Thomas Reynolds

Southern Africa (SA) is highly sensitive to rainfall changes, as water availability significantly influences agriculture, ecosystems, and the region's socio-economic stability. Observations reveal substantial multi-decadal changes in December–February precipitation during the second half of the 20^th century, characterized by enhanced rainfall over the southern part of SA (hereafter SSA), including Madagascar (MDG), and drying to the north. More recently, however, this long-term wetting tendency has reversed, with widespread drying observed across much of the region since the mid-2000s. Despite their global significance, their impact of anthropogenic aerosols on southern African precipitation has received limited attention, and the underlying mechanisms remain unclear. We show that East Asian (EAS) anthropogenic aerosols played a key role in driving enhanced precipitation over SSA and MDG between 1945 and 2005, alongside the influence of internal variability. Increased EAS sulfate emissions strengthened interhemispheric temperature and pressure gradients, inducing a southward shift of the Intertropical Convergence Zone and associated Hadley circulation, thereby enhancing moisture convergence over SSA and MDG. After the mid-2000s, rapid reductions in EAS aerosols reversed this circulation response and contributed to declining precipitation. Applying this physical framework to near-future scenarios from the Regional Aerosol Model Intercomparison Project further suggests that continued reductions in aerosols will lead to further hydroclimatic adjustments. The recent decline in precipitation (2006–2020) coincides with reduced gross primary productivity and leaf area index, as well as intensified fire-weather conditions. These findings highlight the sensitivity of southern African hydroclimate and ecosystems to remote anthropogenic aerosol emissions.

Southern Africa (SA) is highly sensitive to rainfall changes, as water availability significantly influences agriculture, ecosystems, and the region's socio-economic stability. Observations reveal substantial multi-decadal changes in December–February precipitation during the second half of the 20^th century, characterized by enhanced rainfall over the southern part of SA (hereafter SSA), including Madagascar (MDG), and drying to the north. More recently, however, this long-term wetting tendency has reversed, with widespread drying observed across much of the region since the mid-2000s. Despite their global significance, their impact of anthropogenic aerosols on southern African precipitation has received limited attention, and the underlying mechanisms remain unclear. We show that East Asian (EAS) anthropogenic aerosols played a key role in driving enhanced precipitation over SSA and MDG between 1945 and 2005, alongside the influence of internal variability. Increased EAS sulfate emissions strengthened interhemispheric temperature and pressure gradients, inducing a southward shift of the Intertropical Convergence Zone and associated Hadley circulation, thereby enhancing moisture convergence over SSA and MDG. After the mid-2000s, rapid reductions in EAS aerosols reversed this circulation response and contributed to declining precipitation. Applying this physical framework to near-future scenarios from the Regional Aerosol Model Intercomparison Project further suggests that continued reductions in aerosols will lead to further hydroclimatic adjustments. The recent decline in precipitation (2006–2020) coincides with reduced gross primary productivity and leaf area index, as well as intensified fire-weather conditions. These findings highlight the sensitivity of southern African hydroclimate and ecosystems to remote anthropogenic aerosol emissions.

Observations show a significant increase in austral summer (December–February, DJF) precipitation over Madagascar and a dipole over southern Africa since the mid-twentieth century, with implications for unique and biodiversity-rich ecosystems in a recognized global biodiversity hotspot. Yet the physical drivers of these long-term changes remain unclear. Over the same period, rapidly increasing anthropogenic aerosol emissions from Asia substantially altered hemispheric energy distributions and are known to influence remote hydroclimate through large-scale atmospheric circulation adjustments. However, their impacts on African rainfall have not been systematically assessed. We addressed this knowledge gap using historical simulations from Coupled Model Intercomparison Project phase 6 (CMIP6) models and idealized single-forcing experiments from the Precipitation Driver Response Model Intercomparison Project (PDRMIP). Our results suggest that Asian anthropogenic aerosol emissions played a key role in the observed increase in austral summer precipitation over Madagascar and southern Africa from 1930 to 2000 alongside the influence of internal variability. Increased sulfate aerosol emissions over Asia led to regional surface cooling and strengthened interhemispheric temperature and sea-level pressure gradients. This caused a southward shift of the Intertropical Convergence Zone (ITCZ) and the associated Hadley circulation, which resulted in enhanced moisture convergence and increased precipitation over Madagascar. In contrast, after 2000, rapid reductions in Asian aerosol emissions reversed the circulation response and contributed to declining precipitation over Madagascar and southern Africa. Applying this physical framework to near-future scenarios from the Regional Aerosol Model Intercomparison Project (RAMIP) further indicates that aerosol emission reductions will continue to drive substantial hydroclimatic adjustments. These precipitation changes from 2000 to 2020 are accompanied by increased vapor pressure deficit (VPD) and reduced leaf area index (LAI) over Madagascar and southern Africa, consistent with increased vegetation water stress. Taken together, our findings highlight how remote anthropogenic aerosol forcing can influence southern African hydroclimate and moisture-sensitive forests, underscoring the broader current and near-future implications for forests and terrestrial ecosystems in the region.

Purpose: This paper presents the structural monitoring results of the world's first 3D-printed steel footbridge, using a fixed sensor network built into the bridge, to better understand both the behaviour of this novel structure and the way it is used. Design/methodology/approach: The bridge was publicly exhibited and then installed for two years in central Amsterdam. The main features of the sensor network installed to monitor its behaviour are described. The bridge's behaviour was studied using a combination of labelled data collected in controlled conditions at the University of Twente and long-term monitoring during normal use in Amsterdam. Findings: The data collected show that thermal behaviour can be effectively decoupled from the response of the bridge due to pedestrian loading and that the pedestrian movements captured by camera can be anonymized as coordinates, which can be correlated with the loads and strains produced by those pedestrians. The Pearson correlation condition is used to identify the type of movement on the bridge, effectively distinguishing between heel-drops, running and walking movements. Originality/value: The richness of such a dataset is demonstrated, measured using embedded sensors and Internet of Things technology. Analysis of these measurements gives insights into the behaviour of a unique large 3D-printed steel structure and the use of a busy piece of urban infrastructure more generally.

Indirect structural health monitoring (iSHM) for bridges typically utilises motorised vehicles. A large number of pedestrian and cycle bridges worldwide cannot practically be accessed by these vehicles. Nevertheless, such bridges are equally susceptible to ongoing accumulation of defects. This paper reports field investigation of using bicycles as exciters and sensor carriers for identifying bridge modal parameters. Data are gathered simultaneously from the moving bicycle and the subject bridge to reduce ambiguity. Bridge modal frequencies estimated using bicycle-mounted sensors are compared to baseline properties estimated using ambient and pedestrian heel drop inputs. Changes in baseline modal frequencies are observed to be correlated with varying temperature, a known cause of environmental and operational variation (EOV). The possible pollution of recorded signals due to human–bicycle interaction dynamics is considered. The combined rider–bicycle–bridge system is observed to exhibit nonstationary frequency behaviour during freewheeling traversals, and bridge resonance due to harmonic pedalling forces is demonstrated. Increased pedalling cadence is correlated with reduced frequency nonstationarity for the combined system. It is suggested that this could be due to an increase in the rider–bike subsystem fundamental frequency caused by rider posture. Collectively, these observations suggest the potential for the use of fleets of bicycles for iSHM, while highlighting the need for greater understanding of potential confounding due to rider–bicycle and rider–bicycle–bridge interaction dynamics as a source of EOV.