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Abstract

Dew deposition is an ecologically important phenomenon in many coastal drylands, but its measurement remains difficult. We report the construction and field-testing of a sturdy device to digitally determine dew deposition during night and early morning hours. Balance readings were compared with dew deposition measurements taken by alternative methods: a plastic sheet of 2 m × 3 m laid out on sandy ground, a plastic sheet of 1 m × 2 m laid out at 1 m height on a wooden surface, and a plastic sheet laid out at 1 m height on a metallic surface. Daily dew deposition rates on our device ranged from 0.055 to 0.192 mm between months with maxima reaching 0.479 mm. Dewfall amounted to 58.4 mm and represented 19% of annual rainfall after the whole observation period of 18 months. Correlation coefficients between the different measuring methods amounted to r = 0.71 (balance – plastic sheet on the ground), r = 0.84 (balance – 1 m high plastic sheet on wooden surface), r = 0.82 (balance – 1 m high plastic sheet on metal surface) and r = 0.99 (1 m high plastic sheet on wooden surface – 1m high plastic sheet on metal surface). Our results suggest that in coastal south-western Madagascar dewfall plays a role in the annual water balance, but its ecological significance remains to be investigated.