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Optional Forcing

HydroPol2D supports multiple types of meteorological and hydrological forcing beyond basic rainfall input.

All forcing configurations are defined through the General_Data.xlsx file, which controls:

  • the type of forcing used,
  • the activation of model components,
  • and the associated input datasets.

The model can operate under different forcing strategies depending on data availability and simulation objectives.

Overview​

HydroPol2D supports the following forcing options:

  • Meteorological forcing for evapotranspiration (Penman–Monteith)
  • Direct evaporation (EE) and transpiration (TT) inputs
  • Spatial rainfall forcing (raster-based or gauge-interpolated)
  • Synthetic design storms (Huff and Alternating Block)
  • External inflow hydrographs
  • Stage boundary conditions

Each forcing type is activated and configured through General_Data.xlsx.

Meteorological Forcing (Penman–Monteith)​

HydroPol2D computes evapotranspiration using a Penman–Monteith formulation when meteorological forcing is provided.

Input source​

Meteorological data are provided through:

  • ETP_input_data.xlsx

Spatial interpolation​

Meteorological variables are distributed spatially using:

  • inverse distance weighting (IDW)

This ensures that atmospheric forcing is consistent across the domain based on available measurement points.

Required variables​

Typical inputs include:

  • air temperature
  • radiation (net or solar)
  • relative humidity
  • wind speed

Role in the model​

Meteorological forcing is used to compute evapotranspiration, which removes water from:

  • surface storage
  • soil moisture

This approach is recommended when full atmospheric forcing is available.

Direct Evaporation and Transpiration Inputs​

HydroPol2D allows direct specification of evaporation and transpiration.

Inputs​

  • evaporation (EE) raster or time series
  • transpiration (TT) raster or time series

Units:

  • mm h−1\mathrm{mm\,h^{-1}}

Role in the model​

These fluxes are applied directly to:

  • surface water storage
  • soil moisture

This approach bypasses the need for meteorological forcing.

Rainfall Forcing​

HydroPol2D supports multiple rainfall input configurations.

1. Concentrated rainfall (uniform)​

Defined through:

  • Rainfall_Intensity_Data.xlsx

Description​

  • rainfall is applied uniformly over the domain
  • defined as a time series

Units:

  • mm h−1\mathrm{mm\,h^{-1}}

2. Gauged rainfall (spatial interpolation)​

Defined through:

  • Rainfall_Spatial_Input.xlsx

Spatial interpolation​

Rainfall fields are computed using:

  • inverse distance weighting (IDW)

Gauge measurements are interpolated to all grid cells based on their spatial location.

Description​

  • multiple gauges can be specified
  • rainfall varies spatially and temporally
  • suitable for observed precipitation datasets

Units:

  • mm h−1\mathrm{mm\,h^{-1}}

3. Raster-based rainfall​

Rainfall can also be provided as:

  • time-varying raster stacks

Units:

  • mm h−1\mathrm{mm\,h^{-1}}

Role in the model​

Rainfall drives:

  • infiltration
  • runoff generation
  • surface flow routing

Design Storms​

HydroPol2D includes built-in synthetic storm generation.

Methods available​

  • Huff distributions
  • Alternating Block method

Configuration​

Defined through General_Data.xlsx, including:

  • total rainfall depth
  • storm duration
  • temporal distribution

The model generates the rainfall hyetograph internally.

External Inflow Hydrographs​

External inflow is defined through:

  • Inflow_Hydrograph.xlsx

Role in the model​

Used for:

  • upstream boundary conditions
  • river inflow
  • dam-break or controlled inflow scenarios

Implementation​

  • multiple gauges can be defined
  • each gauge is associated with spatial coordinates
  • inflow is distributed across all cells associated with each gauge

Units:

  • m3 s−1\mathrm{m^3\,s^{-1}}

Stage Boundary Conditions​

Stage boundary conditions are defined through:

  • Stage_Hydrograph.xlsx

Role in the model​

Used for:

  • downstream control
  • backwater effects
  • hydraulic constraints

Implementation​

  • stage is prescribed as water depth or elevation
  • all cells associated with the boundary receive the same imposed value

Units:

  • m\mathrm{m}

Control Through General_Data.xlsx​

The General_Data.xlsx file defines:

  • which forcing components are active
  • which datasets are used
  • temporal resolution
  • unit consistency

It acts as the central interface between user-defined inputs and the model.

Interaction Between Forcing Components​

The forcing inputs interact as follows:

  • rainfall introduces water into the system
  • evapotranspiration removes water from storage
  • meteorological variables control energy-driven fluxes
  • inflow hydrographs add external discharge
  • stage boundaries constrain hydraulic response

These interactions define the system dynamics.

Practical Considerations​

  • ensure temporal consistency across all forcing inputs
  • verify units before simulation
  • avoid mixing incompatible time resolutions
  • confirm correct spatial placement of gauges
  • ensure interpolation inputs are well distributed spatially
  • match forcing resolution with the model time step

Summary​

Optional forcing in HydroPol2D enables flexible simulation setups ranging from simple rainfall-driven scenarios to fully coupled meteorological-hydrological systems.

All forcing configurations are managed through General_Data.xlsx, allowing users to:

  • switch between forcing strategies
  • integrate external datasets
  • and define synthetic events

The selected forcing approach should reflect:

  • the objective of the simulation
  • data availability
  • and the required level of physical representation