This Collaborative Programme aims at improving the scientific understanding of hydrological processes under modified climatic boundary conditions and at studying possible impacts of changing hydrological cycle components (precipitation, runoff, snow, etc) on the environment and the society. Meeting emerging societal challenges, in fact, is another aspect this CP intends to address. Current key topics of the CHC—CP include:

Global precipitation changes and runoff. Precipitation changes at the global level display a complex pattern, without a clear-cut average trend in the last century but with an apparent tendency to the intensification of the hydrological cycle in many areas of the world. Using observations and (global to hydrological) model simulations, this research task studies current and expected changes of precipitation at the global and European scale, with a specific focus on extreme episodes and their effects on mean runoff and intense flooding and drought events.
Interaction between climate and hydrological/land surface processes. Modifications of the water cycle significantly affect land surface properties and ecosystem functioning and are at the same time driven by changes in vegetation and land surface changes. In order to better understand these complex interactions, this CP uses a hierarchy of models working at different spatial and temporal resolutions, compared to/validated against in-situ and EO data.
Climate hot spot regions: Mediterranean region and Global Mountains. The Mediterranean basin and mountains areas are among the regions which are referred to as “climate change hot-spots”. In these regions climate change signals are amplified, as are their possible effects. Studying these areas would allow to develop appropriate adaptation and mitigation measures in the coming decades.
Societal challenges related to impact of changes in the hydrological cycle. Among the expected impacts of observed and projected changes in the hydrological cycle are the lack of water for drinking, agriculture, industry and energy production, which imposes risks for civil security. Impact-oriented research aims at effectively responding to crucial societal challenges resulting from changes in different components the hydrological cycle and to support adaptation and risk mitigation strategies.

Precipitation changes at the global level display a complex pattern, without a clear-cut average trend in the last century but with an apparent tendency to the intensification of the hydrological cycle in many areas of the world. Global climate models indicate possible global precipitation changes before the end of the century, with an intensity and pattern that depend on the specific climate scenario and are not always consistent between the different models.

Precipitation is a particularly difficult variable, as it is characterized by strong intermittency at all scales and strong orographic dependence, which makes it often hard to model and to measure (see Fig. 1). The measurement of precipitation itself, either by ground stations, radars or satellites, is still a challenging task, which becomes especially hard for solid precipitation at high latitudes or altitudes. These difficulties could hamper efforts to understand and model the hydrological cycle and its variability.

We work based on a list of science topics. The science topics can be adjusted and allow flexible participation of ECRA and non-ECRA partners. The general strategy starts from fundamental physical concepts, continues via process understanding and goes towards the best possible numerical simulations of the global and regional changes of extreme events, including composition-climate interactions, feedback and impacts.