Human footprint on the global hydrological cycles

It is well known that various human activities are locally changing the hydrological cycles on the Earth. Climate change due to anthropogenic changes in atmospheric composition caused by greenhouse gas and aerosol emissions is altering the water cycle, including precipitation, evapotranspiration, runoff, groundwater infiltration, water temperature, and water quality. However, apart from such climate change impacts, are the changes in the hydrological cycle due to human activities basically local, and are the global impacts limited to climate change?

Irrigation not only uses river flows and groundwater, but also lowers surface temperatures to the extent that it must be considered in global climate change assessments, increasing evapotranspiration unnecessarily, especially in arid regions, and creating areas where evapotranspiration is greater than precipitation over continents that use upstream river runoff and fossil ground water for irrigation. This negative runoff is not only detectable in data from dense river flow observation networks, but is also suggested by the net divergence of water vapor in the atmosphere. These effects have also been observed and estimated from changes in total terrestrial water storage using gravity observations.

In recent years, human activities such as dam water storage and irrigation have been incorporated into so-called earth system models, which predict future climate change based on socioeconomic scenarios. As the local applicability of such global models is improving, there is an urgent need to further develop numerical models that can adequately represent both natural and human systems, and to interactively incorporate limiting factors such as water hazards and water supply and demand when constructing future projections of socioeconomic scenarios.