Andries Kruger - Academia.edu (original) (raw)

Papers by Andries Kruger

South African Journal of Science, 2016

While various extreme wind studies have been undertaken for South Africa for the purpose of, amon... more While various extreme wind studies have been undertaken for South Africa for the purpose of, amongst others, developing strong wind statistics, disaster models for the built environment and estimations of tornado risk, a general analysis of the strong wind hazard in South Africa according to the requirements of the National Disaster Management Centre is needed. The purpose of the research was to develop a national profile of the wind hazard in the country for eventual input into a national indicative risk and vulnerability profile. An analysis was undertaken with data from the South African Weather Service’s long-term weather stations to quantify the wind hazard on a municipal scale, taking into account that there are more than 220 municipalities in South Africa. South Africa is influenced by various strong wind mechanisms occurring at various spatial and temporal scales. This influence is reflected in the results of the analyses which indicated that the wind hazard across South Afr...

Weather and climate extremes, Dec 1, 2022

DTU Wind Energy, 2021

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&lt;p&gt;An atlas of the 50-year gust wind at a resolution of 3 s is calculated o... more &lt;p&gt;An atlas of the 50-year gust wind at a resolution of 3 s is calculated over South Africa, at a spatial resolution of 3.3 km at several heights, including 10 m and 60 m where measurements are available.&lt;/p&gt;&lt;p&gt;In developing the atlas, first, 30-year wind climate (1990 - 2019) is simulated using the Weather Research and Forecasting (WRF) model. The WRF model was initialized and forced with the ERA5 data, with three nested domains and the innermost one, covering the whole country, has a spatial resolution of 3.3 km. The model outputs include the wind time series at several heights (50 m, 100 m and 200 m) every 30 minutes. The 50-year 30-min winds at several heights are then obtained by application of a suitable extreme value distribution. Afterwards, the Kaimal turbulence model is applied, in connection with an assumption of Gaussian process for the time series in the time scale 30 min to 3 s, to obtain the corresponding 3 s gust value to the 30-min values of the 50-year winds.&lt;/p&gt;&lt;p&gt;There is a prevalence of a variety of strong wind events in South Africa, including mid-latitude cyclones, fronts and thunderstorms. The different physical mechanisms have different levels of challenges to the simple modeling approaches applied above. For more than 100 measurement stations, the 50-year gust values have also been calculated, mostly at 10 m, some at 60 m. They are used to validate the modeled values and identify regions and areas where our meso-to-turbulence modeling needs improvement or adjustment to eventually produce a verified extreme gust atlas.&lt;/p&gt;

Extreme wind atlases of South Africa were developed using three reanalysis data and recently deve... more Extreme wind atlases of South Africa were developed using three reanalysis data and recently developed approaches. The results are compared with the maps produced using standard wind measurements over the region. It was found that different reanalyses with the same approach provide similar spatial distribution of the extreme wind with coarse resolution data giving smaller extreme winds. The CFSR surface winds at 38 km horizontal resolution provides the best spatial distribution of the extreme winds.

Bulletin of the American Meteorological Society, 2020

DR ANDRIES KRUGER obtained his MSc degree from the University of Cape Town in the Geographical an... more DR ANDRIES KRUGER obtained his MSc degree from the University of Cape Town in the Geographical and Environmental Sciences, and his PhD from the University of Stellenbosch in Civil Engineering, with research topic “Wind Climatology and Statistics of South Africa relevant to the Design of the Built Environment”. Since 1985 he has been involved in the observation, analysis and research of historical climate at the South African Weather Service. This included climate change and variability research, the authoring of general climate publications, and other climatological studies through consultation. He is the author or co-author of a substantial number of scientifi c publications.

Bulletin of the American Meteorological Society

Extreme precipitation occurring on consecutive days may substantially increase the risk of relate... more Extreme precipitation occurring on consecutive days may substantially increase the risk of related impacts, but changes in such events have not been studied at a global scale. Here we use a unique global dataset based on in situ observations and multimodel historical and future simulations to analyze the changes in the frequency of extreme precipitation on consecutive days (EPCD). We further disentangle the relative contributions of variations in precipitation intensity and temporal correlation of extreme precipitation to understand the processes that drive the changes in EPCD. Observations and climate model simulations show that the frequency of EPCD is increasing in most land regions, in particular, in North America, Europe, and the Northern Hemisphere high latitudes. These increases are primarily a consequence of increasing precipitation intensity, but changes in the temporal correlation of extreme precipitation regionally amplify or reduce the effects of intensity changes. Chang...

International Journal of Climatology, 2021

The temporal and spatial distribution of the frequency of breaking highest and lowest daily maxim... more The temporal and spatial distribution of the frequency of breaking highest and lowest daily maximum and minimum temperature records over the period of 1951–2019 has been investigated for South Africa. Temperature records are station specific and defined as either larger or smaller than any previous values in a time series of specific year‐days. Daily maximum and minimum temperatures from homogenized time series of 25 weather stations in South Africa were analysed. Aspects considered to influence the frequency of record‐breaking events were the warming trend and variance. The study found that the record‐breaking frequencies of the highest daily maximum (high Tmax) and some high daily minimum temperature (high Tmin) records were higher than the theoretically expected number in a stationary climate. This was particularly apparent near the end of the analysis period. The ratio of highest maximum to lowest minimum temperature records was almost an equal 1:1 ratio near the start of the analysis period and increased to a about 4:1 in the last decade of the period. Focusing on the last decade, that is, 2010–2019 the study found that there is a different spatial pattern between the occurrence of high Tmax and high Tmin records. For high Tmax records the highest number were mostly recorded by stations over the central parts of the country (e.g., Kimberley, Glen College and Bloemfontein). In contrast, the highest number of high Tmin records were less confined spatially. Even when considering the general warming due to climate change, many more high temperature records are broken than expected in certain regions and on average. We deduce that the higher than expected numbers of high Tmax and high Tmin records in the latter part of the analysis period were mainly due to the variability in the warming trend with acceleration in the last decade.

Please help us populate SUNScholar with the post print version of this article. It can be e-maile... more Please help us populate SUNScholar with the post print version of this article. It can be e-mailed to: scholar@sun.ac.zaIngenieursweseSiviele Ingenieurswes

For the first time in serveral years, the El Nino-Southern Oscillation did not dominate regional ... more For the first time in serveral years, the El Nino-Southern Oscillation did not dominate regional climate conditions around the globe. A weak La Ni a dissipated to ENSOneutral conditions by spring, and while El Nino appeared to be emerging during summer, this phase never fully developed as sea surface temperatures in the eastern conditions. Nevertheless, other large-scale climate patterns and extreme weather events impacted various regions during the year. A negative phase of the Arctic Oscillation from mid-January to early February contributed to frigid conditions in parts of northern Africa, eastern Europe, and western Asia. A lack of rain during the 2012 wet season led to the worst drought in at least the past three decades for northeastern Brazil. Central North America also experienced one of its most severe droughts on record. The Caribbean observed a very wet dry season and it was the Sahel's wettest rainy season in 50 years. Overall, the 2012 average temperature across glo...

DR ANDRIES KRUGER obtained his MSc degree from the University of Cape Town in the Geographical an... more DR ANDRIES KRUGER obtained his MSc degree from the University of Cape Town in the Geographical and Environmental Sciences, and his PhD from the University of Stellenbosch in Civil Engineering, with research topic "Wind Climatology and Statistics of South Africa relevant to the Design of the Built Environment". Since 1985 he has been involved in the observation, analysis and research of historical climate at the South African Weather Service. This included climate change and variability research, the authoring of general climate publications, and other climatological studies through consultation. He is the author or co-author of a substantial number of scientific publications.

Bulletin of the American Meteorological Society, 2019

Editor’s note: For easy download the posted pdf of the State of the Climate for 2019 is a low-res... more Editor’s note: For easy download the posted pdf of the State of the Climate for 2019 is a low-resolution file. A high-resolution copy of the report is available by clicking here. Please be patient as it may take a few minutes for the high-resolution file to download.

Bulletin of the American Meteorological Society, 2017

Editor’s note: For easy download the posted pdf of the State of the Climate for 2017 is a low-res... more Editor’s note: For easy download the posted pdf of the State of the Climate for 2017 is a low-resolution file. A high-resolution copy of the report is available by clicking here. Please be patient as it may take a few minutes for the high-resolution file to download.

International Journal of Climatology, 2016

Previous assessments of historical trends of measured surface temperature in South Africa have al... more Previous assessments of historical trends of measured surface temperature in South Africa have all shown a general upward trend, in both mean and extreme values, over recent decades. In addition, some regional differences in trends have been identified. Most of these studies focused on the period from about 1961 up to the last year that could be included before publication, as only climate stations situated in the same position for the entire analysis period were analysed. A data homogenisation procedure enabled the combination of time series of stations from which trend analysis could be applied, extending the common analysis period for this study back to around 1931. The trend results, based on the WMO ETCCDI indices, continue to show the general warming trend shown in previous analyses, with a general increase in extreme warm events, and a general decrease in extreme cold events across South Africa. The analysis of seasonal trends show that, while there are noteworthy differences on a regional basis, austral summer shows on average the strongest warming, followed by autumn, winter and spring. The central interior, which exhibited significant cooling in previous analyses, now shows non-significant or similar trends when compared to the other parts of South Africa. There is no countrywide acceleration in the warming trends, but some regional consistencies in the temporal changes in trends could be determined, i.e. increases in trends in the central interior and decreases in trends along most of the coastal region.

The complexity of the wind climate of Cape Town and its surroundings can be shown by the measurem... more The complexity of the wind climate of Cape Town and its surroundings can be shown by the measurements of specific wind phenomena by weather stations around Table Mountain. It is shown that there are substantial differences between wind speed characteristics affecting various parts of the city. These differences between the wind at the different locations are further complicated by the main strong wind mechanisms prevailing in the region, i.e. north-westerly winds from passing extratropical cyclones, mainly in the austral winter, and southeasterlies from ridging high-pressure systems, mainly in the summer months. This initial investigation is the precursor of a broader study involving wind tunnel modelling, wind measurements and climate modelling, to provide a comprehensive analysis of the spatial variability of strong winds in the Cape Peninsula.

International Journal of Climatology, 1999

Regions of correlation between South African late summer rainfall and sea-surface temperature (SS... more Regions of correlation between South African late summer rainfall and sea-surface temperature (SST) in the NINO3 region were identified. Regions identified for late summer showed a much better spatial coherence than was the case for early summer. These regions were then compared with eight homogeneous rainfall regions in South Africa, identified by Mason (Mason, S.J. 1998. Int. J. Climatol., 18,

South African Journal of Science, 2016

Weather and climate extremes, Dec 1, 2022

DTU Wind Energy, 2021

Bulletin of the American Meteorological Society, 2020

Bulletin of the American Meteorological Society

International Journal of Climatology, 2021

DR ANDRIES KRUGER obtained his MSc degree from the University of Cape Town in the Geographical an... more DR ANDRIES KRUGER obtained his MSc degree from the University of Cape Town in the Geographical and Environmental Sciences, and his PhD from the University of Stellenbosch in Civil Engineering, with research topic "Wind Climatology and Statistics of South Africa relevant to the Design of the Built Environment". Since 1985 he has been involved in the observation, analysis and research of historical climate at the South African Weather Service. This included climate change and variability research, the authoring of general climate publications, and other climatological studies through consultation. He is the author or co-author of a substantial number of scientific publications.

Bulletin of the American Meteorological Society, 2019

Bulletin of the American Meteorological Society, 2017

International Journal of Climatology, 2016

International Journal of Climatology, 1999