Different Models

Here we will show you the different models that are available in eWaterCycle and what their benefits, outputs and needs are. The outputs will be in daily form, unless mentioned otherwise. NOTE the following notebooks are from their respective GitHub pages and are not meant for this getting started guide specifically.

HBV

HBV (Hydrologiska Byråns Vattenbalansavdelning) is a conceptual hydrological model. For more information on its history, see this paper. The actual model implemented here sit looks most like the original model from 1976.

The model simplifies the entire water cycle into a few key processes and splits them up in five buckets:

• Snow reservoir

• Interception reservoir

• Unsaturated reservoir

• Fast reservoir

• Slow reservoir

These buckets can be seen as reservoirs that store water and release it based on the catchment characteristics.

A retrospective on hydrological catchment modelling based on half a century with the HBV model. https://hess.copernicus.org/articles/26/1371/2022/

The structure of the HBV model is shown below.

Image from the TU Delft course ENVM1502 - “River Basin Hydrology” by Markus Hrachowitz.

With the abbreviations:

HBV Model Reservoirs Code Description Sp Snow reservoir Si Interception reservoir Su Unsaturated reservoir Sf Fast reservoir Ss Slow reservoir

HBV Model Inputs Code Description Units P Precipitation mm/day Ep Potential evaporation mm/day T Temperature °C

HBV Model Parameters Code Description Units Imax Interception capacity mm Ce Soil runoff coefficient - Sumax Max soil moisture storage mm Beta Shape parameter for runoff generation - Pmax Percolation threshold mm/day Tlag Routing lag time days Kf Fast runoff recession coefficient 1/day Ks Slow runoff recession coefficient 1/day Fm Snowmelt factor -

Benefits

• A well-established, conceptual model ideal for simple catchment-scale studies.

• Easy to set up and fast to run, making it great for:

  • Academic research,

  • Education and training,

  • First-look flood modeling.

• Requires minimal data; good for data-scarce regions.

• Calibrated models are robust for flood forecasting and climate impact assessments.

• Suitable for hydrologists who prefer a lightweight, proven model with a long history of application.

Outputs

• discharge

Model Needs

• Forcing:

  • Precipitation

  • Incoming solar radiation

  • Temperature

• Calibration parameters:

  • Imax: Interception capacity

  • Ce: Soil runoff coefficient

  • Sumax: Max soil moisture storage

  • Beta: Shape parameter for runoff generation

  • Pmax: Percolation threshold

  • Tlag: Routing lag time

  • Kf: Fast runoff recession coefficient

  • Ks: Slow runoff recession coefficient

  • Fm: Snowmelt factor

PCRGlobWB 1.0

PCRGlobWB (PCRaster Global Water Balance) is a large-scale hydrological model with official documentation. eWaterCycle documentation.

PCR-GLOBWB is a large-scale hydrological model intended for global to regional studies and developed at the Department of Physical Geography, Utrecht University (Netherlands). PCR-GLOBWB provides a grid-based representation of terrestrial hydrology with a typical spatial resolution of less than 50×50 km (currently 0.5° globally) on a daily basis. Similar to other large-scale hydrological models, PCR-GLOBWB is essentially a leaky bucket type of model applied on a cell-by-cell basis. For each grid cell, PCR-GLOBWB uses process-based equations to compute moisture storage in two vertically stacked soil layers as well as the water exchange between the soil and the atmosphere and the underlying groundwater reservoir. Exchange to the atmosphere comprises precipitation, evapotranspiration and snow accumulation and melt, which are all modified by the presence of the canopy and snow cover. The exchange with the underlying groundwater reservoir comprises deep percolation and capillary rise and vertical fluxes are shown in next figure.

Model concept of PCR-GLOBWB. Left: layers describing the soil hydrology including the canopy, snow cover, soil layers 1 & 2 and the groundwater reservoir 3 as well as the exchange of moisture between them; right: specific runoff components and the direct gains/losses over the drainage network returning discharge along the channel when routed. Taken from https://globalhydrology.nl/research/models/pcr-globwb-1-0/

Sub-grid variability is taken into account as follows:

• fraction of cell covered with short and tall vegetation;

• fraction covered with freshwater, being either a river, lake or reservoir;

• fraction glaciers;

• sub-grid elevation distribution determining the accumulation and melt rate of snow and ice as well as fraction of the river plain flooded (optional);

• soil type distribution and its effect on soil hydrological properties;

• distribution of water-holding capacity of the soil resulting in variable saturation excess overland flow [Improved Arno Scheme, 2] as a result of variations in soil depth, effective porosity and elevation distribution.

Benefits

• A physically-based, global hydrological model designed for large-scale water balance studies.

• Ideal for modeling water availability, groundwater dynamics, and human water use (e.g., irrigation, reservoirs).

• Used in scientific publications and global water assessments (e.g., ISIMIP, World Resources Institute).

• Strong for long-term scenario analysis under climate and socio-economic change.

• Supports multi-decadal simulations and integrates with Earth system models.

Outputs

PCRGlobWB has many different outputs:

Variables	Variables	Variables	Variables
accumulated_land_surface_baseflow	accumulated_land_surface_runoff	accumulated_total_surface_runoff	bare_soil_evaporation
baseflow	bottom_elevation_of_lowermost_layer	bottom_elevation_of_uppermost_layer	channel_storage
consumptive_water_use_for_irrigation_demand	consumptive_water_use_for_non_irrigation_demand	desalination_source_abstraction	desalination_source_abstraction_volume
direct_runoff	discharge	domesticWaterConsumptionVolume	domesticWaterWithdrawalVolume
evaporation_from_irrigation	evaporation_from_irrigation_volume	flood_innundation_depth	flood_innundation_volume
fossil_groundwater_abstraction	fossil_groundwater_storage	fraction_of_desalinated_water_allocation	fraction_of_non_fossil_groundwater_allocation
fraction_of_other_water_source_allocation	fraction_of_surface_water	fraction_of_surface_water_allocation	groundwater_capillary_rise
groundwater_depth_for_layer_1	groundwater_depth_for_layer_2	groundwater_depth_for_top_layer	groundwater_head_for_layer_1
groundwater_head_for_layer_2	groundwater_head_for_top_layer	groundwater_recharge	groundwater_storage
groundwater_thickness_estimate	groundwater_volume_estimate	industryWaterConsumptionVolume	industryWaterWithdrawalVolume
industry_water_withdrawal	infiltration	interception_evaporation	interception_storage
interflow	irrigationWaterWithdrawalVolume	irrigation_gross_demand	irrigation_gross_demand_volume
irrigation_withdrawal	lake_and_reservoir_storage	land_surface_actual_evaporation	land_surface_evaporation
land_surface_evaporation_fraction	land_surface_potential_evaporation	land_surface_runoff	land_surface_water_balance
livestockWaterConsumptionVolume	livestockWaterWithdrawalVolume	livestock_water_withdrawal	local_water_body_flux
lower_soil_saturation_degree	lower_soil_storage	lower_soil_transpiration	netLqWaterToSoil_at_irrigation
netLqWaterToSoil_at_irrigation_volume	net_liquid_water_to_soil	non_fossil_groundwater_abstraction	non_irrigation_gross_demand
non_irrigation_gross_demand_volume	non_paddy_irrigation_withdrawal	paddy_irrigation_withdrawal	precipitation
precipitation_at_irrigation	precipitation_at_irrigation_volume	reference_potential_evaporation	relativeGroundwaterHead
return_flow_from_groundwater_abstraction	return_flow_from_irrigation_demand_withdrawal	return_flow_from_non_irrigation_demand_withdrawal	snow_free_water
snow_free_water_evaporation	snow_melt	snow_water_equivalent	surface_water_abstraction
surface_water_abstraction_volume	surface_water_level	surface_water_storage	temperature
top_elevation_of_uppermost_layer	top_water_layer	top_water_layer_evaporation	totalPotentialMaximumGrossDemand
total_abstraction	total_evaporation	total_evaporation_fraction	total_fraction_water_allocation
total_gross_demand	total_gross_demand_volume	total_groundwater_abstraction	total_groundwater_abstraction_volume
total_groundwater_storage	total_thickness_of_active_water_storage	total_thickness_of_water_storage	total_transpiration
total_volume_of_water_storage	total_runoff	transpiration_from_irrigation	transpiration_from_irrigation_volume
upper_soil_saturation_degree	upper_soil_storage	upper_soil_transpiration	water_body_actual_evaporation
water_body_evaporation_fraction	water_body_potential_evaporation

Model Needs

• Forcing

  • Precipitation

  • Temperature

• Parameter set

  • cloneMap

    • We have the needed data stored, you just need to give it your region.

A GitHub page on the inputs for PCRGlobWB 2.0.

Wflow

Let us start with the documentation of Wflow, which is available here. Wflow is a fully distributed, open-source hydrological modeling framework developed by Deltares. It supports multiple process representations (e.g., HBV, SBM, routing) and is designed for both research and operational use, including flood forecasting and water resource management. In addition to the standard implementation, Wflow Julia is also available in via WflowJl, offering improved performance and integration with the growing Julia ecosystem for scientific computing.

Benefits

• Ideal for catchment to regional-scale modeling with high spatial detail.

• More flexible and extensible than HBV or PCR-GlobWB.

• Better for operational and real-time forecasting scenarios.

• Uses modern formats (NetCDF, YAML) and integrates easily into scientific workflows (e.g., eWaterCycle).

• Strong support for modularity, making it easier to adapt to specific hydrological or climatic contexts.

Outputs

• Discharge

• Precipitation

• Evapotranspiration

• Runoff

• Soil moisture

• Storage – groundwater, snow, canopy, etc.

• Infiltration and percolation

• Snow water equivalent – if snow processes are modeled

Model Needs

• Forcing

  • Precipitation

  • Temperature

  • Evapotranspiration

• Parameter set

  • requires HydroMT [work in progress]