This is chapter 7 of the State of Environmental Science in Svalbard (SESS) report 2020 (https://sios-svalbard.org/SESS_Issue3). Svalbard was long seen as a canary in the coalmine for climate change. Now this early warning system has suffered irreparable damage. Svalbard has warmed 2-6 times faster than the rest of the world, and we can expect further increase in air temperature (by 4–7°C), precipitation (by 45–65%) and more frequent heavy rainfall and floods. Contrary to predictions from regional climate models, freshwater fluxes from some glacierised catchments have steadily decreased for over a decade. Yet in rainfall dominated watersheds, water discharge has been increasing. To understand the implications, we must improve hydrological research in Svalbard. Ground newly uncovered by receding glaciers develops permafrost when exposed to harsh Arctic winters. Simultaneously, permafrost thaw produces new water sources and flowpaths. Current hydrogeological models do not account for such complexity. The boundaries of the hydrological year have shifted due to earlier onset of snowmelt, and later freeze up. Other weaknesses in hydrological research come from scarcity of long-term monitoring, outdated methods and data for evaporation and condensation and a lack of data on precipitation change with elevation. As every new broken record reminds us, it is more urgent than ever to understand Svalbard’s hydrology.