宁夏土壤水文参数空间分布及干旱指标改进研究

土壤相对湿度是干旱监测和评估中最常用的指标之一,但这一指标的有效水下限较为模糊,实际应用中会将一部分土壤有效水排出在外,从而高估干旱的程度,因此有必要对其进行改进。利用2016-2019年宁夏回族自治区气象局122个土壤湿度观测站0-50 cm土壤田间持水量(%)和凋萎湿度(%)的测定数据,分析了宁夏境内土壤水文参数空间分布特征,并引入土壤相对凋萎湿度,以改善当前干旱监测评估中最旱等级土壤水下限模糊的问题。结果表明:宁夏0-20 cm和20-50 cm土壤水文参数的空间分布特征较为相似,田间持水量、凋萎湿度、有效水和相对凋萎湿度的波动范围均呈南低北高的特点;数值大小上,田间持水量、凋萎湿度、有效水整体呈南大北小,而相对凋萎湿度南小北大;分布区间上,田间持水量、凋萎湿度、有效水、相对凋萎湿度集中在15.0%-25.0%、3.0%-6.0%、10.0%-20.0%、10.0%-30.0%之间。基于相对凋萎湿度改进的干旱指标,在宁夏除特旱上限对应的土壤相对湿度波动范围较大外,轻旱、中旱和重旱对应的土壤相对湿度空间波动范围均较小;轻旱、中旱、重旱和特旱的上限对应的土壤相对湿度分别主要介于82.1%-90.0%、64.2%-80.0%、46.3%-60.0%、28.4%-50.0%之间。改进后的干旱指标其物理意义更加明确,能客观反映较低土壤水分对植物有效性真实情况,研究对提高干旱监测评估的准确性有一定现实意义。

Spatial Distribution of Soil Hydrological Parameters and Improvement of Drought Index in Ningxia Hui Autonomous Regions

Soil relative moisture is one of the drought indicators and commonly used in drought monitoring and estimation, while the lower limit of available water for this index is still not clear. In this paper, based on the data of 0-50 cm soil field capacity and wilting moisture obtained from the 122 soil moisture observation stations in the years of 2016-2019 in Ningxia Hui Autonomous Regions, spatial distribution of soil hydrological parameters was analyzed firstly, and by introducing the relative soil wilting moisture, the lower threshold of available water was cleared for extreme drought. The results showed that the soil hydrological parameters had the similar distribution between 0-20 cm and 20-50 cm soli layers, fluctuation range of the field capacity, wilting moisture, available water and relative wilting moisture all showed the trend of higher in northern and lower in southern of Ningxia. Field capacity, wilting moisture, available water were all had higher value in southern than in northern, while value of the relative wilting moisture was higher in northern than in southern. Field capacity, wilting moisture, available water and relative wilting moisture were mainly 15.0%-25.0%, 3.0%-6.0%, 10.0%-20.0%, 10.0%-30.0%, respectively. Soil relative moisture for extreme drought was higher in northern and lower in southern of Ningxia, while for other drought levels(light, moderate and heavy), there were slight fluctuations. The values of soil relative moisture for light, middle, heavy and extreme drought levels were mainly between 82.1%-90.0%, 64.2%-80.0%, 46.3%-60.0%, 28.4%-50.0%, respectively. The improved drought index has more clear physical meaning, can objectively reflect the lower soil moisture to the plant availability. The study would be helpful to improve the accuracy of drought monitoring and assessment.