Parsimonious spatial representation of tropical soils within dynamic rainfall—runoff models

Abstract

Introduction Models are used increasingly to simulate hydrological processes within tropical regions. There is now a wealth of publications addressing evaporation modelling (particularly wet-canopy evaporation) of local areas of tropical forest in, for example, Niger (Gash et al.

Soil pipe distribution and hydrological functioning within the humid tropics: a synthesis

“…Figure 8 shows the measured Ks of the Danum soil profile after being up-scaled to a lateral Ks value (adapted from Chappell et al, 1998Chappell et al, , 2004b. The broken line in the same figure shows the effective lateral Ks values derived from inversion of a catchment model (TOPMODEL) applied to rainfall-runoff data from the Baru catchment (similarly adapted from Chappell et al, 1998Chappell et al, , 2004b. The latter implicitly includes the dominant runoff pathways (thus, potentially, the effects of soil piping) on catchment-scale runoff generation.…”

BARUMODEL: Combined Data Based Mechanistic models of runoff response in a managed rainforest catchment

“…0.1-50 km 2 ) in the wet tropics has sufficient data on soil/rock characteristics, soil depths, soil surface characteristics and canopy characteristics, to allow accurate physics-based modelling of distributed water pathways to be made (see e.g. Beven, 2000Beven, , 2001bBeven, , 2002Chappell et al, 1998Chappell et al, , 2004cChappell and Sherlock, 2005;Croke et al, 2004). Without reliable estimates of parameter values representative of the whole catchment, forest use/change predictions become unrealistic.…”

“…Bathurst et al, 2004;Ott and Uhlenbrook, 2004). More recently, other scientists have, however, suggested that these physics-based catchment models may not be giving reliable results of hydrological change following forestry or other land cover/use change scenarios due largely to the large uncertainties in the calibrated parameter values (Parkinson and Young, 1998;Beven, 2001a,b;Beven and Freer, 2001;Chappell and Fowell, 2003;Chappell et al, 2004c). Models requiring calibration of a smaller number of parameter estimates thus giving smaller uncertainty have started to be used to simulate land cover/use change scenarios.…”

“…where R eff is the effective rainfall (mm); R the gross rainfall (mm); u cat (t À 1) the unsaturated zone storage variable at the previous time-step (mm); and t cat the dimensionless non-linearity term for the whole catchment response (Chappell et al, 2004c). The non-linearity term (t cat ) is determined by an iterative process applied to the combined BOSM and TF sub-models, where the objective function is the Nash and Sutcliffe (1970) efficiency measure, R 2 t .…”

“…Thus, the non-linear form of the DBM model of catchment response has five DRCs or parameters for a first-order model of the response, namely t u , h, TC (or ), ssP (or P) and d. Only five model parameters is considerably less than 1000's of parameter values typically required by distributed, physics-based models, and consequently such DBM parameter sets are much better defined (Young, 2001;Chappell et al, 2004c). The net rainfall is that proportion of the gross rainfall which reaches the ground by stemflow and (direct or indirect) throughfall (see e.g.…”