Bruce Hewitson

University of Cape Town | UCT · Department of Environmental and Geographical Science

In many regions of the world, frequent and continual dry spells are exacerbating drought conditions, which have severe impacts on vegetation biomes. Vegetation in southern Africa is among the most affected by drought. Here, we assessed the spatiotemporal characteristics of meteorological drought in southern Africa using the standardized precipitati...

A renewed focus on southern Africa's winter rainfall zone (WRZ) following the Day Zero drought and water crisis has not shed much light on the spatial patterns of its rainfall variability and climatological seasonality. However, such understanding remains essential in studying past and potential future climate changes. Using a dense station network...

The 2014–2018 drought over South Africa's winter rainfall zone (WRZ) created a critical water crisis which highlighted the region's drought and climate change vulnerability. Consequently, it is imperative to better understand the climatic characteristics of the drought in order to inform regional adaptation to projected climate change. In this pape...

Preamble A CORDEX white paper describing the scientific challenges in regional climate modelling and setting the basis for the CORDEX science plan and for a better-informed decision-making process at regional scale was made publicly available in May 2021 (Solman et al. 2021). While the first paper focused primarily on dynamical downscaling, here we...

Although climate change is a global phenomenon, its manifestations and consequences are different in different regions, and therefore climate information on spatial scales ranging from sub-continental to local is used for impact and risk assessments. Chapter 10 assesses the foundations of how regional climate information is distilled from multiple,...

Understanding what motivates people to act on climate change provides an opportunity to design more effective interventions, in particular, climate services interventions, by aligning them with factors that strongly influence action. Climate change risk perceptions have been shown to underlie action on climate change. Therefore, this study performs...

In many regions of the world, frequent and continual dry spells are exacerbating drought conditions, which have severe impacts on vegetation biomes. Vegetation in southern Africa is among the most affected by drought. Here, we assessed the spatiotemporal characteristics of meteorological drought in southern Africa using the Standardized Precipitati...

The results of a large ensemble of regional climate models lead to two contrasting but plausible scenarios for the precipitation change over West Africa, one where mean precipitation is projected to decrease significantly over the Gulf of Guinea in spring and the Sahel in summer, and the other where summer precipitation over both regions is project...

Supplementary Information for the paper "A tale of two futures: contrasting scenarios of future precipitation for West Africa from an ensemble of regional climate models"

As established in earlier research (Quagraine et al. 2019), analysis of the combined roles (co-behavior) of multiple climate processes provides useful insights into the drivers of regional climate variability, especially for regions with no singular large-scale circulation control. Here, we extend the previous study in order to examine the performa...

Abstract Understanding the variability of the Tropical Rain Belt (TRB) in Africa is a challenging task due to complex interactions among global, regional and local drivers of rainfall. A simple method that provides a set of three indices describing large‐scale spatial–temporal characteristics of the TRB over central and southern Africa is introduce...

We employ a large ensemble of Regional Climate Models (RCMs) from the COordinated Regional-climate Downscaling EXperiment to explore two questions: (1) what can we know about the future precipitation characteristics over Africa? and (2) does this information differ from that derived from the driving Global Climate Models (GCMs)? By taking into acco...

Climate change has severely impacted southern African vegetation over the last decades. Recent studies have shown that limiting the global warming level to well below 2 °C above pre-industrial level may reduce the catastrophic effects of anthropogenic climate change. However, there is limited knowledge on the response of vegetation to climate chang...

The study develops an approach to assess co-behaviour of climate processes. The regional response of precipitation and temperature patterns over southern Africa to the combined roles (co-behaviour) of El Niño Southern Oscillation (ENSO), Antarctic Oscillation (AAO) and Inter-Tropical Convergence Zone (ITCZ) is evaluated. Self-Organizing Maps (SOMs)...

This study examines the projected changes in the characteristics of the El Niño Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) in terms of mean state, intensity and frequency, and associated rainfall anomalies over eastern Africa. Two regional climate models driven by the same four global climate models (GCMs) and the corresponding GCM s...

Decision-scale relevant climate information on climate change is needed to inform policy and decision making, but often involves high uncertainty. To enhance confidence in interpreting regional climate projections, it is important to understand the underlying physical processes driving the change. This study explores a methodology to investigate cl...

Multi-decadal regional projections of future climate change are introduced into a linear statistical model in order to produce an ensemble of austral mid-summer maximum temperature simulations for southern Africa. The statistical model uses atmospheric thickness fields from a high-resolution (0.5° × 0.5°) reanalysis-forced simulation as predictors...

The climate change agenda is populated by actors and agencies with different objectives, values, and motivations, yet many seek decision scale climate information to inform policy and adaptation responses. A central element of this network of activity is the climate information website (CIW) that has seen a rapid and organic growth, yet with variab...

Multi-decadal regional projections of future climate change are introduced into a linear statistical model in order to produce an ensemble of austral mid-summer maximum temperature simulations for southern Africa. The statistical model uses atmospheric thickness fields from a high-resolution (0.5° x 0.5°) reanalysis-forced simulation as predictors...

This paper describes the motivation for the creation of the Vulnerability, Impacts, Adaptation and Climate Services (VIACS) Advisory Board for the Sixth Phase of the Coupled Model Intercomparison Project (CMIP6), its initial activities, and its plans to serve as a bridge between climate change applications experts and climate modelers. The climate...

The Vulnerability, Impacts, Adaptation, and Climate Services (VIACS) Advisory Board was created to provide a strong bridge between climate change applications experts and climate modelers for the Sixth Phase of the Coupled Model Intercomparison Project (CMIP6). The climate change application community comprises researchers and other specialists who...

The study focuses on the analysis of extreme precipitation events of the present and future climate over southern Africa. Parametric and non-parametric approaches are used to identify and analyse these extreme events in data from the Coordinated Regional Climate Downscaling Experiment (CORDEX) models. The performance of the global climate model (GC...

Co-production is increasingly recognized as integral to appropriate use and uptake of climate information into decision-making. However, the success of co-production is contingent on an innate understanding of the context in which it is being implemented. Climate knowledge co-production in Africa is unique and requires a nuanced approach because of...

This study presents an evaluation of the ability of 10 regional climate models (RCMs) participating in the COordinated Regional climate Downscaling Experiment - Africa (CORDEX-Africa) to reproduce the present-day spatial distribution of annual cycles of precipitation over the South African region and its borders. As found in previous studies, annua...

We analyze and intercompare the performance of a set of ten regional climate models (RCMs) along with the ensemble mean of their statistics in simulating daily precipi-tation characteristics during the West African monsoon (WAM) period (June–July–August–September). The experi-ments are conducted within the framework of the COordinated Regional Down...

A White Paper of the Climate Services Partnership Working Group on Climate Service Ethics

This book evaluates -using for the first time a single consistent methodology and the state-of-the-arte climate scenarios-, the impacts of climate change on hydro-power and irrigation expansion plans in Africa’s main rivers basins (Niger, Senegal, Volta, Congo, Nile, Zambezi, Orange); and outlines an approach to reduce climate risks through suitabl...

The ability of climate models to simulate atmospheric teleconnections provides an important basis for the use and analysis of climate change projections. This study examines the ability of COordinated Regional climate Downscaling EXperiment models, with lateral and surface boundary conditions derived from Coupled Global Climate Models (CGCMs), to s...

The history of attempts to spread scientific know-how beyond western centres of excellence is littered with failures. Capacity building needs long-term commitment, a critical mass of trainees, and a supportive home environment.

We evaluate the performance of two global circulation models (GCMs) over Southern Africa, as part of the efforts to improve the skill of seasonal forecast from a multi-model ensemble system over the region. The two GCMs evaluated in the study are the Community Atmosphere Model version 3 (CAM3) and the Hadley Centre Atmospheric Model version 3 (HadA...

This chapter serves as an introduction to Part B of this volume. It provides context for an assessment of regional aspects of climate change in different parts of the world, which are presented in the following nine chapters. While the main focus of those chapters is on the regional dimensions of impacts, adaptation, and vulnerability (IAV), this c...

he possibility of future climate change in Ghana has received much attention due to repeated droughts and floods over the last decades. The savanna zone which is described as the food basket of Ghana is highly susceptible to climate change impact. Scenarios from 20-year time slices of the near future – 2046-2065 – and the far future – 2081-2100 – c...

We examine the ability of an ensemble of 10 Regional Climate Models (RCMs), driven by ERA-Interim reanalysis, in skillfully reproducing key features of present-day precipitation and temperature (1990–2008) over West Africa. We explore a wide range of time scales spanning seasonal climatologies, annual cycles and interannual variability, and a numbe...

Climate is one of many factors to be considered in adapting systems to environmental and societal change and often it is not the most important factor. Moreover, given considerable model inadequacies, irreducible uncer-tainties, and poor accessibility to model output, we may legitimately ask whether or not regional climate projections ought to have...

In the charismatic wetlands of the Okavango Delta, Botswana, the annual floods of 2009–2011 reached magnitudes last seen 20–30 years ago, considerably affecting life of local populations and the economically important tourism industry. In this study, we analyse results from an attribution modelling system designed to examine how anthropogenic green...

Monthly-mean precipitation, mean (TAVG), maximum (TMAX) and minimum (TMIN) surface air temperatures, and cloudiness from the CORDEX-Africa regional climate model (RCM) hindcast experiment are evaluated for model skill and systematic biases. All RCMs simulate basic climatological features of these variables reasonably, but systematic biases also occ...

The delivery of downscaled climate information is increasingly seen as a vehicle of climate services, a driver for impacts studies and adaptation decisions, and for informing policy development. Empirical-statistical downscaling (ESD) is widely used; however, the accompanying responsibility is significant, and predicated on effective understanding...

This study evaluates the ability of 10 regional climate models (RCMs) from the Coordinated Regional Climate Downscaling Experiment (CORDEX) in simulating the characteristics of rainfall patterns over eastern Africa. The seasonal climatology, annual rainfall cycles, and interannual variability of RCM output have been assessed over three homogeneous...

This study evaluates the ability of 10 regional climate models (RCMs) from the Coordinated Regional Climate Downscaling Experiment (CORDEX) in simulating the characteristics of rainfall patterns over eastern Africa. The seasonal climatology, annual rainfall cycles, and interannual variability of RCM output have been assessed over three homogeneous...

The contribution of Cut-off Lows (CoLs) to precipitation and extreme rainfall frequency in South Africa has been quantified from 402 station records over the period 1979–2006. Firstly, 500 hPa CoL trajectories over Southern Africa and surrounding oceans were determined and their features thoroughly analyzed. In a second step, using daily precipitab...

This study evaluates the ability of 10 regional climate models (RCMs) from the Coordinated Regional Climate Downscaling Experiment (CORDEX) in simulating the characteristics of rainfall patterns over eastern Africa. The seasonal climatology, annual rainfall cycles, and interannual variability of RCM output have been assessed over three homogeneous...

The authors evaluate the ability of 10 regional climate models (RCMs) to simulate precipitation over Southern Africa within the Coordinated Regional Climate Downscaling Experiment (CORDEX) framework. An ensemble of 10 regional climate simulations and the ensemble average is analyzed to evaluate the models' ability to reproduce seasonal and interann...

The chapter highlights selected scientific advances made under WCRP leadership in understanding climate variability and predictability at regional scales with emphasis on the monsoon regions. They are mainly related to a better understanding of the physical processes related to the ocean-land-atmosphere interaction that characterize the monsoon var...

500-hPa Cut-off Low (CoL) trajectories over Southern Africa and surrounding oceans are established following the method presented by Favre et al. (2011). The contribution of CoLs to precipitation has been quantified from 402 in situ records over South Africa and during the 1979 to 2006 period. By composite analysis, a geographical window in which t...

Climate and weather extreme events can have powerful impacts on human society and infrastructures as well as ecosystems and wildlife. The ability of the COordinated Regional Downscaling Experiment (CORDEX)Regional Climate Models (RCMs) to capture patterns of extreme rainfall over Africa south of 10 degree S in their control simulations is assessed....

Downscaling seeks to add appropriate temporal and spatial variance to low resolution GCM predictor fields. In doing so, there is a deterministic component that is conditioned by the GCM, and a residual component which may be considered as undetermined and/or stochastic variance. For application in many sectors, such as hydrology, extreme events, or...

The need for credible regional climate change projections for use in adaptation actions and decision making is well recognised. The CORDEX activity has evolved in large part as a response to this need. For the most part, CORDEX has so far been dominated by regional climate modelling (RCM) activities. However, implicit in CORDEX is the use of statis...

In this study, we present the collation and analysis of the gridded land-based dataset of indices of temperature and precipitation extremes: HadEX2. Indices were calculated based on station data using a consistent approach recommended by the World Meteorological Organization (WMO) Expert Team on Climate Change Detection and Indices, resulting in th...

We analyse temperature and precipitation changes for the late decades of the 21st century (with respect to present day conditions) over 23 land regions of the world from 18 recent transient climate change experiments with coupled atmosphere-ocean General Circulation Models (AOGCMs). The analysis involves two different forcing scenarios and nine mod...

The characteristics of Southern Cut-off Lows (CoLs) are studied for the period 1979–2008. The systematic identification of CoLs is realized by applying an original automated scheme using mean daily geopotential height and air temperature at 500hPa NCEP-DOE II Reanalysis data. From closed lows’ trajectories established from the Equator to the polar...

Despite the significant progress mentioned above, some gaps and challenges continue to persist. The spatial coverage, quality and access to climate data and information remain a major challenge in most SADC member states. There is lack of scientific capacity, research infrastructure and skills to communicate knowledge in a way that would translate...

This study investigates the relationship between the errors in surface wind speeds forecast with the Weather Research and Forecasting (WRF) model in two regions of South Africa, and the synoptic scale circulation features found for these areas. The archetype circulation scenarios are identified using a Self-Organising Map (SOM) and the hourly wind...

Recent global climate change studies have concluded with a high confidence level that the observed increasing trend in the global-mean surface air temperatures since mid-20th century is triggered by the emission of anthropogenic greenhouse gases (GHGs). The increase in the global-mean temperature due to anthropogenic emissions is nearly monotonic a...

This paper presents an evaluation of the simulated coupling between cloud base height (CBH) and surface fluxes over selected Coordinated Enhanced Observing Period (CEOP) reference stations by five regional climate models as part of a transferability intercomparison experiment. The model results are compared with station data obtained during the fir...