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

The present study investigate the impacts of warms Southwestern Indian Ocean (SWIO) tropical storms (TSs) and cyclones (TCs) on rainfall pattern and vegetation productivity indices in the cost area of Tanzania using field surveys, remote sensing and statistical modelling tools. The result revealed that over the last 34 December to March (DJFM) and November to May (NM) TCs seasons, 74 (during DJFM) and 90 (during NM) TCs and 154 (during DJFM) and 184 (during NM) TSs were 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 TCs the highest SST anomaly (-0.5 TO +2.5oCo was observed. Seasonal northward and southward oscillating environmental wind shear (Evws) varied between 0 to 15ms-1 (at 00 to 150s), while the zone mean wind (umst) ranging between -5 and -15ms-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 compare to northern coastal area of Tanzania. The seasonal (DJFM and NM) TCs/TSs statistical modelling showed strong correlations) p≤0.02) between the observed and the cross- validated TCs/ TSs (0.52< r < 0.84). The assessment of the model skills revealed 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.