Abstract
High-resolution rainfall data from two stations in the northern KwaZulu-Natal Drakensberg provide insight into the effect of altitude on individual rainfall event characteristics. The effect of altitude on the duration and erosivity (rainfall intensity and kinetic energy) of concurrent rainfall on the escarpment and in the foothills is analysed using 5-min interval data for the calendar year 2003. A cumulative total of 229 rainfall events, measured at the Royal Natal National Park station (1 392 m a.m.s.l.) and a temporary station on the escarpment at Sentinel Peak (3 165 m a.m.s.l.), were considered, of which 79 rainfall events were found to fall concurrently at the two stations. The data indicate that the concurrent events generate rainfall for longer on the escarpment, but that the amount of rain produced as well as the intensity at which it falls is less than that in the foothills, both in summer and winter. The escarpment appears to limit erosivity, with only 11 events meeting the set criteria for erosivity in the foothills but failing to meet the same criteria on the escarpment. This decrease in erosivity contrasts with previous models for the Drakensberg that demonstrate higher erosivity in the upper reaches, but concurs with studies in mountainous regions elsewhere which found that erosivity decreases with altitude. It is tentatively suggested that the difference in rainfall characteristics could be related to the sources of precipitation and the manner in which the escarpment zone affects the formation and distribution of rainfall. The paper also highlights the need for further research into the association between rainfall structure and synoptic conditions and the effect that the escarpment has on modifying large-scale rainproducing systems in the KwaZulu-Natal Drakensberg.
Highlights
The KwaZulu-Natal Drakensberg reaches altitudes over 3 000 m, is part of the Main Escarpment of southern Africa, and is the watershed border between KwaZulu-Natal and Lesotho
Mean seasonal rainfall energy was derived from the relationship between annual kinetic energy and mean annual rainfall for Soil Loss Estimation Model of Southern Africa (SLEMSA), and long-term average annual erosivity as well as the seasonal distribution of erosivity were obtained from iso-erodent maps for Revised Universal Soil Loss Equation (RUSLE) and Universal Soil Loss Equation (USLE) (Smith et al, 2000)
Of the 113 and 116 rainfall events measured, 79 rainfall events were isolated that produced rainfall simultaneously at Sentinel Peak and Royal Natal National Park (RNNP)
Summary
The KwaZulu-Natal Drakensberg reaches altitudes over 3 000 m, is part of the Main Escarpment of southern Africa, and is the watershed border between KwaZulu-Natal and Lesotho. Subsequent to this study, actual data became available on rainfall totals and total erosivity in the KwaZulu-Natal Drakensberg (see Nel and Sumner, 2007) and it was suggested that altitude has a pronounced inverse effect on the intensity and cumulative erosivity of high rainfall events (Nel and Sumner, 2007; Nel, 2007). The lack of erosive rainstorms during early and late summer on the escarpment, and significant erosive rains during this period at lower altitudes in the foothills, are provided as reasons for erosive rainfall events on the escarpment producing less cumulative kinetic energy and erosivity (Nel and Sumner, 2007). The kinetic energy of these rainfall events was analysed to test the hypothesis that rainfall erosivity decreases with an increase in altitude
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
