Abstract
During the passage of tropical cyclone (TC) Batsirai (2022), the mountainous regions of Réunion Island and the eastern part of Madagascar experienced devastating floods. TC Batsirai passed north of Réunion Island (minimum distance of ∼ 210 km) before making landfall along the eastern coast of Madagascar. Using a non-hydrostatic research atmospheric model at 2 km resolution, we conducted a control simulation with realistic topography (CTL) and three flattened-terrain experiments (FLT
all
, FLT
mdg
, and FLT
reu
) to assess orographic effects. Relative to the flattened-terrain experiments, the presence of terrain increased localized rainfall by 96 % (2906 mm) over Réunion Island (CTL versus FLT
reu
) and 82 % (830 mm) over Madagascar (CTL versus FLT
all
), respectively. Over Réunion Island, orographically uplifted low-level moisture sustained 60 h of heavy rainfall (10 mm h
−1
), with a peak of 96 mm h
−1
, although the cyclone's intensity and track were minimally affected. In Madagascar, terrain not only intensified precipitation (19 h of heavy rainfall with a peak intensity of 92.8 mm h
−1
) but also altered the TC trajectory, delaying landfall by about 12 h and shifting it approximately 30 km south. These findings highlight the critical role of complex orography in shaping localized rainfall and TC behaviour in the southwest Indian Ocean.