Hydropower systems have played an important historical role in the development of hydrology (Koutsoyiannis, 2014). Scientific and technical questions underlying hydropower planning and operation motivated the archiving of time series of hydro-meteorological data and their statistical analysis (Hurst, 1951), paving the way for the fields of hydrologic design (Kleme¨ et al., 1981). Currently, with the increasing promotion of renewable energies, hydropower is expected to play a central role as both energy storage and balancing energy source to supplement highly-intermittent renewable energies – solar andwind in particular. Integrating hydropower, solar andwind power in a modern portfolio of renewable energies, and balancing power use with other critically important usages of water, brings new challenges to the hydrological community and new opportunities for better understanding of fundamental hydrological processes. New questions arise concerning the dependence of these climate-related energy sources on meteorological (precipitation, temperature,wind, and solar radiance) aswell as on hydrological variables (river flows). Despite substantial work on the space–time variability of each hydro-meteorological variable individually (e.g. Tarroja et al., 2013 for the case of solar power), advances on their joint analysis are still limited. In this commentary, we analyse three specific challenges that integration of hydropower with solar and wind energy sources is placing to the hydrological community and which are central to the effective use of renewable energy and water resources, namely (i) to initiate hydro-meteorological frameworks for the analysis of space–time co-fluctuations between runoff regimes and solar radiation, wind and temperature climatology, (ii) to understand how land use and climate change may affect the nature of these co-fluctuations, and (iii) to develop quantitative analysis of the interactions between the use of water for power generation and its use for other purposes, including the preservation of aquatic ecosystems.