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North-West University (2019)

Characterising rainfall using a high density rain gauge network in the Mooi River catchment

Hauptfleisch, Reinhardt Gustav

Titre : Characterising rainfall using a high density rain gauge network in the Mooi River catchment

Auteur : Hauptfleisch, Reinhardt Gustav

Université de soutenance : North-West University

Grade : Master of Science in Geography and Environmental Management 2019

Résumé
Understanding and measuring rainfall is of critical importance for agriculture, disaster mitigation, drought relief and water resource management practises. With the advancement of technology, methods of earth observation have greatly improved. Satellite and weather radar can provide high resolution real-time measurements of rainfall. These instruments, however, need calibration and ground validation which can be accomplished with rain gauges. Therefore, the need to better understand and characterise spatial variability of rainfall using a rain gauge network is of great importance. The objectives of this study was, firstly, to evaluate the use syphon tipping bucket rain gauges to accurately characterise rainfall, secondly characterise the spatial variability of rainfall with a high density rain gauge network and finally to optimise the high density rain gauge network. A dense network of 15 syphon tipping bucket rain gauges spread out over the 3294 km2 Mooi River catchment in the North West and Gauteng provinces of South Africa, was used to characterise rainfall for the 2014/2015 rainfall season. Methods to evaluate the use of syphon tipping bucket rain gauges to determine the spatial variability of rainfall and to optimise a rain gauge network are described. Because tipping bucket rain gauges can produce misleading reports, this study suggests easily programmable diagnostic check that can be used in an operational environment to identify and eliminate any errors associated with rain gauge data. These checks were tested on the data obtained from the rain gauges in the Mooi River catchment and a variety of confirmed errors were found. The spatial variability of rainfall over the catchment was defined for rainfall accumulation periods ranging from 1 min to 14 days. It was evident that rainfall exhibits high spatial variability at shorter accumulation periods between 1 and 30 min with very poor correlation between gauges even at the shortest separation distances of 8 km. For longer accumulation periods, the daily scale for example, there is a good correlation between all the gauges of the network, even at 80 km separation distances. Therefore, the current rain gauge network in the Mooi River catchment is dense enough to provide information of rainfall at a daily resolution, but when high resolution rainfall data at a finer time scales are needed (e.g. 5-minute accumulations), the network is not dense enough. In order to accurately estimate the spatial variability of rainfall, a dense network of instruments is required, which will typically entail large installation and operational costs.

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