Status: this preprint was under review for the journal HESS but the revision was not accepted.
Assessment of statistical characteristics of point rainfall in the Onkaparinga catchment in South Australia
M. M. Rashid,S. Beecham,and R. Chowdhury
Abstract. Spatial and temporal variations in statistical characteristics of point rainfall are important for rainfall modelling. The main objective of this study was to investigate the statistical characteristics of point rainfall and to identify a probability distribution that can model the full spectrum of daily rainfall in the Onkaparinga catchment in South Australia. Daily rainfall data from 1960 to 2010 at thirteen rainfall stations were considered. Statistical moments and autocorrelation coefficients were estimated for rainfall depths at different temporal resolutions. The heterogeneity of monthly rainfall was tested using the Precipitation Concentration Index (PCI). Interannual variability of annual and seasonal PCI was observed. The catchment was characterized by unstable monthly rainfall with PCIs of more than 10 for all rainfall stations. Relatively strong and significant autocorrelation coefficients were observed for rainfall depths at finer (daily and monthly) temporal resolutions. The performance of different distribution models was examined considering their ability to regenerate various statistics such as standard deviation, skewness, frequency distribution, percentiles and extreme values. Model efficiency statistics of modelled percentiles of daily rainfall were found to be useful for optimum threshold selection in the hybrid distributions. A hybrid of the gamma and generalized pareto (GP) distributions was found to be more efficient than any single distribution (Weibull, gamma and exponential) for modelling the full range of daily rainfall across the catchment. In addition to this, a hybrid of the Weibull and GP distributions was also proposed. The outcomes from this study will assist water engineers and hydrologists to understand the spatial and temporal characteristics of point rainfall in the Onkaparinga catchment and will hopefully contribute to the improvement of rainfall modelling and downscaling techniques.
Received: 05 Apr 2013 – Discussion started: 14 May 2013
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