Multiple time scale characteristics of rainfall and its impact on soil salinization in the typical easily salinized area in Huang-Huai-Hai Plain, China

On the basis of monthly rainfall data over 50 years, we analyzed temporal properties of annual and seasonal rainfall variability by using and comparing two kinds of continuous wavelet transforms. Furthermore, we deduced its impacts on soil salinization in the area of Huang-Huai-Hai Plain, China. Results showed that the annual rainfall collected by the studied area showed a decreasing trend during period 1960–2009 at a climatic tendency rate of 14.43 mm/10 years. The Morlet wavelet is better at capturing local feature of rainfall oscillatory behaviors at fine time scales, and the Mexican Hat wavelet is better at revealing global feature of rainfall period. Combining Wavelet transform with wavelet power spectrum and its confidence test, we found the 8-year dominant period of annual rainfall and the 5-, 6-, 10- and 12-year dominant periods of seasonal rainfall, respectively. The annual and seasonal rainfall trends in the near future and their impacts on soil salinization are deduced based on the rainfall dominant periods and the prominent correlation between rainfall and soil salinity changes. The annual rainfall will still be in a relatively low period in the subsequent year after 2009 and then revert to a relatively high period during 2011–2014. The subsequent summer variability of rainfall may be helpful for reducing the soil salinization, while the opposite trends of spring and autumn rainfall variability may aggravate the soil salinization. This suggests sustainable irrigation and drainage measures to prevent soil salinization in this area.

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