Fine-scale rainfall over New Caledonia under climate change
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Fine‑scale rainfall over New Caledonia under climate change Cyril Dutheil1,2,3 · C. Menkes2 · M. Lengaigne4 · J. Vialard4 · A. Peltier5 · M. Bador6 · X. Petit1 Received: 24 October 2019 / Accepted: 22 September 2020 © The Author(s) 2020
Abstract Global climate models projections indicate no clear future rainfall changes over the Southwestern Pacific islands in response to anthropogenic forcing. Yet, these models have low (~ 100–200 km) spatial resolution and suffer from large systematic biases, such as the trademark “double ITCZ”. Here, 4 km-resolution simulations were used with a nested regional atmospheric model, which resolves the New Caledonian mountainous topography. The resulting present-day rainfall amount, spatial structure, seasonal cycle, and extremes compare much better with observations than at 20 km resolution. We applied projected changes from global climate models under the RCP8.5 scenario at the boundaries, following an approach that corrects both their present-day and projected sea surface temperature biases. Unlike climate models, our refined projections reveal an 18% decrease in annual mean rainfall over New Caledonia by 2080–2100, especially on the leeward side of the island (up to 30%) and during the hot season (that accounts for ~ 80% of the rainfall decrease). This drying is robust without bias correction, and much stronger than at ~ 20 km resolution. It is mainly driven by circulation changes. A weather regime classification further demonstrates that ~ 80% of the hot season drying relates to a strong anti-cyclonic and air subsidence anomalies centred on the north of NC, which reduces moisture convergence over the archipelago. The frequency and intensity of extreme precipitation events is also reduced by ~ 20% by 2080–2100. This drastic projected drying would have dramatic impacts on water resources and terrestrial ecosystems, pleading for carefully-planned adaptation policies for New Caledonia. Keywords Climate change · Downscaling · Regional climate models · Precipitation · New caledonia
1 Introduction
* Cyril Dutheil cyril.dutheil@io‑warnemuende.de 1
IRD (Institut de Recherche Pour Le Développement)‑Sorbonne Universités (UPMC, Université Paris 06)‑CNRS‑MNHN‑IPSL, LOCEAN Laboratory, IRD Nouméa BP A5, 98848 Nouméa cedex, New Caledonia
2
IRD, ENTROPIE (UMR 9220), BP A5, 98848 Nouméa cedex, New Caledonia
3
Present Address: Present address: Department of Physical Oceanography and Instrumentation, Leibniz Institute for Baltic Sea Research Warnemünde, Rostock, Germany
4
LOCEAN-IPSL, Sorbonne Universités, UPMC, Université Paris 06, CNRS-IRD-MNHN, Paris, France
5
Météo France, Nouméa, New Caledonia
6
Climate Change Research Centre and ARC Centre of Excellence for Climate Extremes, School of BEES, University of New South Wales, Sydney, NSW, Australia
The New Caledonia (NC) archipelago is located in the Southwest Pacific about 1500 km to the east of Australia and to the north of New Zealand (Fig. 1a). While the average annual rainfall is high (~ 5 mm.day−1), water is reg
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