The Southern African region suffers from a severe lack of the hydrological data upon which most water resource planning, management and operations rely. The 18th SANCIAHS National Hydrology Symposium, held at the University of KwaZulu-Natal in Durban from 14 to 16 September 2016, provided the Water Research Commission (WRC) with an opportunity to launch one of its significant studies that will help hydrology practitioners in solving rainfall data challenges.
The SANCIAHS biennial conference is a forum that showcases the best hydrology research and practice in South Africa. It is also a platform that helps to showcase the WRC-funded hydrology studies.
A WRC study entitled, ’New methods of infilling Southern African rain-gauge records enhanced by annual, monthly and daily precipitation estimates tagged with uncertainty’ was amongst the first topical items presented during the opening plenary session of the conference, which was attended by leading members of Southern Africa’s hydrology community-of-practice, as well as postgraduate students from various universities in South Africa.
Mr Wandile Nomquphu, the research manager leading water resource assessment and planning related studies at the WRC said,”The new product is key to the hydrological practitioners, policy makers and decision-makers as rainfall is the main input in hydrological assessments, water resource modelling, and other information generation, and helps to guide decision making such as civil construction, travel, agriculture and disaster management.”
The newly-developed mathematical and statistical tool will help hydrology practitioners to use maps of real estimates over quaternary catchments in the Southern African region, that indicate daily, monthly and annual rainfall records, to make their rainfall estimates more meaningful. This technique was developed and tested successfully on daily records in most parts of the Southern African region. Leading the development of these mathematical tools were Geoff Pegram and Scott Sinclair of Pegram and Associates and András Bárdossy from Universität Stuttgart.
The study will assist hydrological practitioners with the infilling of gauge data and interpolation over space, using a tool which has been developed and tested against other existing methods and found to be a meaningful improvement.
This WRC study is an update of the MAP (mean annual precipitation) maps of observed and repaired rainfall records over South Africa. It also offers mean monthly precipitation (MMP) maps crafted from observed and infilled data.
Over the years, hydrologists have expressed serious concern over the dwindling rain gauge network. “Without a reasonably dense gauge network in the wetter regions, there is no meaningful way of ground referencing remotely-sensed rainfall using satellites and radar, whose rainfall measurements we know to be biased”, said Pegram while presenting the details of the new tool.
Prof Pegram further noted: ”The sad truth is that we are working with a dying resource. The SAWS raingauge network currently has approximately 1 200 live gauges – about the same number as were recorded daily by weather stations and volunteers in the 1930s – down from a peak of near 3 000 in the 1970s. Unless these are augmented soon, to allow us to infill the records backwards in time using the methods devised herein, there will be insufficient gauged readings of actual rainfall at ground level against which to calibrate and adjust radar and satellite estimates of rainfall.”
Pegram further commented, “We point out that the sudden drop off by approximately 500 gauges in the year 2000 is an artefact of the data-set. Prior to 2000 the database contained gauges from organizations other than SAWS (South African Weather Services); however, only SAWS gauges are in the database after 2000. Nevertheless, there is still a very real and concerning drop-off in the number of gauges.”
The report presented to the WRC by Pegram, Sinclair and Bárdossy recommended that the WRC and other concerned research-orientated bodies with a strong voice should prevail upon the large institutions currently managing gauge networks such as SAWS, ARC (Agricultural Research Council) and DWS (Department of Water and Sanitation) to immediately deploy a complementary set of rain gauges, so that the average density over the wetter part of the country is increased to an inter-gauge spacing of closer than 25 km. If the gauges are sparser than 35 km apart then there is a very small spatial correlation link between them at the daily scale, and they might as well be treated as independent, stand-alone gauges.
Over the past few years the WRC has been sponsoring students that present outstanding hydrology research papers and posters at SANCIAHS conferences. This year the WRC awarded five student prizes, three of which were won by students involved in WRC-funded research.
Exciting news at the conference was the announcement that the next International Association of Hydrological Sciences (IAHS) Conference is coming to Africa, only its second visit to the continent in the history of the IAHS. IAHS 2017 will be held in Port Elizabeth from 9-14 July 2017.
WRC Report No. 2241/1/15 entitled New methods of infilling Southern African rain gauge records enhanced by annual, monthly and daily precipitation estimates tagged with uncertainty can be downloaded free of charge from the WRC Knowledge Hub www.wrc.org.za.