Ecology, Environment and Conservation Paper

Vol 25, May Suppl. Issue, 2019; Page No.(166-172)

STOCHASTIC SOIL EROSION RISK MODELLING AND SIMULATIONUSING FOURNIER INDEX

Bernard Moeketsi Hlalele

Abstract

Approximately 280 million tons of cereal crop is lost from 108 million hectares of croplands through soilerosion. This study aimed to (i) monitor soil erosion hazard over 48 year- long precipitation time series, (ii)determine if changes exist for informed decision making and (iii) provide management stakeholders withrelevant and scientifically sound information for effective proactive disaster management. Fourier indexdata was computed annually, and for four seasons; spring, summer, autumn and winter, for the years 1967to 2014. Each series was fitted to a suitable distribution and then, based on the fitted distributions, marginalprobabilities were computed according Fournier index categories: <20, 20-40, 40-60, 60-80, 80-100 and >100.After some exploratory analyses trying out various distributions, the following distributions were fitted tothe data: Gumbel, three-parameter Weibull and three- parameter log-normal. Q-Q plots were generated toassess the fit of the various distributions. Overall, the three-parameter log-normal distribution provided atleast a reasonably good fit to all five data sets. In order to have a model (distribution) that fits reasonablywell to all five data sets (rather than fitting possibly different distributions to the five data sets), and to havea model with a reasonably simple functional form, the three-parameter log-normal distribution was chosen.Based on the fitted three-parameter log-normal distributions the required probabilities were calculated.The greatest soil loss was detected in summer and autumn with 89% and 66% respectively. However, nosignificant loss of soil was found on annual basis.

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