Characteristic of rainfall to produce water-logging in cropland

According to shallow groundwater, extensive distribution of lowland in the Four-lake Watershed and local practice in agricultural production, more than 50 mm of rainfall is regarded as a rainfall that possibly produce water-logging in cropland. Analysis showed that this kind of rainfall is characterized by the following: most of the rainfall emerged in the first ten days of May and in the last ten days of June, and averagely once every 2.6-2.9 years, the duration of the rainfall process was mostly within 7 days, mainly lasted for 3-5 days; in the area rainfall with precipitation from 50.1 to 100 mm usually results in subsurface water-logging in cropland, and occurs in the area 3.8 times a year, it may emerge from March to September, during which rainfall is quite frequent in May and June; rainfall more than 100 mm often causes surface water-logging in farmland, which mainly occurred in June, July and August, its frequency is 32.76%, 43.10% and 24.14% respectively; in rainy season, short interval (within 7 days) of the rainfall often results in Concomitance of Surface Water-logging and Subsurface Water-logging (CSWSW) which is very common in the Four-lake watershed and may occur from March to August, especially at the end of spring and the beginning of summer owing to the impact of the subtropical monsoon climate, generally, no less than 2 times CSWSW is highly frequent for winter wheat from jointing to mature period (Mar. to May), and for cotton at seedlings stage (May to mid-June) and in the period of cotton budding and bollsetting (mid-June to August), this will greatly affect crop growth.