Abstract
Abstract. This work investigates how the integrated land use of northern South America has affected the present day regional patterns of hydrology. A model of the terrestrial ecosystems (ecosystem demography model 2: ED2) is combined with an atmospheric model (Brazilian Regional Atmospheric Modeling System: BRAMS). Two realizations of the structure and composition of terrestrial vegetation are used as the sole differences in boundary conditions that drive two simulations. One realization captures the present day vegetation condition that includes deforestation and land conversion, the other is an estimate of the potential structure and composition of the region's vegetation without human influence. Model output is assessed for differences in resulting hydrometeorology. The simulations suggest that the history of land conversion in northern South America is not associated with a significant precipitation bias in the northern part of the continent, but has shown evidence of a negative bias in mean regional evapotranspiration and a positive bias in mean regional runoff. Also, negative anomalies in evaporation rates showed pattern similarity with areas where deforestation has occurred. In the central eastern Amazon there was an area where deforestation and abandonment had lead to an overall reduction of above-ground biomass, but this was accompanied by a shift in forest composition towards early successional functional types and grid-average-patterned increases in annual transpiration. Anomalies in annual precipitation showed mixed evidence of consistent patterning. Two focus areas were identified where more consistent precipitation anomalies formed, one in the Brazilian state of Pará where a dipole pattern formed, and one in the Bolivian Gran Chaco, where a negative anomaly was identified. These locations were scrutinized to understand the basis of their anomalous hydrometeorologic response. In both cases, deforestation led to increased total surface albedo, driving decreases in net radiation, boundary layer moist static energy and ultimately decreased convective precipitation. In the case of the Gran Chaco, decreased precipitation was also a result of decreased advective moisture transport, indicating that differences in local hydrometeorology may manifest via teleconnections with the greater region.
Highlights
It has been held that massive and widespread Amazonian deforestation would lead to regional reductions in precipitation, evaporation, and moisture convergence, with slight increases in surface temperature (Henderson-Sellers et al, 1993; Nobre et al, 1991; Lean and Warrilow, 1989; Dickinson and Henderson-Sellers, 1988)
The literature documenting Amazonian land conversion and the surrounding areas is significant, the reader is referred to a small selection of non-exhaustive references for some background (Cardille and Foley, 2003; Skole and Tucker, 1993; INPE, 2003; Geist and Lambin, 2002; Laurance et al, 2001; Nepstad et al, 2001; Soares-Filho et al, 2006)
The work presented here is motivated by a need to better understand how the history of land conversion has influenced the hydrology of the region
Summary
It has been held that massive and widespread Amazonian deforestation would lead to regional reductions in precipitation, evaporation, and moisture convergence, with slight increases in surface temperature (Henderson-Sellers et al, 1993; Nobre et al, 1991; Lean and Warrilow, 1989; Dickinson and Henderson-Sellers, 1988). Stems, and bare earth have variable light-scattering properties, such that intact forest canopies composed of dark vegetation typically have lower shortwave radiation albedo than areas with exposed soil (Chapin et al, 2002) This directly impacts the surface energy balance via net radiation. Pastures and converted agricultural systems are generally associated with soil degradation such as decreased infiltration rates, nutrient loss and increased surface runoff, subject to variability and factors such as the soil texture and the existence of perennial under-story vegetation (Benegas et al, 2014) Practices such as grazing and agriculture promote soil compaction and decreased infiltration (Martinez and Zinck, 2004; Lal, 1996), and intense fires used for clearing lands may reduce soil organic matter that may favor infiltration (Kennard and Gholz, 2001). Canopy structure influences the turbulent exchange of heat, moisture and momentum with the atmosphere (Raupach et al, 1996)
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