5th iLEAPS Science Conference Abstracts - E1

Abstracts – Session E1

Land-atmosphere processes and agricultural transformation in Africa

E101 ORAL-0196: Land Surface Controls on Central African Rainfall

David Crowhurst1, Simon Dadson2, Richard Washington2

1NERC DTP in Environmental Research, University of Oxford, United Kingdom 2School of Geography and the Environment, University of Oxford, United Kingdom

Central Africa is one of three major hotspots of convective rainfall1,2. Studies of land surface controls on rainfall in other tropical regions hint that erroneous simulation of land surface quantities could contribute to the inter-model spread in Central African rainfall3. Results from a multimodel experiment further show that rainfall in global climate models (GCMs) might be erroneously sensitive to changes in soil moisture in Central Africa4. In wet climates, rainfall should be sensitive to net incoming radiation, rather than soil moisture4,5. However, a strong coupling between soil moisture and rainfall is simulated in CMIP3 models in Central Africa, when theory suggests this should not be the case4,5. In Central Africa, some studies suggest that a negative coupling between soil moisture and rainfall is in operation6,7. However, no studies have been performed to determine what the mechanisms linking soil moisture with rainfall are. This is because there are no observations of land surface quantities and the corresponding coupling relationships upon which to evaluate model performance. The aim of my DPhil project is therefore to analyse data from models and observations to develop an understanding of the land surface controls on Central African rainfall. First, I will determine the seasonal cycle of quantities connected with land surface coupling in Central Africa in a range of up to date CMIP5 GCMs. Second, I will evaluate the ability of these GCMs to represent land surface quantities observed from a flux tower that will be deployed in Gabon, Central Africa for a continuous year. Third, I will perform a sensitivity experiment on a strong performing model to identify processes relating changes in soil moisture to changes in rainfall. The work will have tangible benefits by improving understanding of the processes that control rainfall amount in this region.

E102 ORAL-0297: Detecting the effect of surface properties on deep convection within West African mesoscale convective systems from 

infrared imagery

Connie Klein1, Christopher Taylor1, 2, Danijel Belušić3

1Centre for Ecology & Hydrology, Wallingford, United Kingdom 2National Centre for Earth Observation, Wallingford, United Kingdom 3Swedish Meteorological and Hydrological Institute, Norrköping, Sweden

Intense rainfall from mesoscale convective systems (MCSs) poses a threat to lives and livelihoods of the West African population through increasingly frequent devastating flooding and loss of crops. However, despite the significant impact of such extreme events, the dominant processes favouring their occurrence are still under debate. Land surface characteristics such as soil moisture and vegetation cover are consistently found to play an important role for the initiation of MCSs as well as for their maintenance. Hence, anthropogenic land-use changes might modify rainfall characteristics in particular regions with potential implications for cropping cycles and urban planning. However, the evaluation of potential effects of land-use changes on precipitation on a local scale is hampered by patchy ground-based and satellite observations.
 
In this study, we therefore use cloud top temperatures from the Meteosat Second Generation as a proxy for rainfall intensities of large MCSs. The images are available at 15 minutes intervals since 2004, providing a reasonable MCS sample size at the local scale. We furthermore conduct a wavelet scale analysis, extracting sub-cloud structures at scales below 35km, to achieve a more robust identification of deep convective cores within the MCSs. With this method we are able to detect changes in the intensely precipitating parts of MCSs during their passage over vegetation boundaries or urban areas, helping us to explore under which circumstances land-use and land-cover changes affect the frequency of intense rainfall.

E103 - ORAL-0162: The climate regulation service offered by miombo woodlands

RJ Scholes1, Sally Wilson1

1Global Change and Sustainability Research Institute, University of the Witwatersrand, Johannesburg, South Africa

Occupying approximately 3.6 million km2 and spanning several countries from Angola to Mozambique, the African miombo woodland is among the world’s largest unexploited but potentially arable land resources, located on a subcontinent where population growth remains high and the demand for food security is pressing. Policy efforts like Reducing Emissions from Deforestation and Forest Degradation (REDD) seek to limit land use changes which add to climate forcing, thereby preserving the climate regulation service offered. This service has mostly been presented in terms of the terrestrial carbon stored in biomass and soils. In reality, there are several mechanisms through which the landscape interacts with the global climate system, including exchanges of carbon dioxide, methane, nitrous oxide, radiatively-active particles, radiant energy and sensible heat. This study quantifies the tradeoff between agricultural development of various types and the climate regulation service provided by the miombo landscape. To achieve this, net radiative forcing and its carbon dioxide emission equivalent over a one century horizon were calculated for an intact (‘historical’) miombo landscape; one developed through extensive subsistence farming and charcoal cutting; one developed using intensive, large-scale commercial farming techniques; and one developed using ‘eco-agriculture’ smallholder techniques. To calculate forcing, net carbon dioxide, methane, and nitrous oxide emissions from all significant sources (e.g. fires, cultivation, ruminants, termites) and changes in surface reflectance (albedo) were assessed.

E104 - ORAL-0154: High fire-derived N deposition in central African forests

Marijn Bauters, Hans Verbeeck, Isaac Makelele, Landry Cizungu, Pascal Boeckx

The African continent holds a share of approximately 70% of the annual global burnt area (222 Mha yr-1). The main cause for this is the occurrence of common slash-and-burn practices parallel with ITCZ movement. Additionally, the Congo Basin, holds the second largest contiguous block of tropical rainforest, but it remains poorly understood and investigated because of logistic, political and research capacity constraints. Several simulation studies have suggested that the forest is subject to higher atmospheric deposition loads compared to the Amazon basin due to 1) abundance of biomass burning and 2) atmospheric circulation on the continent, but no field data has been presented until today. We have set up a N flux monitoring network in different forest types and locations in the Democratic Republic of the Congo (DRC) where continuous measurements of the throughfall deposition loads were carried out. We present several lines of evidence that strongly underpin that the deposition load is much higher than what is simulated or suggested for the remote forest of the DRC, including: wind back-trajectory and satellite fire detection, black carbon air column density, seasonality in N deposition, along with organic molecular characterisation of the deposition samples via FT ICR mass spectrometry. Finally, we also show that this high fire-derived N deposition has repercussions for the N cycle of central African forests, and hence for the biogeochemical parameterizations of these forests, which in turn might affect the global carbon budget.

E105 - ORAL-0401: SOIL-ATMOSPHERE GREENHOUSE GAS FLUXES ON THE MARGINS OF THE CONGO FOREST: EFFECTS OF FOREST

CONVERSION TOWARDS SMALLHOLDER AGRICULTURAL LANDS AND AGRICULTURAL INTENSIFICATION

Michael Dannenmann1, Denis Sonwa2, Steve Kengdo2, Charles Njine2, Mariana Rufino3, Javier Tejedor1, Louis Verchot4

1Karlsruhe Institute of Technology, Institute of Meteorology and Climate research, Atmospheric Environmental Research, Garmisch-Partenkirchen, Germany 2CIFOR, Yaounde, Cameroon 3University of Edinburgh, Edinburgh, United Kingdom 4CIAT, Cali, Colombia

The forests of the Congo Basin are subject to deforestation and land use change, which may severely influence the soil-atmosphere exchange of greenhouse gases (GHG). However, due to absence of analytical capacities in Central Africa, there is a severe lack of knowledge on fluxes of CO2, CH4 and N2O at the soil-atmosphere interface, which introduces large uncertainties into regional and national GHG reporting. The objectives of this study were to quantify GHG emissions from typical land use on the margins of the Congo forests, to analyze seasonal variability and environmental controls of soil-atmosphere GHG fluxes across a land use gradient and explore options of sustainable intensification of maize cultivation. In Cameroon, we quantified fluxes of CO2, CH4, and N2O at the soil – atmosphere interface in secondary forests, cocoa agroforests, unfertilized mixed crop fields, and three different types of maize cultivation: unfertilized control, maize intercropped with N fixing beans, maize applied with mineral nitrogen fertilizer. We found highest CO2 and N2O emissions, and net CH4 uptake in the secondary forest with lower values observed in cocoa agroforest and in particular in extensive mixed crop fields. Intercropping with N fixing beans did not alter soil N2O emissions from maize fields. In contrast, application of mineral N increased soil N2O emissions by more than a factor of five. Our work highlighted the importance of soil moisture as the universal driver of GHG fluxes and in particular for N2O indicates a strong decrease in soil emissions after forest conversion to extensive crop fields. Vice versa, agricultural intensification based on mineral N fertilizer can increase N2O emissions to levels significantly higher than those observed in secondary forests. In this context, our trial with intercropped N fixing beans provided first pointers towards a sustainable intensification of agriculture in the study region.

E106 - ORAL-0019: Impacts of climate and land use on N2O and CH4 fluxes from different tropical ecosystems in the Mt Kilimanjaro region, Tanzania

Adrian Gütlein1, Friederike Gerschlauer1, Ralf Kiese1

1KIT IMK-IFU, Garmisch-Partenkirchen, Germany

We will present a study on quantifying the impacts of climate and land use on soil N2O and CH4 fluxes from tropical forest, agroforest, arable and savanna ecosystems in the Mt. Kilimanjaro region, Tanzania. To do so, we measured GHG fluxes from twelve different ecosystems along climate and land-use gradients at Mt. Kilimanjaro, combining long-term in-situ chamber and soil-core incubation techniques. Both methods showed similar patterns of GHG exchange. Although there were distinct differences from ecosystem to ecosystem, soils generally functioned as net sources and sinks for N2O and CH4, respectively. N2O emissions correlated positively with soil moisture and total soil nitrogen content. CH4 uptake rates correlated negatively with soil moisture and clay content and positively with SOC. Due to moderate soil moisture contents and the dominance of nitrification in soil N turnover, N2O emissions of tropical forests were generally low, and it is likely that ecosystem N losses are driven instead by nitrate leaching. Particularly, forest soils with well-aerated litter layers were a significant sink for atmospheric CH4 (up to 4 kg C ha-1 yr-1) regardless of low mean annual temperatures at higher elevations. Land-use intensification significantly increased the soil N2O source strength and significantly decreased the soil CH4 sink. However, when decreases in aboveground and belowground carbon stocks were also taken into account, enhanced soil non-CO2 GHG emissions following land-use conversion from tropical forests to home gardens and coffee plantations were only a small factor in the total GHG emissions; but particularly enhanced N2O emissions significantly contributed to total GHG emissions under conversion of savanna into grassland or maize. Overall, we found that the protection and sustainable management of aboveground and belowground carbon and nitrogen stocks of agroforestry and arable systems is most crucial for mitigating GHG emissions from land-use change.

E107 - ORAL-0307: Source characterization and risk assessment of VOCs at a grazed savannah grassland agricultural landscape in South Africa

Kermeels Jaars1, Mika Vestenius2, Pieter van Zyl1, Johan Paul Beukes1, Heidi Hellén2, Ville Vakkari2, Marcell Venter1, Miroslav Josipovic1, Hannele Hakola2

1Chemical Resource Beneficiation, North-West University, Potchefstroom, South Africa 2Finnish Meteorological Institute, Helsinki, Finland

Volatile organic compounds (VOCs) can have significant impacts on climate and human health. In order to develop climate change reduction strategies and to assess the impacts of VOCs on human health, it is crucial to determine the sources of VOCs, which can be emitted from biogenic and anthropogenic sources. The concentrations of VOCs were measured for more than two years at Welgegund Atmospheric Measurement Station, a regional background station on a commercial farm ~100 km west of Johannesburg. Positive matrix factorisation (PMF) model was used to identify the sources of VOCs collected. In addition, a risk assessment study was also performed in view of the major source regions affecting Welgegund in order to quantify the impacts of anthropogenic VOCs measured at Welgegund on human health. Ten sources were resolved by the PMF model, of which five factors were associated with biogenic emissions and five with anthropogenic sources. Three of the biogenic factors were characterised by a specific biogenic species, i.e. isoprene, limonene and 2-methyl-3-buten-2-ol (MBO), while the other two biogenic factors comprised mixtures of biogenic species with different tracer species. One anthropogenic factor was associated with emissions from a densely populated anthropogenic source region to the east of Welgegund with a large number of industrial activities, while another anthropogenic factor could be related to coal combustion. An anthropogenic factor was also identified that reflected the influence of solvents on atmospheric VOC concentrations, while two anthropogenic factors were determined that indicated the influence of farming activities in close proximity to Welgegund. A lifetime cancer risk and non-cancer hazard ratio assessment study conducted for VOCs in relation to three source regions identified indicated that the non-cancerous influence of VOCs measured in the source regions is significantly lower compared to the cancerous influence of these species on human health, which raises concern.

E108 - POSTER-0013: Implications of Urban Roof System Changes on Microclimate, Ecosystem and Increased Flood Events

ALIYU BARAU1

1Bayero University Kano, Kano, Nigeria

One aspect that seems least researched is the multiple implications of socio-technical transitions of urban building roofing forms in developing countries. This represents a socio-technical transitions because it involves the co-evolution of lifestyle and infrastructural changes in urban areas which could have some consequences on ecosystems, microclimate, and vulnerability of cities. This paper examines the nature of transition of roofing systems forms in Kano city, northern Nigeria within a period of over one century. The research questions driving the study are: what is the local type and form of roofing system used in Kano in the last 100 years? Which roofing systems replaced the local roofing system? What are implications of roofing system change on urban sustainability and resilience? In answering these questions, a suite of interdisciplinary methods were used to address the complexity of the study problem. Thus, climate data, literature review, old photographs, old and recent remotely sensed data and interviews with building experts were used to understand the nature and implications of roofing system transitions. The key findings of the study suggest a strong correlation between roofing system transition and urban environmental system changes. For instance, since 1970s the roofing system has progressively changed from low to a high albedo materials. Similarly, over the last 30 years, urban temperature has increased by 2-5 degree Celsius. It was evident that flood incidents have spurred due to increased run-off from now dominating diagonal and water proof roof tops that replaced the predominantly flat and grassy mud roof tops of the past. This study has improved our understanding of the effects of transitions of urban built-up structures and how they interfere with urban climate and ecosystem. 

E109 - POSTER-0302: Soil carbon, nitrogen and phosphorus in a mangrove swamp – rice chronosequence in Guinea-Bissau (West Africa)

Anna Andreetta1, Michele Eugenio D'Amico2, Guia Cecchini1, Roberto Comolli3, Matteo Lotti1, Stefano Carnicelli1, Streng Cerise4

1Department of Earth Sciences - University of Firenze, Firenze, Italy 2DISAFA - University of Torino, Grugliasco, TO, Italy 3Department of Earth and Environmental Sciences - University of Milan-Bicocca, Milano, Italy 4LVIA, Cuneo, Italy

The largest area of rice production in reclaimed mangroves is located in Guinea-Bissau, where it represents a cropping system significant for national food security. However, coastal ecosystems such as mangroves are an important carbon and nutrient sink. Thus, a greater knowledge on the effects of land use change on soil properties is crucial to ensure appropriate and conservative land management practices.
 
We investigated soil organic carbon, nitrogen and phosphorus concentrations and stocks in a survey encompassing several regions along a climate gradient following a mangrove swamp – rice – abandoned field chronosequence. Stocks were estimated in 0–10, 10–20, 20–40 and 40–80 cm soil layers using an equivalent soil mass (ESM) approach. Decreases in soil organic carbon (SOC) stock due to conversion of mangroves into rice fields were significant in the deepest layers (40-80 cm) while no changes were registered for the 0-40 cm layer. On the other hand, phosphorus (P) significantly decreased in the upper part of the soils (0-40 cm), from mangrove to rice cultivation. Nitrogen (N) was the least susceptible to land use changes, showing significant differences only in the topsoil (0-10 cm). A strong positive relation was also found between P concentration and soil pH (R2=0.83), pointing to a further fragility of this peculiar ecosystem where soil acidification hazards due to cultivation and changes in water regimes could further decrease P availability.
 
P appears to be the nutrient that should be considered more carefully and a better understanding of allochthonous P sources, such as atmospheric aerosol (with Saharan dust as likely dominant source) and marine derived material sound to be a challenging research perspective. Furthermore, since agricultural practices alter natural tidal water dynamics, a deeper knowledge of hydrological parameters considering soil and atmospheric characters should better inform policy decisions for development and conservation of wetlands.

E110 - POSTER-0422: ESTIMATION OF CARBON FOOTPRINT OF TEA PRODUCTS AT NYABIHU TEA FACTORY, RWANDA

Gabriel Habiyaremye1, Theogene Niyonzima1, Jean Nduwamungu2

1University of Lay Adventists of Kigali, Kigali, Rwanda 2University of Rwanda – College of Agriculture and Veterinary Medicine, Busogo Campus, Musanze, Rwanda

The carbon footprint arose out of the debate on climate change, as a tool to measure GHG emissions. This research carried out at Nyabihu tea factory for carbon footprint estimation in tea life cycle was focusing on different key processes and phases or steps through which Nyabihu tea passes until it is delivered to the auction site (Mombasa). The study’s data showed that carbon footprint from tea production depends on different factors including, transport, burning fuel woods, energy use and fertilizers application which contributed to releasing nitrous oxides (N2O), carbon dioxide (CO2) and methane (CH4) in the atmosphere. The amount of the these GHGs  emitted from the life cycle was expressed in terms of the amount of carbon dioxide equivalent (CO2eq) units as calculated by the Cool Farm Tool 1.1 software. The emission from total area is 150467.4 tCO2eq. Most of carbon dioxide equivalents were found to be released from off farm activities with a total of 135 kg CO2 eq per kilogram. The total annual emission from the tea life cycle is -365.31 kgCO2eq per kilogram of finished product. But in terms of compounds the largest emissions in CO2 equivalents come from N2O where 0 kgs of N2O equate to 0.696 kgCO2eq per kilogram and the least is from CH4 (i.e. 0.0 kgCO2eq of CH4 per one kilogram). Measures to reduce emissions in order to protect the environment were undertaken by Nyabihu tea factory. These include enhanced sequestration through forest and agro forestry trees plantation which accounted for sequestration of 406744.48116 t CO2/hectare sequestered. In order to reduce carbon dioxide and other greenhouse gases emissions, agricultural techniques including appropriate use of fertilizers should be changed to help efficient sequestration of carbon in the soils since soil can act as an effective carbon sink. Furthermore, the management of wastes and tea crop residues through incorporation into the soil will provide more advantageous carbon storage.