John H. Marsham

University of Leeds · School of Earth and Environment

Humid heatwaves are a growing risk to human and animal health, especially in tropical regions. While there is established research on dry-bulb temperature heatwaves, greater understanding of the meteorological drivers is urgently needed. In this study, we find that recent rainfall is a key control on the occurrence of humid heatwaves and its effect...

Plain Language Summary Movements of tropical air are driven by interactions between large, continental–scale circulations and localized deep convection — cells of ascending moist air reaching to the tropopause. These cells can aggregate to form Mesoscale Convective Systems (MCSs), long–lived thunderstorm clusters with large cold cloud shields that...

Mesoscale Convective Systems (MCSs) play a critical role in tropical rainfall patterns and circulations. To reduce persistent biases and improve understanding of the climate system, international groups have called for unprecedented investment in global convection-permitting (CP) climate models. It is essential such models accurately represent MCSs...

Simulating the West African monsoon (WAM) system using numerical weather and climate models suffers from large uncertainties, which are difficult to assess due to nonlinear interactions between different components of the WAM. Here we present a fundamentally new approach to the problem by approximating the behavior of a numerical model – here the I...

Existing weather models are known to have poor skill at forecasting rainfall over East Africa, where there are regular threats of drought and floods. Improved forecasts could reduce the effects of these extreme weather events and provide significant socioeconomic benefits to the region. We present a novel machine learning-based method to improve pr...

The Maritime Continent (MC) regularly experiences powerful convective storms that produce intense rainfall, flooding and landslides, which numerical weather prediction models struggle to forecast. Nowcasting uses observations to make more accurate predictions of convective activity over short timescales (∼ 0–6 h). Optical flow algorithms are effect...

Simulating the West African monsoon (WAM) system using numerical weather and climate models suffers from large uncertainties, which are difficult to assess due to non-linear interactions between different components of the WAM. Here we present a fundamentally new approach to the problem by approximating the behavior of a numerical model – here the...

East Africa is highly vulnerable to extreme weather events, such as droughts and floods. Skillful seasonal forecasts exist for the October–November–December short rains, enabling informed decisions, whereas seasonal forecasts for the March–April–May (MAM) long rains have historically had low skill, limiting preparation capacity. Therefore, improved...

The Maritime Continent (MC) regularly experiences powerful convective storms that produce intense rainfall, flooding and landslides, which numerical weather prediction models struggle to forecast. Nowcasting uses observations to make more accurate predictions of convective activity over short timescales (~0–6 hours). Optical flow algorithms are eff...

Abstract This study assessed the sensitivity of the West African climate to varying vegetation fractions. The assessment of a such relationship is critical in understanding the interactions between land surface and atmosphere. Two sets of convection‐permitting simulations from the UK Met Office Unified Model at 12 km horizontal resolution covering...

The Maritime Continent experiences some of the world’s most severe convective rainfall, with an intense diurnal cycle. A key feature is offshore propagation of convection overnight, having peaked over land during the evening. Existing hypotheses suggest this propagation is due to the nocturnal land breeze and environmental wind causing low-level co...

The EUREC⁴A (Elucidating the role of clouds–circulation coupling in climate) and ATOMIC (Atlantic Tradewind Ocean‐Atmosphere Mesoscale Interaction Campaign) joint field campaign gathered observations to better understand the links between trade‐wind cumulus clouds, their organization, and larger scales, a large source of uncertainty in climate proj...

Climate change is predicted to increase rainfall intensity in tropical regions. Convection permitting (CP) climate models have been developed to address deficiencies in conventional climate models that use parameterised convection. However, to date, precipitation projections from CP climate models have not been used in conjunction with hydrological...

Precipitation across East Africa shows marked interannual variability. Seasonal forecast skill for the OND short rains is significantly higher than for the MAM long rains, which also exhibit poorly understood decadal variability. On sub‐seasonal time‐scales rainfall is influenced strongly by the phase of the Madden–Julian Oscillation (MJO); here we...

Many natural forests in Southeast Asia are degraded following decades of logging. Restoration of these forests is delayed by ongoing logging and tropical cyclones, but the implications for recovery are largely uncertain. We analysed meteorological, satellite and forest inventory plot data to assess the effect of Typhoon Doksuri, a major tropical cy...

The CORDEX Flagship Pilot Study ELVIC (climate Extremes in the Lake VICtoria basin) was recently established to investigate how extreme weather events will evolve in this region of the world and to provide improved information for the climate impact community. Here we assess the added value of the convection-permitting scale simulations on the repr...

Global efforts to upgrade water, drainage, and sanitation services are hampered by hydrometeorological data-scarcity plus uncertainty about climate change. Intensity–duration–frequency (IDF) tables are used routinely to design water infrastructure so offer an entry point for adapting engineering standards. This paper begins with a novel procedure f...

Testbeds have become integral to advancing the transfer of knowledge and capabilities from research to operational weather forecasting in many parts of the world. The first high-impact weather testbed in tropical Africa was recently carried out through the African SWIFT program, with participation from researchers and forecasters from Senegal, Ghan...

Climate change is expected to increase the frequency and intensity of rainfall extremes. Understanding future changes in rainfall is necessary for adaptation planning. Eastern Africa is vulnerable to rainfall extremes because of low adaptive capacity and high future population growth. Convection-permitting climate models have been found to better r...

Children (<5 years) are highly vulnerable during hot weather due to their reduced ability to thermoregulate. There has been limited quantification of the burden of climate change on health in sub-Saharan Africa, in part due to a lack of evidence on the impacts of weather extremes on mortality and morbidity. Using a linear threshold model of the rel...

The Leeds Africa Climate Hackathon aimed to generate user‐relevant narratives of possible future climate in East and West Africa relevant to hydroelectric power generation and agriculture respectively. Here we discuss how the virtual hackathon was organised, present the results, and examine the lessons learned from running such a hackathon. We foun...

The West African monsoon has a clear diurnal cycle in boundary layer properties, synoptic flow, and moist convection. A nocturnal low-level jet (LLJ) brings cool, moist air into the continent and we hypothesize that it may support storms by providing vertical wind shear and a source of moisture. We use idealized simulations to investigate how the m...

Vertical wind shear is known to play a key role in the organization and intensity of mesoscale convective systems (MCSs) in West and Central Africa. A decadal increase in vertical wind shear has recently been linked to a decadal increase in intense MCSs over the Sahel. Here, the effects of vertical wind shear on MCSs over West and Central Africa ha...

This document outlines the suggested procedures for the operational production of nowcast warnings by African National Meteorological and Hydrological Services (NMHSs) developed by the Global Challenges Research Fund (GCRF) African SWIFT (Science for Weather Information and Forecasting Techniques) project. Information from geostationary satellites...

In tropical convective climates, where numerical weather prediction of rainfall has high uncertainty, nowcasting provides essential alerts of extreme events several hours ahead. In principle, short-term prediction of intense convective storms could benefit from knowledge of the slowly-evolving land surface state in regions where soil moisture contr...

The CORDEX Flagship Pilot Study ELVIC (climate Extremes in the Lake VICtoria basin) was recently established to investigate how extreme weather events will evolve in this region of the world and to provide improved information for the climate impact community. Here we assess the added value of the convection-permitting scale simulations on the repr...

The ability to predict heavy rain and floods in Africa is urgently needed to reduce the socioeconomic costs of these events and increase resilience as climate changes. Numerical weather prediction in this region is challenging, and attention is being drawn to observationally based methods of providing short-term nowcasts (up to ∼6-h lead time). In...

The West African monsoon (WAM) is the dominant feature of West African climate providing the majority of annual rainfall. Projections of future rainfall over the West African Sahel are deeply uncertain with a key reason likely to be moist convection, which is typically parameterized in global climate models. Here, we use a pan-Africa convection per...

The ‘silent revolution’ of numerical weather prediction (NWP) has led to significant social benefits and billions of dollars in economic benefits to mid-latitude countries, however the level of benefit in sub-Saharan Africa has been very limited, despite the potential to save lives, improve livelihoods, protect property and infrastructure and boost...

The lake–land breeze circulation over Lake Victoria was observed in unprecedented detail with a research aircraft during the HyVic pilot flight campaign in January 2019. An evening and morning flight observed the lake and land breezes respectively under mostly dry conditions. The circulation was observed at various heights along a transect across t...

Due to associated hydrological risks, there is an urgent need to provide plausible quantified changes in future extreme rainfall rates. Convection-permitting (CP) climate simulations represent a major advance in capturing extreme rainfall and its sensitivities to atmospheric changes under global warming. However, they are computationally costly, li...

Tailored climate change information is essential to understand future climate risks and identify relevant adaptation strategies. However, distilling and effectively communicating decision-relevant information from climate science remains challenging. In this paper, we develop and apply an iterative stakeholder engagement approach and a Site Specifi...

The summertime Sahara and Sahel are the world’s largest source of airborne mineral dust. Cold-pool outflows from moist convection (‘haboobs’) are a dominant source of summertime uplift but are essentially missing in global models, raising major questions on the reliability of climate projections of dust and dust impacts. Here we use convection-perm...

The canonical view of the Maritime Continent (MC) diurnal cycle is deep convection occurring over land during the afternoon and evening, tending to propagate offshore overnight. However, there is considerable day-to-day variability in the convection, and the mechanism of the offshore propagation is not well understood. We test the hypothesis that l...

Africa is poised for a revolution in the quality and relevance of weather predictions, with potential for great benefits in terms of human and economic security. This revolution will be driven by recent international progress in nowcasting, numerical weather prediction, theoretical tropical dynamics and forecast communication, but will depend on su...

East Africa is highly reliant on agriculture and has high rates of soil erosion which negatively impact agricultural yields. Climate projections suggest that rainfall intensity will increase in East Africa, which is likely to increase soil erosion. Soil erosion estimates require information on rainfall erosivity, which is calculated using sub-daily...

Land-atmosphere interactions have an important influence on Amazon precipitation (P), but evaluation of these processes in climate models has so far been limited. We analysed relationships between Amazon P and evapotranspiration (ET) in CMIP5 models to evaluate controls on surface moisture fluxes and assess the credibility of regional P projections...

This poster investigates the performance of the convection-permitting models associated with an aerosols module. We also show how the accumulted rainfaill can be improve by mineral dust over West Africa

Haboob occurrence strongly impacts the annual variability of airborne desert dust in North Africa with more dust raised from erodible surfaces in the early summer (monsoon) season when deep convective storms are common but soil moisture and vegetation cover are low. On 27 June 2018, a large dust storm is initiated in North Africa associated with an...

There is a huge opportunity for the African continent to benefit from the ‘silent revolution’ in weather forecasting that has been realised in the mid-latitudes throughout the twentieth century. While there are tremendous societal and economic benefits from advancing the science behind weather forecasting in sub-Saharan Africa, there are also signi...

Water recycled through transpiring forests influences the spatial distribution of precipitation in the Amazon and has been shown to play a role in the initiation of the wet season. However, due to the challenges and costs associated with measuring evapotranspiration (ET) directly and high uncertainty in remote-sensing ET retrievals, the spatial and...

There is a great demand to improve predictions of high‐impact weather across the African continent. This is because of the high frequency of intense convective storms that often produce severe flooding, strong winds and lightning, combined with the vulnerability of people, infrastructure and businesses to such hazards. The skill of numerical weathe...

A coherent synoptic sequence, mostly over North Africa, is identified whereby an upper‐level midlatitude trough (in November–March) excites several days of quasi‐stationary near‐surface warming across the Sahara, leading to rainfall events over northern Congo (NC), and perturbed weather more widely. Ahead of NC rainfall events, composite sequences...

Pan-Africa convection-permitting regional climate model simulations have been performed to study the impact of high resolution and the explicit representation of atmospheric moist convection on the present and future climate of Africa. These unique simulations have allowed European and African climate scientists to understand the critical role that...

Constructing climate information to inform climate change risk-related decision-making is challenging and requires a rigorous interrogation and understanding of multiple lines of evidence and an assessment of the values, limits and uncertainties involved. Critically, there is no definitive approach agreed on by all climate scientists. Rather, a ran...

Squall lines dominate rainfall in the West African Sahel, and evidence suggests they have increased in intensity over recent decades. Stronger wind shear may be a key driver of this trend and could continue to strengthen with climate change. However, global numerical models struggle to capture the role of shear for organised convection, making pred...

Ethiopia and South Sudan contain several population centers and important ecosystems that depend on July–August rainfall. Here we use two models to understand current and future rainfall: the first ever pan-African numerical model of climate change with explicit convection and a parameterized model that resembles a typical regional climate model at...

The Eastern Africa precipitation seasonal cycle is of significant societal importance, and yet the current generation of coupled global climate models fails to correctly capture this seasonality. The use of convective parametrisation schemes is a known source of precipitation bias in such models. Recently, a high-resolution regional model was used...

Plain Language Summary Lightning depends on ascending air in thunderstorms and the collision of cloud ice particles, which charge the thundercloud. Many climate models have too coarse a resolution to reliably capture these processes. We focus on Africa, which has some of the most frequent lightning in the world. We use a model that is much higher r...

The East African long rains constitute the main crop‐growing season in the region. Interannual predictability of this season is low in comparison to the short rains, and recent decadal drying contrasts with climate projections of a wetter future (the “East African climate paradox”). Here, we show that long rains rainfall totals are strongly correla...

Water recycled through transpiring forests influences the spatial distribution of precipitation in the Amazon and has been shown to play a role in the initiation of the wet season. However, due to the challenges and costs associated with measuring evapotranspiration (ET) directly, plus the high uncertainty and discrepancies across remote-sensing re...

Satellite nowcasting potentially provides a vital opportunity to mitigate against the risks of severe weather in tropical Africa, where population growth and climate change are exposing an ever growing number of people to weather hazards. Numerical weather prediction demonstrates limited skill for much of Africa and weather radars are rare. However...

Current climate precipitation and temperature extremes have been identified by decision makers in West Africa among the more impactful weather events causing lasting socio-economic damage. In this article, we use a plausible future-climate scenario (RCP 8.5) for the end of the 21st Century to explore the relative commonness of such extremes under g...

This guide provides a practical overview of the first pan-African, kilometre-scale convection-permitting regional climate simulations (CP4-Africa), run as part of the Future Climate for Africa (FCFA) programme’s Improving Model Processes for African Climate (IMPALA) project. CP4-Africa provides the first convection-permitting resolution, multi-year...

Due to high present-day temperatures and reliance on rainfed agriculture, sub-Saharan Africa is highly vulnerable to climate change. We use a comprehensive set of global (CMIP5) and regional (CORDEX-Africa) climate projections and a new convection-permitting pan-Africa simulation (and its parameterized counterpart) to examine changes in rainfall an...

Improved atmospheric predictions across time-scales are important for the development of greater resilience of the West African population to hazardous weather and climate change. The EU-funded project Dynamics- Aerosol-Chemistry-Cloud Interactions in West Africa (DACCIWA) produced the most comprehensive observational dataset of the atmosphere over...