用小时降雨资料估算降雨侵蚀力的方法

降雨侵蚀力是进行土壤流失量预报的基本因子,EI₃₀是迄今得到广泛应用的定量指标,但它的计算需要降雨过程资料,使其推广应用受到很大限制。用自动气象观测提供的高精度等间隔降雨资料,代替降雨过程资料,是估算降雨侵蚀力指标的首选。国际上对此已有研究,发现有很大的地区差异性。为此,本文在水蚀严重的中国东部季风区选择5个代表站点,共456次降雨过程资料,建立了用60 min等间隔雨量资料估算次降雨侵蚀力的计算方法。研究结果表明:直接用60 min等间隔资料计算的降雨侵蚀力指标值,与用降雨过程资料计算的结果相比,降雨动能E差异较小,主要差异体现在最大30 min雨强I₃₀上,由此导致降雨侵蚀力指标EI₃₀的差异也十分明显。利用自动气象观测小时雨量资料计算降雨侵蚀力指标值,通过公式(EI₃₀)_bp=1.730(EI₃₀)₆₀转换,可以较精确地估算全国降雨侵蚀力,与用日、月和年降雨量资料的估算值相比,能够提高土壤侵蚀预报精度。

Calculation of rainfall erosivity by using hourly rainfall data

Rainfall erosivity shows the potential ability of the soil loss caused by rainfall and it is a very important factor for predicting soil loss from agricultural hillslopes. EI₃₀ is a widely used index for quantifying rainfall erosivity. The 'E' portion of this value represents the rainfall energy, and the 'I₃₀' portion represents the maximum, contiguous 30-minute rainfall intensity during the storm. Normally, EI₃₀ values are calculated from breakpoint rainfall information taken from continuous recording rain gauge charts, however, in many places in China the detailed chart-recorded rain gauge data relative to storm intensities are not readily available. Obviously, the more detail of the rainfall data was used, the more accurate of EI values were given. In order to take advantage of hourly rainfall data in automatic meteorological observation stations and improve the precision of EI values. A total of 456 storm events in 5 soil conservation stations over eastern China were used to determine if EI values could be calculated by using hourly rainfall data (60-min interval data). Results indicated that the values of EI₃₀ based on the 60 min interval data were less than those calculated from breakpoint data. The average conversion factors (ratio of values calculated from the breakpoint data to those from 60 min interval data) for the five stations are 1.105 for the estimation of E values, 1.668 for I₃₀ values, and 1.730 for EI₃₀ values. The differences between two kinds of EI values based on breakpoint data and hourly rainfall data are mainly caused by maximum 30-min rainfall intensity. Hourly rainfall data can be used to accurately determine the rainfall erosion index values by using this function:(EI₃₀)_bp=1.730(EI₃₀)₆₀.The result could be used to improve the estimation of rainfall erosivity indices, and hence prediction of soil erosion in China.