A GIS Based Water Balance Study of Africa - Physical Land Resources

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29Table 3.1 Summary of annual minimum, maximum and mean values of PrecipitationPrecipitation (mm)SeasonMinimum Maximum AverageWinter 0 1606 317Summer 0 2633 354Annual 0 3667 6713.3.5 POTENTIAL EVAPOTRANSPIRATION (PET)PET is a measure of the ability of the atmosphere to remove water through the process ofevaporation and transpiration. The FAO introduced the definition of PET as theevapotranspiration of a reference crop under optimal conditions, having the characteristics ofwell watered grass with an assumed height of 12 centimeters, a fixed surface resistance of 70seconds per meter and an albedo of 0.23 (Allen et al. 1998). Among several equations to estimatePET, the FAO application of the Penman-Monteith equation (Allen et al. 1998), is currentlywidely considered as a standard method (Walter et al. 2000). Data on referenceevapotranspiration used for this study is available from the Consortium for Spatial Information(CGIAR-CSI) Global Aridity Index (Global-Aridity) and Global Potential Evapotranspiration(Global-PET) Climate Database. The dataset is a representation of monthly average Potentialevapotranspiration estimates covering the period 1950-2000. It is distributed through theCGIAR-CSI GeoPortal (http://www.csi.cgiar.org). Fig 3.9 and Table 3.2 respectively show theaverage annual potential evapotranspiration map and some statistical values.
30° 30° 30° 10° 10° 30° 50° 70°10° 10°30(mm)Pet_annual0 - 100100 - 500500 - 10001000 - 15001500 - 20002000 - 3000No DataNWE3000 0 3000 6000 MilesS10° 10°Fig 3.9: Map of annual average Potential Evapotranspiration of Africa30° 30°10° 10° 30° 50° 70°Table 3.2 Summary of PET values on a seasonal and annual base30°PET (mm)SeasonMinimum Maximum AverageWinter 223 1285 874Summer 202 1463 971Annual 449 2383 1845
Page 5 and 6: 4LIST OF FIGURESFigure 1.1: Flowcha
Page 7 and 8: 6SUMMARYNkezeah, A.J., 2010. A GIS
Page 9 and 10: 81.2. OBJECTIVE OF THE RESEARCHThe
Page 11 and 12: 101.4. ORGANISATION OF THE REPORTTh
Page 15: 14independent water balances. Thus
Page 18 and 19: 17c is the vegetation coefficient [
Page 20 and 21: 19GROUNDWATER RECHARGERecharge refe
Page 22 and 23: 21CHAPTER 3MATERIALS AND METHODS3.1
Page 24 and 25: 233.3.1. TOPOGRAPHY AND SLOPEThe to
Page 26 and 27: 25textural types were dominated by
Page 29: 283.3.4 PRECIPITATION INPUT DATAThe
Page 33 and 34: 32CHAPTER 4RESULTS AND DISCUSSION4.
Page 35 and 36: 30° 30° 10° 10° 30° 50° 30°3
Page 37 and 38: 30° 30° 10° 10° 30° 50° 30°3
Page 39 and 40: Figure 4.5: Annual average Runoff M
Page 41 and 42: 30° 30° 10° 10° 30° 50° 30°4
Page 43 and 44: 30° 30° 10° 10° 30° 50° 30°4
Page 45 and 46: 70°(mm)444.2.6. TRANSPIRATIONTrans
Page 47 and 48: 46areas of Cental-West Africa. The
Page 49 and 50: 48variations of these components ar
Page 51 and 52: 50CHAPTER 5CONCLUSION AND RECOMMEND
Page 53 and 54: 52REFERENCESAlemaw, B.F., and Chaok
Page 55 and 56: 54Stone, D.B., Moomaw, C.L., Davis,

A GIS Based Water Balance Study of Africa - Physical Land Resources

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