Collaboration diagram for Runtime Forcing API:

Functions
SWMM_ENGINE_API int	swmm_forcing_node_lat_inflow (SWMM_Engine engine, int idx, double value, int mode, int persist)
	Force a lateral inflow at a node.

SWMM_ENGINE_API int	swmm_forcing_node_head_boundary (SWMM_Engine engine, int idx, double value, int mode, int persist)
	Force a head boundary at an outfall node.

SWMM_ENGINE_API int	swmm_forcing_node_quality (SWMM_Engine engine, int node_idx, int pollutant_idx, double mass_rate, int mode, int persist)
	Force a quality mass flux at a node.

SWMM_ENGINE_API int	swmm_forcing_link_flow (SWMM_Engine engine, int idx, double value, int mode, int persist)
	Force a flow in a link.

SWMM_ENGINE_API int	swmm_forcing_link_setting (SWMM_Engine engine, int idx, double value, int mode, int persist)
	Force a control setting on a link (pump, orifice, weir, outlet).

SWMM_ENGINE_API int	swmm_forcing_link_quality (SWMM_Engine engine, int link_idx, int pollutant_idx, double value, int mode, int persist)
	Force pollutant quality on a link.

SWMM_ENGINE_API int	swmm_forcing_subcatch_rainfall (SWMM_Engine engine, int idx, double value, int mode, int persist)
	Force rainfall on a subcatchment (bypasses gage lookup).

SWMM_ENGINE_API int	swmm_forcing_subcatch_evap (SWMM_Engine engine, int idx, double value, int mode, int persist)
	Prescribe a potential evapotranspiration (PET) rate on a subcatchment.

SWMM_ENGINE_API int	swmm_forcing_subcatch_snowfall (SWMM_Engine engine, int idx, double value, int mode, int persist)
	Prescribe snowfall on a subcatchment.

SWMM_ENGINE_API int	swmm_climate_get_evap_rate (SWMM_Engine engine, double *value)
	Get the current climate-derived evaporation rate.

SWMM_ENGINE_API int	swmm_forcing_climate_temperature (SWMM_Engine engine, double value, int mode, int persist)
	Prescribe the air temperature used for snowmelt and temperature-derived evaporation.

SWMM_ENGINE_API int	swmm_climate_get_temperature (SWMM_Engine engine, double *value)
	Get the current air temperature (read-only).

SWMM_ENGINE_API int	swmm_forcing_climate_wind (SWMM_Engine engine, double value, int mode, int persist)
	Prescribe the wind speed used in rain-on-snow melt.

SWMM_ENGINE_API int	swmm_climate_get_wind_speed (SWMM_Engine engine, double *value)
	Get the current wind speed (read-only).

SWMM_ENGINE_API int	swmm_forcing_climate_evap (SWMM_Engine engine, double value, int mode, int persist)
	Prescribe the system-wide evaporation rate.

SWMM_ENGINE_API int	swmm_climate_set_dry_only (SWMM_Engine engine, int flag)
	Set the evaporation DRY_ONLY option at runtime.

SWMM_ENGINE_API int	swmm_climate_get_dry_only (SWMM_Engine engine, int *flag)
	Get the evaporation DRY_ONLY option.

SWMM_ENGINE_API int	swmm_forcing_gage_rainfall (SWMM_Engine engine, int idx, double value, int mode, int persist)
	Force rainfall on a rain gage (affects all linked subcatchments).

SWMM_ENGINE_API int	swmm_forcing_clear (SWMM_Engine engine, int type, int idx)
	Clear forcing on a specific element and channel.

SWMM_ENGINE_API int	swmm_forcing_clear_all (SWMM_Engine engine)
	Clear ALL forcings on ALL elements.

Detailed Description

Author: Caleb Buahin caleb.nosp@m..bua.nosp@m.hin@g.nosp@m.mail.nosp@m..com

Copyright: Copyright (c) 2026 Caleb Buahin. All rights reserved.

License\n MIT License

Function Documentation

◆ swmm_climate_get_dry_only()

SWMM_ENGINE_API int swmm_climate_get_dry_only	(	SWMM_Engine	engine,
		int *	flag )

Get the evaporation DRY_ONLY option.

Parameters

	engine	Engine handle.
[out]	flag	Receives 0/1.

Returns: SWMM_OK or error code.

◆ swmm_climate_get_evap_rate()

SWMM_ENGINE_API int swmm_climate_get_evap_rate	(	SWMM_Engine	engine,
		double *	value )

Get the current climate-derived evaporation rate.

Returns the broadcast evaporation rate the engine would apply in the absence of any PET forcing, including monthly adjustments (read-only). Intended for caller-side composition: read this rate, apply your own adjustment logic, and prescribe the result via swmm_forcing_subcatch_evap.

Parameters

	engine	Engine handle.
[out]	value	Receives the rate in user units (in/day US, mm/day SI).

Returns: SWMM_OK or error code.

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◆ swmm_climate_get_temperature()

SWMM_ENGINE_API int swmm_climate_get_temperature	(	SWMM_Engine	engine,
		double *	value )

Get the current air temperature (read-only).

Parameters

	engine	Engine handle.
[out]	value	Receives the temperature in user units (deg F US, deg C SI).

Returns: SWMM_OK or error code.

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◆ swmm_climate_get_wind_speed()

SWMM_ENGINE_API int swmm_climate_get_wind_speed	(	SWMM_Engine	engine,
		double *	value )

Get the current wind speed (read-only).

Parameters

	engine	Engine handle.
[out]	value	Receives the wind speed in user units (mph US, km/hr SI).

Returns: SWMM_OK or error code.

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◆ swmm_climate_set_dry_only()

SWMM_ENGINE_API int swmm_climate_set_dry_only	(	SWMM_Engine	engine,
		int	flag )

Set the evaporation DRY_ONLY option at runtime.

Parameters

engine	Engine handle.
flag	Nonzero suppresses evaporation during rainfall.

Returns: SWMM_OK or error code.

◆ swmm_forcing_clear()

SWMM_ENGINE_API int swmm_forcing_clear	(	SWMM_Engine	engine,
		int	type,
		int	idx )

Clear forcing on a specific element and channel.

Parameters

engine	Engine handle.
type	Forcing channel (SWMM_ForcingType enum).
idx	Element index within that channel.

Returns: SWMM_OK or error code.

◆ swmm_forcing_clear_all()

SWMM_ENGINE_API int swmm_forcing_clear_all ( SWMM_Engine engine )

Clear ALL forcings on ALL elements.

Parameters

engine Engine handle.

Returns: SWMM_OK or error code.

◆ swmm_forcing_climate_evap()

SWMM_ENGINE_API int swmm_forcing_climate_evap	(	SWMM_Engine	engine,
		double	value,
		int	mode,
		int	persist )

Prescribe the system-wide evaporation rate.

Replaces (OVERRIDE) or augments (ADD) the climate-derived evaporation rate after all sources and monthly adjustments, so it reaches every consumer. Per-subcatchment PET forcing (swmm_forcing_subcatch_evap) still takes precedence on its subcatchment.

Parameters

engine	Engine handle.
value	Evaporation rate in user units (in/day US, mm/day SI); must be >= 0 for OVERRIDE.
mode	SWMM_FORCING_OVERRIDE or SWMM_FORCING_ADD.
persist	SWMM_FORCING_RESET or SWMM_FORCING_PERSIST.

Returns: SWMM_OK or error code.

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◆ swmm_forcing_climate_temperature()

SWMM_ENGINE_API int swmm_forcing_climate_temperature	(	SWMM_Engine	engine,
		double	value,
		int	mode,
		int	persist )

Prescribe the air temperature used for snowmelt and temperature-derived evaporation.

Applied before derived climate quantities (saturation vapor pressure, psychrometric constant, Hargreaves moving average) are computed, so all temperature consumers stay consistent. An OVERRIDE prescription replaces the climate data-source value and bypasses monthly adjustments; ADD augments it.

Parameters

engine	Engine handle.
value	Air temperature in user units (deg F US, deg C SI).
mode	SWMM_FORCING_OVERRIDE or SWMM_FORCING_ADD.
persist	SWMM_FORCING_RESET or SWMM_FORCING_PERSIST.

Returns: SWMM_OK or error code.

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◆ swmm_forcing_climate_wind()

SWMM_ENGINE_API int swmm_forcing_climate_wind	(	SWMM_Engine	engine,
		double	value,
		int	mode,
		int	persist )

Prescribe the wind speed used in rain-on-snow melt.

An OVERRIDE prescription replaces the monthly/climate-file value; ADD augments it.

Parameters

engine	Engine handle.
value	Wind speed in user units (mph US, km/hr SI). Must be >= 0 for OVERRIDE.
mode	SWMM_FORCING_OVERRIDE or SWMM_FORCING_ADD.
persist	SWMM_FORCING_RESET or SWMM_FORCING_PERSIST.

Returns: SWMM_OK or error code.

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◆ swmm_forcing_gage_rainfall()

SWMM_ENGINE_API int swmm_forcing_gage_rainfall	(	SWMM_Engine	engine,
		int	idx,
		double	value,
		int	mode,
		int	persist )

Force rainfall on a rain gage (affects all linked subcatchments).

Parameters

engine	Engine handle.
idx	Gage index.
value	Rainfall rate (in/hr for US, mm/hr for SI).
mode	SWMM_FORCING_OVERRIDE or SWMM_FORCING_ADD.
persist	SWMM_FORCING_RESET or SWMM_FORCING_PERSIST.

Returns: SWMM_OK or error code.

◆ swmm_forcing_link_flow()

SWMM_ENGINE_API int swmm_forcing_link_flow	(	SWMM_Engine	engine,
		int	idx,
		double	value,
		int	mode,
		int	persist )

Force a flow in a link.

Parameters

engine	Engine handle.
idx	Link index.
value	Flow rate (CFS for US, CMS for SI).
mode	SWMM_FORCING_OVERRIDE or SWMM_FORCING_ADD.
persist	SWMM_FORCING_RESET or SWMM_FORCING_PERSIST.

Returns: SWMM_OK or error code.

◆ swmm_forcing_link_quality()

SWMM_ENGINE_API int swmm_forcing_link_quality	(	SWMM_Engine	engine,
		int	link_idx,
		int	pollutant_idx,
		double	value,
		int	mode,
		int	persist )

Force pollutant quality on a link.

Same semantics as swmm_forcing_node_quality: OVERRIDE sets the link concentration directly (not mass-balanced); ADD injects a mass rate (mass/sec) tracked in the quality mass-balance forcing bucket.

Parameters

engine	Engine handle.
link_idx	Link index.
pollutant_idx	Pollutant index.
value	Concentration (OVERRIDE) or mass rate (ADD).
mode	SWMM_FORCING_OVERRIDE or SWMM_FORCING_ADD.
persist	SWMM_FORCING_RESET or SWMM_FORCING_PERSIST.

Returns: SWMM_OK or error code.

◆ swmm_forcing_link_setting()

SWMM_ENGINE_API int swmm_forcing_link_setting	(	SWMM_Engine	engine,
		int	idx,
		double	value,
		int	mode,
		int	persist )

Force a control setting on a link (pump, orifice, weir, outlet).

Parameters

engine	Engine handle.
idx	Link index.
value	Setting value (0.0–1.0 for fraction open; pump speed).
mode	SWMM_FORCING_OVERRIDE or SWMM_FORCING_ADD.
persist	SWMM_FORCING_RESET or SWMM_FORCING_PERSIST.

Returns: SWMM_OK or error code.

◆ swmm_forcing_node_head_boundary()

SWMM_ENGINE_API int swmm_forcing_node_head_boundary	(	SWMM_Engine	engine,
		int	idx,
		double	value,
		int	mode,
		int	persist )

Force a head boundary at an outfall node.

Parameters

engine	Engine handle.
idx	Node index (must be OUTFALL type).
value	Boundary head (ft for US, m for SI).
mode	SWMM_FORCING_OVERRIDE (only valid mode for head boundary).
persist	SWMM_FORCING_RESET or SWMM_FORCING_PERSIST.

Returns: SWMM_OK or error code.

◆ swmm_forcing_node_lat_inflow()

SWMM_ENGINE_API int swmm_forcing_node_lat_inflow	(	SWMM_Engine	engine,
		int	idx,
		double	value,
		int	mode,
		int	persist )

Force a lateral inflow at a node.

Parameters

engine	Engine handle.
idx	Node index.
value	Lateral inflow rate (CFS for US, CMS for SI).
mode	SWMM_FORCING_OVERRIDE or SWMM_FORCING_ADD.
persist	SWMM_FORCING_RESET or SWMM_FORCING_PERSIST.

Returns: SWMM_OK or error code.

◆ swmm_forcing_node_quality()

SWMM_ENGINE_API int swmm_forcing_node_quality	(	SWMM_Engine	engine,
		int	node_idx,
		int	pollutant_idx,
		double	mass_rate,
		int	mode,
		int	persist )

Force a quality mass flux at a node.

Parameters

engine	Engine handle.
node_idx	Node index.
pollutant_idx	Pollutant index.
mass_rate	Mass injection rate (mass/sec in concentration units × CFS).
mode	SWMM_FORCING_OVERRIDE or SWMM_FORCING_ADD.
persist	SWMM_FORCING_RESET or SWMM_FORCING_PERSIST.

Returns: SWMM_OK or error code.

◆ swmm_forcing_subcatch_evap()

SWMM_ENGINE_API int swmm_forcing_subcatch_evap	(	SWMM_Engine	engine,
		int	idx,
		double	value,
		int	mode,
		int	persist )

Prescribe a potential evapotranspiration (PET) rate on a subcatchment.

The prescribed rate replaces (OVERRIDE) or augments (ADD) the climate-derived evaporation rate for the subcatchment's surface, LID, and groundwater upper-zone evaporation. An OVERRIDE rate is applied as-is, bypassing the DRY_ONLY option and monthly adjustments. Actual evaporation remains capped by available water, so losses are tracked through the normal runoff continuity totals.

Parameters

engine	Engine handle.
idx	Subcatchment index.
value	PET rate in user units (in/day for US, mm/day for SI).
mode	SWMM_FORCING_OVERRIDE or SWMM_FORCING_ADD.
persist	SWMM_FORCING_RESET or SWMM_FORCING_PERSIST.

Returns: SWMM_OK or error code.

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◆ swmm_forcing_subcatch_rainfall()

SWMM_ENGINE_API int swmm_forcing_subcatch_rainfall	(	SWMM_Engine	engine,
		int	idx,
		double	value,
		int	mode,
		int	persist )

Force rainfall on a subcatchment (bypasses gage lookup).

Parameters

engine	Engine handle.
idx	Subcatchment index.
value	Rainfall rate (in/hr for US, mm/hr for SI).
mode	SWMM_FORCING_OVERRIDE or SWMM_FORCING_ADD.
persist	SWMM_FORCING_RESET or SWMM_FORCING_PERSIST.

Returns: SWMM_OK or error code.

◆ swmm_forcing_subcatch_snowfall()

SWMM_ENGINE_API int swmm_forcing_subcatch_snowfall	(	SWMM_Engine	engine,
		int	idx,
		double	value,
		int	mode,
		int	persist )

Prescribe snowfall on a subcatchment.

The prescribed rate replaces (OVERRIDE) or augments (ADD) the gage-derived, temperature-split snowfall used for snow pack accumulation, plowing, and melt computation. Only meaningful for subcatchments with an assigned snow pack.

Parameters

engine	Engine handle.
idx	Subcatchment index.
value	Snowfall rate in user units (in/hr for US, mm/hr for SI), as snow water equivalent. Must be >= 0 for OVERRIDE.
mode	SWMM_FORCING_OVERRIDE or SWMM_FORCING_ADD.
persist	SWMM_FORCING_RESET or SWMM_FORCING_PERSIST.

Returns: SWMM_OK or error code.

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Functions

Detailed Description

Function Documentation

◆ swmm_climate_get_dry_only()

◆ swmm_climate_get_evap_rate()

◆ swmm_climate_get_temperature()

◆ swmm_climate_get_wind_speed()

◆ swmm_climate_set_dry_only()

◆ swmm_forcing_clear()

◆ swmm_forcing_clear_all()

◆ swmm_forcing_climate_evap()

◆ swmm_forcing_climate_temperature()

◆ swmm_forcing_climate_wind()

◆ swmm_forcing_gage_rainfall()

◆ swmm_forcing_link_flow()

◆ swmm_forcing_link_quality()

◆ swmm_forcing_link_setting()

◆ swmm_forcing_node_head_boundary()

◆ swmm_forcing_node_lat_inflow()

◆ swmm_forcing_node_quality()

◆ swmm_forcing_subcatch_evap()

◆ swmm_forcing_subcatch_rainfall()

◆ swmm_forcing_subcatch_snowfall()