Ecology

  2009 DEC 25 - (VerticalNews.com) -- "This paper deals with the uncertainty involved in geographical migration of hydrological model structures, commonly known as regionalization. Regionalization relies on the hypothesis that calibrated parameter sets from a donor catchment can be useful to predict discharge of an ungauged catchment," scientists in London, the United Kingdom report.

  "However, since every catchment is unique, model parameters need to be adapted for differences between a calibration and a prediction catchment, either by transformation or further selection. This process is inherently uncertain. Model parameters, and therefore the required changes, do not exactly represent quantities that we can measure or calculate. This paper outlines an approach to learn about how model parameters should be transformed between a gauged and an ungauged catchment. The approach consists of an iterative process, in which a model structure is applied successively to gauged catchments. After each step, parameter behavior is evaluated as a function of catchment properties and intercatchment similarities. The method is illustrated with an application of a customized version of TOPMODEL to a set of catchments in the Ecuadorian Andes. First, parameter sets are generated for a donor catchment. This model ensemble is then used to predict the discharge of the other catchments, after applying a stochastic parameter transformation to account for the uncertainty in the model migration. The parameter transformation is then evaluated and improved before further application. The case study shows that accurate predictions can be made for predicted basins," wrote W. Buytaert and colleagues, University of London, Imperial College ...read more

  2009 DEC 25 - (VerticalNews.com) -- According to recent research from Durham, the United Kingdom, "We investigate how well a width-averaged morphodynamic model can simulate gravel transport and aggradation along a highly irregular 38-km reach of lower Fraser River and discuss critical issues in this type of modeling. Bed load equations with plausible parameter values predict a gravel input consistent with direct measurements and a sediment budget. ...read more

  2009 DEC 25 - (VerticalNews.com) -- According to recent research published in the journal Water Resources Research, "We study the observed geographic distribution of freshwater fish species in the Mississippi-Missouri river system, focusing on the size and spatial distribution of geographic ranges. We use a particular metric of geographic distribution known as environmental resistance, a biogeographic index that quantifies the pointwise average spatial loss of community similarity to identify biogeographic regions of the river basin. ...read more