Contrasting hydrological seasonality with latitude in the South American Chaco: The roles of climate and vegetation activity

Abstract

As the largest dry forest of the continent, the South American Chaco covers a broad latitudinal gradient (18°–33°S) with extremely flat topography, homogeneous vegetation structure and similar summer-rain regime. Despite high deforestation rates, Chaco is still dominated by native forests, offering a unique opportunity to explore the role of biophysical controls dictated by latitudinal gradients on its hydrological functioning. In this study, we used GRACE-derived satellite data, climatic information and river flow records to analyse the seasonality of total water storage and its relationship with climatic factors and plant activity across the whole latitudinal gradient of the Chaco region. Our results showed a strong reduction in the intensity and duration of the hydrological dry period towards the southern and more temperate portion in despite similar rainfall seasonality. Mean seasonal fluctuation of water storage was three times higher (119.1 ± 46.0 vs. 38.6 ± 12.4 mm year−1) for the northern (<26°S) than for the southern Chaco portion (>26°S), a pattern that matched the river flow seasonality of the main rivers of the region. A higher temporal coupling of rainfall and actual evapotranspiration towards the south appears to drive the observed latitudinal hydrological shift, highlighting the importance of atmospheric water demand and plant activity regulating the water cycle at Chaco regional scale.