The purpose of the special issue is to give an overview of the results of the multidisciplinary research project MEDUP, which is a 3-year project funded by the ANR (French National Research Agency).

MEDUP deals with the quantification and identification of sources of uncertainties associated with the forecast and climate projection for Mediterranean high-impact weather events. The propagation of these uncertainties on the environment is also considered, as well as how they may combine with the intrinsic uncertainties of the vulnerability and risk analysis methods. An original feature of MEDUP is to address these questions at one and the same time for weather forecasting (from 3h up to 10 days forecast range, with a focus on shorter range), seasonal forecasting (from 1 month to 3 month range) and climate scenario simulations (from 1960 to 2050). MEDUP is also innovative in considering the whole uncertainty chain, from the atmospheric modelling of high-impact weather events to their consequences on the environment. The atmospheric modeling uncertainties will be thus propagated on the vulnerability of the hydrosystems taking into account the feedbacks of landuse/ land-cover changes and also interpreted in terms of economic losses, as well as in terms of consequences on individual decision making and risk management in the region. The MEDUP project lies within the framework of HyMeX, in developing modeling and forecasting tools which could be deployed during this 10-year program.