“…For the correlation function diagram of precipitation and soil moisture (Fig. 2), the initial time lag interval is all k = 0, indicating that the soil moisture in different soil layers of fixed dunes increase rapidly after precipitation (Oyekale 2017). It can be judged from figure 2 that the period of the correlation function between the precipitation and the soil moisture in the 0-20 cm, 20-40 cm, 40-60 cm, 60-80 cm, 80-100 cm, and 100-120 cm layers is 1.5, 2, 2, 2, 1 and 3.5 time lag intervals (1 time lag is 10 days), indicating that the values of the peaks and valleys on the precipitation diagram are separated by 1.5, 2, 2, 2, 1 and 3.5 time lag intervals, and reflected by corresponding peaks and valleys on the soil moisture dynamic diagram at the soil depth of 20 cm, 40 cm, 60 cm, 80 cm, 100 cm and 120 cm.…”