Impacts of south western Indian ocean tropical cyclones and storms on the rainfall pattern and vegetation productivity over Tanzania

The present-day study investigated the impacts of warmed Southwestern Indian Ocean (SWIO) tropical storms (TSs) and cyclones (TCs) on rainfall pattern and vegetation productivity indices in the coast area of Tanzania using field surveys, remote sensing and statistical modeling tools. The results revealed that over the last 34 December to March (DJFM) and November to May (NM) TCs season, 74 (during DJFM) and90 (during NM) TCs and 154 (during DJFM) and 184 and90 (during NM) TCs was observed. Higher sea surface temperature (SST) anomaly (0.4 to 0.9oC) and higher area averaged SST (27.5 to 28.75oC) over SWIO occurred during September to November (SON) and December to May, while for the case study of TCs the highest SST anomaly (-0.5 to +2.5oC) was observed. Seasonal northward and southward oscillating environmental wind shear (Evws) varies between 0 to 15 ms-1 (at 0o to 15oS) while the zonal mean wind (Umst) ranging between -5 and -15 ms-1 were observed during DJFM. The contribution of TCs/TSs to DJFM rainfall was very significant, with highest rainfall influence over the hinterlands and southern parts of Tanzania compared to the northern coastal areas of Tanzania. The seasonal (DJFM) and NM) TCs/TSs statistical modeling showed strong correlation (p≤0.02) between the observed and the cross-validated TCs/TSs (0.52<r<0.84). the assessment of the model skills revealed highest skill (76%) for the NM TCs model. NDVI change over Rufiji during TCs (Besija and Fobane) was reduced and enhanced by <-0.19 and > 0.31, respectively. Moreover, EVI and NDVI results were consistent with the patterns shown by analysis of rainfall data.