Climate Change and Dew and Rain Evolution in Semi-arid South-Western Madagascar between 1991 and 2033 (Extrapolated)

In the context of global warming and increasing scarcity of fresh water resources, it becomes siginificant to evaluate the contribution and evolution of non-rainfall waters such as dew. This study therefore evaluates the relative dew and rain contributions in three sites in south-western of Madagascar (Ifaty, Toliara and Andremba), a semi-arid region which suffers of a strong water deficit. The studied period is 1991 – 2023, with extrapolation to 2033. Dew is calculated from meteo data using a well-established energy model. The extrapolation uses an artificial neural network approach. While the yearly dew/rain ratio remains modest (3-4%) dew forms regularly (2-3 days in average between events), in contrast to rain (10-15 days). The evolutions of dew and rain are similar, with an increase from 1991 to 2000, a decrease up to 2018 and a further increase till 2033. These oscillations follow the Indian Ocean dipole variations and should be influenced by the climate change. Dew contribution to the water balance is important during the dry season (Apr.-Oct.), up to 80%. Dew therefore appears to be a reliable and sustainable resource for plants, small animals and population, especially during droughts.