Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Titre : Spatial aspects of rainfall and the water budget in semi-arid West Africa.

Auteur : Flitcroft, I D.

Université de soutenance : University of Reading

Grade : Doctor of Philosophy (PhD) 1989

Résumé
The water balance of the semi-arid tropics is investigated with particular reference to its spatial availability over areas of a few hundred square kilometres. Results from an experiment carried out during two wet seasons in the Republic of Niger, using a grid of raingauges and neutron probe access tubes over an area of 144 km2, are used to derive results which show the spatial variations of rainfall, soil moisture, evaporation and surface runoff. A new method to estimate area average rainfall over hundreds of square kilometres from a limited number of gauges is derived from kriging theory. The method gives unbiased, least squares estimates of area falls from a linear, weighted combination of the gauge values and the mean rain per rain day. Calculation of the weights requires that the average spatial correlation structure (correlogram) of the rainfall field is known. Also required is an estimate of the mean rain per rain day for the appropriate season. The best estimates of area falls from a gauge are substantially less than the gauge values when the gauge reading is much above the mean rain per rain day. The differences increase when larger areas are considered and when the gauge is separated from the centre of the area. These cases are studied and further generalised to the situation where the separation of the gauge from the centre of the area is only known in a stochastic sense. This application of the method is used to assess the accuracy of gauge readings as ground truth for satellite based estimates of rainfall. The spatial variation of soil moisture is examined on the same scale as the rainfall in a region of stabilised sand dunes. Variation of components of the water budget are found to be larger than variations of rainfall due to significant local variations in surface runoff and evaporation on scales of tens of metres. A model applied to measurement of soil moisture provides information on the variation of the water budget over the area.

Mots clés : Rainfall in semi-arid tropics Meteorology Climatology Geography Meteorology Geography

Présentation : EThOS (UK)

Proquest Dissertations & Theses