Testing the realism of a topography-driven model (FLEX-Topo) in the nested catchments of the Upper Heihe, China

Abstract. Understanding runoff processes in a basin is of paramount importance for the effective planning and management of water resources, in particular in data-scarce regions such as the Upper Blue Nile. Hydrological models representing the underlying hydrological processes can predict river discharges from ungauged catchments and allow for an understanding of the rainfall-runoff processes in those catchments. In this paper, such a conceptual process-based hydrological model is developed and applied to the upper Gumara and Gilgel Abay catchments (both located within the Upper Blue Nile Basin, the Lake Tana sub-basin) to study the runoff mechanisms and rainfall-runoff processes in the basin. Topography is considered as a proxy for the variability of most of the catchment characteristics. We divided the catchments into different runoff production areas using topographic criteria. Impermeable surfaces (rock outcrops and hard soil pans, common in the Upper Blue Nile Basin) were considered separately in the conceptual model. Based on model results, it can be inferred that about 65 % of the runoff appears in the form of interflow in the Gumara study catchment, and baseflow constitutes the larger proportion of runoff (44-48 %) in the Gilgel Abay catchment. Direct runoff represents a smaller fraction of the runoff in both catchments (18-19 % for the Gumara, and 20 % for the Gilgel Abay) and most of this direct runoff is generated through infiltration excess runoff mechanism from the impermeable rocks or hard soil pans. The study reveals that the hillslopes are recharge areas (sources of interflow and deep percolation) and direct runoff as saturated excess flow prevails from the flat slope areas. Overall, the model study suggests that identifying the catchments into different runoff production areas based on topography and including the impermeable rocky areas separately in the modeling process mimics the rainfall-runoff process in the Upper Blue Nile Basin well and yields a useful result for operational management of water resources in this data-scarce region.

Section: Performance In Comparison With the Benchmark Modelsmentioning

confidence: 55%

Section: Transferability Of Model Parameters To Other Ungauged Catchmmentioning

confidence: 94%

Analyzing runoff processes through conceptual hydrological modeling in the Upper Blue Nile Basin, Ethiopia

Dessie

Verhoest

Pauwels

et al. 2014

“…This result contradicts to what appears to be a general belief about the higher predictive uncertainty of complex models, and shows that if a complex model is properly constrained then it can perform well during the evaluation period while providing even lower predictive uncertainty than a simpler model. Result of the recent study by Gao et al (2014) had shown that a more complex, but simultaneously constrained and calibrated model, can provide better predictions of extreme events outside of the calibration period as well as capturing the flow duration curve in nested catchments for the large scale Heihe basin in China. Meanwhile, Hrachowitz et al (2014) reported similar results for a small-scale catchment in France, using 11 different model structures and 20 different runoff signatures.…”

Section: Constraints In Environmental Modelsmentioning

confidence: 99%

A constraint-based search algorithm for parameter identification of environmental models

Gharari

Shafiei

Hrachowitz

et al. 2014

Self Cite

Abstract. Many environmental systems models, such as conceptual rainfall-runoff models, rely on model calibration for parameter identification. For this, an observed output time series (such as runoff) is needed, but frequently not available (e.g., when making predictions in ungauged basins). In this study, we provide an alternative approach for parameter identification using constraints based on two types of restrictions derived from prior (or expert) knowledge. The first, called parameter constraints, restricts the solution space based on realistic relationships that must hold between the different model parameters while the second, called process constraints requires that additional realism relationships between the fluxes and state variables must be satisfied. Specifically, we propose a search algorithm for finding parameter sets that simultaneously satisfy such constraints, based on stepwise sampling of the parameter space. Such parameter sets have the desirable property of being consistent with the modeler's intuition of how the catchment functions, and can (if necessary) serve as prior information for further investigations by reducing the prior uncertainties associated with both calibration and prediction.

“…Kumar et al, 2010;Gao et al, 2014a;Fenicia et al, 2016). In spite of that they are sometimes collectively and inaccurately referred to as "lumped" models.…”

Section: Conceptual Modelsmentioning

confidence: 99%

HESS Opinions: The complementary merits of competing modelling philosophies in hydrology

Hrachowitz

Clark

2017

Self Cite

162

129

Abstract. In hydrology, two somewhat competing philosophies form the basis of most process-based models. At one endpoint of this continuum are detailed, high-resolution descriptions of small-scale processes that are numerically integrated to larger scales (e.g. catchments). At the other endpoint of the continuum are spatially lumped representations of the system that express the hydrological response via, in the extreme case, a single linear transfer function. Many other models, developed starting from these two contrasting endpoints, plot along this continuum with different degrees of spatial resolutions and process complexities. A better understanding of the respective basis as well as the respective shortcomings of different modelling philosophies has the potential to improve our models. In this paper we analyse several frequently communicated beliefs and assumptions to identify, discuss and emphasize the functional similarity of the seemingly competing modelling philosophies. We argue that deficiencies in model applications largely do not depend on the modelling philosophy, although some models may be more suitable for specific applications than others and vice versa, but rather on the way a model is implemented. Based on the premises that any model can be implemented at any desired degree of detail and that any type of model remains to some degree conceptual, we argue that a convergence of modelling strategies may hold some value for advancing the development of hydrological models.