Some aspects of the spatial variation of rainfall over a small instrumented catchment
Richardson, E. J.
PublisherUniversity of Exeter
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The central theme of this research project was the investigation of the spatial variation of rainfall over a small area. The rainfall was measured over a 369 ha basin in East Devon by a network of forty-five inexpensive gauges installed at 30.5 cm. The accuracy of the rain gauges was evaluated and the systematic gauge error amounted to 6%. The gauge sampling error, or random error, of rainfall measurement was found to be approximately 4%. The rain gauge network revealed patterns of rainfall that varied considerably from storm event to storm event. The spatial variability of rainfall of the storms as expressed by the coefficient of variation exceeded 4.5% on all occasions and 10% on eighteen occasions. The variability was not simply due to systematic or random errors, even though the amounts of rainfall involved tended to be low; the range in rainfall (decile range) was no more than 4.0 mm for forty-two storm events. The storm rainfall amounts were related to various meteorological and topographical factors. The storms of convectional origin had a greater spatial variability than storms experiencing no convection and more clearly-defined rainfall gradients. Storms of Tropical air mass origin had a lower variability than storms of Arctic or Polar origin whilst Arctic storms had the greatest variability for low rainfall amounts. There was a tendency for storm rainfall to increase downwind particularly with the wind from a southerly direction, probably as a result of interaction with the topography. The degree of explanation of the spatial variation of storm rainfall afforded by the topographical variables of altitude, exposure and vegetation influence was low.