Abstract We present a characterization of the variability of clouds over the southwest Indian Ocean between 2007 and 2010. Cloud occurrence is derived from the DARDAR (raDAR/liDAR) mask, a synergistic product based on Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) and CloudSat measurements. It provides a target classification for hydrometeors. We demonstrate that this product is suitable for studying the vertical, spatial and seasonal cloud distribution in the southwest Indian Ocean. The variability of cloud occurrence increases approaching the tropics: the average maximum amplitude of monthly occurrence is ∼7% between 30°S and 60°S and ∼14% between 10°S and 30°S. The 10–30°S latitudinal band exhibits the largest contrasts: summer (winter) total cloud occurrence is mainly driven by high‐ (low‐) level clouds. The vertical distribution of clouds differs on either side of 55°E and this is related to a land–ocean contrast and to large‐scale influence. In winter, east of 55°E, the maximum of cloud occurrence corresponds to warm and mixed‐phased precipitating clouds associated with the Mascarene High. In summer, west of 55°E, the vertical distribution of cloud occurrence is driven by deep convection associated with the InterTropical Convergence Zone and the Near Equatorial Trough. The vertical distribution of cloud occurrence shows an interannual variability that is related to El Niño events. The influence of other oscillation modes should be further investigated.
We provide here the dataset of the first observatory from the French network of critical zone observatories (OZCAR) located in an insular tropical and volcanic context, integrating a “Tropical Montane Cloud Forest”: The ERORUN-STAFOR observatory. This collaborative observatory is located in the northern part of La Réunion island (Indian Ocean) within the watershed of Rivière des Pluies (45.0 km²) which hosts the TMCF of Plaines des Fougères, one of the best preserved natural habitats in La Réunion Island. Since 2015, the ERORUN-STAFOR monitoring in collaboration with local partners collected a multidisciplinary dataset with a constant improvement of the instrumentation over time. At the watershed scale and in its vicinity, the ERORUN-STAFOR observatory includes 10 measurement stations covering the upstream, midstream and downstream part of the watershed. The stations record a total of 48 different variables through continuous (sensors) or periodic (sampling) monitoring. The dataset consists of continuous time series variables related to (i) meteorology, including precipitation, air temperature, relative humidity, wind speed and direction, net radiation, atmospheric pressure, cloud water flux, irradiance, leaf wetness and soil temperature (ii) hydrology, including water level and temperature, discharge and electrical conductivity (EC) of stream, (ii) hydrogeology, including groundwater level, water temperature and EC in two piezometers and one groundwater gallery completed by soil moisture measurements under the canopy. The dataset is completed by periodic time series variables related to (iv) hydrogeochemistry, including field parameters and water analysis results. The periodic sampling survey provides chemical and isotopic compositions of rainfall, groundwater, and stream water at different locations of this watershed. The ERORUN-STAFOR monitoring dataset extends from 2014 to 2022 with an acquisition frequency from 10 min to hourly for the sensor variables and from weekly to monthly frequency for the sampling. Despite the frequent maintenance of the monitoring sites, several data gaps exist due to the remote location of some sites and instrument destruction by cyclones. This observatory is a unique research site in an insular volcanic tropical environment offering three windows of observation for the study of critical zone processes through upstream-midstream-downstream measurements sites. This high-resolution dataset is valuable to assess the response of volcanic tropical watersheds and aquifers at both event and long-term scales (i.e. global change). It will also allow various progress in understanding the significant role of the TMCFs in the recharge processes, the hydrogeological conceptual model of volcanic islands, the watershed hydrosedimentary responses to extreme climatic events and their respective evolution under changing climatic conditions.
Forecasting cyclone-induced inundations in the French Overseas Territories raises specific issues, as most of them are steep volcanic islands with a complex orography and presenting (1) very dense water systems with numerous gullies and potential intense water flows (2) a lack of continental shelf that leads to an important exposure of the coast to high waves and overtopping despite the presence of fragmented barrier reefs (3) complex interactions between marine and river water supplies in river inlet environments. To date, there is no forecasting system taking into account all these specificities.
This presentation gives an overview of the research project SPICy that aims at tackling the issue of cyclone-induced marine and river floods forecast in the French Overseas Territories through the realization of a demonstrator for the pilot site of Reunion Island. To reach this objective, the project addresses various challenges, focusing on : (1) the assessment of meteorological forecast uncertainties with the development of ensemble tracks generation techniques (2) high resolution meteorological modelling taking into account orography and real-time data assimilation to improve local rainfall predictions (3) the extension of meteorological forecast information to marine and river floods through the development of dedicated modules, notably in urban areas (4) the consideration of marine/river interaction (5) the management of computation times and the investigation of optimization techniques including the use of meta-models (6) the development of users interfaces to provide relevant information to emergency managers.
The originality of the project is the interdisciplinary approach that enables to build a comprehensive strategy to holistically address cyclone-induced inundations forecast issues for this type of Territory. Beyond the development and combination of physical models, the novelty of SPICy also lies in the consideration of crisis operators’ needs at an early stage of the project and the realization of crisis exercises.
This work is supported by the French National Research Agency (ANR – 14 – CE03 – 0013). More details on the project are available at http://spicy.brgm.fr.
This paper presents the development, validation and performance of a modelling chain dedicated to cyclone-induced coastal hydrodynamics and marine inundation forecast for Reunion Island (Indian Ocean). Usually, cyclone-induced inundation forecasting systems concern generalized overflowing, for which broad low-lying areas are affected and waves can be neglected (as for the US east coast). Reunion Island presents specific issues: (1) it is surrounded by fragmented fringing reefs that can generate considerable wave-induced setup (2) local marine inundations are due to overtopping only. Thus, it demands the development of dedicated models requiring limited computing resources in order to give results for different scenarios in a delay compatible with crisis management. Beyond the implementation and optimization of classical wave and surge models (Wavewatch3 and MARS2DH) from 10km to 100m resolution, a method was developed to compute efficiently wave-induced setup and overtopping at the scale of the island. It is based on (1) a delimitation of homogeneous coastline segments regarding on morphological and exposition criteria (2) simulations of setup and overtopping for each segment with 1D cross-shore profiles of SWAN and SWASH models. For a pilot site at local scale, marine inundation is also calculated with a high resolution Non Linear Shallow Water equations model, comprising an explicit representation of the buildings and integrating overtopping discharge from SWASH profiles. This chain was extensively tested for historical cyclones with high resolution analysed cyclonic wind and pressure fields from Meso-NH (with bogussing) atmospheric model. Comparisons were made against buoys, altimetry and tide gauge measurements as well as inundation extent observations. First results show that this chain can provide meaningful
Abstract Tropical volcanic islands are biodiversity hotspots where the Critical Zone (CZ) still remains poorly studied. In such steep topographic environments associated with extreme climatic events (cyclones), deployment and maintenance of monitoring equipment is highly challenging. While a few Critical Zone Observatories (CZOS) are located in tropical volcanic regions, none of them includes a Tropical Montane Cloud Forest (TMCF) at the watershed scale. We present here the dataset of the first observatory from the French network of critical zone observatories (OZCAR) located in an insular tropical and volcanic context, integrating a ‘Tropical Montane Cloud Forest’: The ERORUN‐STAFOR observatory. This collaborative observatory is located in the northern part of La Réunion island (Indian Ocean) within the 45.0 km 2 watershed of Rivière des Pluies (i.e., Rainfall river) which hosts the TMCF of Plaines des Fougères, one of the best preserved natural habitats in La Réunion Island. Since 2014, the ERORUN‐STAFOR monitoring in collaboration with local partners collected a multidisciplinary dataset with a constant improvement of the instrumentation over time. At the watershed scale and in its vicinity, the ERORUN‐STAFOR observatory includes 10 measurement stations covering the upstream, midstream and downstream part of the watershed. The stations record a total of 48 different variables through continuous (sensors) or periodic (sampling) monitoring. The dataset consists of continuous time series variables related to (i) meteorology, including precipitation, air temperature, relative humidity, wind speed and direction, net radiation, atmospheric pressure, cloud water flux, irradiance, leaf wetness and soil temperature, (ii) hydrology, including water level and temperature, discharge and electrical conductivity (EC) of stream, (iii) hydrogeology, including (ground)water level, water temperature and EC in two piezometers and one horizontally drilled groundwater gallery completed by soil moisture measurements under the canopy. The dataset is completed by periodic time series variables related to (iv) hydrogeochemistry, including field parameters and water analysis results. The periodic sampling survey provides chemical and isotopic compositions of rainfall, groundwater, and stream water at different locations of this watershed. The ERORUN‐STAFOR monitoring dataset extends from 2014 to 2022 with an acquisition frequency from 10 min to hourly for the sensor variables and from weekly to monthly frequency for the sampling. Despite the frequent maintenance of the monitoring sites, several data gaps exist due to the remote location of some sites and instrument destruction by cyclones. Preliminary results show that the Rivière des Pluies watershed is characterized by high annual precipitation (>3000 mm y −1 ) and a fast hydrologic response to precipitation (≈2 h basin lag time). The long‐term evolution of the deep groundwater recharge is mainly driven by the occurrence of cyclone events with a seasonal groundwater response. The water chemical results support existing hydrogeological conceptual models suggesting a deep infiltration of the upstream infiltrated rainfall. The TMCF of Plaine des Fougères shows a high water storage capacity (>2000% for the Bryophytes) that makes this one a significant input of water to groundwater recharge which still needs to be quantified. This observatory is a unique research site in an insular volcanic tropical environment offering three windows of observation for the study of critical zone processes through upstream‐midstream‐downstream measurements sites. This high‐resolution dataset is valuable to assess the response of volcanic tropical watersheds and aquifers at both event and long‐term scales (i.e., global change). It will also provide insights in the hydrogeological conceptual model of volcanic islands, including the significant role of the TMCFs in the recharge processes as well as the watershed hydrosedimentary responses to extreme climatic events and their respective evolution under changing climatic conditions. All data sets are available at https://doi.org/10.5281/zenodo.7983138 .
