The rainfall of any area is a rich resource that can be harnessed for a range of purposes. For example, the onset and cessation of rainfall have been studied for various areas of Nigeria for the improvement of rain fed agriculture [1] -[5] . Furthermore, [6] employed rainfall data to explain the effect of deforestation on climate change over the Anambra River Basin. He utilized a 20-year rainfall data to calculate dates of onset, end and duration of the rainy season thus establishing a rainfall pattern that has been altered after the area was deforested to create 5000 hectares of rice fields. Furthermore, rainfall patterns have been studied to ascertain its effect on water supply in some localities. [7] investigated the effects of droughts, rainfall and rural water supply in Northern parts of Nigeria, while [8] utilized rainfall trends of 11 meteorological stations over a period of 34 years (1971-2004) to establish the extent of flooding in Northern Nigeria. While some of these researchers employed trend analysis in their studies, others merely calculated the beginning and end of the rain using various methods, of which the most universal are the walter and ogive. However, ascertaining the rainfall trend only does not reveal a sequence or pattern that must necessarily repeat itself after an interval of time which are used to predict adverse climatic events that may be employed for production and adoption of suitably desired responses. For example cycles and periodicities are utilized in the prediction of the rainfall amounts for any particular year or time which could form the basis for the forecast of extreme climatic conditions in an area such as drought and flooding as well as associated soil and meteorological problems. Forecasts are usually helpful for issuing warnings concerning the incoming extreme events. The failures of researchers either to regularly engage in this type of study or for government to use research findings of such studies for planning are reasons why we are often taken unawares by the often repeat of the events. It is no longer news that every year floods destroy property worth billions of Naira in most urban and rural areas of Nigeria which could have been prevented had people known the years, month or even the day that may likely experience such events based on the amount of expected rainfall. The study of the cycles and periodicities of rainfall in Awka region is one of the attempts to provide the needed information on the forecast of rainfall of the area with a view to employing the knowledge revealed in issuing warning to inhabitants about the likelihood or otherwise of such events. Adherence to such warnings will however help in no small measure to minimize the repeated adverse effects of the events in the area.

The statistical package which calculated the harmonics of our rainfall data for Awka region produced the result on Table 2 and the graph depicting the cycles on Figure 2.

As is usual with the practice 3 dominant cycles are usually selected. These are Harmonic’s 1, 6, and 11. The representative cycles have periodicities of 35, 5.20 and 2.84 years. Their details and presented in Table 3.

It would therefore appear that the dominant cycle of rainfall series of Awka Region and one that explains 26.4% of the variance is that with a periodicity of 35 years. This means that this cycle repeats itself every 35 years and associated with the rainfall amounts of 181.66 mm. When the cycle repeats itself this long, it is a clear analogy to the 35-year normal period which the climatologists use.

Also the second dominant cycle in the area is the one which explains 18.30% of the variance and this could be interpreted to mean that the cycle repeats itself 6 times every 5.20 years which is roughly once every year approximately with an amplitude of 149.62 mm. Finally the third dominant cycle shows that it has a periodicity of

^*Important harmonics. Source: Author’s calculation.

Source: Author’s calculation

11 times in 2.50 years and is translated to mean once in approximately 4 months with the total rainfall amounts (amplitude) of 126.13 mm. What all these mean is that we shall be having 149.62 mm amount about once every year and 126.13 mm once every 4 months. However the amount of 181.66 m is once every 35 years. The graphical presentation of the harmonics and percentage of variance explained could be seen in Figure 2. From that figure it is easily discernible that the 1st, 6th and 11th harmonics are clearly dominant.

Awka region has been known for extreme climatic events of flooding which ravages every part of Awka urban area and outlying regions every rainy season. Although, there are anthropogenic factorsgiven rise to flooding, if one of natural factor which is the rainfall events are well predicted, it would help in no small measure in alleviating the often terrible effects of flooding in the area. [13] tried to identify the causes of flooding in Awka town, but removed the pivotal role of rainfall, but other studies such as those of [14] -[17] , located the primary cause of flooding on rainfall events, in other areas of Nigeria. The historic Sokoto flooding of 2010 and those of Kano and other parts of arid northern parts of Nigeria are all traced to the sudden upsurge of rainfall amounts in the affected areas. Also flooding has led to other problems in Awka region of Nigeria, and one of the major problems is soil erosion. The fact that the upland areas of the region is made up of highly friable sandstones which are susceptible to erosion and characterise by the infamous Agulu-Nanka gully erosion, is an indication of the deleterious effect of rainfall on the landscape. [18] [19] established the paramouncy of rainfall as a factor of soil erosion in our study area.

The use of cycles and periodicities of rainfall to check the problems of flooding and soil erosion is therefore of supreme importance. This is because the result will definitely help to identify the years that are likely to receive large amounts of rainfall which will form the basis upon which warning signals could be sent to the inhabitants of possible flooding. [20] for instance did suggest that the ability to predict the weather conditions always help warn people to relocate from either a flood or erosion prone areas during a manifest wet year.

We have in this study determined through harmonic analysis the cycle of rainfall in Awka region of Nigeria which can surely be used to predict the cycle and periodicities of rainfall in the area with a view to employing the result to inform the inhabitants of impending extreme climatic conditions. Against this background we strongly recommend that the identified cycles in this study be employed for the flood and erosion plans of the area. We identified these two problems because they are the ones that have mostly devastated the area. Also we recommend that similar study should be done in other small regions of the country especially the areas which are experiencing aggressive urbanization. Finally, this result could be used in all the areas with similar rainfall characteristics as Awka region.