Topographic, Pedologic, and Land Cover Controls on the Generation of Hillslope Runoff and the Water Balance in Amazonian Lowlands
Thursday, 9 June 2016
Thomas Dunne, University of California Santa Barbara, Santa Barbara, CA, United States, Helmut Elsenbeer, University of Potsdam, Potsdam, Germany and John-Andrew C Ballantine, University of Connecticut, Groton, CT, United States
Abstract:
We conducted surveys of soil hydraulic properties and topography in various physiographic regions of the Amazonian lowland under forest and in pasture to investigate the conditions determining hillslope runoff responses to rainfall and to deforestation. We summarize vertical profiles of in-situ-measured soil hydraulic properties and characteristic hillslope profiles of various regions. We then use these measurements in a transient numerical model of the soil-saprolite aquifer underlying hillslopes to calculate the response of runoff to rainfall-induced recharge for a range of idealized hillslopes representative of physiographic regions in the Amazon Basin. We examine where small-scale measurements of hydraulic conductivity appear to represent hydrological response, and for what purposes larger-scale estimation of hydraulic conductivity of uncertain origin appears to be necessary. The results quantify the role of lateral transfers of flows to stream channels and how they might be regionalized for efficient computation of hydrologic response at larger scales. We use the results to propose how entire hillslopes respond to deforestation and rainfall over rainstorms and seasons, and thereby to recommend field experiments that could be conducted to test these proposals. We also examine how the hydraulic and topographic controls on hillslope runoff could affect evapotranspiration and the regional water balance.
