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Nel W.,University Of Fort Hare | Anderson R.L.,University of Pretoria | Sumner P.D.,University of Pretoria | Boojhawon R.,University of Mauritius | And 2 more authors.
Geografiska Annaler, Series A: Physical Geography | Year: 2013

The Erosivity Index (EI) and the Modified Fournier Index (MFI) are two commonly used methods in calculating the R factor of the universal soil loss equation/revised universal soil loss equation formula. Using Mauritius as a case study, the value of high-resolution data versus long-term totals in erosivity calculations is investigated. A limited number of four Mauritius Meteorological Services stations located on the west coast and the Central Plateau provided the study with detailed rainfall data for 6 years at 6-min intervals. Rainfall erosivity for erosive events was calculated using different set interval data. In this study, within the EI, the use of 6-min rainfall intervals during erosive rainfall gave estimates of around 10% more erosivity than the 30-min time intervals and 33% more rainfall erosivity than the 60-min rainfall measurements. When the MFI was used to determine erosivity through annual and monthly rainfall totals, substantially higher erosivity than the EI method was calculated in both regions. This stems from the large amount of non-erosive rainfall that is generated on Mauritius. Even when the MFI was used to calculate erosivity through monthly and annual rainfall totals derived purely from erosive rainfall, erosivity calculations were not comparable to those from high-resolution data within the EI. We suggest that for the computation of erosivity, rainfall data with the highest possible resolution should be utilised if available and that the application of annual and monthly rainfall totals to assess absolute soil erosion risk within a high rainfall tropical environment must be used with caution. © 2013 Swedish Society for Anthropology and Geography. Source


Nel W.,University Of Fort Hare | Hauptfleisch A.,University of Pretoria | Sumner P.D.,University of Pretoria | Boojhawon R.,University of Mauritius | And 2 more authors.
Physical Geography | Year: 2016

Mauritius is a volcanic island with a raised interior where extreme rainfall events dominate rainfall erosivity. Intra-event characteristics of the 120 highest erosive events at six selected locations between 2004 and 2008 were analyzed to provide the first detailed intra-storm data for a tropical island environment. On Mauritius, spatial variation is evident in the characteristics of extreme erosive rainfall recorded at the stations, with a noticeable increase in rainfall depth, duration, kinetic energy, and erosivity of extreme events with altitude. Extreme events in the raised interior (central plateau) show high variability of peak intensity over time as well as a higher percentage of events in which the greatest intensity occurs in the latter part of the event. Intra-event distribution of rainfall in the interior of the island shows that rainfall there has a higher potential to exceed infiltration rates as well as the ability to generate high peak runoff rates and cause substantial soil loss. The study suggests that even though within-event rainfall characteristics are complex, they have implications for soil erosion risk, and that, in tropical island environments, the within-storm distribution of rainfall should be incorporated in soil-loss modeling. © 2016 Informa UK Limited, trading as Taylor & Francis Group Source


Nel W.,University Of Fort Hare | Mongwa T.,University Of Fort Hare | Sumner P.,University of Pretoria | Anderson R.,University of Pretoria | And 4 more authors.
Physical Geography | Year: 2012

Mauritius is a typical tropical volcanic island with a distinct elevated central plateau above 550 m.a.s.l. Rainfall depth, duration, intensity, kinetic energy, and erosivity were analysed for 385 erosive rainfall events at five locations over a five-year period (2004 to 2008). Two Mauritius Meteorological Services stations located on the west coast and three sited on the Central Plateau provide detailed rainfall data at 6-minute intervals. Erosive storm events are found to differ markedly between the coastal lowlands and the elevated interior with regard to the frequency, the total rainfall generated, the duration, total kinetic energy, and total erosivity of individual events. However, mean kinetic energy, mean and maximum rainfall erosivity (EI30), and maximum intensities (I30) from individual erosive events do not show this distinct differentiation. The distribution of kinetic energy and erosivity generated by individual events at the two altitudes are also significantly different. Although erosivity measured during summer exceeds that recorded in winter, the data indicate that large percentages of winter rainfall events on Mauritius are erosive and rainfall from non-tropical cyclones can pose a substantial erosion risk. Soil erosion risk occurs from storm-scale to synoptic-scale events, and extreme rainfall events generate the bulk of the erosivity. This paper also highlights that the use of rainfall records at an event scale in soil erosion risk assessments on tropical islands with a complex topography increases the effectiveness of erosivity estimates. Source


Vincent L.A.,Environment Canada | Aguilar E.,Rovira i Virgili University | Saindou M.,British Petroleum | Hassane A.F.,British Petroleum | And 9 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2011

A workshop on climate change indices was held at the Mauritius Meteorological Services in October 2009 to produce the first analysis of climate trends for the countries of the western Indian Ocean. Scientists brought their long-term daily temperature and precipitation for a careful assessment of data quality and homogeneity, and for the preparation of climate change indices. This paper reports on the trends in daily and extreme temperature and precipitation indices for 1961-2008. The results indicate a definitive warming of surface air temperature at land stations. Annual means of the daytime and nighttime temperatures have increased at a similar rate, leading to no discernible change in the diurnal temperature range. Significant increasing trends were found in the frequency of warm days and warm nights, while decreasing trends were observed in the frequency of cold days and cold nights. Moreover, it seems that the warm extremes have changed more than the cold extremes in the western Indian Ocean region. Trends in precipitation indices are generally weak and show less spatial coherence. Regionally, a significant decrease was found in the annual total rainfall for the past 48 years. The results also show some increase in consecutive dry days, no change in daily intensity and consecutive wet days, and a decrease in extreme precipitation events. Temperature indices are highly correlated with sea surface temperatures of the region, whereas weak correlations are found with the precipitation indices. Copyright 2011 by the American Geophysical Union. Source

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