Abstract

This paper analyses the trend in rainfall and water balance characteristics of Awka, Nigeria using the monthly rainfall data retrieved from the archives of the Nigeria Meteorological Agency in Lagos from 1976 to 2015. The tools employed for the study are linear regression analysis, cumulative sum (CUSUM) technique, Walter’s cumulative index analysis and Thornthwaite’s method. Rainfall was observed to have declined and generally below the climatological mean in the first decade, while from1988 to early 2000s, rainfall has maintained a steady rise. The length of rainy season has shown significant number of variations, but has recorded a general increase. The rainfall onset and cessation periods were predominantly March/April and October, respectively though significant changes in onset periods has been evident in the last 10 years with 6 out of the 10 having onset occurring in February. This study observed a reduction by one month in the periods of soil moisture utilization and increase by the same amount in the periods of soil moisture recharge. As a consequence, amount of water surplus has increased.  However, this study provides explanation on the current state of rainfall in relation to climatic water budgeting for Awka and as such important for agricultural and water resource planning.

Key words: Cumulative sum technique, water balance components, Walter’s cumulative index analysis, Thornthwaite’s method.