Extension of the Representative Elementary Watershed approach for cold regions: constitutive relationships and an application

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Abstract. This paper presents the development and implementation of a distributed model of coupled water nutrient processes, based on the representative elementary watershed (REW) approach, to the Upper Sangamon River Basin, a large, tile-drained agricultural basin located in central Illinois, mid-west of USA. Comparison of model predictions with the observed hydrological and biogeochemical data, as well as regional estimates from literature studies, shows that the model is capable of capturing the dynamics of water, sediment and nutrient cycles reasonably well. The model is then used as a tool to gain insights into the physical and chemical processes underlying the inter-and intra-annual variability of water and nutrient balances. Model predictions show that about 80% of annual runoff is contributed by tile drainage, while the remainder comes from surface runoff (mainly saturation excess flow) and subsurface runoff. It is also found that, at the annual scale nitrogen storage in the soil is depleted during wet years, and is supplemented during dry years. This carryover of nitrogen storage from dry year to wet year is mainly caused by the lateral loading of nitrate. Phosphorus storage, on the other hand, is not affected much by wet/dry conditions simply because the leaching of it is very minor compared to the other mechanisms taking phosphorous out of the basin, such as crop harvest. The analysis then turned to the movement of nitrate with runoff. Model results suggested that nitrate loading from hillslope into the channel is preferentially carried by tile drainage. Once in the stream Correspondence to: H. Li (hli23@illinois.edu) it is then subject to in-stream denitrification, the significant spatio-temporal variability of which can be related to the variation of the hydrologic and hydraulic conditions across the river network.

Section: A Spatially Distributed Hydrological Modelmentioning

confidence: 99%

Water and nutrient balances in a large tile-drained agricultural catchment: a distributed modeling study

Sivapalan

Tian

et al. 2010

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“…For comparison, DDF S is calibrated on runoff using a semi-distributed hydrological model -THREW which has been applied in several studies (Tian et al, 2006Mou et al, 2008;. The calibration follows the stepwise procedure developed by He et al (2014) but was slightly modified because of the local characteristic of the study basin (see Sect.…”

Section: Methodsologymentioning

confidence: 99%

Estimating degree-day factors from MODIS for snowmelt runoff modeling

Parajka

Tian

et al. 2014

Abstract. Degree-day factors are widely used to estimate snowmelt runoff in operational hydrological models. Usually, they are calibrated on observed runoff, and sometimes on satellite snow cover data. In this paper, we propose a new method for estimating the snowmelt degree-day factor (DDF S ) directly from MODIS snow covered area (SCA) and ground-based snow depth data without calibration. Subcatchment snow volume is estimated by combining SCA and snow depths. Snow density is estimated to be the ratio between observed precipitation and changes in the snow volume for days with snow accumulation. Finally, DDF S values are estimated to be the ratio between changes in the snow water equivalent and difference between the daily temperature and the melt threshold value for days with snow melt. We compare simulations of basin runoff and snow cover patterns using spatially variable DDF S estimated from snow data with those using spatially uniform DDF S calibrated on runoff. The runoff performances using estimated DDF S are slightly improved, and the simulated snow cover patterns are significantly more plausible. The new method may help reduce some of the runoff model parameter uncertainty by reducing the total number of calibration parameters. This method is applied to the Lienz catchment in East Tyrol, Austria, which covers an area of 1198 km 2 . Approximately 70 % of the basin is covered by snow in the early spring season.

“…Zehe et al (2013) propose a thermodynamic approach to represent catchment-scale preferential flow. The mass, energy and momentum balance closure problem presents a significant challenge (Beven, 2006a;Zehe and Sivapalan, 2007; see also the editor's comment on my paper), although there has been some progress (Reggiani et al, 2000;Reggiani and Schellekens, 2003;Reggiani and Reintjes, 2005;Tian et al, 2006;Mou et al, 2008). Kleidon and Schymanski (2008) suggest that the optimality principle can help with the scaling of hydrologic fluxes; knowing the hydrologic fluxes at a larger scale can provide a "big" picture, and a top-down approach can be used to infer the boundary fluxes of ungauged basins at smaller scales.…”

Section: On the Future Of Hydrological Modelingmentioning

confidence: 99%

HESS Opinions: Advocating process modeling and de-emphasizing parameter estimation

Bahremand

2016

Abstract. Since its origins as an engineering discipline, with its widespread use of "black box" (empirical) modeling approaches, hydrology has evolved into a scientific discipline that seeks a more "white box" (physics-based) modeling approach to solving problems such as the description and simulation of the rainfall-runoff responses of a watershed. There has been much recent debate regarding the future of the hydrological sciences, and several publications have voiced opinions on this subject. This opinion paper seeks to comment and expand upon some recent publications that have advocated an increased focus on process-based modeling while de-emphasizing the focus on detailed attention to parameter estimation. In particular, it offers a perspective that emphasizes a more hydraulic (more physics-based and less empirical) approach to development and implementation of hydrological models.