Conditional modelling approach to multivariate extreme value distributions: application to extreme rainfall events in South Africa

2021 ◽  
Author(s):  
Legesse Kassa Debusho ◽  
Tadele Akeba Diriba
Keyword(s):  
South Africa ◽  
Extreme Rainfall ◽  
Extreme Value ◽  
Extreme Value Distributions ◽  
Extreme Rainfall Events ◽  
Rainfall Events ◽  
Multivariate Extreme Value ◽  
Modelling Approach

scholarly journals A Numerical Model Study of an Intense Cutoff Low Pressure System over South Africa

2007 ◽  
Vol 135 (3) ◽  
pp. 1128-1150 ◽  
Author(s):  
A. T. Singleton ◽  
C. J. C. Reason
Keyword(s):  
South Africa ◽  
Numerical Model ◽  
Extreme Rainfall ◽  
South Coast ◽  
African Region ◽  
Extreme Rainfall Events ◽  
Rainfall Events ◽  
Low Level ◽  
Southern African Region ◽  
Cutoff Low

Abstract Investigations of extreme rainfall events in the southern African region are limited by the paucity of the observational network. Furthermore, the lack of full radar coverage for South Africa makes quantitative precipitation estimation difficult. Therefore, numerical modeling represents the most effective method for improving the understanding of the mechanisms that contribute to extreme rainfall events in this region with the caveat that accurate validation of model simulations is hampered by the limited observations in the region. This paper describes an intense cutoff low event over South Africa that led to record rainfall and flash flooding along the south coast of the country and adjoining hinterland. Analyses from the Global Forecast System model showed that the cutoff aloft was accompanied by a strong low-level jet (LLJ) impinging onto the south coast where rainfall was heaviest, and that lapse rates were steep in the lower troposphere. Simulations of the event were carried out using a numerical model [i.e., the fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5)], which showed that severe convection occurred over the ocean on the right-hand side of the LLJ, and at its leading edge where it impinged on the coastal topography. This topography was also very important in providing additional forcing for the ascent of moist air. A factor separation technique was used to show that surface heat fluxes from the warm sea surface temperature (SST) of the Agulhas Current were important in enhancing low-level cyclogenesis, and that topography was important in maintaining the position of the low-level coastal depression, which led to favorable conditions for rainfall remaining in the same area for an extended period of time. It is suggested that improved representation of the tight topographic and SST gradients of the southern African region in NWP models or postprocessing systems would help to provide more accurate forecasts of the amount and location of heavy precipitation during cutoff low events where surface forcing is important.

Estimation of Extreme Rainfall in South Africa and Development of Methods to Account for Non-stationary Climate Data

2020 ◽  
Author(s):  
Katelyn Johnson ◽  
Jeff Smithers
Keyword(s):  
South Africa ◽  
Frequency Analysis ◽  
Return Period ◽  
Extreme Rainfall ◽  
Climate Data ◽  
Extreme Rainfall Events ◽  
Rainfall Events ◽  
New Approach ◽  
Design Rainfall ◽  
High Return

<p>The estimation of design rainfalls and design floods are required by engineers and hydrologists to design and quantify the risk of failure of hydraulic structures. Extreme design rainfall quantities such as high-return period rainfalls and the probable maximum precipitation (PMP) are needed to design high-hazard hydraulic structures. In South Africa, previous design rainfall estimates have been produced up to the 200 year return period. PMP estimates were last determined nearly 50 years ago based on only 30 years of data. Most studies on extreme rainfall reported are based on frequency analysis assuming stationary conditions. Previous studies in South Africa have assumed a stationary climate. However, the assumption of a stationary climate in rainfall and flood frequency analysis has been challenged owing to evidence of climate change. Recent literature indicates that the magnitude and frequency of extreme rainfall events has been changing and this is likely to continue in future. Hence, methods to account for trends in extreme rainfall events in a changing environment need to be developed. In addition, the concept of PMP, particularly as used for the design and safety evaluation of large dams in South Africa, is being challenged with the recommendation that high-return period design rainfalls be used in these assessments. The aims of this study are: (i) to estimate extreme design rainfall values, with a focus on return periods greater than 200 years, (ii) to update PMP estimates using updated data and modernised methods, and (iii) to account for non-stationary climate data in the estimation of these extreme rainfall events in South Africa. Frequency analysis using LH-moments, which more accurately fit the upper tail of distributions, have been used to estimate high-return period design rainfalls. Regular L-moments are shown to overestimate the extreme rainfall quantities when compared to LH-moments by giving undue favour to outliers. PMP estimates have been determined using a storm maximisation and transposition approach. Radial Basis Functions (RFBs) have been used to transpose PMP estimates to ungauged locations, producing PMPs for the entire country. Approximately 80 % of the new PMPs are greater than the previous estimates. This is probably due to the many limitations of the old approach and differences used in the new approach, indicating that the new approach undertaken in this study may provide improved estimates. The PMP represents the upper limit of extreme rainfall, however, comparisons of high-return period rainfalls to the PMP show that the PMP is sometimes exceeded by the high-return period rainfalls. To develop methods to estimate extreme design rainfall events in a non-stationary climate, this study explores the impacts of climate drivers, such as the Southern Oscillation Index (SOI), and changes in atmospheric variables, such as dew point temperature, on high-return period rainfalls and the PMP.</p>

Using regional climate models to simulate extreme rainfall events in the Western Cape, South Africa

2015 ◽  
Vol 36 (2) ◽  
pp. 689-705 ◽  
Author(s):  
Babatunde J. Abiodun ◽  
Sabina Abba Omar ◽  
Chris Lennard ◽  
Chris Jack
Keyword(s):  
South Africa ◽  
Climate Models ◽  
Regional Climate ◽  
Extreme Rainfall ◽  
Regional Climate Models ◽  
Western Cape ◽  
Extreme Rainfall Events ◽  
Rainfall Events

scholarly journals Comparison of parameters of the generalized extreme value distribution associated with extreme rainfall events in Central America

Uniciencia ◽  
2020 ◽  
Vol 34 (1) ◽  
pp. 111-128
Author(s):  
Helen S. Guillén-Oviedo ◽  
Luis R. Cid-Serrano ◽  
Eric J. Alfaro-Martínez
Keyword(s):  
Central America ◽  
Hypothesis Test ◽  
Extreme Value Distribution ◽  
Extreme Rainfall ◽  
Extreme Value ◽  
Value Distribution ◽  
Generalized Extreme Value Distribution ◽  
Generalized Extreme Value ◽  
Extreme Rainfall Events ◽  
Rainfall Events

The generalized extreme value distribution (GEVD) was used to model extreme rainfall events in Central America for a period of 30 years, beginning in 1971. Data consisted of daily rainfall records of 103 meteorological stations located throughout the isthmus. Central America was divided into 3 regions: Pacific, Caribbean and an intermediate zone. A bootstrap hypothesis test was used to compare the parameters of location, scale and form of the 3 regions. The results of the study showed significant differences between the 3 regions, mainly in terms of location and scale parameters.

scholarly journals Review: Methods for the estimation of extreme rainfall events

Water SA ◽  
2019 ◽  
Vol 45 (3 July) ◽  
Author(s):  
KA Johnson ◽  
JC Smithers
Keyword(s):  
South Africa ◽  
Extreme Events ◽  
Extreme Rainfall ◽  
Hydraulic Structures ◽  
Future Research ◽  
Extreme Rainfall Events ◽  
Rainfall Events ◽  
Extreme Floods ◽  
New Approaches ◽  
Risk Of Failure

The estimation of design rainfalls is necessary to estimate the exceedance probabilities of extreme floods required to design hydraulic structures and to quantify the risk of failure of these structures. New approaches to estimating extreme rainfall events are being developed internationally. This paper reviews methods for estimating design rainfalls, particularly extreme events, in South Africa and internationally, and highlights the need to update methods used for estimating extreme rainfall events in South Africa as a platform for future research.

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