Agriculture is under the full scale influence of climate in which rainfall forms the dominant component mainly because of its effect on crop production in countries whose economy is largely depends on agriculture. The spatial and temporal distribution of rainfall is, thus, the most important determinant of crop production levels from year to year as a result of its erratic and unreliable nature. It can gave the influence of El Nino Southern Oscillation event and other global oceanic and atmospheric phenomena play a great role in climate variation on inter annual and/or inter seasonal scales. The book also insights the importance of the knowledge of water requirement for a given area in order to understand the actual and potential benefits of the area. This belief, however, that there exists sufficient knowledge in determining the water requirement of any crop during all growth stages at any location. The information generated from this study will have valuable contribution in advising the farmers, extension agents, agronomists, and policy makers, other groups involved in crop production and as base line for future study.