The experiment on
precipitation infiltration and redistribution was conducted in an artificial shrub sand dune at Shapotou
Desert Experimental Research Station, Chinese Academy of Sciences, from August 17 to September 30, 2001. The study site is located at southeast of the Tengger Desert at an elevation of \{1 330\} m (MSL) with latitude of 37°27′N and longitude of 104°57′E. The climate of Shapotou region is semi\|arid. A mean monthly maximum temperature of 24\^3℃ was recorded during July and the lowest value of -6\^9℃ during January. The average monthly relative humidity was the lowest (32\^7%) during April, while the highest value of 54\^1% during August. The sunshine hours during January and October range from 6.9 to 6\^7 hour per day, and 7\^0 to 8\^2 hour per day in the remaining months. Average annual rainfall is 191\^1 mm, of which 83% is received during May through September. During the experimental period, there were seven individual rainfall events, the
precipitation varying from 1\^5 mm to 40\^7 mm. The maximum
infiltration rate for precipitation of 40\^7 mm was up to 0\^42 mm\5min -1 , under a maximum rainfall intensity of 3\^4 mm h -1 (14:00～15:00, Sep.18), with an average initial volumetric soil moisture of 5\^4%. For the precipitation of 38\^9 mm, the individual rainfall event started at around 16:00, August 17, 2001, lasting for about 26 hours to 18:00, August 18, 2001, it has an average rainfall intensity of 1\^50 mm\5h -1 . The highest rainfall intensity of 5\^3 mm\5h -1 was recorded between 9:00～10:00, Aug 18, the overall precipitation amounts for 38\^9 mm. The result indicated that the infiltration rate differed significantly under each individual rainfall with different initial soil moisture status and rainfall intensity. A drier soil profile favors the infiltration process, and obviously, there is a simple linear relationship between the infiltration rate and the rainfall intensity, whilst that the infiltration rate has a 10 times magnitude of the rainfall intensity. It has no contribution to the soil water supplement if the intensity of an individual rainfall event is less than 0\^46 mm\5h -1 . Due to the soil-water uptake by vegetation root activities, the overall cumulative infiltration depth was less than 60 cm under an individual precipitation of around 40 mm with a intensity of 1\^50 mm\5h -1 . At a certain soil depth of 140 cm, where featured by the concentration of rooting system, the soil moisture was depleted gradually, though it still varied in a fluctuation way of 12 h periodically between daytime and night, mainly due to the vegetation water consumption at daytime and the soil moisture flow concentration at night, the difference from dawn to the end of daytime was around 0\^1%～0\^3%.