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University of Wales, Swansea (1986)

Evaporation and soil moisture depletion in the Gedaref Region of east-central Sudan

Musa, S.B

Titre : Evaporation and soil moisture depletion in the Gedaref Region of east-central Sudan

Auteur : Musa, S.B

Université de soutenance : University of Wales, Swansea

Grade :Doctor of Philosophy (PhD) 1986

This thesis aims to study evaporation, the depletion of soil moisture during the rainy season and to test the applicability of various evaporation estimation methods in the hot semi-arid conditions of the Gedaref Region of the Sudan (annual rainfall between 300mm and 700mm). Evaporation variables and some climatic factors were measured in the field in a rainfed area, 40KM east of Gedaref Town, from July 30th to December 31st 1983. The methods employed in the measurement of evaporation include a Class A pan, a Piche atmometer, and 20 weighable lysimeters for the assessment of actual and potential rates of bare soil evaporation and evapotranspiration. The four evaporation variables (Pan, Piche, PE and potential bare soil evaporation) increased in magnitude from August towards December. Monthly mean Piche evaporation, for example, increased from 9.7 mm/day in August to 13.5 mm/day in December. This increase of evaporation towards December, despite the decrease in solar radiation, is attributed to the effects of advected heat in the dry months (October to December). Established evaporation estimation methods tested for applicability (which include the Penman Formula, the Thornthwaite method and the Blaney-Criddle method) proved to be inadequate in the Gedaref Region. The original Penman (1948) equation, for example, greatly under-estimated measured PE with mean monthly deviations as high as 5.41 mm/day. New regression models were therefore developed and the Penman Formula was revised in a search for better estimation methods. The four regression models developed were found to approximate measured PE values very closely such that the highest mean monthly deviation was only 0.38 mm/day. The newly revised Penman Formula gave good results too, with the highest mean monthly deviation being 0.89 mm/day. In addition to these five estimation equations developed, the 10-day averages of the wet bulb depression in degrees Celsius (without the application of any correction factor) also closely approximated the measured PE with the highest mean monthly deviation being only 0.89 mm/day.


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