All the field “experiments” indicated in the sub-title above include the hydrological cycle in some or all of its aspects and thus require the use of “hydrological sciences”. Is hydrology actually included in them? This depends on the definition of hydrology used. The paper briefly describes the different definitions of “hydrology” in the context of the scientific objectives and concepts of these experiments and related scientific activities. It further evaluates the role actually assigned to hydrologists in past cross-disciplinary endeavours to conduct “field experiments” and goes on to propose adjustments to this role in the GEWEX Continental-scale International Project (GCIP). Related activities are analysed in some detail in this framework and proposals are presented for increased inter-disciplinary communication.