HyMeX (*) an experimental program dedicated to the hydrological cycle in Mediterranean *Hydrological cycle in the Mediterranean eXperiment Presented by Olivier Nuissier (1) On behalf of Véronique Ducrocq (1), Philippe Drobinski (2), Piero Lionello (3) and the HyMeX ISSC (1) GAME-CNRM, Météo-France & CNRS, Toulouse, France (2) IPSL-LMD, CNRS, Palaiseau, France (3) Department of Science of Materials, University of Lecce, Italy

Motivations, societal stakes The Mediterranean basin: A nearly enclosed sea surrounded by very urbanized littorals and mountains from which numerous rivers originate Need to advance our knowledge on processes within each Earth compartment, but also on processes at the interfaces and feedbacks in order to progress in the predictability of high-impact weather events and their evolution with global change. A region prone to high-impact events related to the water cycle: Heavy precipitation, flash-flooding during fall Severe cyclogeneses, strong winds, large swell during winters Droughts, heat waves, forest fires during summers Water resources: a critical issue Freshwater is rare and unevenly distributed in a situation of increasing water demands and climate change (180 millions people face water scarcity) The Mediterranean is one of the two main Hot Spot regions of the climate change A unique highly coupled system ( Ocean-Atmosphere-Continental surfaces)

Main Objectives Major disciplines: Meteorology, Oceanography, Hydrology, Climatology, Societal sciences In order to make progress in: the observational and modelling systems, especially of coupled systems. This requires new processes modelling, parameterization development, data assimilation of new observation types for the different Earth compartments, reduction of uncertainty in climate modelling. The prediction capabilities of high-impact weather events, The accurate simulation of the long-term water cycle, The definition of adaptation measures, especially in the context of global change. to improve our understanding of the water cycle, with emphases on the predictability and evolution of intense events by monitoring and modelling: the Mediterranean coupled system (atmosphere-land-ocean), its variability (from the event scale, to the seasonal and interannual scales) and characteristics over one decade in the context of global change to evaluate the societal and economical vulnerability to extreme events and the adaptation capacity.

Main Scientific Topics Better understanding of the long-term water cycle over the Mediterranean basin: variability and trend Key questions: What is the variability of the components of the water cycle (precipitation, evaporation, run- off, transport, etc) within a context of global climate change ? What are the impacts on the water resources ?

Main Scientific Topics Better understanding of the intense events: processes and contribution to the trend Key questions: What are the ingredients and their interactions necessary to produce an extreme event ? What will be the evolution of intense events with the global climate change ? Mediterranean cyclogeneses Regional winds (Mistral, Bora, Tramontana) Mesoscale convective systems Slow-moving frontal systems Coastal orographic precipitation

Monitoring the vulnerability factors and adaptation strategies facing high- impact weather events Key questions: How to reduce the impacts of the extreme events and climate change ? Main Scientific Topics

EOP Enhanced existing observatories and operational observing systems in the target areas of high-impact events: budgets and process studies (+ dedicated short field campaigns) LOP Enhanced current operational observing system over the whole Mediterranean basin: budgets (data access data policy) SOP Special observing periods of high-impact events in selected regions of the EOP target areas (aircrafts, ships,…): process studies Observation strategy « Nested » approach necessary to tackle the whole range of processes and interactions and estimate budgets ?

--- Target Areas of the first EOP/SOP series Hydrometeorological sites Ocean sites Key regions for dense water formation and ocean convection First EOP/SOP series SOP1 in order to document: - Heavy precipitation and Flash-flooding - Ocean state prior the formation of dense water SOP2 in order to document: - Dense Water Formation and Ocean convection - Cyclogenesis and local winds EOP/SOP for the NW Med. TA Phasing with T-NAWDEX campaign field

Modelling Strategy The AROME-WMED model is a research version of the M é t é o-France AROME NWP system running its own 3-hourly rapid update assimilation cycle at 2.5 km. See also Doerenbecher et als Poster about balloons deployment during HyMeX The HyMeX modelling strategy includes: The improvement of convective-scale deterministic forecast systems to improve the prediction capabilities of Mediterranean high-impact weather events. HyMeX field campaigns should provide an unique high-resolution database to validate these new NWP systems: microphysical properties (polarimetric radars, aircraft measurements), marine boundary layer characteristics and air-sea fluxes measurements (buoys, research vessels), novel high-resolution moisture measurements (GPS delays on board ships, radar refractivity, water vapor from lidar, etc). Some versions of these systems will run in real-time during the SOPs to serve as guide for the dedicated instrumentation. Other on-going studies based on NWP and modeling systems are carried out to prepare the deployment of observation platforms (aircraft, vessels, sounding, lidars, etc)

Modelling Strategy M0M1M2M3 M4M5M6M7 M8M9M10 24h- simulated rainfall from AROME model from 1 Nov at 12 UTC See also Nuissier et als Poster for example of such systems The HyMeX modelling strategy includes: The design of high-resolution ensemble modelling systems dedicated to the study of the predictability of Mediterranean heavy precipitation and severe cyclogenesis. Quantifying and rating the different sources of uncertainty at various scales that impact the forecast of Mediterranean intense events is one goal of HyMeX through the design of multiscale and nested ensemble forecast systems, possibly based on mesoscale ensemble data assimilation techniques. OP M0 M1 M2 M3 M4 M5 M6 M7 M8 M9 M10 OBS RAD Simulated discharges (m 3.s -1 ) with ISBA-TOPMODEL The coupling of these ensemble forecast systems with hydrological models to issue probabilistic forecast of the impact in terms of hydrological response. Advances in knowledge of the hydrological and hydraulic responses as well as of the soil water content state before and during the precipitation events should help to improve these hydrological models.

Modelling Strategy Example of Impact of the assimilation of radar reflectivity for an HPE Observed radar rainfall Rainfal forecast without radar reflectivity assimilation Rainfal forecast with radar reflectivity assimilation From Caumont et al, 2009 The HyMeX modelling strategy includes: The development of regional coupled systems (ocean-atmosphere, atmosphere-land, ocean-land-atmosphere) and downscaling methods to reduce uncertainties of the future climate regional projections for Mediterranean intense events. The development of new process modelling, parameterization development, novel data assimilation systems for the different Earth compartments. For example, improvement of air-sea flux parameterizations or development of data assimilation in cloud and precipitation systems are major objectives of HyMeX and part of the observation strategy is designed to serve these objectives.

Thank you for your attention for remarks and questions contact Véronique Ducrocq