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MAP Rain – New FEH 2013 Rainfall Return Period calculator

FEH is the industry standard used to estimate local flood risk and develop resilient infrastructure.

New service calculates Rainfall Return Period for any location using the FEH 2013 methodology

MAP Rain now includes the updated FEH (Flood Estimation Handbook) 2013 methodology as well as the original FEH99 method. This lets users calculate Return Periods for any location and any date in the past 4 years using the MAP Rain dashboard. These Return Periods are available for both Points and Polygons.

You can use the dashboard to calculate:

  • The depth (mm) and duration (hours) of rainfall that generates the largest Return Period on a particular day
  • The depth (mm) of rain for the location that generates a specific Return period for a specific rainfall duration (hours)
  • Predicted Rainfall Alerts
    MAP Rain can also apply the FEH 2013 methodology to the forecast rainfall so that we can send you e-mail alerts for any significant rain events that may impact flooding hotspots.

    API calls
    We have built two API calls into MAP to let you integrate the FEH 2013 return period calculations directly into your own applications.

    Returns depth (mm), duration (hours) and Return Period for a particular day and location

    Inputs

    Date 17th Sept 2017 (rainy day)
    Location in Long Lat (WGS84) or OS Easting and Northing

    Returns

    Rain Event Start and End Time 14:30 to 16:00
    Duration 1.5 hours
    Max Depth 16.68 mm
    Return Period 1 in 2.45 years

    Returns depth of rain (mm) for a specific duration (hours), return period and location

    Inputs

    Location in Long Lat (WGS84) or OS Easting and Northing
    Duration 5 hours
    Return Period 1 in 20 years

    Returns
    Max Depth 47.72 mm

    Acknowledgement
    FEH Return Periods calculated by Meniscus through use of FEH1999 and FEH2013 DDF model © and Database right NERC (CEH).

    Stewart, E. J.; Jones, D. A.; Svensson, C.; Morris, D. G.; Dempsey, P.; Dent, J. E.; Collier, C. G.; Anderson, C. A.. 2013 Reservoir Safety – Long Return Period Rainfall. Project FD2613 WS 194/2/39 Technical Report (two volumes). Joint Defra/Environment Agency Flood and Coastal Erosion Risk Management R&D Programme.

    MAP Rain – new geometry gives large rural agencies ability to focus on urban areas

    We are pleased to announce the introduction of a new geometry in MAP RAIN that delivers big cost reductions. This is ideal for large rural agencies who want rainfall analytics data for their urban areas.

    A new Multi-Polygon geometry delivers rainfall analytics for just the areas that area of specific interest to you. Before this, we had to provide rainfall and associated data for the whole area of interest.

  • Example: A Lead Flood Authority with a large predominately rural area of say 10,000km2 only wants real time and predictive rainfall analytics and access to FEH data for the urban areas, say 750km2. Previously, we had to provide rainfall data for the whole 10,000 km2 area and then add Polygons within this for specific catchments of interest. With the new Multi-Polygon geometry we can provide the customer with these analytics for JUST the urban areas. This delivers a big reduction in the cost of accessing rainfall analytics information from MAP Rain. I.e.MAP Rain prices are based on 750km2 rather than 10,000km2.
  • Example of multi-polygon area

    To receive a quote for using MAP Rain in your are then please send us a message from the Contact Page

    MAP Rain – new rainfall grid imagery

    We recently updated MAP Rain to display rainfall as an image making it much faster to display new images. Previously we displayed rainfall for each individual 1 km square cell. MAP Rain processes data in km squares using the Ordnance Survey Grid Reference system but the dashboard uses the WGS84 projection. So to produce a suitable image we have to go through several stages.

  • Use the four corners of the visible area of the map and return the min/max Easting and Northings required to fully display the image. We add a small amount to each side to ensure it is covered on the screen.
  • Render an image for these Easting and Northings values from the internal grid that represents the data at the relevant time.
  • Then ‘warp’ this image to change the projection from a flat grid reference to the representation of that grid on the map. This is why the top and bottom of the returned trapezoid are curved and it is wider at the top than the bottom (imagine taking a sheet of paper and placing on a globe). We then display this image on the dashboard.
  • This process allows us to return different ‘zoom’ levels of the image with each having a better resolution. Most other mapping solutions limit the zoom level as they only display the one image for the whole of the UK.

    Areal FEH99 calculation – Return Period calculation for polygons

    As part of our aim of continuing to add complex rainfall analytics into MAP Rain you can now return a FEH99 Return Period for a polygon – this is the Areal FEH99 methodology as set out in the Flood Estimation Handbook.

    How to run

  • From the dashboard click on Rainfall Return Period
  • Set the date you are interested in using the top date selector
  • Select the polygon you are interested in
  • Select the “Get Return Period for Item” option under Rainfall Return Period
  • MAP Rain will then calculate the Return Period and display all the coefficients and results in the map results pane along with a graph of the rainfall intensity for 3 days – includes the previous and the next days.