Linkage Between the Frequency of Tropical Cyclones in the Southwestern Indian Ocean to the Rainfall in Kenya During the March to May Season

Abstract

The economic activities in Kenya are heavily reliant on rainfall, particularly during the primary rainy season which occurs from March to May. This study investigates the relationship between the extended rainy season (March–April–May) and the frequency of tropical cyclones in the Southwestern Indian Ocean (SWIO). It examines monthly tropical cyclone frequency in the SWIO from November 1979 to April 2019 as well as MAM rainfall data from 1980 to 2019. To investigate the distribution of MAM rains in Kenya, time series and spatial maps were analyzed. The statistical significance was evaluated using the Student test, the trend's seasonal significance was ascertained using the Mann-Kendall trend test, and the percentage deviation from the norm was measured using coefficients of variation. Subsequently, the Taylor diagram was employed to conduct correlation analysis. The coefficient of variation calculation reveals that arid and semiarid lands (ASALs) are exceptionally susceptible to their significant fluctuation throughout the March–April–May season, which is characterized by unreliable signals across all zones. Based on Mann-Kendall analysis, the seasonal rainfall trend is insignificant in eleven out of the twelve homogenous zones. There has been a significant change in the trend of Zone 2 (Moyale Station). Tropical storm occurrences in the Southwest Indian Ocean shown a slight inverse correlation with long-term seasonal precipitation in the majority of areas. The analysis of long-term MAM rainfall, in comparison to the MAM seasons of 2006 and 2019, reveals that the 2019 MAM season exhibits a negative deviation across all zones due to a significant occurrence of cyclones. In contrast, the 2006 MAM season exhibits a positive deviation from the average as a result of more rainfall in most uniform zones and a lower number of documented tropical cyclones. An important examination demonstrated a strong correlation between tropical cyclones and seven out of the twelve homogeneous zones. Tropical storm occurrences in the southern Indian Ocean adversely affect Kenya's long rain season. Further investigation is required to ascertain the impact of tropical cyclone intensities on the daily, weekly, and decadal patterns of rainfall and its distribution during the season.