Innovative trend analysis of long-term spatial-temporal rainfall patterns over Botswana: Implications for water resources management

Botswana, Southern Africa The study explores the utility of newer trend analysis methods, such as the innovative trend analysis method (ITA), to identify trends in seasonal and annual rainfall data using long-term rainfall data in Botswana. The results were compared with those from traditional methods (TMs), such as the Mann-Kendall (MK) test and Sen’s slope (SS) methods. The utility of the ITA method has not been explored in Botswana and Southern Africa. Furthermore, rainfall variability is evaluated using the precipitation concentration index (PCI) method. The results reveal that most rainfall data show trends when using the ITA method than the TMs for both seasonal rainfall (December-February, DJF), (March-May, MAM), (September-November, SON) and annual rainfall data. Significant trends were detected as follows: The ITA (TMs) returned 81.3 (0) % for annual rainfall, 43.8 (0) % for DJF, 75.0 (12.5) % for MAM, and 75.1 (0) % for SON rainfall, respectively, indicating the superiority of ITA over the TM methods, which is consistent with the literature. For example, the TMs did not reveal any significant increase in annual rainfall in the study area, while the ITA methods identified 19 % of the stations with increased annual rainfall. Furthermore, the TMs did not reveal any decline in annual rainfall compared to 63 % from the ITA, and the pattern is also evident in the seasonal rainfall. The ITA results, therefore, show that rainfall in Botswana has changed significantly from what was previously reported from the TMs. Specifically, most stations showing increased (decreased) rainfall are from the Kgalagadi (southern/northern) regions. The negative changes may adversely affect the availability and sustainability of water resources in these regions, and the effects of climate change could further worsen these. • Long-term rainfalll dataset allowed for a comprehensive rainfall analysis in Botswana. • The innovative trend analysis (ITA) detected more rainfall trends compared to the traditional methods. • The western and dry Kgalagadi region has experienced increased rainfall than previously reported. • Rainfall has significantly declined in the eastern and northern regions, which are dominated by dams and tourism. • Rainfall variability is high and considered irregular based on the precipitation concentration index (PCI).