Abstract

The rainfall amount and number of rainy days determines the length of growing season, which equally determines the types of crops to be planted in a particular region. This study analyzed the pattern of rainfall in Samaru Zaria, Kaduna State, Northern part of Nigeria from 1961-2017 using data collected from the Institute for Agricultural Research Samaru, Zaria. The result from this research reveals that an inverse relationship exists between the amount of rainfall and the rainy days. Hence, the higher the rainfall amount the lower the rainy days and vice versa. This is attributed to the current change in climate which increases the intensity of annual rainfall but shortens the duration of the rainy days. The equations generated for amount of rainfall pattern was (y= 3.162x - 5270.9) and number of rainy days was obtained as (y = -0.172x + 417.85). As expected, the months of November to March had the lowest mean rainy days (MRDs) <1 day. As a recurrent pattern for the period of study, the onset of appreciable rainy days was observed in the month of April and the number of rainy days increased steadily to reach its peak in August and a sharp decline in October. From the obtained data, the onset and cessation of rainfall could be predicted to fall towards the end of April and September respectively.

1. Introduction

Nigeria is home to over 170 million people who constantly depend mainly on food production obtained from rain-fed agricultural cropping systems. As the population of the country increases the demand for food and energy also increases ¹. This in turn contributes to pronounced global warming effects which is a major factor influencing the world climatic conditions. One major effect of global warming is the variability in rainfall and climate patterns over several biomes of the earth ².

Shifts in rainfall patterns may lead to an overall drying trend in some ecological regions, and to increased rainfall in other regions, including Africa ³. Rainfall is likely to become increasingly aggregated, with wet years projected to become wetter and dry years drier, while the frequency of extreme wet and dry years is expected to increase. On an annual (seasonal) time scale, the number of rainfall events is likely to decrease, while rainfall intensity is likely to increase due to greater atmospheric moisture retention with increased air temperatures. Potential manifestations of increased seasonal variability include more extreme hot days during the growing season, a shift in rainfall toward heavier but less frequent rainfall events, and longer periods between rains-which, when coupled with increased rates of evapotranspiration under warmer temperatures, which could negatively affect crop growth ⁴

This work aimed at examining the changing pattern of rainfall amount and rainy days in Samaru, Kaduna State using rainfall amount and rainy days as a prediction parameter and their effect on crop production with the specific objective of studying the trend of rainfall amount and rainy days in Samaru for 57 years and to examine the pattern of rainy days variation per decade from 1961-2017.

2. Materials and Method

The study area is located in Zaria in the Northern Guinea Savanna zone of Nigeria. Samaru is located at 07° 38E 11° 11N and an altitude of 686m above sea level. The soils found in the area are largely Alfisols and Ultisols ⁵. Zaria lies within a region, which has a tropical savanna climate with distinct wet and dry seasons. Adequate rainfall amount is received in Zaria area during the rain fed cropping periods of June to September ^{5, 6}. The Mean annual rainfall of the study area is reported to be 1015.9 mm with an onset and cessation of rainfall as 21^st May and 7^th October respectively. The mean maximum air temperature is 29.7°C while the mean minimum air temperature is 13.3°C ^{7, 8}. The study area has a coefficient variation (CV) of 15.2 ⁸. Fifty-seven (57) years meteorological rainfall data for Samaru, Kaduna state corresponding to periods of 1961-2017 was used in this study which was sourced from the archives of the Institute for Agricultural Research Meteorological station Ahmadu Bello University Zaria, Kaduna.

The parameters analyzed included the rainy days and the total amount of rainfall throughout the study period. The rainy days were categorized into decades; 1960s, 1970s, 1980s, 1990s, 2000s and 2010s as shown in Table 1. The MRD was obtained as a benchmark to determine the varying pattern of rainy days over the study period. MRD were obtained by dividing the sum of the monthly rainy days in a decade by the number of years in question. Conversely, the total monthly rain amount was obtained by summation of monthly rainfall amount recorded in a month in the IAR weather station.

3. Result and Discussions

From analysis of rainfall and rainy days data as observed in Figure 1 and Figure 2, the average number of the rainy days for individual months in the years and the mean rainy days were deduced. The mean monthly rainy days were grouped into 6 periods which included the 1960s, 1970s, 1980s, 1990s, 2000s and the 2010s.

The mean rainy days for the analyzed periods differed significantly between the months. As expected, the months of November to March had the lowest MRDs (<1 day). Throughout the study years, the onset of appreciable rainy days was observed in the month of April with a mean MRD of 3.5 days. The number of days gradually increased with its peak in August. From the obtained data the onset and cessation of rainfall could be predicted to fall towards the end of April and late September from where it the number of days of rainfall begins to reduce drastically to only about 3.8 days per month in October.

Our finding clearly showed that the month of August had the highest number of rainy days across all the periods, however a decrease from 19.0 days in the 1960s to 16.0s in the 2010s was observed. This may be due to the current challenges with climate change which increases the intensity of annual rainfall but shortens the duration of the rainy days.

On the other hand, the increasing equation of y= 3.162x + 5270.9 of rainfall and a converse decreasing equation of y= -0.172x + 417.85 in the number of rainy days over the study years indicates that the number of rainy days might continue to decrease in the coming years as the rainfall amount and intensity increases ⁹. These fluctuating trends implies adverse effect on food security, and agriculture due to factors such as; flooding, droughts, stronger soil erosion, short length of growing season for crops, leaching of nutrients in the soil, crop damage, crop failure, and poor seedling emergence.

4. Conclusion and Recommendations

Historical rainfall and rainy days data obtained from the Meteorological unit of the Institute for Agricultural Research, Ahmadu Bello University Zaria were analyzed for the trends and characteristics of the two parameters. It can be inferred that rainfall amount in the study area is predicted to continually increase with fewer rainy days. This irregular pattern observed in rainfall would pose threat to food security, crop production and the length of growing season in the study area. To mitigate these challenges, further detailed research should be conducted on climate change in other regions of the country and more research Institute for monitoring greenhouse gases should come to limelight. Also, detailed meteorological data and records should be made electronic and accessible in all parts of the country as well as enforcing and implementation of Government policies against illegal deforestation, burning of fossil fuel and unnecessary generation of greenhouse gases.

Acknowledgments

My specific thanks goes to my lovely family members; the Lawals and Ajilas for their unconditional love and support. I appreciate my dedicated supervisor and the great Institute for Agricultural Research Samaru, for the opportunity to contribute my quota to agricultural research. To all my friends, I am grateful for your contributions and courage that sustained me throughout the duration of this study.

References