Variations in onset, cessation of the long rainfall (MAM) season and it’s impact on maize yields in Iganga district, Uganda

Abstract

Variations in rainfall patterns has an impact on rainfall dependent sectors especially those in agricultural production. Knowledge on variations in rainfall patterns and its impact on yields is vital in agriculture. The specific objectives of this study were on the assessment of rainfall and maize trends, variations in the onset and cessation of rainfall in the March, April, May (MAM) season and the effect of start and end of the long rains on crop yield product (maize) in Iganga district. To achieve the objectives, gridded rainfall point data (secondary) from 1990 – 2022 for Iganga district and Annual MAM maize yield data (secondary) from 2013-2022 in Iganga was obtained from Iganga district agricultural office. Climate data tool (CDT) software, which considers the methodology of a Pentad approach of wet days, Evapotranspiration and a regression using Pearson’s correlation coefficient in SPSS, were the methodology employed to achieve the changes in the onset, cessation dates and the correlation between rainfall onset, cessation and maize yields respectively. Trend’s significancy of the MAM rainfall and maize yields were tested using the Mann-Kendall trend test, the P-Value approach and level of significancy. Likewise, onset, cessation, length of the rainfall season significancy on maize yield using P-value approach were further re- evaluated using the Mann-Kendell tau statistic. Results showed an increasing trend in rainfall for March, April, while May was decreasing with P-values 0.64,0.49,0.35, respectively that were not statistically significant yet the MAM long rainfall season showed an increasing trend with a P-value of 0.35 that was statistically insignificant. The MAM maize production (2013-2022) showed an increasing trend in maize yields with a Sens’s slope of 92.863 tons and a significant P-Value (0.043) showing a positive trend over the years. Study findings regarding variations in rainfall onset showed 26th February as the earliest and 8th April as the latest onset date. Rains started 24 times in March which accounted for 75% of total occurrences. 1st May was the earliest date while 26th June was the latest cessation date. The rains ended 21 times in May which accounted for 66% of the total occurrences. The relationship between onset, cessation and maize yields was analyzed using Pearson correlation showed (-0.091 with a P- value of 0.420), (0.188 with a P- value 0.960) respectively, which is a negative (inverse) relationship for onset and a positive relationship for cessation. While Mann-Kendall tau statistical analysis showed onset results (-0737, P-value 0.3293), cessation results (0.1345, P-value 0.0746), length of season results showed (0.1585, P-value 0.0355). The results showed that the time of cessation of the rains and length of the growing season have more effect on maize yields than onset in the study area. UNMA should therefore collaborate with the local farmers and give timely information about when the rains will start and end to avoid food insecurity.