Risk evaluation of sub-surface waterlogging of summer crops based on DHSVM model on county scale

Abstract: Sub-surface waterlogging is one of the main agricultural meteorological disasters affecting summer crops in Jianli County, Hubei Province, China. For sub-surface waterlogging is caused by the long-term influence of high soil moisture on crops, it is not easily identified. Few studies were found on the risk evaluation and zonation of crops injured by sub-surface waterlogging. The researchers of this paper firstly adjusted the parameters of DHSVM (distributed hydrology soil vegetation model) by using soil moisture data collected from February 13 to May 20 in 2014 and verified it with the data collected from May 25 to September 23 in 2014. The result showed that the DHSVM could be used to simulate the soil moisture changes in Jianli County. Based on this model, the influencing parameters of waterlogging injury were input, which included meteorology, soil physical properties, groundwater levels, topography, drainage and irrigation conditions, and the farming system. Then the spatial distributions of soil surface moisture were simulated using the DHSVM with a step of 24 h during the growth seasons (March and April) of summer crops from 1970 to 2014. Also the waterlogging moisture indicators were also used to analyze the injury times of each grid in Jianli County (waterlogging injury occurs when the water level is less than 60 cm and surface soil moisture is higher than 95% of soil saturation for 5 days), and the spatial resolution was 90 m. In this way, the spatial distribution of the sub-surface waterlogging injured ratio (SWIR) was calculated, as well as the indicator of the degree of sub-surface waterlogging injury. According to the different range of SWIR value, the research areas which were at the risk of the sub-surface waterlogging injury, were consequently classified into 4 grades: the severe damage zone (SWIR greater than or equal to 0.6), the moderate damage zone (SWIR greater than or equal to 0.3 and less than 0.6), the mild damage zone (SWIR greater than or equal to 0.1 and less than 0.3), and the damage-free zone (SWIR less than 0.1). Thus the zonation of sub-surface waterlogging injury of summer crops was mapped. With some risk evaluation of each zone, the zonation conformed to the actual situation. Since the method used in this paper is based on the model and all the damage factors are taken into account, it is more accurate than the division only using the meteorological elements and proved to be an applicable method for the zonation of sub-surface waterlogging injury on the county scale.