Climate change has adversely affected agricultural productivity leading to decline in food production. The influence of climate change on crops and livestock persists despite irrigation, improved plant and animal hybrids. The continued dependence of agricultural production on climatic factors and the relative dependence of human existence on agricultural products create the need for a comprehensive consideration of the relationship between climate and crop production. This study measured the relationship between annual maize/yam yield as dependent variable and seasonal rainfall as independent variables in four states in Nigeria. It has been proven in the past that yearly rainfall value has no influence on annual crop yield, but seasonal or monthly rainfall does. There is a positive and significant relationship between summed up rainfalls of June/July/August and annual maize yields for the thirty-five years under study. The bi-monthly rainfall values did not influence a major part of total annual maize yield, as it records weak relationship with annual maize yield. On the other hand, bi-monthly rainfall values (May/June and July/August) have positive and significant relationship with annual yam yield. The first quarter- March/April/May rainfall values for each of the states have a positive and significant relationship with annual yam yield. This implies that the rainfall value for this quarter is very essential for annual yam yield for each of the states.