It’s nearly 70 years since Marshall and Palmer (1948) published their paper on the distribution of raindrops with size and the empirical scaling relationship equating the measured radar reflectivity, Z with the rainfall rate, R: Z= aRb. Since then, the relationship has been widely used to generate rainfall estimates from radar. With the roll-out of dual-polarisation to the UK radar network nearing completion, the Met Office is now making use of this new technology to improve radar rainfall estimates and supplement the Marshall–Palmer relationship.
After serving on the UK Inter-Agency Committee and its predecessor NERC Steering Committee since 1988, Professor Chris Collier provides a retrospective look on radar hydrology. “Radar has been used as an important tool for meteorological research, and, more recently, in operational forecasting over the last sixty years or so. However, its use in hydrology has only flowered over about half this period. In the UK the instigation of radar hydrology can arguably be traced back to the Dee Weather Radar Project (DWRP), which began in 1966, and then was referred to in 1974 as the Dee Weather Radar and Hydrology Project.
The Inter-Agency Committee on the Hydrological Use of Weather Radar held its 60th meeting on 4 November 2014. A major focus of the meeting was to plan the 2013-2015 Session Report which is due to be published towards the end of 2015. The Committee-led workshop on merging radar and raingauge data was reviewed and the Committee agreed that its 2015-17 Community Plan should “monitor” and “encourage” research and operational implementation in this area to address the gaps and realise the opportunities identified.
There are some unique challenges with the operational use of radar in Scotland:
- The radar coverage is inconsistent across the country, particularly in Dumfries and Galloway and the Highlands, including Inverness
- The mountainous nature of the landscape means that the radar might not be able to “see” in all directions as the beam is blocked by hills
- The post processing algorithms do not fully account for orographic enhancement of rainfall over high ground
- Radar doesn’t perform very well when it is snowing due to the different reflective properties of snow compared to rain
However, radar remains a vital tool in flood forecasting as Linda Speight reports on floodforecastingservice.net
The RainGain International Workshop on Urban Pluvial Flood Modelling took place on 6th October 2014 at the Met Office Headquarters in Exeter, UK. Ninety people attended, including practitioners and academics from a number of universities, water companies, engineering consultants, local authorities, and regional and national environmental and meteorological agencies from across Europe. Report by Susana Ochoa-Rodriguez (Imperial College London).
Weather Radar and Hydrology 2011 provided a forum for the exchange of experiences and ideas on the use of weather radar in hydrology with a particular emphasis on user applications for flood forecasting and water management. The full set of papers from the symposium, held at the University of Exeter in April 2011, are available through the International Association of Hydrological Sciences.
Hydrological use of weather radar continues to grow across the water industry. Initiatives across many research and industry groups are aimed at maximising the value of the UK radar network and various networks of raingauges to provide the best possible spatial estimates of rainfall. This workshop provided a forum for industry leads and experts to share techniques and experiences in merging radar and raingauge data. A principle aim was to recognise any UK-wide strategic opportunities whilst recognising differing user requirements.
Providing the best possible spatial representation of rainfall is vital to support hydrological applications, whether for urban drainage management or flood forecasting. This principle applies at various spatial and temporal scales for rainfall estimates in both gridded and catchment-average form.
The Inter-Agency Committee on the Hydrological Use of Weather Radar is the only national body in the United Kingdom bringing together operational agencies and research bodies with the common purpose of advancing the use of weather radar in hydrology, especially in support of flood management. It operates under the auspices of stakeholder organisations and with support from the Natural Environment Research Council (NERC). We promote and encourage research in this area.