Seasonal source variability of carbonaceous aerosols at the Rwanda Climate Observatory

Abstract. Sub-Saharan Africa (SSA) is a global hot spot for aerosol emissions, which affect the regional climate and air quality. In this paper, we use ground-based observations to address the large uncertainties in the source-resolved emission estimation of carbonaceous aerosols. Ambient fine fraction aerosol was collected on filters at the high-altitude (2590 m a.s.l.) Rwanda Climate Observatory (RCO), a SSA background site, during the dry and wet seasons in 2014 and 2015. The concentrations of both the carbonaceous and inorganic ion components show a strong seasonal cycle, with highly elevated concentrations during the dry season. Source marker ratios, including carbon isotopes, show that the wet and dry seasons have distinct aerosol compositions. The dry season is characterized by elevated amounts of biomass burning products, which approach ∼95 % for carbonaceous aerosols. An isotopic mass-balance estimate shows that the amount of the carbonaceous aerosol stemming from savanna fires may increase from 0.2 µg m−3 in the wet season up to 10 µg m−3 during the dry season. Based on these results, we quantitatively show that savanna fire is the key modulator of the seasonal aerosol composition variability at the RCO.

Download Full-text

Seasonal source variability of carbonaceous aerosols at the Rwanda climate Observatory

10.5194/acp-2019-1027 ◽

2019 ◽

Author(s):

August Andersson ◽

Elena N. Kirillova ◽

Stefano Decesari ◽

Langley DeWitt ◽

Jimmy Gasore ◽

...

Keyword(s):

Environmental Sustainability ◽

Fine Fraction ◽

Inorganic Ions ◽

Health Impact ◽

Dry Season ◽

Sub Saharan Africa ◽

Carbonaceous Aerosols ◽

Wet Season ◽

Aerosol Composition ◽

Background Site

Abstract. Sub-Saharan Africa (SSA) is a global hotspot for aerosol emissions, affecting regional environmental sustainability. In this paper we use atmospheric observations to address one of the major uncertainties of the, e.g., climate and health impact of SSA aerosols: the quantitative contributions from different emissions sources. Ambient fine fraction aerosol (PM2.5) were collected on filters at the high altitude (2590 m a.s.l.) Rwanda Climate Observatory (RCO), an SSA background site, during dry and wet seasons in 2014 and 2015. The concentrations of both carbonaceous aerosols and inorganic ions show a strong seasonal cycle, with highly elevated concentrations during the dry season. Source marker ratios, including carbon isotopes, show that the wet and dry seasons have distinct aerosol compositions. The dry season is characterized by elevated amounts of biomass burning products, approaching ~ 95 % for carbonaceous aerosols. An isotopic mass-balance estimate shows that the amount of the carbonaceous aerosols stemming from savanna fires may increase from ~ 0.6 μg/m3 in the wet season up to ~ 10 μg/m3 during the dry season. Taken together, we here quantitatively show that savanna fire is the key modulator of the seasonal aerosol composition variability at the RCO, an SSA background site.

Download Full-text

A Mechanistically Credible, Poleward Shift in Warm-Season Precipitation Projected for the U.S. Southern Great Plains?

Journal of Climate ◽

10.1175/jcli-d-16-0316.1 ◽

2017 ◽

Vol 30 (20) ◽

pp. 8275-8298 ◽

Cited By ~ 13

Author(s):

Melissa S. Bukovsky ◽

Rachel R. McCrary ◽

Anji Seth ◽

Linda O. Mearns

Keyword(s):

Great Plains ◽

Climate Models ◽

Climate Model ◽

Global Climate Model ◽

Regional Climate ◽

Warm Season ◽

Dry Season ◽

Wet Season ◽

Southern Great Plains ◽

Poleward Shift

Abstract Global and regional climate model ensembles project that the annual cycle of rainfall over the southern Great Plains (SGP) will amplify by midcentury. Models indicate that warm-season precipitation will increase during the early spring wet season but shift north earlier in the season, intensifying late summer drying. Regional climate models (RCMs) project larger precipitation changes than their global climate model (GCM) counterparts. This is particularly true during the dry season. The credibility of the RCM projections is established by exploring the larger-scale dynamical and local land–atmosphere feedback processes that drive future changes in the simulations, that is, the responsible mechanisms or processes. In this case, it is found that out of 12 RCM simulations produced for the North American Regional Climate Change Assessment Program (NARCCAP), the majority are mechanistically credible and consistent in the mean changes they are producing in the SGP. Both larger-scale dynamical processes and local land–atmosphere feedbacks drive an earlier end to the spring wet period and deepening of the summer dry season in the SGP. The midlatitude upper-level jet shifts northward, the monsoon anticyclone expands, and the Great Plains low-level jet increases in strength, all supporting a poleward shift in precipitation in the future. This dynamically forced shift causes land–atmosphere coupling to strengthen earlier in the summer, which in turn leads to earlier evaporation of soil moisture in the summer, resulting in extreme drying later in the summer.

Download Full-text

Aerosol characterisation including oxidative potential as a proxy of health impact

Clean Air Journal ◽

10.17159/caj/2019/29/2.7517 ◽

2019 ◽

Vol 29 (2) ◽

Author(s):

Miroslav Josipovic ◽

Catherine Leal-Liousse ◽

Belinda Crobeddu ◽

Armelle Baeza-Squiban ◽

C. Keitumetse Segakweng ◽

...

Keyword(s):

Organic Carbon ◽

Black Carbon ◽

Fine Fraction ◽

Health Impact ◽

Coarse Fraction ◽

Dry Season ◽

Wet Season ◽

Oxidative Potential ◽

Ionic Content ◽

Vaal Triangle

This study aimed to characterise aerosols sampled in the vicinity of a major industrialised area, i.e. the Vaal Triangle. It included thedetermination of oxidative potential as a predictive indicator of particle toxicity. Aerosol samples were collated through the cascadefiltering during an eight-month period (12 h over three days in one week). Three size fractions were analysed for organic carbon(OC), black carbon (BC) and oxidative potential (OP), while ionic content was presented as monthly and seasonal concentrations. Thecontinuous measurement of black carbon by an optical attenuation instrument was collated concurrently with cascade filtering. Thecarbonaceous content was low compared to the ionic one. Within the carbonaceous concentrations, the organic carbon was higherthan concentrations of black carbon in both seasons in the ultra-fine fraction; the opposite was the case for the fine fraction, whilethe coarse fraction concentrations of organic carbon in the dry season had higher concentrations than black carbon in the wet seasonand organic carbon in the wet season. The OP tended to increase as the size was decreasing for wet season aerosols, whereas, forthe dry season, the highest OP was exerted by the fine fraction. The ultrafine fraction was the one showing the most contrasting OPbetween the two seasons. Continuous monitoring indicated that the higher BC concentrations were recorded in the dry/winter partof the year, with the daily pattern of concentrations being typically bimodal, having both the morning and evening peaks in bothseasons. Within the ionic content, the dominance of sulphate, nitrate and ammonium was evident. Multiple linear correlations wereperformed between all determined compounds. Strong correlations of carboxylic acids with other organic compounds were revealed.These acids point to emissions of VOC, both anthropogenic and biogenic. Since they were equally present in both seasons, a mixtureof sources was responsible, both present in the wider area and throughout the year.

Download Full-text

Effects of the hippopotamus on the chemistry and ecology of a changing watershed

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1800407115 ◽

2018 ◽

Vol 115 (22) ◽

pp. E5028-E5037 ◽

Cited By ~ 17

Author(s):

Keenan Stears ◽

Douglas J. McCauley ◽

Jacques C. Finlay ◽

James Mpemba ◽

Ian T. Warrington ◽

...

Keyword(s):

Water Chemistry ◽

Aquatic Insect ◽

Dry Season ◽

Fish Abundance ◽

Sub Saharan Africa ◽

Aquatic Communities ◽

Wet Season ◽

Water Abstraction ◽

Hydrological Variability ◽

Invertebrate Diversity

Cross-boundary transfers of nutrients can profoundly shape the ecology of recipient systems. The common hippopotamus, Hippopotamus amphibius, is a significant vector of such subsidies from terrestrial to river ecosystems. We compared river pools with high and low densities of H. amphibius to determine how H. amphibius subsidies shape the chemistry and ecology of aquatic communities. Our study watershed, like many in sub-Saharan Africa, has been severely impacted by anthropogenic water abstraction reducing dry-season flow to zero. We conducted observations for multiple years over wet and dry seasons to identify how hydrological variability influences the impacts of H. amphibius. During the wet season, when the river was flowing, we detected no differences in water chemistry and nutrient parameters between pools with high and low densities of H. amphibius. Likewise, the diversity and abundance of fish and aquatic insect communities were indistinguishable. During the dry season, however, high-density H. amphibius pools differed drastically in almost all measured attributes of water chemistry and exhibited depressed fish and insect diversity and fish abundance compared with low-density H. amphibius pools. Scaled up to the entire watershed, we estimate that H. amphibius in this hydrologically altered watershed reduces dry-season fish abundance and indices of gamma-level diversity by 41% and 16%, respectively, but appears to promote aquatic invertebrate diversity. Widespread human-driven shifts in hydrology appear to redefine the role of H. amphibius, altering their influence on ecosystem diversity and functioning in a fashion that may be more severe than presently appreciated.

Download Full-text

Modelling the impact of a Sub-Saharan metropolis (Kampala) on the local climate during specific meteorological conditions of a dry season

10.5194/egusphere-egu21-11145 ◽

2021 ◽

Author(s):

Oscar Brousse ◽

Jonas Van de Walle ◽

Matthias Demuzere ◽

Alberto Martilli ◽

Nicole van Lipzig ◽

...

Keyword(s):

Urban Canopy ◽

Building Energy ◽

Dry Season ◽

Meteorological Conditions ◽

Sub Saharan Africa ◽

Wave Radiation ◽

Local Climate ◽

Local Climate Zones ◽

Sub Saharan ◽

The Impact

In order to build resilient cities in face of climate change in Sub-Saharan Africa, much is to be done to understand the impact of rapid and uncontrolled urbanization on the local climate in the region. Recent efforts by Brousse et al. (2019, 2020) demonstrated that using generic urban parameter information &#160;derived out of Local Climate Zones (LCZ&#160;; Stewart and Oke, 2012) maps created through the World Urban Database and Access Portal Tool framework (Ching et al. 2018) may be used to model the impact of Sub-Saharan African cities on their local climate &#8211; using the case of Kampala, the capital city of Uganda. These studies showed that despite the characteristic data scarcity on urban typologies that is present in Sub-Saharan Africa, LCZ could be used as a solution for modelling and studying the urban climates in the region.Yet these conclusions were only obtained through the use of the bulk-level urban canopy model TERRA_URB, embedded in the COSMO-CLM regional climate model. We therefore test the applicability of a more complex urban canopy models &#8211; the Building Effect Parameterization coupled to the Building Energy Model (BEP-BEM) &#8211; over the region. To do so, we focus on short periods with specific meteorological conditions during the dry season spanning from December 2017 to February 2018. These are obtained through a k-means clustering over hourly weather measurements given by the automatic weather station located at the Makerere University, in the city-center of Kampala. Wind direction and speed, 2-meter air temperature, incoming short-wave radiation, precipitation, daily temperature range, 2-meter air relative humidity and near-surface pressure are used to depict 5 weather typologies (ie. clusters) during the dry season. We chose to keep only periods with 5 consecutive days of one weather typology, which results in three 5-day periods of distinct typology. We then run the model for these periods and evaluate its outputs against the state-of-the-art simulation by Brousse et al. (2020) as well as in-situ and satellite observations for certain meteorological variables. After that, we show the effect of the recent urbanization on the local climate for each of those three periods and relate it to the variability in urban heat.This study is the first to model a tropical African city at 1 km horizontal resolution using the BEP-BEM model embedded in WRF. The latter could have major implications as more complex urban canopy models coupled to building energy models could shed light on the impact of the built environment on the livability of indoor and outdoor environments in these cities. Furthermore, insights could indeed be gained on the contribution of air conditioning heat fluxes to outdoor temperatures and the energetic consumption needed to keep indoor environments at an optimal temperature. Additionally, by resolving the urban environment in three dimensions, BEP-BEM could help increase our understanding of how specific urban planning and architectural adaptation strategies (like green or cool roofs, roof top solar panel, new building materials, urban greening etc.) may increase the citizens&#8217; thermal comfort and reduce negative health impacts under specific weather conditions.

Download Full-text

Improving Accuracy of Malaria Diagnosis in Underserved Rural and Remote Endemic Areas of Sub-Saharan Africa: A Call to Develop Multiplexing Rapid Diagnostic Tests

Scientifica ◽

10.1155/2020/3901409 ◽

2020 ◽

Vol 2020 ◽

pp. 1-7 ◽

Cited By ~ 2

Author(s):

Rasheed O. Makanjuola ◽

Andrew W. Taylor-Robinson

Keyword(s):

Low Income ◽

Diagnostic Tests ◽

Medical Condition ◽

Hot Spot ◽

Rapid Diagnostic Tests ◽

Sub Saharan Africa ◽

Low Income Countries ◽

Patient Treatment ◽

Sub Saharan ◽

Effective Diagnosis

Clinical infection with malaria, caused by parasites of the genus Plasmodium, is considered a serious medical condition with the potential to become a life-threatening emergency. This is especially relevant to low-income countries in tropical and subtropical regions of the world where high rates of malaria-related morbidity and mortality are recorded. As a means to combat this major global public health threat, rapid and effective diagnosis remains the frontline action to initiate a timely and appropriate medical intervention. From all the approaches to parasite detection, rapid diagnostic tests, so-called RDTs, are the easiest to use and most cost-effective. However, some of the limitations inherent in this methodology could hinder effective patient treatment. A primary drawback is that the vast majority of commercially available RDTs detect only one of the five species of human malaria, P. falciparum. While this is the main cause of infection in many areas, it excludes the possibility of infection with another parasite (P. vivax, P. ovale, P. malariae, and P. knowlesi) or of mixed infections containing different species. Hence, a diagnosis of non-P. falciparum malaria is missed. In turn, in resource-constrained settings where optimal microscopy is not available, a misdiagnosis of bacterial infection based on signs and symptoms alone often results in an inappropriate prescription of antibiotics. Here, we discuss how effective diagnosis of malaria and indiscriminate use of antibiotics in sub-Saharan Africa, a hot spot for P. falciparum transmission, may both be addressed by the development of innovative multiplexing RDTs that detect two or more species of Plasmodium.

Download Full-text

Impact of climate change on crop suitability in sub-Saharan Africa in parameterized and convection-permitting regional climate models

Environmental Research Letters ◽

10.1088/1748-9326/ab9daf ◽

2020 ◽

Vol 15 (9) ◽

pp. 094086

Author(s):

Sarah Chapman ◽

Cathryn E Birch ◽

Edward Pope ◽

Susannah Sallu ◽

Catherine Bradshaw ◽

...

Keyword(s):

Climate Change ◽

Climate Models ◽

Regional Climate ◽

Regional Climate Models ◽

Sub Saharan Africa ◽

Impact Of Climate Change ◽

Crop Suitability ◽

Sub Saharan

Download Full-text

Water flow pathways and the water balance within a head-water catchment containing a dambo: inferences drawn from hydrochemical investigations

Hydrology and Earth System Sciences ◽

10.5194/hess-3-581-1999 ◽

1999 ◽

Vol 3 (4) ◽

pp. 581-591 ◽

Cited By ~ 9

Author(s):

M. P. McCartney ◽

C. Neal

Keyword(s):

Water Balance ◽

Stream Water ◽

Management Strategies ◽

Dry Season ◽

Sub Saharan Africa ◽

Flow Paths ◽

Headwater Catchments ◽

Sub Saharan ◽

Flow Pathways ◽

Water Catchment

Abstract. Dambos, seasonally saturated wetlands, are widespread in headwater catchments in sub-Saharan Africa. It is widely believed that they play an important role in regional hydrology but, despite research conducted over the last 25 years, their hydrological functions remain poorly understood. To improve conceptualisation of hydrological flow paths and investigate the water balance of a small Zimbabwean catchment containing a single dambo, measurements of alkalinity and chloride in different water types within the catchment have been used as chemical markers. The temporal variation in alkalinity is consistent with the premise that all stream water, including the prolonged dry season recession, is derived predominantly from shallow sources. The proposition that dry season recession flows are maintained by water travelling at depth within the underlying saprolite is not substantiated. There is evidence that a low permeability clay lens, commonly present in many dambos, acts as a barrier for vertical water exchange. However, the highly heterogeneous chemical composition of different waters precludes quantitative hydrograph split-ting using end member mixing analysis. Calculation of the chloride mass-balance confirms that, after rainfall, evaporation is the largest component of the catchment water budget. The study provides improved understanding of the hydrological functioning of dambos. Such understanding is essential for the development and implementation of sustainable management strategies for this landform.

Download Full-text

Partial milking of cattle in smallholder herds on the Accra Plains: some factors affecting daily partial milk yield and milk composition

Animal Science ◽

10.1017/s0003356100020511 ◽

1992 ◽

Vol 54 (1) ◽

pp. 15-21 ◽

Cited By ~ 3

Author(s):

S. A. Okantah

Keyword(s):

Milk Yield ◽

Milk Composition ◽

Dry Season ◽

Sub Saharan Africa ◽

Factors Affecting ◽

Stage Of Lactation ◽

Lactation Length ◽

Sub Saharan ◽

Quadratic Effects ◽

Accra Plains

AbstractDaily partial milk yield of Sanga cows in 13 smallholder agropastoralist herds at two locations on the Accra Plains was recorded through monthly sampling. Estimates of mean daily partial milk yield and milk composition were computed from 1266 observations. The unadjusted mean daily partial milk yield was 875 (s.e. 11) g. The composition of milk: total solids (TS), fat (F) and solid-not-fat (SNF) were 131 (s.e. 14), 41 (s.e. 11) and 90 (s.e. 7) g/kg respectively. Least squares estimate of mean daily partial milk yield were 808·2 and 462·4 g with average s.e. of 41·8 for wet and dry season respectively. The wet and dry season differences in daily partial milk yield, TS and F were highly significant (P < 0·01). Seasonal difference in SNF was not significant.Herd difference in partial milk yield, TS, F and SNF were highly significant (P < 0·02). There were no significant effects of location on daily partial milk yield and SNF, although location effects on F and TS were significant (P < 0·05). The highest milk yield was observed in cows in third lactation and the lowest in cows in seventh lactation (P < 0·01). Daily partial milk yield peaked in the 3rd month of lactation. On average, lactation length was 210 to 240 days. Both linear and quadratic effects of stage of lactation were highly significant (P < 0·01). Lactation curve parameters for partially milked cows were also estimated. The implications of the results for milk production in sub-Saharan Africa were discussed.

Download Full-text

On the Hydroclimate-Vegetation Relationship in the Southwestern Amazon During the 2000–2019 Period

Frontiers in Water ◽

10.3389/frwa.2021.648499 ◽

2021 ◽

Vol 3 ◽

Author(s):

Omar Gutierrez-Cori ◽

Jhan Carlo Espinoza ◽

Laurent Z. X. Li ◽

Sly Wongchuig ◽

Paola A. Arias ◽

...

Keyword(s):

Vegetation Index ◽

Normalized Difference Vegetation Index ◽

Regional Climate ◽

Dry Season ◽

Shortwave Radiation ◽

Wet Season ◽

Evergreen Forests ◽

Terrestrial Water ◽

Southern Amazonia ◽

Hydroclimatic Variability

The southern Amazonia is undergoing a major biophysical transition, involving changes in land use and regional climate. This study provides new insights on the relationship between hydroclimatic variables and vegetation conditions in the upper Madeira Basin (~1 × 106 km2). Vegetative dynamics are characterised using the normalized difference vegetation index (NDVI) while hydroclimatic variability is analysed using satellite-based precipitation, observed river discharge, satellite measurements of terrestrial water storage (TWS) and downward shortwave radiation (DSR). We show that the vegetation in this region varies from energy-limited to water-limited throughout the year. During the peak of the wet season (January-February), rainfall, discharge and TWS are negatively correlated with NDVI in February-April (r = −0.48 to −0.65; p < 0.05). In addition, DSR is positively correlated with NDVI (r = 0.47–0.54; p < 0.05), suggesting that the vegetation is mainly energy-limited during this period. Outside this period, these correlations are positive for rainfall, discharge and TWS (r = 0.55–0.88; p < 0.05), and negative for DSR (r = −0.47 to −0.54; p < 0.05), suggesting that vegetation depends mainly on water availability, particularly during the vegetation dry season (VDS; late June to late October). Accordantly, the total rainfall during the dry season explains around 80% of the VDS NDVI interannual variance. Considering the predominant land cover types, differences in the hydroclimate-NDVI relationship are observed. Evergreen forests (531,350 km2) remain energy-limited during the beginning of the dry season, but they become water-limited at the end of the VDS. In savannas and flooded savannas (162,850 km2), water dependence occurs months before the onset of the VDS. These differences are more evident during extreme drought years (2007, 2010, and 2011), where regional impacts on NDVI were stronger in savannas and flooded savannas (55% of the entire surface of savannas) than in evergreen forests (40%). A spatial analysis reveals that two specific areas do not show significant hydroclimatic-NDVI correlations during the dry season: (i) the eastern flank of the Andes, characterised by very wet conditions, therefore the vegetation is not water-limited, and (ii) recent deforested areas (~42,500 km2) that break the natural response in the hydroclimate-vegetation system. These findings are particularly relevant given the increasing rates of deforestation in this region.

Download Full-text