Hydrological change is a central part of global change 1-3 . Its drivers in the past need to be understood and quantified for accurate projection of disruptive future changes 4 . Here we analyse past hydro-climatic, agricultural and hydropower changes from twentieth century data for nine major Swedish drainage basins, and synthesize and compare these results with other regional 5-7 and global 2 assessments of hydrological change by irrigation and deforestation. Cross-regional comparison shows similar increases of evapotranspiration by non-irrigated agriculture and hydropower as for irrigated agriculture. In the Swedish basins, non-irrigated agriculture has also increased, whereas hydropower has decreased temporal runoff variability. A global indication of the regional results is a net total increase of evapotranspiration that is larger than a proposed associated planetary boundary 8 . This emphasizes the need for climate and Earth system models to account for different human uses of water as anthropogenic drivers of hydro-climatic change. The present study shows how these drivers and their effects can be distinguished and quantified for hydrological basins on different scales and in different world regions. This should encourage further exploration of greater basin variety for better understanding of anthropogenic hydro-climatic change.Drivers of freshwater changes are multiple and difficult to distinguish and quantify 9-12 . Global increase of evapotranspiration (ET) by irrigation and a parallel decrease by deforestation has been estimated by spatial compilation of crop and forest data 2 . Furthermore, spatial analysis of relatively short-term (30-year) data has shown effects of large dams and their reservoirs on atmospheric variables of convective available potential energy, specific humidity and surface evaporation extending over distances of around 100 km away from reservoir shorelines 13 . Such spatial results indicate ET changes by different land and water uses, but do not reveal the actual change dynamics and timing. Moreover, global averaging hides the spatial variation of ET and its regional change drivers and further effects on water change (through changed water loss by ET to the atmosphere 5,7,14 ) and climate change (through changed latent heat flux 6,15 and atmospheric circulation 16 ).Hydrological model interpretation of consistently long, twentieth century time series of relevant hydro-climatic and landwater use data has distinguished between climate and irrigation drivers of ET change in the drainage basins of the Aral Sea in Central Asia 5,6 and Mahanadi River in India 7 (Fig. 1a). Both of these basins represent areas with major irrigation developments that have driven increases of ET and associated water loss to the atmosphere. Direct temporal analysis of long-term hydro-climatic and land-water use data, accounting for the water balance constraints of hydrological basins, can thus complement spatial studies, particularly for the twentieth century, which has seen large land-water use changes, wh...

2017-08-25T16:31:17

No abstract