The Sahel makes up a transition zone between the extremely dry desert in the north and the sub-humid climate in the south. The vegetation growth in Sahel rangelands is driven by the highly seasonal rainfalls brought by the convective storms of the West African monsoon that reaches the Sahel in rainy season between June and October with a peak rainfall in September. Mean annual rainfall varies from 150 to 600 mm. In adaptation to the regular rainfall seasonality, solar radiation, temperature and air humidity, the herbaceous vegetation is largely dominated by short cycle annual plants, associated with more or less scattered woody plants among which deciduous dominate. Both resources are grazed by livestock in communal rangelands. Annual herbaceous germinate with the first rains, sometimes between May and July, depending on years and locations. Their growth starts slowly for a couple of weeks during which grasses seedlings establish their rooting system and tillers. The growing dynamic of the herbaceous vegetation during the rainy season is, however, not well understood. During the rainy season of 2017 from 24 June to 10 October, the weekly biomass growth of three rangelands plots in Northern Senegal was assessed. The biomass of herbaceous plants was measured using a destructive approach. The first rain in 2017 was quite early (end of June). However, the rain stopped after one month and the second rain wasn't until August. This unexpected rainfall shortage resulted in a cessation of vegetation growth. During this period, the grass did not grow and stayed in early phenological stages.