About

Background

Rainfall map SEPA work in partnership with the Met Office to oversee a network of volunteer rainfall observers spread across Scotland. In March 2016 the observers numbered 136. These volunteer rainfall observers contribute to the national rainfall network, the aim of which is to provide a sufficient coverage of ‘spot’ measurements to accurately capture the distribution of rainfall across Scotland.

The existing model for rainfall observers is very long established and for example, a few current observers have been observing since the 1960’s and another observer in Ayrshire is continuing a family tradition of rainfall observing that started in 1898. The rainfall archive is used by government bodies, industry and researchers for a number of functions such as managing Scotland’s water resource, planning sustainable economic development, climate research and developing measures for flood management. The Met Office produces products such as rainfall distributions maps (opposite) that aid the evaluation of data. Rainfall distribution maps can be found on the Met Office website.

A new development in 2016 – rainfall observing with SEPA is now open to all

The established network of observers have to meet strict criteria before their data is accepted into the national rainfall archive. For example, observations have to be taken at 9am GMT each day and the gauge must be situated in a location with acceptable exposure conditions. These criteria have restricted the uptake of interested members of the public in the past.

To overcome this restriction, SEPA is developing a new rainfall archive, referred to as the B-standard, to accommodate observers who can’t meet the criteria of the A-standard. Although B-standard data will not be entered in the national archive, it can be entered, archived and viewed in this website and it will be accessible for downloading and viewing by anybody who is interested in the data. The data will also be automatically sent to the Met Office WOW database for use in a number of real time applications and will be of value to SEPA for understanding flood risk.

A new development in 2016 – web data entry and data visualisation for all rainfall observers

The new data entry portal and data display facilities on this website are open to any person, school or organisation that observes rainfall or who want to start rainfall observing. Simply register and then start entering your data. For A-standard observers (definition provided above) the primary method of sending rainfall observations remains unchanged; daily observations are recorded on the supplied cards and then posted monthly to SEPA before being transferred to the Met Office for archiving in the National Rainfall Archive.

This online service should be viewed as a complementary option for A-standard observers submitting daily records and there are a number of benefits to be had from using the service. The instant transfer of data from the online service will allow SEPA and the Met office to have faster access to your data and will expand the potential data use to a number of ‘real time’ applications such as computer model calibration and extreme weather reporting.

It also provides observers with a useful platform to visualise their own data archive and facilitates a comparison with data from other observations around Scotland. To clarify the position on data submission for A-standard observers, this online data entry portal does not replace filling in and posting the rainfall card. This practice should be continued as before. Once the online system ‘beds in’, SEPA may consider it as an alternative option for A-standard observers to submit observations.

How to start rainfall observing

Picture2If you are able to observe rainfall on a daily basis at 9am GMT (10am in British summer time) and have a secure garden or plot of land that is not overshadowed by trees or structures, you may meet the criteria of a A-standard observer and your data can contribute to the national rainfall archive.

Enquiries can be emailed to SEPA at Rainfall@sepa.org.uk using the subject title ‘I want to start observing rainfall’. If your site meets the necessary criteria, SEPA will supply you with a UK standard Mark 2 raingauge, a glass measure, a supply of rainfall cards and instructions. Standard mark 2 gauges are either made from copper or stainless steel to the dimensions shown opposite.

Raingauges suitable for SEPA’s B-standard rainfall observer can be purchased from numerous suppliers that can be found on the web. A key feature is to ensure the gauge has a capacity to record an equivalent rainfall depth of at least 100mm. The plastic Remex Rain Gauge shown below is an example of suitable design that is relatively cheap to buy and easy to install. SEPA currently only supplies plastic Remex Rain Gauges to B-standard observers who are participating in a school project that SEPA is trialling in 2016. Subject to the success of the school trial in 2016 and the availability of funding, there is potential for SEPA to supply gauges more widely to B-standard observers in the future.

Guidance on where and how to install a rain gauge

Example rainfall mapIdeally, the rain gauge should be positioned in an open area such as a lawn away from trees or other tall structures that could otherwise overshadow the gauge. As a guide, the gauge should be no closer than twice the height of surrounding high objects. For example, a gauge would ideally be located at least 10m away from a 5m high structure such as a tree or house. Lawns or areas with gravel provide ideal surroundings for a raingauge. Ground conditions to avoid are long undergrowth that could choke the gauge or concrete where the raindrops falling around the gauge could splash into the gauge and provide an overestimation. Children or dogs can both compromise a rainfall accumulation and may influence where best to locate the gauge.

A UK standard Mark 2 gauge used by A-Standard observers must be positioned in the ground so that the top of the gauge is 30cm from the ground surface and other gauge types should be installed in a fashion that emulates this where possible. It is also important to make sure the gauge is level. This can be checked by placing a spirit level across the rim of the gauge.

It is accepted that the ideal conditions described above may not be possible for many observers and positioning the gauge in the most pragmatic position out of harm’s way will be fine and will provide interesting data for use in the B-standards archive. For example, if your garden has limited open space and is heavily used by the family, then mounting the gauge at the top of a garden post might be the best option.

When and how to observe rainfall

The Met Office SPOT-ON Observers Guide (Precipitation v5 03/13) provides detailed guidance on making rainfall observations for A-standard observers. The majority of the guidance will also be of interest to B-standards observers. The only information that won’t be transferable are instructions that specifically relate to the operation of a UK standard Mark 2 gauge and the requirement to assign observations to the hydrometric day at GMT time.

B-standard observers simply record the date and time on their watch when the observation was taken.  A rainfall observation should be made as near to 9am GMT as possible each day. Please note that 9am GMT is 10am during British summer time. If you cannot observer at or near to 9am GMT each day, then other times are acceptable for the B-Standard archive, although it is preferable for the observations to be taken roughly at the same time each day.  

The key steps for all observers are:

  1. Remove the upper rim and funnel from the body of the gauge and either lift out the measuring tube if this is built into the gauge design, or empty the contents of the collection bottle into a separate measuring tube.
  2. Hold the measuring tube vertically up to eye level and read the water level in mm from the graduations on the measuring tube. The observation should be recorded to the nearest 10th of mm if the scale of the measuring cylinder permits. Although some gauge designs may not have 0.1mm graduations, it might still be possible to estimate to the nearest 10th of a mm. For example, the reading below would be recorded as 22.3mm.measuring tube
  3. Note down the observed rainfall reading along with the date and time of observation. It is also useful to note down other relevant comments such as ‘snow’ or ‘some water spilled by mistake’.
  4. A-standard observers should fill in the rainfall card as instructed. They can also enter their data in the web data entry portal. A point to note for A-standard observers is that the web system automatically backdates the rainfall to the hydrometric day and to GMT time.
  5. All B-standard observers should enter their data in the web data entry portal. This should ideally be done on a daily basis as close to the observation as possible.

If you are unable to make an observation each day, such as at weekends, holidays or periods of sickness, then the ideal solution is to try and have a ‘deputy’ who can stand in. If a willing deputy is not available, then an accumulated total over the period can be submitted if the gauge capacity hasn’t been exceeded.

Daily rainfall accumulations and the concept of the hydrological day

Ideally the observation will be taken as near to 9am GMT as your personal circumstance allows. The observation will represent accumulated rainfall since the last observation, which will usually have been around 9am GMT on the previous day. This 24 hour period from 9am to 9am is called the Hydrological Day and this is the standard timeframe to record daily rainfall. The concept of the Hydrological Day was established to accommodate the fact that it’s not practical for observers to make observations at midnight! This website assigns the rainfall accumulation against the date of the observation, which is at the end of the 24 hour period. This is contrary to the convention where the accumulation is assigned to the date at the start of the 24 hour period. If you want to assign the accumulation to the conventional date that corresponds with the Hydrological Day, the figures can simply be exported from this website and backdated by one day in a spreadsheet such as excel. This conversion will be done automatically by SEPA and the Met Office behind the scene before the data is stored in their databases.

An explanation of the time periods used in the map

  • Today’s Observation – Representing recorded rainfall in the 24 hour period preceding 9am today
  • Two most recent observations – Representing recorded rainfall in the 48 hour preceding 9am today
  • Three most recent observations – Representing recorded rainfall in the 72 hour period preceding 9am today

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