Inter-annual rainfall variability and droughts occurrence during sowing and mid-season rice farming calendar in the forest belt of Nigeria

Abstract

This study examined the trends of rainfall and the intensity of drought during sowing season and mid-season of rice farming calendar in the rainforest belt of Nigeria using data spanning 52 years (1961-2012) for five synoptic weather stations. The trends were investigated using simple linear regression and second order polynomial, while the significance of the trends was evaluated using Pearson's Product Moment Correlation. The drought intensities during the two seasons were computed as percentage derivations from the mean. Rainfall during the sowing season witnessed upward trends in Ondo, Port Harcourt, Benin and Calabar at annual rates of 0.450 mm, 1.005 mm, 3.581 mm and 2.144mm respectively with statistical significance in Benin (0.398, p<0.01) and Calabar (0.295, p< 0.05) while Warri witnessed insignificant decline at an annual rate of -0.525 mm. Rainfall in the midseason witnessed insignificant increase in Warri, Ondo, Port Harcourt and Calabar at annual rates of 0.096 mm, 0.118 mm, 0.172 mm and 0.016 mm respectively. Rain-days declined insignificantly in all the stations during the sowing season with the exception of Port Harcourt which witnessed significant decrease (-0.268, p<0.05) while mid-season rain-days declined in all the stations but only significantly in Warri (-0.301, p<0.05) and Ondo (-0.366, p<0.01). The droughts intensities varied mainly between slight and moderate intensities during the two seasons with pockets of severe and disastrous intensities in Port Harcourt and Warri. It was concluded that rainfall trends was upward in all the stations with the exception of Warri and Benin with declining trends during the sowing season and mid-season respectively while rain-days were decreasing in the two seasons coupled with droughts mainly of slight and moderate intensities. The study suggested an early rainfall forecast and timely irrigation for optimal rice production in the region.

Keywords: Rainfall, rain-days, drought, rice, rainforest belt, Nigeria