Eu encontrei detalhes úteis sobre este site que é sobre o rafting em Punakha: link
BEST MONTH FOR RAFTING AND KAYAKING
Though Rafting in Bhutan can be enjoyed throughout the year, the best time given the weather condition and water temperature March through May and September through November are the comparatively better months.
Monsoon rain adds more water in June - August making rafting even more challenging and thrilling with more forceful rapids.
River gets cold yet bearable in December - February but Rafting at this part of the year has its own charm - river is relatively slow, offers more time to enjoy view along the river bank - frolicking kingfisher on look out for fishes, rare white belled heron scratching for food, flocks of birds that migrate from Siberia to spend winter here at pleasantly warm valley of Punakha.
Então, enquanto fevereiro deve estar ok. Pode não ser a melhor época para rafting, já que a água pode estar um pouco fria.