The Arctic System and its hydrology play a central role in regulatfing Earth´s climate and the impacts of a warming Arctic are already raising serious concerns about the stability of the sensitive balance between climate conditions, freshwater input, oceanic circulation and the state of cryospheric components.

The Arctic-HYDRA program consists of a core network for the observation of the Arctic Hydrological Cycle (Arctic HYCOS) coupled with a suite of intensive, focussed process studies that are based on in-depth measurements and modelling of the individual components of the AHC. Furthermore, hydrological models and data assimilation techniques will be developed to generate a comprehensive, integrated description of the AHC including the feedbacks between the atmosphere, cryosphere and the oceans. The program will have a data management and information system in accordance with IPY and WMO protocol. It will establish links with other relevant clusters, e.g., on meteorology, climatology, cryosphere, including permafrost, snow cover and glaciers, biosphere and societal issues affected by the AHC. The main scientific goals of the Arctic HYDRA program are:

• To characterize variability in the Arctic Hydrological Cycle (AHC)
• To examine linkages between atmospheric forcing and continental discharge to the ocean
• To assess the historical response of the Arctic Ocean to variations in freshwater input from rivers and net precipitation over the ocean
• To attribute to specific elements of the AHC or to external forcing the sources of observed spatial temporal variability in the land-ocean- ice-atmosphere system
• To detect emerging changes in the contemporary state of the AHC in near real time and to place such changes into a broader historical context.