The role of rangelands as hydrological regulators in the Pampas and Chaco

JOBBÁGY, E.G, FERNÁNDEZ R.J., NOSETTO M.D, SANTONI C.S AND MARCHESINI V A.

Rosario

Congreso; IX International Rangeland Congress- Diverse Rangelands for a Sustainable Society; 2011

INTA & Argentinean Association for Range Management

The influence of vegetation on the partitioning of precipitation inputs between wet (i.e., deep drainage and runoff) and dry (evapotranspiration) water fluxes controls water exchange with the atmosphere, streams, ground water, and the soil. Evapotranspiration, both as a component of the energy balance and a source of moisture to the atmosphere, may affect mesoscale circulation patterns and regional weather (Kelliher et al., 1993). Transpiration, the principal component of evapotranspiration over land, is tightly coupled with vegetation productivity in most ecosystems (Monteith, 1988). Deep drainage is the main water source that feeds groundwater bodies and, together with surface runoff, determines the water yields of watersheds. Changes in plant cover affecting the balance of liquid and vapor water can have a strong impact on ecosystem functioning, with important consequences on ecosystems services such as water, food, and hydroelectric power provision as well as hydrological and climatic regulation. Two contiguous plains in Southern South America, the subhumid Pampas (Argentina) and the semiarid Chaco (Argentina, Paraguay, Bolivia), are becoming the most important agricultural territories of the continent, as they emerge as global grain suppliers. Both regions face a fast expansion of annual crops over herbaceous rangelands and pastures (Pampas) and woody rangelands (Chaco). The combination of fast vegetation changes, increasing sensitivity to global market signals, ongoing and expected climate changes, and an extremely flat topography make these two regions particularly sensitive to rapid and non-linear hydrological shifts. More evident to society in the subhumid Pampas, less so in the semiarid Chaco, these hydrological vulnerabilities pose an urgent challenge for rural development and highlights the value of rangelands beyond their specific role supplying animal products.