The HBV-NP model

The HBV-NP simulates nitrogen (N) and phosphorus (P) transport and transformation at the catchment scale (from 1 km² to > 1 000 000 km²). The objectives are usually to estimate transport, retention and source apportionment, to separate human impact from anthropogenic, and to evaluate climate and management scenarios. It is based on the hydrological HBV model, which gradually has been equipped with a N routine (Bergström et al. 1987, Brandt 1990, Arheimer and Wittgren 1994, Arheimer and Brandt, 1998). The P routine has recently been developed within VASTRA - the Swedish Water Management Research Programme.

HBV-NP is a dynamic mass-balance model, which is run at a daily time-step, including all sources in the catchment coupled to the water balance:

where:

c = concentration of nutrient fraction
V = water volume of groundwater, river or active part of lake
in = inflow (e.g. for groundwater: soil leakage from various land uses; for lakes/wetlands: upstream rivers and local discharge, precipitation on the surface)
out = outflow to river, lake or downstream subbasin, evaporation
D = atmospheric deposition on water surfaces
P = emissions from point sources or rural households
F = retention (removal or release), see Table 1.

The spatial resolution of the model depends on the subbasin division in each application. The HBV-N has been applied in large-scale studies, covering southern Sweden (145 000 km² divided into 3700 catchments; Arheimer and Brandt, 1998), the country of Sweden (450 000 km² divided into 1000 subbasins; the TRK project), and the Baltic Sea drainage basin (~1 720 000 km² divided into 30 subbasins; Pettersson et al., 2000). The model has also been used for more detailed studies, as for the Genevadsån River (200 km² divided into 70 subbasins; Arheimer and Wittgren, 2002; Arheimer et al, 2003). Additionally, the model has been applied in Matsalu River in Estonia (Lidén et al., 1999), and in XX and XX Rivers in Germany (Fogelberg, 2003).

References

User information (Table 2)

Evaluations/applications (Table 3)

MODEL STRUCTURE

When applying the model the river basin may be divided into several coupled subbasins, for which the calculations are made separately, and this gives the spatial distribution of the model results. The hydrological part (i.e. HBV-96) consists of routines for accumulation and melt of snow, accounting of soil moisture, lake routing and runoff response. The model includes a number of free parameters, which are calibrated against observed time-series of river discharge and riverine nutrient concentrations. For large-scale catchment applications, the calibration procedure is made step-wise for surface runoff, tile drains and groundwater, rivers and lakes, with simultaneous consideration to several monitoring sites in a region.

In the nutrient routine, soil leaching concentrations are assigned to the water percolating from the unsaturated zone to the response reservoir of the hydrological HBV model (Fig. 1). Different concentrations are applied to water originating from different combinations of land use and soils. The arable land may be further divided into a variety of crops and management practices, for which the nutrient leaching is achieved by using field-scale models, e.g., SOILN (Johnsson et al., 1987); or ICECREAM (Tattari et al., 2001) extended with macropore flow. For P, also soil surface erosion and water transport is considered, using a GIS-based model component, e.g. DelPi (Hellström, 2003). In addition to the diffuse soil-leaching, nutrient load is also added from point-sources, such as rural households, industries, and wastewater treatment plants. Atmospheric deposition is added to lake surfaces, while deposition on land is implicitly included in the soil-leaching. The model simulates residence, transformation and transport of N and P in groundwater, rivers, wetlands and lakes. The model considers that stream bank erosion, as well as sedimentation and suspension processes in the rivers may have an impact on the river load. The equations used to account for the nutrient turnover processes are mainly based on empirical relations between physical parameters and concentration dynamics. The fractions modelled are: dissolved inorganic nitrogen (DIN), dissolved organic nitrogen (DON), particulate phosphorus (PP), and soluble reactive phosphorus (SRP). Calculations are made with a daily time-step. Simultaneous calibration of water balance and nutrient concentrations may be performed (Pettersson et al., 2001).

Figure 1 (click for figure in a new window)
Schematic structure of one subbasin in the HBV-NP model concept, when it is coupled to the field-scale models SOILN and ICECREAM, and the GIS-based DelPi model.

References

Andersson, L. and Arheimer, B. (2003): Modelling of human and climatic impact on nitrogen load in a Swedish river 1885-1994. Hydrobiologia (in press).

Andersson, L. and Arheimer, B., (2001). Consequences of changed wetness on riverine nitrogen - human impact on retention vs. natural climatic variability. Regional Environmental Change 2:93-105.

Andersson, L., Hellström, M., Persson, K. (2002): A nested model approach for phosphorus load simulation in catchments: HBV-P. In: Proceedings Nordic Hydrological Conference. Röros, Nor-way. August 2002, pp. 229-238.

Andersson, L., Persson, K., Hellström, M. (2002): Fosfortransport och koncentrationer i vattendrag. Utveckling och test av modellverktyg för uppföljning av miljömål, samt scenarier av hur uppställda mål kan nås. VASTRA working paper. (In Swedish) 

Andreasson, J. (2002): Skogsläckaget och retentionen av kväve norr om Dalälven. VASTRA working paper. (In Swedish)

Arheimer, B. (1998) Riverine Nitrogen - analysis and modelling under Nordic conditions. Ph.D. thesis. Kanaltryckeriet, Motala. pp. 200.

Arheimer, B. and Bergström, S. (1999). Modelling nitrogen transport in Sweden: influence of a new approach to runoff response. In: Heathwaite, L. (Ed.) Impact of Land-Use Change on Nutrient Loads from Diffuse Sources. International Association of Hydrological Sciences, IAHS Publication no. 257.

Arheimer, B. and Brandt, M., (1998). Modelling nitrogen transport and retention in the catchments of southern Sweden. Ambio 27(6):471-480.

Arheimer, B. and Brandt, M., (2000). Watershed modelling of non-point nitrogen pollution from arable land to the Swedish coast in 1985 and 1994. Ecological Engineering 14:389-404.

Arheimer, B. and Wittgren, H. B., (1994). Modelling the effects of wetlands on regional nitrogen transport. Ambio 23(6):378-386. 

Arheimer, B. and Wittgren, H.B., (2002). Modelling Nitrogen Retention in Potential Wetlands at the Catchment Scale. Ecological Engineering 19(1):63-80.

Arheimer, B., Torstensson, G. and Wittgren, H.B (2003): Landscape planning to reduce coastal eutrophication: Constructed Wetlands vs. Agricultural Practices. Landscape and Urban Planning (in press).

Bergström, S., Brandt, M. & Gustafson, A., (1987). Simulation of runoff and nitrogen leaching from two fields in southern Sweden. Hydrological Science Journal 32(2-6):191-205.

Brandt, M. and Ejhed, H. (2003): TRK-Transport, Retention, Källfördelning. Belastning på havet. Swedish Environmental Protection Agency, Report No. 5247.

Brandt, M., (1990). Simulation of runoff and nitrogen transport from mixed basins in Sweden. Nordic Hydrology, 21:13-34. 

Fogelberg, S. (2003): Modelling nitrogen retention at the catchment-scale: Comparison of HBV-N and MONERIS. Master thesis, Uppsala Technical University, Report (in press).

Hellström, 2002, DelPi. An ArcView GIS 3.x extension for Estimating diffuse Loads of Sediment and Phosphorus from arable catchments.

Johnsson, H., Bergström, L. and Jansson, P.-E., 1987. Simulated nitrogen dynamics and losses in a layered agricultural soil. Agriculture, Ecosystems and Environment 18:333-356.

Lidén, R., Vasilyev, A., Loigu, E., Stålnacke, P., Grimvall, A. and Wittgren, H. B., (1999). Nitrogen source apportionment - a comparison between a dynamic and a statistical model. Ecological Modelling 114:235-250.

Marmefelt, E., Arheimer, B. and Langner, J., (1998). An integrated biogeochemical model system for the Baltic Sea. Hydrobiologia 393:45-56.

Pettersson, A., Arheimer, B. and Johansson, B., (2001). Nitrogen concentrations simulated with HBV-N: new response function and calibration strategy. Nordic Hydrology 32(3):227-248.

Tattari, S., Bärlund, I., Rekolainen, S., Posch, M, Siimes, K., Tuhkanen, H-R, Yli-Halla, M. (2001). Modeling sediment yield and phosphorus transport in Finnish clayey soils. Transactions of the ASAE Vol. 44, no. 2, pp. 297-307.

Wittgren, H. B., Gippert, L., Jonasson, L., Pettersson, A., Thunvik, R., and Torstensson, G. (2001). An actor game on implementation of environmental quality standards for nitrogen. In: Steenvoorden, J., Claessen, F. and Willems, J. (Eds) Agricultural Effects on Ground and Surface Waters. IAHS Publ. no. 273.

Table 1 Description of the retention (F) in Eq. 1.

Groundwater equations   River equations   Lake equations

Explanations of symbols (+/-)1 = retention (+1) if increasing temperature, production (-1) if decreasing temperature AL = lake surface area AG = soil surface area corig = cin at initial time-step () G = groundwater h = river channel depth IN = inorganic nitrogen kn = calibration parameter L = lake ON = organic nitrogen PP = particulate phosphorus q = discharge = discharge at bankful channel R = river SRP = soluble reactive phosphorus sedP = sedimentation of particulate phosphorus resuspP = resuspension of particulate phosphorus Sack = accumulated sediment t = time-step = n-day-mean air temperature v = water flow velocity x = river channel length

Table 2 General HBV-NP model information.

Data requirement	Subbasin division and coupling, altitude and land cover distribution, time-series of precipitation and temperature (time-series of observed water discharge and concentrations at some site), soil leaching concentration for each landcover type, lake depths, atmospheric N-deposition on water surfaces, emissions from rural households and point-sources (i.e., wastewater treatment plants, industries).
Additional data requirement when coupled to SOILNDB, ICECREAM, and DelPi	Rh, wind, cloudiness, soil type (texture) and average soil P and organic matter, crop distribution, crop sequence (or non-existent combinations), crop management and yield, fertilization and manuring, N fixation rates in ley, deposition rates, river network, slope, livestock density.
Applicability	The model runs partly under a Windows graphical user interface (IHMS), and a new modern interface will be available in 2004.
Operational experience and skills requirement of users	Two weeks of training for model setup and applications. Basic knowledge in hydrology and limnology. Advanced GIS knowledge is normally needed for database setup.
Licence agreements	The model has not yet been delivered outside SMHI.
Cost indication	Application to one catchment require about 2 weeks work of an experienced modeller if necessary database is already available. Database setup may be time-consuming. (Field-scale models of arable root-zone leaching may take an additional 2 months to set-up.)
Training	Individual training at SMHI is possible on request.

Table 3 Some documented model evaluations and applications.

Type of study	Details	References
Participation in model comparison studies	1. HBV-N soil leaching routine compared to SOIL-N model 2. Compared with statistical MESAW model 3. Compared with MONERIS 4. Model results of southern Sweden compared to previous estimates at various scales 5. Comparison with 7 other models used in Europe in the EuroHarp project (ANIMO, REALTA, N-LESS, MONERIS, SWAT, EveNFlow, NOPOLU)	1. Bergström et al., 1987 2. Lidén et al., 1999 3. Fogelberg, 2003 4. Arheimer and Brandt, 1998 5. (On-going project)
Sub-modules that are checked in- dependently	1. HBV-N soil leaching routine 2. HBV-P in small agricultural catchments 3. N leaching from forests 4. Nutrient discharge, turnover, and concentration in individual waterbodies, such as groundwater, rivers, wetlands and lakes	1. Bergström et al., 1987; Brandt, 1990 2. Andersson et al., 2002 3. Andreasson, 2002 4. Arheimer, 1998; Arheimer and Brandt, 1998
Sensitivity analysis	1. Parameter sensitivity 2. Impact of hydrological model structure 3. Impact of calibration strategy	1. Arheimer and Wittgren, 1994; Arheimer, 1998 2. Arheimer and Bergström, 1999; Pettersson et al., 2001 3. Pettersson et al., 2001
Large-scale nitrogen mapping and source apportionment	1. Southern Sweden (145 000 km2) 2. Sweden (450 000 km2) 3. Baltic Sea drainage basin (1 720 000 km2) 4. Coupling to coastal zone biogeochemical model and atmospheric deposition model	1. Arheimer and Brandt, 1998 2. Brandt and Ejhed, 2003 3. Pettersson et al., 2000 4. Marmefeldt et al., 1998
Scenario analysis	Impact on N load through: 1. Constructed wetlands 2. Changes in national agriculture policy 3. Historical changes in human impact and climate 4. Negotiation among polluters to fulfil water quality standards 5. Remedial measures to reduce coastal eutrophication 6. Following-up environmental goals for P	1. Arheimer and Wittgren, 1994, 2002 2. Arheimer and Brandt, 2000 3. Andersson and Arheimer, 2001, 2003 4. Wittgren et al., 2000 5. Arheimer et al., 2003 6. Andersson et al., 2002