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NEVINA

Calculations of catchment areas, field parameters

and water flow indices

User guide

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Contents
About NEVINA ............................................................................................................................................3

What's new in the latest version: ................................................................................................................3

NEVINA can be used for, among other things: ...................................................................................................4

Possibilities:................................................................................................................................................4

Important things to consider:................................................................................................................................4

Error in calculation of catchment area:................................................................................................................5

Start screen........................................................................................................................................7

Calculation of catchment areas, field parameters, low water indices and flood values..................................................................9

Procedure for finding field parameters, low water indices and flood values for a catchment area........10

Navigating the map................................................................................................................................10

Select Point ..............................................................................................................................................11

Generate Precipitation Field........................................................................................................................11

Edit Precipitation Field........................................................................................................................11

Generate Field Parameters ...................................................................................................................13

Generate Indexes...................................................................................................................15

More about flood values ..............................................................................................................................17

Export to Shape ...........................................................................................................................................18

Export to PDF...................................................................................................................18

Find water flow index stations................................................................................................................19

Precipitation-runoff model........................................................................................................................20

Map layer list ......................................................................................................................................21

References........................................................................................................................................................21

Appendix ................................................................................................................................................22

Appendix 1: Tables of explanations and definitions of parameters calculated in NEVINA. ...............22

Appendix 2: PDF of catchment parameters ..............................................................................................25

Appendix 3: PDF of low tide indices........................................................................................................26

Appendix 4: PDF of regional flood calculation........................................................................................28

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About NEVINA
NEVINA (Precipitation Field and Water Flow Index Analysis) is a map service where you can easily generate
catchment area boundaries for a chosen point in a watercourse, calculate field parameters, climate and hydrological
parameters, estimate low water indices and flood values. This is information that can be used as a supporting
basis in connection with license applications, flood calculations and other types of hydrological analyses.

The tool is accessible via the browser and is based on the same user interface as NVE-Atlas, but with extended
functionality. Software from ESRI is used.

NEVINA calculates the catchment area and field parameters based on natural field boundaries, i.e. existing regulations in the
field are not taken into account. All field parameters, low water indices and flood values are calculated automatically. Both field
parameters and calculated water flows contain a varying degree of uncertainty and must not be perceived as exact values. This
applies in particular to low water indices and flood values, where the uncertainty varies greatly depending on geographical
location and hydrological conditions.

As NEVINA now exists, it is well suited for use in early planning of a project. In any further analysis such as a
license application or dimensioning of a project, the values from the map must be supplemented with a professional
hydrological assessment and analyses of water flow series. The extent of such an assessment depends on the
nature of the project.

The product is based on automated routines and may contain errors. Use the tool wisely and always perform a
quality check of the results before use.

A more detailed description of field parameters and specific GIS calculations in NEVINA can be found in Voksø
(2024). The report also discusses some of the development work on earlier versions of the application.

See Engeland et al. (2008) for more information on the calculation methodology for low water indices, Glad et al.
(2015) for calculations of flood values in small fields (NIFS) and Engeland et al. (2020) for regional flood formulae
(RFFA-2018).

What's new in the latest version:

New functionality

Version 4 published 24.04.2024

• Separate PDF report for data from the runoff map, which shows, among other things, monthly mean runoff
and the variation in annual runoff over the normal period. The report also shows the water balance in the
catchment area, the change in annual mean runoff from the normal period 1961-1990 to 1991-2020 and
the uncertainty in the calculated annual mean runoff.

• Direct link from the front page of NEVINA to SERIEKART, for easier retrieval of station data.

• The selection of stations used to calculate the runoff map can be displayed in the map in addition to the
water flow index stations.

• The runoff map stations have their own tab in the station report.

• The runoff map is included as a selectable map layer.

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• Previous calculations for a selected catchment area can be retrieved by specifying a GUID, which can be
can be found at the bottom of the pdf reports.

• Changed elevation model from 25x25 m to 20x20 m.

Version 3 (2022):

• Version history (with overview of changes/bug fixes)

• Use of own flood data when calculating flood indices, cf. "Simplified local + regional analysis"

• New pdf report adapted to use own flood data

• URL to PQRUT has been expanded with field parameters for estimating model parameters according to Filipova
et al. (2016)

• Several new features in the NEVINA data model

Bugfix (2022):

• Uncertainty bands for RFFA-2018

• Several small fixes/ends to text in user interface and pdf reports

• Linked to the correct map layer when displaying water flow stations

NEVINA can be used for, among other things:

• Calculate catchment areas and associated field parameters such as field area, effective sea percentage,
lowland percentage, hypsographic curve, etc. See Appendix 1 for a complete overview.

• Calculate climate and hydrological parameters (precipitation, temperature and average runoff)

• Estimate low water indices (normal low water flow, 5th percentiles and BFI). See Appendix 3 for a complete
overview.

• Calculate flood values. See appendix 4 for a full overview.

• Auxiliary tool for selecting hydrological measuring stations.

Possibilities:

• Download a PDF report with all available information about the catchment area.

• Export results to shape file for use in other GIS tools.

• Export a map section to file.

• Manually edit catchment boundaries and field parameters.

• Create a report on a selection of measuring stations

Important to think about:

As a user, you must assess the reasonableness of the generated data yourself. In some areas NEVINA works well,
while in other places the tool may give implausible values. Always consider that the field boundaries look reasonable.

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before generating field parameters. Also check that field and climate parameters seem reasonable, and compare
estimated low water indices and flood values with results from monitoring stations in the area.

Error in calculation of catchment area:

Catchment area calculations may fail without any visible error or incorrect results. There may be several reasons for
this.

1. The point is set too far from the riverbed, zoom in and try again

2. The precipitation field to be calculated is a tributary, but the result is based on the main river and therefore gives
an incorrect result. The calculation uses a search radius of 75 meters. Move the point further up the river and
try again.

3. Errors in the underlying data.

4. Sea downstream is included in sea percentage/effective sea percentage. Move the point further up the river and
try again.

Here is an example of how important it is to place the point a little further into the river course.

Report to the email address: NEVINA@nve.no if it is not successful after a few attempts.

The precipitation field that is generated is either completely automatic from the baseline data or a combination of
automatically generated and precipitation fields upstream of the point obtained from REGINE (REGIster over Nedbørfelt).

The calculation reflects the baseline data and the watershed may be incorrect when generating the catchment area.

Report back if you discover:

• Errors in the river network: For example, disjointed river networks or field boundaries crossing
the river network.

• Significant errors in generating field boundaries.

• Error in REGINE.

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• Error in field parameters

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Search function for

Email for station, location

Start window Window to change
feedback of hydroelectric
background map power plant, river network, etc.
Menu for making Help function
calculations in Version history
NEVINA

Standard
zoom level

Arrows for

to bread

Select relevant
measuring stations

Scale
Map layer list

Processing information
History of completed tasks
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To see more of the map, you can hide the entire left menu. You can also hide the overview map on the
right side. You can also pan with the arrow keys on your keyboard to the left, right, up and down.

Click the arrow to hide If you have feedback or Click the arrow to
the entire left menu questions about NEVINA, hide the overview map
click on "feedback"

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Calculation of catchment areas, field parameters, low water indices and flood values

The following window is used to calculate catchment boundaries, field parameters, low water indices
and flood values. In this window, the file format for exporting the data is selected and it is also possible to
proceed to a simple rainfall-runoff model. This is where the new function where you can enter your own flood
values has been added.

Blue background marks which process is active in NEVINA. Black text marks which functions are available. The
different steps in the process normally go from top to bottom and are activated by the user.
In the image above, the user can select a point that defines the outlet of the catchment area.

Also use the help function in NVE Atlas to get more information about different thematic layers, navigation and
search function. Note that as this is a general description of layers in NVE Atlas, there are thematic layers that
are not available in NEVINA.

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Procedure for finding field parameters, low water indices and flood values for a
catchment area

Below is the general procedure for calculating field parameters, low water indices and flood values.

Navigating the map

Start by zooming in to the desired area by dragging a rectangle with Shift + left mouse button. You can also move the
map with the mouse, and use the "wheel" on the mouse to zoom in/out, or with + and -
the buttons.

zoom

Once you have zoomed in sufficiently, the “river network” will appear as lines on the map. Find the point in the river
that defines the outlet of the catchment area. The point should be placed on or as close as possible to the river network.
If the point is not connected to the river network, NEVINA cannot calculate all parameters. It may be necessary to
zoom in even further to more easily mark the correct location in the river. For example, if you know the elevation of
the point, you can use the elevation curves in the map to find the correct point.

You can also easily search for hydroelectric power plants, reservoirs or place names. If you want to display water flow
stations while navigating around the map, you can do so under "FIND WATER FLOW INDEX STATIONS" or under
"MAP LAYER LIST".

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Select Point
Once you have found the location in the watercourse where the catchment area is to be calculated, click on the selected location in the map.

The point is placed in red at the selected location.

Alternatively, you can enter the GUID to retrieve a previous calculation. The GUID can be found, for example, at the bottom of the
page in the PDF reports.

Generate Precipitation Field

When the point is correctly placed, click the "Generate Precipitation Field" button. The precipitation field is calculated and drawn
on the map. This usually takes less than a minute. Normally, a small area downstream of the point is included. If you see that the
point is placed incorrectly, simply select the point again.

Edit Precipitation field

If desired, it is possible to edit the catchment area by clicking on "Edit Rainfall Area". In some cases, it is necessary to edit the
catchment area to get the most correct field boundaries possible. This can be, for example:

• The field boundary deviates significantly from the regine boundaries. Regine boundaries are a good indication of where the
field boundaries are, but in some cases they can also be incorrect. The user must therefore assess for themselves
where the field boundaries should be.

• If the boundary crosses a river, NEVINA has drawn the wrong boundaries and the catchment area must be edited.

• If the field extends all the way down to the coast, it may be difficult for NEVINA to calculate the field boundaries.
This can be because the river network sometimes stops a little before the coast. In those cases, place the point a little
further up the river so that it meets the river network.

• If there are obvious errors in the river network, e.g. a river network is not drawn continuously through a body of water and
stops in the water. The calculation will then stop where the river network stops. Send

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an email with information about the error via the feedback button in NEVINA, so that this can be corrected
up.

The tools for editing the catchment area appear under "Edit Rainfall Area" when the catchment area has been generated.

The desired mode is activated by clicking on one of the options.

• Add a polygon: Click and drag on the map to draw a polygon. Release the mouse button to
end the polygon. The recorded geometry is added to the catchment area.

• Subtract a polygon: Click and drag on the map to draw a polygon. Release the mouse button to
to end the polygon. Recorded geometry is subtracted from the catchment area.

• Edit Breakpoints: Click and drag on breakpoints in the catchment area to adjust the line.

Original
field boundary

Offset
breakpoint
t

NOTE: If the field boundaries are changed, some field parameters will be calculated incorrectly or not calculated at all.
This applies in particular to effective sea percentage, river length and river gradients. If parts of

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If the catchment area is removed so that the field boundaries break a river course, river length and river gradients will not
be calculated.

When you are satisfied with the field boundaries, click on the next menu item.

Generate Field Parameters

Click on "Generate field values" to start the calculations.

The processing information in the lower left corner shows the status of the calculations. This usually takes between 5 - 15
minutes. If there are many calculations being performed at the same time, you will be placed in a queue.
Please be patient and wait your turn. If you restart the process, you will be placed last in the queue.

The report with the calculated field parameters will be opened when the calculation is complete (see figure below). It is
possible to change some field parameters (white fields) if necessary. For example, if you see that the effective sea
percentage is incorrect, it is possible to enter the correct value so that the low tide indices are calculated based on the
correct values. If a field parameter is changed, this will be marked in the PDF file with a 1 next to the field parameter.

A climate factor (used in RFFA-2018) of 0%, 20% or 40% must also be selected to generate field parameters. A climate
surcharge is applied in some areas, because future climates will contribute to an increase in flooding in some areas of the
country. You can read more about this under the section "more about flood values" or you can read more and find out which
surcharge is recommended in different places here https://publikasjoner.nve.no/rapport/2020/rapport2020_10.pdf

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White fields can

edited

Select climate factor

Changed field parameter,

marked with a 1

If the field boundaries have changed significantly or some field parameters have not been calculated, a yellow
triangle with an exclamation mark will appear next to field parameters that have not been calculated correctly.
The parameter value is then automatically set to -999, and you must change the value manually to later calculate
all low water indices and flood values. By hovering the mouse pointer over the triangle, you will get some
additional information about the parameter that has not been calculated.

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If a field is changed,

it is marked with a yellow

triangle with an exclamation mark.
Information is available by
hovering the mouse pointer over
the triangle.

It is rare to get a completely correct minimum altitude as it is difficult to see the exact altitude on the map.
If there are small differences from the specified data (if the intake point is specified in advance) then it will
not affect the other results significantly. If there are large differences then it may give a different area than
what is correct, and it may be necessary to do the calculations again.

Click "Continue" when you have checked the values and want to proceed with the calculations.

Generate Indexes
Low water indices and flood values are generated based on regression equations consisting of field and
climate parameters. This is described in more detail in Engeland et al. (2008), Glad et al. (2015), Engeland
et al. (2020) and Beldring et al. (2022). The values calculated must be expected to have a large degree of
uncertainty. The results are therefore only intended to be a starting point for further analysis.

There is now a new option where you can enter your own flood measurements.

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When you check "I want to enter my own flood measurements", this window will appear.

Here you can enter your own measurements. If you need more or fewer rows, click "Add row" or "Delete row".
When you enter measurements, "Median flood (day)" and "Mean flood (culmination)" will be calculated. The values
entered are used to update the index floods in the formulae RFFA-2018 (day) and RFFA-NIFS (culmination). The
largest observed annual flood for each of the years for the catchment area must be entered.

To calculate flood indices as inflow to the lowest lake/reservoir, tick "I want to calculate inflow flood to reservoir".
When calculating inflow flood, the expected effect of the lowest reservoir/lake is removed. This means that the
field parameters effective sea percentage and field length are calculated without the lowest reservoir/lake, but it
does not take into account any other reservoirs located upstream. Effective sea percentage is calculated for the
total area of the catchment area, but the reservoir/lake area has been changed to "unclassified area".
The parameter is named "Effective Sea – Inflow". The field length is calculated from the inlet to the reservoir/lake
and to the furthest point in the catchment area. The parameter is named "Field length – Inflow".
Inflow flows are often used as input data when routing through reservoirs.

Then click on "Generate Indexes". The report window will open when the calculation has been run. The window
contains three tabs, one for Low Water Indexes and two for flood values, NIFS Flood Values and RFFA2018 Flood
Values. Low water indices are given in il/s/km2 and flood values in m3 /s. The flood values are given with a 95%
confidence interval.

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It is possible to change field parameters and then generate indices/flood values again. New values will then be calculated
based on the changed field parameters. For an explanation of the abbreviations used when copying the data and for all
parameters presented in NEVINA, see Appendix 1.

Click "Continue" to export to shape or pdf.

More about flood values

NIFS Flood values are calculated using a formula that has been developed for catchments under approximately 50 km2
and applies to peak floods. Field parameters included in the formula are the area, the effective sea percentage and the
normal runoff (l/sÿkm2 ). The validity of the formula is strictly limited to the parameter intervals that are included in the
analysis basis for the regression equations. These intervals are as follows:

Area: 0.2 – 53 km2

Normal runoff: 9 – 163 l/s·km2

Effective sea percentage: 0 – 21%

This does not mean that the formula cannot be used beyond these intervals, but rather that the uncertainty may be greater
at the outer edges and beyond these. The formula was developed for natural unregulated catchments, and is consequently
less suitable for calculations in urban and/or regulated areas.
For a more detailed description of the formula, please refer to Stenius and Glad (2015).

RFFA-2018 is recommended for use on fields over 60 km2 For more information about RFFA-2018 Flood Values, please
refer to Engeland et al. (2020).

According to Lawrence (2016), floods are expected to increase in size by the year 2100 due to a changing climate. It is
recommended that all small catchments (catchment area less than 100km2 ) receive a climate premium in flood values of
at least 20%. Research is ongoing to determine climate premiums for

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momentary floods in small catchments. Until the results from these projects are available, a climate surcharge of at least
1.2 for daily average floods and 1.4 for peak floods in small and fast catchments is recommended.

Export to Shape
If you want to save the catchment area as a shape file for use in another GIS tool, click "Export to Shape".

When the export process is complete, a link to the download file will appear. By clicking on the link, the data will be
downloaded as a zip file.

NB - If you download the wrong shape file, you can try clearing the browser cache (Ctrl + F5) and re-running the calculation.

Export to PDF
To get the data and a map section of the catchment area, click "Export to PDF" and "Create report for ..." Here you can
select reports for catchment areas, low water indices and flood indices, and now also for flood indices with your own
measurements. By clicking on one of the four options, the report will be downloaded in a new tab.
Examples and explanations of the reports that are generated can be seen in the attachments.

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Find water flow index stations

Under the menu "Find water flow index stations" you can find current comparison stations for a catchment area. The
measuring stations shown in the map are the same as those used in Engeland et al. (2008), Glad et al. (2015),
Engelang et al. (2020), Lawrence (2016) and Beldring et al. (2023). This is not a complete station network, but a
selection of measuring stations that have been used in the preparation of regional regression equations for low water
indices and flood calculations, as well as climate change studies and the runoff map.

By checking "Show water flow index stations", water flow stations will appear on the map. Press "Select from map"
and select the measuring stations you are interested in by entering points that define a polygon by pressing the left
mouse button with the mouse. Selected measuring stations will appear in a table with five tabs where certain field
parameters, low tide, flood - RFFA2018, Flood - NIFS and Climate are shown. This can be downloaded as a PDF,
respectively low tide and flood. It is also possible to download the information as a Shape file for use in GIS tools.

(You can also show water flow stations under the map layer list. These are now in a new blue color so you can see
the difference between them.)

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Low water indices and flood values in NIFS were calculated in 2007/2008 and 2013/2014, respectively. Such
calculations are "fresh", and the basic data and results may change due to new data, changed water flow curves or
choices in the analysis.

The values are therefore only intended as a preliminary study, before analyses are carried out again on
updated water flow series.

Rainfall-runoff model
The rainfall-runoff model simulates runoff for a catchment area. Model parameters are adapted to the catchment
area based on field parameters that have been generated in NEVINA. The purpose of the model is to convert a
rainfall pattern to water flow, i.e. flood, and should provide the best possible dynamic description of the flood pattern
without the number of model parameters becoming too large (Midttømme et al. 2011). To run the model, rainfall can be
obtained from the Meteorological Institute. A calibration of the model against observed water flow can be done if
there is a water flow station in the watercourse. IVF curves can be downloaded from eKlima or the Climate Service
Center and extreme precipitation can be ordered from MET.

In the rainfall-runoff model, you can click on the circles with question marks to get information about the parameters
in the model. These can be changed as needed and desired. If the parameters are changed, the model must be
recalibrated.

The result of the model simulation will represent an unregulated flood course for the catchment area.
For more information about the rainfall-runoff model, see Guide to flood calculations (NVE guide no. 1/2022) or
Andersen et al. (1983).

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Map layer list

In the layer list you can choose what to show on the map. There are many different layers such
as water flow stations, REGINE unit, etc., see example on the left. If a layer is grayed out, it cannot be
shown on the map. When you have zoomed in sufficiently, it will be possible to activate the layer.

References
Andersen, JH, Hjukse, T., Roald, L., Sælthun, NR (1982): Hydrological model for flood calculations.
NVE Report 2-1983.

Beldring, S., Engeland, K., Holmqvist, E., Pedersen, AI, Ruan, G., Veie, CA, Cabrol, J. (2022):
Runoff map for Norway 1991-2020. NVE Report no. 36/2022

Engeland, K., Glad, P., Hamududu, BH, Li, H., Reitan, T., Stenius, SM (2020): Local and regional
flood frequency analysis. NVE Report no. 10/2020.

Engeland, K., Hisdal, H., Orthe, NK, Petersen-Øverleir & A., Voksø, A. (2008): Low water map for
Norway. NVE Assignment report A no. 5-2008.

Glad, P., Reitan, T. and Stenius, S. (2015): National formulae for flood calculations in small catchments.
NVE Report 13-2015.

Midttømme, GH, Hisdal, H., Holmqvist, E., Nøtsund, Ø., Pettersson, LE, and Sivertsgård R. (2011):
Guidelines for flood calculations. NVE Guidelines no. 04-2011.

Lawrence, D. (2016): Climate change and future floods in Norway. NVE Report 81-2016.

NVE (2022): Guide to flood calculations. NVE guide no. 1/2022.

Stenius, S. and Glad, PA (2015): Guide for flood calculations in small fields. NVE Report 7-2015.

Voksø, A. (2024): NVE's river network – from idea to nationwide dataset. NVE Report 6-2024.

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Attachment

Appendix 1: Tables of explanations and definitions of parameters calculated in NEVINA.

Table 1. Water flow parameters calculated in NEVINA.

Parameters Abbreviation Unit Explanation

Middle runoff (1961- QN l/s/km2 Specific runoff calculated from NVE's runoff map for the period
1990) (mm/year) 1961-1990. Source: Beldring et al. (2002)

Mean runoff (1991- QN l/s/km2 Specific runoff calculated from NVE's runoff map for the period
2020) (mm/year) 1991-2020. Source: Beldring et al. (2022)

Uncertainty in the medium- % Simplified estimate of the uncertainty in the mean runoff from the runoff
runoff 1991-2020 map for a catchment area. The uncertainty interval indicates the
standard deviation of the calculated mean runoff (1991-
2020). Source: Beldring et al. (2022).

Normal low water flow - l/s/km2 Calculated by first sorting each year's water flow values
(daily means) in an unregulated series from largest to smallest. From the
sorted annual series, water flow number 350 is removed. For each year
in the observation series, water flow number 350 is removed in this
way. These water flows form a new series that is again sorted.
Ordinary low water flow is then the lowest value in this series
after the lowest third of the observations have been removed.

In NEVINA, normal low water flow is estimated by regression against field

parameters.

-
5th percentile l/s/km2 The water flow that is below 5% of the time in a
observation period. This parameter is estimated in NEVINA using
regression equations against field parameters. 5th
percentiles are calculated for the entire year, summer season
(1/5-30/9) and winter season (1/10-30/4).

Base flow -
l/s/km2 The inflow coming from groundwater.

BFI - -
Proportion of total inflow coming from groundwater (0 –
1).

Index flood (QM): QM l/s/km2 Median annual maximum flood (RFFA-2018, daily average)
Median flood

Index flood (QM): QM l/s/km2 Average annual maximum flood (RFFA-NIFS, culmination)
Middle flood

QT/QM QT/QM -
The relationship between T-year flood and mean/median flood
(flood frequency factor)

Flood uncertainty (97.5%) - m3 /s The upper limit of estimated flood values with 95% confidence
interval

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-
Flood uncertainty (2.5%) m3 /s The lower limit of estimated flood values with 95% confidence interval

- %
Air conditioning surcharge Expected increase in flood values due to the effects of climate
change until the end of the century with high emissions of greenhouse gases.

Culmination factor Qmom/Qday - Ratio between culmination flood (instantaneous flood) and daily average flood,
Qmom/Qdøgn.

Table 2. Climate parameters presented in NEVINA.

Parameter Unit Explanation

-
Climate region Norway is divided into 8 different regions (South, East, West, Central, North,
Bre-sør, Bre-nord and Finnmark) which determine which regression equations
are used to calculate Low Tide Indices.

Annual precipitation mm Average annual precipitation. Precipitation from the Meteorological Institute as
average values for the period 1961-1990. Retrieved from a grid with a resolution of 1x1
km. Source: MET

Summer precipitation mm Average precipitation in the summer season (1/5-30/9), 1961-1990. Source:
MET

Winter precipitation mm Average precipitation in the winter season (1/10-30/4), 1961-1990. Source:
MET

Precipitation June mm Average precipitation in June, 1961-1990. Source: MET

Precipitation July mm Average precipitation in July, 1961-1990. Source: MET

Rain and snowmelt in May mm Average precipitation in May, 1961-1990. Source: SeNorge v2.0

Rain and snowmelt in June mm Average precipitation in June, 1961-1990. Source: SeNorge v2.0

Rain and snowmelt annually 4d mm Average annual 4-day precipitation, 1961-1990. Source: SeNorge v2.0

Rain and snowmelt mm Average precipitation in November, 1961-1990. Source: SeNorge v2.0
November

Annual temperature °C Average temperature over the entire year, 1961-1990. Source: SeNorge v2.0

Summer temperature °C Average temperature during the summer season (1/5-30/9), 1961-1990.
Source: SeNorge v2.0

Winter temperature °C Average temperature during the winter season (1/10-30/4), 1961-1990.
Source: SeNorge v2.0

Temperature February °C Average temperature in February, 1961-1990. Source: SeNorge v2.0

Temperature March °C Average temperature in March, 1961-1990. Source: SeNorge v2.0

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Temperature July °C Average temperature in July, 1961-1990. Source: SeNorge v2.0

Temperature August °C Average temperature in August, 1961-1990. Source: SeNorge v2.0

Precipitation (corrected) mm Average annual precipitation. Corrected precipitation taken from the runoff map
1991-2020. Source: Beldring et al. (2022)

Evaporation mm Estimated mean annual evaporation 1991-2020. Source: Beldring et al. (2022)

Table 3. Field parameters calculated in NEVINA.

Parameters Abbreviations Unit Explanation

Area A km2 Area of the catchment area.

Efficient sea ASE % The area of lakes in a catchment area is weighted depending on the proportion
of the area that drains to the sea. The weights are summed for all lakes.

River length Electricity

km The length from the outlet to the top of the river.

Total river length km Total length of all rivers within the field.
ETL,net

River gradient EG m/km The slope of the river calculated as the difference in elevation between the top and
outlet points divided by the river length.

River gradient1085 EG,1085 m/km The same as river gradient but the bottom 10 and those
The top 15 percent have been removed.

Field length FL
km The length from the outlet of the catchment area to the furthest point on the
field boundary.

- oh
Slope The slope of the field.

DT Characteristic size for the catchment area and says something about the total
Drainage density km-1
length of rivers compared to area (ELT /A).

Hmin Hmin m. Lowest elevation in the catchment area.

Hn Hn above sea level n% of the catchment area is lower than the specified altitude.
Source: Hydra II

Hmax Hmax m. Highest point in the catchment area.

Glacier
ABR % Proportion of glaciers in the field.

Farmland AJORD % Proportion of cultivated land in the field.

Bog AMYR % Proportion of bog in the field.

Clay ALEIRE % Proportion of clay in the field. Loose material map from NGU (Loose material types

41 and 43). Source: NGU

Sea ASJO % Proportion of sea in the field. II

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Forest ASHWOOD % Proportion of forest in the field.

Snow Mountain ASF % Percentage of low mountains above the tree line.

Urban AU % Proportion of urban areas in the field.

Unclassified area ARREST % Proportion of unclassified area in the field.

Efficient sea – inflow ASE-T % The area of lakes in a catchment area is weighted depending on the proportion
of the area that drains to the sea. The effective lake percentage is calculated
for the total area of the catchment area, but the reservoir
/lake area has been changed to "unclassified area".

Field length - inlet FL-T km The length from the inlet to the reservoir/lake to the furthest point on the field
boundary.

Appendix 2: PDF of catchment parameters

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Appendix 3: PDF of data from the runoff map

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Appendix 4: PDF of low tide indices

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Appendix 5: PDF of regional flood calculation

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