Hydrological changes due to land-use change from Brazilian savanna to managed Eucalyptus

Abstract:

Before the large people influx and development of the central part of Brazil in the sixties, due to new capital Brasília, Cerrado, a typical Brazilian savanna-type vegetation, used to occupy about 2 million km², going from the Amazon tropical forest, in the north, to the edges of what used to be the Atlantic forest in the southeast. Today, somewhat 50% of this area has given place to agriculture, pasture and managed forests. Understanding how Cerrado interacts with the atmosphere and how this interaction will be modified with this land-use change is a crucial step towards improving predictions of future climate-change scenarios.

Cerrado is a vegetation adapted to a climate characterized by two distinct seasons, a wet season (Nov-Mar) and dry season (May-Ago), with April and October being transitions between seasons. Typically, 75% of precipitation happens in the wet-season months and only 5% during dry-season. In this study, it is investigated the potential impacts of the substitution of Cerrado to the eco-hydrological characteristics of the region. The focus here is Eucalyptus plantation which have increased substantially in the last decade due to government incentives. Two eddy-covariance (EC) systems were installed, one in an undisturbed Cerrado Stricto area and other in a recently-established Eucalyptus plantation. The two areas are 1,400m apart and are subjected to the same meteorology and similar edaphic conditions. Besides instrumentation typical of EC towers, a soil-moisture profiling system were installed in each site.

Data from the towers will be used to parameterized a Soil-Vegetation-Atmosphere (SVAT) model to simulate hydrological and atmospheric boundary layer (ABL) processes in order to understand how the two vegetation cover modulates the exchange of mass and energy between the biosphere and atmosphere. Simulations of 30-day dry down from saturation to complete water stress were performed and were analyzed on how ABL respond to soil moisture changes. Preliminary results show that replacing Cerrado for Eucalyptus causes reduction in ABL temperature, increase in ABL water-vapor mixing ratio and slightly reduces ABL height. Consequences of those changes on the hydrology could be most important in the season transition stages.