Detection of solar dimming and brightening effects on Northern Hemisphere river flow
Gedney, N., Huntingford, C., Weedon, G. P., Bellouin, N., Boucher, O. and Cox, P. M. (2014) Detection of solar dimming and brightening effects on Northern Hemisphere river flow. Nature Geoscience, 7 (11). pp. 796-800. ISSN 1752-0894
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To link to this item DOI: 10.1038/ngeo2263
Anthropogenic aerosols in the atmosphere have the potential to affect regional-scale land hydrology through solar dimming. Increased aerosol loading may have reduced historical surface evaporation over some locations, but the magnitude and extent of this effect is uncertain. Any reduction in evaporation due to historical solar dimming may have resulted in an increase in river ﬂow. Here we formally detect and quantify the historical effect of changing aerosol concentrations, via solar radiation, on observed river ﬂow over the heavily industrialized, northern extra-tropics. We use a state-of-the-art estimate of twentieth century surface meteorology as input data for a detailed land surface model, and show that the simulations capture the observed strong inter-annual variability in runoff in response to climatic ﬂuctuations. Using statistical techniques, we identify a detectable aerosol signal in the observed river ﬂow both over the combined region, and over individual river basins in Europe and North America. We estimate that solar dimming due to rising aerosol concentrations in the atmosphere around 1980 led to an increase in river runoff by up to 25% in the most heavily polluted regions in Europe. We propose that, conversely, these regions may experience reduced freshwater availability in the future, as air quality improvements are set to lower aerosol loading and solar dimming.