Soil Moisture Trends

Another line of evidence for changes in regional evaporation rates has come from the study of soil moisture data from an extensive network of stations in the Ukraine where plant available soil moisture for the top 1 m of soil is determined gravimetrically every 10 days from April to October at 141 stations from fields with either winter or spring cereals. The data, from 1958 to 2002 [74], shows that soil moisture increased until approximately 1980 and then levelled off. No trends in rainfall were observed for this region while air temperature increased slightly. As noted above, one of the first reports of dimming was from this region during the period in question [41]. The observed changes in soil moisture were opposite to the predictions that global warming would lead to soil desiccation [75,76]. Thus, Robock and Li [74] concluded that the changes in soil moisture were evidence of dimming and its reduction of regional evaporation rates. Subsequent modelling with a sophisticated land surface model, which included a decreasing trend of solar radiation along with increasing CO2 and global warming, demonstrated similar increases in soil moisture [77].

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