A wavelet analysis of the relationship between Loess Plateau erosion and sunspots

Abstract The Chinese Loess Plateau is one of the most rapidly eroding regions in the world. The purpose of this study is to find out to which extent soil erosion on the Loess Plateau is driven by sunspot activity. We analyzed the relation between annual sediment discharge (from 1919 to 2010) from the Loess Plateau and the relative sunspot number, using Complex Morlet wavelets. We divided sediment discharge into 2 periods: before and after 1980 the year where the large-scale implementation of soil and water conservation techniques started. Before 1980, sediment discharge followed a 6 and 11-year period, the 11-year period being the most important one within a 25-year scale. After 1980, the impact of soil and water conservation techniques on the soil erosion in the Loess Plateau became obvious. The period of sediment discharge changed to, 4, 7 and 12-year periods, the 12-year period dominating the record. Similar analyses were conducted for the sunspot relative number, with an 11-year period dominating the record from 1919 to 2010. In different periods, the population, farm land area, land use/cover patterns and other factors have changed significantly. Although this has certainly affected sediment magnitudes, solar activity remains a clear (indirect) forcing factor for soil erosion in the Loess Plateau throughout the period of analysis. This underlines that solar activity influences Earth processes and argues for a more complete analysis of the pathways through which this happens.