causes, we analyzed long-term trends (1980-2019) in climatic variables (precipitation and reference evapotranspiration) as well as vegetation (NDVI and cropped areas) across the region, summarizing data by ecoregion unit and sub-unit and performing detailed analyses in focal zones. Our findings indicate that climatic trends do not support the generation of water surpluses. Specifically, across the region the average reference evapotranspiration increased by approximately 20 mm per decade, while precipitation remained largely unchanged except for a notable decrease (-30 mm per decade) in the Dry Chaco sub-region. In contrast, the NDVI displayed a browning trend across most of the region, suggesting a decline in the transpiration capacity of agroecosystems, largely driven by the expansion of rainfed croplands, whose area nearly tripled during the study period. At the focal sites, this browning corresponded with significant rises in water-table levels (~1 m per decade) and an intensified response to precipitation events; for a given amount of rainfall, water-tables now rise more than in previous periods. Overall, these results suggest that land cover changes have reduced ecosystem transpiration capacity, intensifying water surpluses and associated hydrological challenges, and highlight the urgent need for adaptive management strategies.

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