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Temporary densification of a rain gauge network to gain knowledge about orographic rain enhancement on the Island of Tahiti - French Polynesia
  • Lydie Sichoix,
  • Lionel Benoit
Lydie Sichoix
University of French Polynesia - GEPASUD Lab

Corresponding Author:[email protected]

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Lionel Benoit
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In tropical islands, interactions between atmospheric circulation and island topography generate complex patterns of orographic rain. Despite recent advances, numerical weather models are still challenged by orographic rain enhancement, in particular because the physical processes responsible for rain generation over tropical islands vary at spatial and temporal scales that are not yet fully resolved in these numerical models. A large part of our knowledge about tropical island precipitation patterns therefore relies on rain observations. However, observing strongly variable rain fields is not an easy task. It requires instruments able to capture rain fluctuations at fine temporal (1 min - 1h) and spatial (100 m - 1 km) scales. To reach these requirements, state of the art rain observation methods rely on remotely sensed weather radar images and in-situ rain gauge measurements, or solely on rain gauge observations in the many areas like Tahiti where radar observations are not available (mainly due to financial cost). In this study we investigate to which extent a temporary densification of the rain monitoring network of Tahiti (lon = 149.5°W, lat = 17.6°S, area = 1042 km2, max altitude = 2241 m) can help us gaining new insights about orographic rain enhancement on a high altitude tropical island with complex topography. To this end, 10 low-cost but high resolution rain gauges have been deployed for one year (Aug 2020 - Aug 2021) in addition to the long term network of around 20 rain gauges operated by the Direction de l’Equipement Tahiti (Groupement d’Etudes et de Gestion du Domaine Public) and the French Weather Service (Météo France Polynésie). Based on this new dataset, we first characterize the space-time patterns of orographic rain enhancement over Tahiti at an unprecedented resolution, and link these emerging patterns to local features of the atmospheric circulation. Next, we investigate the added value of our temporary network for purposes of rain mapping (i.e., spatial interpolation of point observations). Finally, we explore the benefits and limitations of temporary rain gauge network densification for orographic rain enhancement observation.