Characteristic analysis of temperature, soil water and salt during maximum freezing depth period based on wavelet transform

Water and salt coupling transfer in freezing and thawing soils is the difficult point and hotspot research of soil water science. In order to understand the variation characteristics of air temperature and water salt, in this study, variation characteristics of daily minimum air temperature, average moisture and salt within 0-40 cm soil depth were analyzed using the Mexican hat function during freezing period in Feb. for 12 years (1994－2006) in Hetao Irrigation District, Inner Mongolia. The results showed that daily minimum air temperature and soil water salt change had a periodic characteristic during study period. The strongest wave period was 3 year, 2 year, 2 year for daily minimum air temperature, average moisture and salt within 0-40 cm soil depth, respectively. The changes of daily minimum air temperature show correlation with that of soil water and salt. High temperature period corresponded to that of the low water and high salinity, respectively. There are two abrupt change points around 1997 and 2000. Scale change of soil salt presented much more complicated compared with that of air temperature and soil water, respectively. These results are useful to soil salinization prevention and water-saving reconstruction in arid-cold area in future research.