Precipitation intensity-duration-frequency curves and their uncertainties for Ghaap plateau

• Published in: Climate risk management 2017, Vol.16 (C), p.1-9
• Main Authors: Tfwala, C.M., van Rensburg, L.D., Schall, R., Mosia, S.M., Dlamini, P.
• Format: Article
• Language: English
• Subjects: Generalized extreme value distribution function; Ghaap plateau; Precipitation intensity-duration-frequency curves; Uncertainty levels
• ISSN: 2212-0963; 2212-0963
• DOI: 10.1016/j.crm.2017.04.004

Engineering infrastructures such as stormwater drains and bridges are commonly designed using the concept of Intensity-Duration-Frequency (IDF) curves, which assume that the occurrence of precipitation patterns and distributions are spatially similar within the drainage area and remain unchanged throughout the lifespan of the infrastructures (stationary). Based on the premise that climate change will alter the spatial and temporal variability of precipitation patterns, inaccuracy in the estimation of IDF curves may occur. As such, prior to developing IDF curves, it is crucial to analyse trends of annual precipitation maxima. The objective of this study was to estimate the precipitation intensities and their uncertainties (lower and upper limits) for durations of 0.125, 0.25, 0.5, 1, 2, 4, and 6h and return periods of 2, 10, 25, 50 and 100years in the Ghaap plateau, Northern Cape Province, South Africa using the Generalized Extreme Value (GEV) distribution. The annual precipitation maxima were extracted from long-term (1918–2014) precipitation data for four meteorological stations (Postmasburg, Douglas, Kuruman and Groblershoop) sourced from the South African Weather Services (SAWS). On average, the estimated extreme precipitation intensities for the plateau ranged from 4.2mm/h for 6h storm duration to 55.8mm/h for 0.125h at 2years return period. At 100year return period, the intensity ranged from 13.3mm/h for 6h duration to 175.5mm/h for the duration of 0.125h. The lower limit of uncertainty ranged from 11.7% at 2years return period to 26% at 100year return period, and from 12.8% to 58.4% for the upper limit for the respective return periods. This methodology can be integrated into policy formulation for the design of stormwater and flood management infrastructures in the Ghaap plateau, where mining is the main economic activity.