Rainfall Generator Dialog

Antecedent Depth

This is the depth of rainfall (in mm) which has fallen in the hour immediately prior to this storm. The maximum depth allowed is 10mm.

For design storms, this field is typically set to 10mm to ensure that any initial loss volume is already filled before the storm commences (worst case)

UCWI

Urban Catchment Wetness Index, defining the antecedent wetness of the catchment.

Figures 9.7 and 9.8 in Volume 1 of the Wallingford Procedure provide a curve of UCWI against annual average rainfall (SAAR) and values for SAAR across the UK. These can be used to provide a design value of UCWI for the catchment location.

New PR (New UK)/UKWIR

The soil (initial) moisture deficit is the fraction difference between the soil porosity and actual moisture content, expressed as a percentage.

Defines the catchment wetness for use with the SCS runoff model.

Initial soil moisture content. Choose one of the following options from the dropdown list:

• ReFH: Uses the original rainfall runoff model to calculate the initial soil moisture content.
• ReFH2: Uses the new version of the rainfall runoff model to calculate the initial soil moisture content.
• User: Enables the field, allowing you to specify the initial soil moisture content.

Initial baseflow (BF0). Choose one of the following options from the dropdown list:

• ReFH: Uses the original rainfall runoff model to calculate the initial baseflow. This option is only available when generating an ReFH rainfall event.
• ReFH2: Uses the new version of rainfall runoff model to calculate the initial baseflow.
Note: When ReFH or ReFH2 is selected for the calculation of the initial baseflow, the value calculated applies to the area specified for the catchment in the Catchments grid in this dialog. This value is then scaled linearly to the subcatchment area when performing a simulation.
• User (catchment): Enables the field, allowing you to specify the initial baseflow. During a simulation, this baseflow is multiplied by the ratio of the subcatchment area (in the network) to the catchment area (in the rainfall profile). For example, if you specify a base flow of 12, and the size of the catchment is 6 ha of which there are 3 subcatchments of 1, 2 and 3 ha, then when the simulation is run, the baseflow used will be 2 (1/6 x 12) for the 1 ha subcatchment, 4 (2/6 x 12) for the 2 ha subcatchment and 6 (3/6 x 12) for the 3 ha subcatchment.
• User (areal): Enables the field and changes its label from ReFH (2) catchment BF0 (m3/s to ReFH (2) areal BF0 (m3/s/ha), allowing you to specify the initial baseflow. During a simulation, this baseflow is multiplied relative to the subcatchment area. For example, if you specify a base flow of 12, and the size of the catchment is 6 ha of which there are 3 subcatchments of 1, 2 and 3 ha, then when the simulation is run, the baseflow used will be 12 (1 x 12) for the 1 ha subcatchment, 24 (2 x 12) for the 2 ha subcatchment and 36 (3 x12) for the 3 ha subcatchment.

Can be set to:

• England, Wales and Northern Ireland
• Scotland

If set to Scotland, the ReFH2 parameter alpha is not invoked.

Initial soil moisture content. Choose one of the following options from the dropdown list:

• ReFH2: Uses the ReFH2 version of the rainfall runoff model to calculate the initial soil moisture content.
• User: Enables the field, allowing you to specify the initial soil moisture content.

Initial baseflow (BF0). Choose one of the following options from the dropdown list:

• ReFH2: Uses the ReFH2 version of rainfall runoff model to calculate the initial baseflow.
Note: When ReFH or ReFH2 is selected for the calculation of the initial baseflow, the value calculated applies to the area specified for the catchment in the Catchments grid in this dialog. This value is then scaled linearly to the subcatchment area when performing a simulation.
• User (catchment): Enables the field, allowing you to specify the initial baseflow. During a simulation, this baseflow is multiplied by the ratio of the subcatchment area (in the network) to the catchment area (in the rainfall profile). For example, if you specify a base flow of 12, and the size of the catchment is 6 ha of which there are 3 subcatchments of 1, 2 and 3 ha, then when the simulation is run, the baseflow used will be 2 (1/6 x 12) for the 1 ha subcatchment, 4 (2/6 x 12) for the 2 ha subcatchment and 6 (3/6 x 12) for the 3 ha subcatchment.
• User (areal): Enables the field and changes its label from ReFH (2) catchment BF0 (m3/s to ReFH (2) areal BF0 (m3/s/ha), allowing you to specify the initial baseflow. During a simulation, this baseflow is multiplied relative to the subcatchment area. For example, if you specify a base flow of 12, and the size of the catchment is 6 ha of which there are 3 subcatchments of 1, 2 and 3 ha, then when the simulation is run, the baseflow used will be 12 (1 x 12) for the 1 ha subcatchment, 24 (2 x 12) for the 2 ha subcatchment and 36 (3 x12) for the 3 ha subcatchment.

Can be set to:

• England, Wales and Northern Ireland
• Scotland

If set to Scotland, the ReFH2 parameter alpha is not invoked.

Initial soil moisture content.

Initial baseflow (BF0).

Rainfall intensities

Rainfall intensities are required for the following average recurrence intervals (ARI) and rainfall durations:

2_{i 1} 2 years ARI, 1 hour duration

2_{i 12} 2 years ARI, 12 hour duration

2_{i 72} 2 years ARI, 72 hour duration

50_{i 1} 50 years ARI, 1 hour duration

50_{i 12} 50 years ARI, 12 hour duration

50_{i 72} 50 years ARI, 72 hour duration

The valid range for these intensities is 0.0 to 200.0 .

Coefficient of skewness

G, average coefficient of skewness (unitless). The valid range for this parameter is 0.0 – 0.8.

Zone number

The zone number is required in applying the temporal pattern. Select a value between 1 and 8. Please refer to Book 2, Volume 2 of Australian Rainfall and Runoff (Inst. Engrs Aust., 1987. Reprinted 1998) which contains a series of maps of design rainfall isopleths for the 8 regions of Australia.

Geographical factors

There are two factors :

F2 (Geographical factor, 2 years, 6 minute duration. Valid range 3.68 – 5.0)

F50 (Geographical factor, 50 years, 6 minute duration. Valid range 13.5 – 18.5).

If durations of less than one hour are required, you can:

- Let the software calculate the F2 and F50 parameters by clicking the Calculate using latitude and longitude check box and typing in the longitude and latitude values in degrees in the Longitudeand Latitude boxes, or

- Type in directly the F2 and F50 values if these are known (Do not click the Calculate using latitude and longitude check box)

ARI (years)

Enter the storm duration in minutes or hours. You can select one or more durations. Permitted values are :10, 15, 20, 25, 30, 45 mins and 1, 1.5, 2, 3, 4.5, 6, 9, 12, 18, 24, 30, 36, 48, 72 hours. There is no option to type in user specific durations.

Storm

Grid

The fields in the grid are automatically populated when rainfall data is generated or imported.

A check in the box in the first grid column indicates that the rainfall data contained in the row will be included in a simulation. Remove the check to exclude any data from a simulation.

The other columns in the grid are described below:

Clicking Disable all excludes all the data, details of which are currently displayed on the storm grid, from a simulation. Any checks displayed in the first column of the grid will be removed.

Clicking Remove disabled storms deletes the data for all storms which have a check displayed in the first column of the grid.

A read-only field which displays the constant infiltration loss, if specified.

Opens the ARR Storm Generator window.

Contact Innovyze if you require further information about generating Australian Rainfall 2016.

Note that a NET Framework 4.8 or newer is required to install a standalone ARR Storm Generator.

The portion of the duration of the event that occurs before the peak.

This must be a value between 0 and 1

Period, in years, between events of the same intensity or of a greater intensity than this storm.

Multiple return periods can be specified, using commas to separate the return period values.

Duration of the rainfall event in minutes.

Storms with different durations can be specified, using commas to separate the durations.

Select method of specifying value for A:

• Calculated - A is calculated from a, C and Return period values

• User - A is user defined

Read-only field set when Calculation of A is set to Calculated.

A is calculated as:

a(1 + Clog₁₀P)

where P is return period

User defined equation constant.

Period, in years, between events of the same intensity or of a greater intensity than this storm.

Multiple return periods can be specified, using commas to separate the return period values.

Duration of the rainfall event in minutes.

Storms with different durations can be specified, using commas to separate the durations.

Catchment descriptor parameters:

Load

Clicking this button loads catchment descriptors from a CSV or XML file(s). The descriptors must have already been exported from the FEH CD application or downloaded from the FEH web service.

See Importing Catchment Parameters from the FEH CD or Web Service for more details.

Return Period

This indicates the period, in years, between events of the same intensity or of a greater intensity than this storm.

F or a valid DDF model, the storm return period must be greater than one year when using the Annual Maximum return period scale. Shorter return periods are allowed for the Peaks Over Threshold return period scale.

To set a return period of less than 1 year when using the Peaks Over Threshold return period scale, you enter the reciprocal of the return period as a negative number. For example:

1 in 6 month storm = 2 in 1 year storm. Enter -2

1 in 3 month storm = 4 in 1 year storm. Enter -4

1 in 1 month storm = 12 in 1 year storm. Enter -12

Return periods greater than 10000 years are not recommended.

The parameters were based on observations of return periods no greater than 1000 years.

Duration

The duration of the rainfall event in minutes. The duration must be between 15 and 15840 minutes (11 days)

The storm duration to be used depends on the size of the catchment.

• Short storms: have higher peak intensities and so will be more critical for small catchments or for local areas of large catchments.
• Long storms: have larger total rainfall depths and so will be more critical for large catchments.

To identify all the problems in a catchment, you must analyse storms with a range of durations from about 15 minutes up to twice the time of concentration of the catchment.

Profile

Choose the Summer profile, the Winter profile or the Synthetic profile

The profile shape defines how high the peak intensities are for a given rainfall depth:

• 50 percentile summer profile : This has high peak intensities. We recommend this for urban areas.
• 75 percentile winter profile : Lower peak and more drawn out. For rural areas.

Return Period Type

Flood data series type:

• Annual Maximum
• Peaks-over-threshold

Multiplying Factor

Factor allowing percentage increase of design rainfall. The Multiplying Factor is applied to the Areal Reduction Factor (ARF) calculated from the UK Rainfall (FEH) Generator input parameters.

Profile ARF = calculated ARF * Multiplying Factor

Displays the catchment descriptor parameters and/or the point descriptor parameters which have been loaded from XML catchment files or XML point files respectively.

Although some of the fields in the grid are read-only, you can still delete rows from it. Highlight the row you want to delete and then press the Delete key.

Load

Loads the catchment descriptors or point descriptors from XML files. The files must have already been downloaded from the FEH web service.

A standard Windows Open file dialog is displayed from which you can select the required XML file.

Return period

This indicates the period, in years, between events of the same intensity or of a greater intensity than this storm. The Return period must be between 2 and 10000 years.

Duration

The duration of the rainfall event in minutes. The Duration must be between 15 and 9000 minutes. If multiple Timesteps are to be used, then a duration must be specified for each timestep. Multiple durations must be separated by a comma.

The interval between timesteps in either in sec (seconds) or % (percentage) depending on which unit is selected in the adjacent dropdown box.

Multiple timestep intervals can also be specified, each of which must be separated by a comma. Note that each timestep must have a corresponding Duration.

For each timestep (in seconds) specified, ensure that the corresponding Duration (in seconds) divided by the timestep (in seconds) is less than 480:

If you are using percentages rather than seconds, each Timestep (in seconds) can be calculated as follows:

where % value is the specified percentage interval between the timesteps.

If no timestep is specified, a default timestep of 60 seconds is used. However, if the default timestep is invalid for the specified Duration, the default timestep is multiplied by 2 until it becomes valid.

Return period type

Flood data series type:

• Annual Maximum
• Peaks-over-threshold

ReFH2 version

Read-only

The version number of the ReFH2 software last used to calculate any of the following fields:

• ReFH2 Cini
• ReFH2 catchment BF0 (m3/s)
• Alpha coefficient
• Areal reduction factor
• Seasonal correction factor

If ReFH2 was not used to calculate the above fields, this field is blank.

Profile

The profile shape defines how high the peak intensities are for a given rainfall depth:

• Summer: 50 percentile summer profile - high peak intensities
• Winter: 75 percentile winter profile - lower peak and more drawn out

Multiplying factor

Factor allowing percentage increase of design rainfall. The Multiplying Factor is applied to the Areal Reduction Factor (ARF) calculated from the UK Rainfall (FEH) Generator input parameters.

Profile ARF = calculated ARF * Multiplying Factor

An alpha adjustment coefficient. Choose one of the following options from the dropdown list:

• ReFH2: Uses the ReFH2 version of the rainfall runoff model to calculate the alpha coefficient.
• User: Enables the field, allowing you to specify the alpha coefficient.

Factor to convert point rainfall to catchment average rainfall:

• ReFH2: Uses the ReFH2 version of the rainfall runoff model to calculate the areal reduction factor.
• User: Enables the field, allowing you to specify the real reduction factor .

Factor used to convert annual maximum rainfall to seasonal rainfall:

• ReFH2: Uses the ReFH2 version of the rainfall runoff model to calculate the seasonal correction factor.
• User: Enables the field, allowing you to specify the the seasonal correction factor.

Performs the following checks:

• The Return period is within the permitted range.
• The Duration is within the permitted range.
• The total number of timesteps per duration is an odd number. The total number of timesteps will be automatically adjusted to ensure that an odd number is used, as required by ReFH2.

A suitable message is displayed if any of the checks are unsuccessful.

If the checks are successful, InfoWorks ICM saves the generated rainfall data and closes the dialog.

For new events, the ReFH2 application now generates the rainfall hyetograph.

For existing events, the ReFH2 application checks the data for any changes, and updates the rainfall hyetograph accordingly.

If the ReFH2 application cannot be found, fails to start, or returns an error, then a suitable message is displayed. In such cases, the event will still be saved but without generating/updating the rainfall hyetograph.

Return Period(s)

Peak Duration

Peak Position

Location

A list of standard regions

Catchment descriptor parameters.

Generate

Generates the rainfall data.

For each row in the Catchments grid with an Easting and a Northing set (i.e. not zero), the 'H' columns are populated with values found for that location. For these rows, the Gauge data column is also populated with the row's easting and northing in the format, Easting, Northing.

A message will be displayed listing the IDs of any catchments with an Easting / Northing for which no 'H' data is defined.

Return period

This indicates the period, in years, between events of the same intensity or of a greater intensity than this rainfall event.

The Return period must be between 1 and 100 years when Return period type is set to Annual maximum.

If the Return period type is set to Peaks-over-threshold, then the Return period must be between 1 and 99 or -12 and -1. Negative return periods are used to represent fractional values, for example, -4 corresponds to ¹/₄.

The default return period is 5 years.

Duration

The duration of the rainfall event in minutes. The duration must be between 15 and 4320 minutes (3 days). The default is 30 minutes.

Interval between timesteps in minutes. This can be set to 5 (default), 10, 15, 20, 30, 60, 180, 240, 360, 720 or 1440 minutes.

Return period type

Flood data series type:

• Annual maximum (default)
• Peaks-over-threshold

Multiplying

Factor allowing percentage increase of design rainfall. This allows scenarios, such as a 10% increase in rainfall to be investigated.

Performs the following checks:

• The values displayed in the 'H' columns are the same as the generated 'H' values for the specified Easting and Northing
• The Return period is within the permitted range
• The Duration is within the permitted range
• The Duration is an exact multiple of the selected timestep
• The Duration is at least twice as long as the selected timestep

A suitable message is displayed if any of the checks are unsuccessful.

If the checks are successful, InfoWorks ICM saves the generated rainfall data and closes the dialog.

The region of Honk Kong that this rainfall applies to. The choices are:

• HKO Headquaters
• North District
• Tai Mo Shan
• West Lantau

Return Period

A list of known return periods from which the appropriate ones can be selected.

The selected return periods are used to determine which parameters should be used to calculate peak intensity of the storm and the intensity at each timestep on either side of the peak when generating the rainfall hyetographs.

Further information about these parameters can be found in the relevant 'Design Rainstorm Profile Intensity-Duration-Frequency Relationships' tables in the Stormwater Drainage Manual, Planning, Design and Management, Fifth Edition, January 2018 produced by the Drainage Services Department, Government of the Hong Kong Special Administrative Region.

Duration

The storm duration in minutes.

Multiplying Factor

Multiplying factor applied as the Areal Reduction Factor.

Return Period

A list of known return periods from which the appropriate ones can be selected.

Alternatively, selecting the User option allows you to enter your own parameter values in the User Defined Parameters section of the dialog. These parameters are used to calculate peak intensity when generating the rainfall hyetograph.

If you select a known return period, this is used to look up the parameters in one of the tables reproduced in the Design Rainfall Generators topic. The table used depends on the choice you make in the Method field.

Duration

The storm duration in minutes.

Method

Select the method to use for generating the rainfall hyetograph. The choices are:

• Gumbel
• Jenkinson's 1955 solution
• Jenkinson's maximum likelihood solution

In addition, there are two choices of data table for looking up the parameters used when calculating peak intensity.

• Earlier analysis (used in the WALLRUS and SPIDA packages)
• More recent analysis (1994) (first available in the HydroWorks package)

See Design Rainfall Generators for details on the tables and calculation method.

Multiplying Factor

Multiplying factor applied as the Areal Reduction Factor.

User Defined Parameters a, b, c

If you choose User in the Return Period box, you should enter the user defined values for a, b and c here. Any specified values will be rounded to 3 decimal places when the rainfall hyetograph is generated.

Catchment area

Used to determine areal reduction factor

2 year 24 hour rainfall depth

Taken from MSMA table 13.3, used to calculate the correction factor for short storms FD in equation 13.3

Location

East or West coast is used to determine which of the temporal patterns in tables 13.B1 or B2 of MSMA are used

ARI

The average return interval in years. For return intervals of less than 2 years, average intensity values are calculated by multiplying the 2 year return interval storm by the correction factors presented in equations 13.5a-d of MSMA

a,b,c,d

The four values used in equation 13.2 of MSMA.

Durations

Storms with different durations can be specified in one go, using commas to separate the durations

Multiplying Factor

This simple multiplying factor allows scenarios, such as a 10% increase in rainfall to be investigated

Catchment area

The size of the area for which the design rainfall is generated.

Location

The region that the temporal pattern is to apply to.

Five regions, as shown in Figure 7.1 of the Hydrological Procedure No 1, are used to determine which of the temporal patterns, shown in Tables 8.6 to 8.10, are used.

Used to determine areal reduction factor. See Tables 9.1 and 9.2 in the Hydrological Procedure No 1.

Note that the minimum ARF area values will apply to any specified Catchment area that is smaller than the ARF minimum area, and the maximum ARF values will apply to any Catchment area that is larger than the maximum ARF area.

ARI

The average return interval.

An interval of 1, 2, 4 or 6 months or 1, 2, 5, 10, 20, 25, 50 or 200 hours can be selected from the dropdown list.

λ Ƙ θ Ƞ

The four values to be used in the equation derived in section 3.6.1 of the Hydrological Procedure No 1.

The values for λ, Ƙ, θ and Ƞ can be found in Table 6.1 (a-d) and Table 6.2 (a-d) and also shown in the generalised isopleths maps in Appendix 1 (Figures 11.1 to 11.4).

The valid range for λ is between 0 and 200, while the valid ranges for Ƙ, θ and Ƞ are between 0 and 1.0

Duration

Storms with different durations can be specified in one go, using commas to separate the durations.

The duration(s) can be specified in minutes, hours or days.

The minimum duration that can be specified is 5 minutes while the maximum can be 4320 minutes, 72 hours or 3 days.

Multiplying factor

This simple multiplying factor allows scenarios, such as a 10% increase in rainfall to be investigated.

The climate change factor (CCF) can be selected from the dropdown list.

The CCFs relevant to the selected Location will be applied when the rainfall is generated. See Tables 10.1 to 10.5 in the Hydrological Procedure No 1 for further information.

Clicking Disable all excludes all the data, details of which are currently displayed on the storm grid, from a simulation. Any checks displayed in the first column of the grid will be removed.

Clicking Remove disabled storms deletes the data for all storms which have a check displayed in the first column of the grid.

Storm

grid

The fields in the grid are automatically populated when rainfall data is imported from the NOAA ATLAS 14 Storm Generator.

A check in the box in the first grid column indicates that the rainfall data contained in the row will be included in a simulation. Remove the check to exclude the rainfall data from a simulation.

The other columns in the grid are described below:

Catchment descriptor parameters:

Load

Clicking this button loads catchment descriptors from a CSV or XML file(s). The descriptors must have already been exported from the FEH CD-ROM or downloaded from the FEH web service.

See Importing Catchment Parameters from the FEH CD or Web Service or more details.

Duration of the rainfall event in minutes.

Return Period Type

Flood data series type:

• Annual maximum
• Peaks-over-threshold

Read-only

The version number of the ReFH2 software currently being run on the PC.

The profile shape defines how high the peak intensities are for a given rainfall depth:

• Summer: 50 percentile summer profile - high peak intensities
• Winter: 75 percentile winter profile - lower peak and more drawn out

Factor allowing percentage increase of design rainfall.

The multiplying factor is applied to the areal reduction factor (ARF) calculated from the ReFH generator input parameters.

Profile ARF = calc ARF x SCF x Multiplying Factor

An alpha adjustment coefficient. Choose one of the following options from the list:

• ReFH2: Uses the ReFH2 rainfall runoff model to calculate the alpha coefficient
• User: Enables the field, allowing you to specify the alpha coefficient

Factor to convert point rainfall to catchment average rainfall:

• Design: Uses a factor calculated from the model
• User: Enables the field, allowing you to specify the factor

Factor used to convert annual maximum rainfall to seasonal rainfall:

• Design: Uses a factor calculated from the model
• User: Enables the field, allowing you to specify the correction factor

Duration

Duration of storm

Intensity Pattern

24-hour rainfall distributions developed by the SCS from available National Weather Service duration frequency data or local storm data.

Only enabled when Duration is set to 24 hrs.

24hr / 6hr depth of design rainfall

Total depth of rainfall over the Duration of the storm

Timestep

Time interval between each intensity value

Multiplying factor

This simple multiplying factor allows scenarios, such as a 10% increase in rainfall to be investigated

5 year 1 hour rainfall (M5-60)

The rainfall depth (in mm) for a 5-year return period rainfall event of 1 hour duration. The value must be between 0 and 100. You can obtain the value for your catchment’s location from the map in Wallingford Procedure Volume 1 Fig. 6.1 (page 43), or the M5-60 map in Volume 3 of the Wallingford Procedure

One hour means any 60 minute period

Rainfall Ratio

The ratio of rainfall depths for a 5 year return period rainfall event of 1 hour duration and a 5 year return period rainfall event of 2 days duration. Ratios across the UK range from 0.12 to 0.46. A typical value for South East England is 0.4.

You can look up ratio values from Volume 1 of the Wallingford Procedure Fig. 6.2 (page 44), or from the map in Volume 3 of the Wallingford Procedure

Two days means a 48 hour period starting at 0900 GMT.

Catchment Area (Ha)

The total catchment area of the drainage system (in hectares).

The software uses this value to determine the areal reduction factor. This factor takes into account the reduction in total rainfall intensity as the storm passes over a catchment (that is, it does not rain at the same intensity on every part of a large catchment)

Location

Choose between England and Wales and Scotland and Northern Ireland, depending on the location of the system you are modelling

Series

Enabled if the Profile field is set to Synthetic. Choose between East and West.

Use the rainfall characteristics to choose whether to use the eastern or western series. Calculate the ratio YR for the catchment as:

Then choose which series is closest to this value, from the table below:

For storms with a return period of greater than 1 year, the choice of series has little effect.

This indicates the period, in years, between events of the same intensity or of a greater intensity than this storm.

If you choose to use the winter or summer profile, the return period must be between 1 and 100 years. If you choose to use the synthetic profile, you can define storms of less than a 1 year return period.

To request a return period of less than 1 year, enter the reciprocal of the return period as a negative number. For example:

1 in 6 month storm = 2 in 1 year storm. Enter -2

1 in 3 month storm = 4 in 1 year storm. Enter -4

1 in 1 week storm = 52 in 1 year storm. Enter -52

The duration of the rainfall event in minutes. The duration must be between 1 and 15840 minutes (11 days)

The storm duration to be used depends on the size of the catchment.

• Short storms: have higher peak intensities and so will be more critical for small catchments or for local areas of large catchments.
• Long storms: have larger total rainfall depths and so will be more critical for large catchments.

To identify all the problems in a catchment, you must analyse storms with a range of durations from about 15 minutes up to twice the time of concentration of the catchment.

Choose the Summer profile, the Winter profile or the Synthetic profile

The profile shape defines how high the peak intensities are for a given rainfall depth:

• 50 percentile summer profile : This has high peak intensities. We recommend this for urban areas.
• 75 percentile winter profile : Lower peak and more drawn out. For rural areas.

Factor allowing percentage increase of design rainfall. The Multiplying Factor is applied to the Areal Reduction Factor (ARF) calculated from the UK Rainfall Generator input parameters.

Profile ARF = calculated ARF * Multiplying Factor