Abstract
Uncertainties in rainfall have increased in the recent past exacerbating climate risks which are projected to be higher in semiarid environments. This study investigates the associated features of rainfall such as rain onset, cessation, length of the rain season (LRS), and dry spell frequency (DSF) as part of climate risk management in Botswana. Their trends were analysed using Mann-Kendall test statistic and Sen’s Slope estimator. The rainfall-evapotranspiration relationships were used in formulating the rain onset and cessation criteria. To understand some of the complexities arising from such uncertainties, artificial neural network (ANN) is used to predict onset and cessation of rain. Results reveal higher coefficients of variation in onset dates as compared to cessation of rain. Pandamatenga experiences the earliest onset on 28th of November while Tsabong the latest on 14th of January. Likewise, earliest cessation is observed at Tshane on 22nd of February and the latest on 30th of March at Shakawe. The shortest LRS of 45 days is registered at Tsabong whereas the northern locations show LRS greater than 100 days. Stations across the country experience strong negative correlation between onset and LRS of − 0.9. DSF shows increasing trends in 50% of the stations but only significant at Mahalapye, Pandamatenga, and Shakawe. Combining the LRS criteria and DSF, Kasane, Pandamatenga, and Shakawe were identified to be suitable for rainfed agriculture in Botswana especially for short to medium maturing cereal varieties. Predictions of onset and cessation indicate the possibility of delayed onset by 2–5 weeks in the next 5 years. Information generated from this study could help Botswana in climate risk management in the context of rainfed farming.
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Acknowledgments
The authors appreciate support provided by the Mobility for Engineering Graduates in Africa (METEGA) and Carnegie Cooperation of New York through RUFORUM in form of research funds. We also acknowledge the Department of Meteorological Services (DMS) of Botswana for their valuable meteorological data. Special gratitude to Gulu University which granted the first author study leave to enable him focus on this study. The authors are also grateful to the anonymous reviewers for their valuable comments on the manuscript.
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Byakatonda, J., Parida, B.P., Kenabatho, P.K. et al. Prediction of onset and cessation of austral summer rainfall and dry spell frequency analysis in semiarid Botswana. Theor Appl Climatol 135, 101–117 (2019). https://doi.org/10.1007/s00704-017-2358-4
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DOI: https://doi.org/10.1007/s00704-017-2358-4