Rainfall-interception-evaporation-runoff relationships in a semi-arid catchment, northern Limpopo basin, Zimbabwe [Relations précipitation-interception-évaporation-écoulement dans un bassin versant semi-aride (nord du Limpopo, Zimbabwe)]
Love D.,WaterNet |
Love D.,Matopos Research Station |
Uhlenbrook S.,UNESCO IHE |
Uhlenbrook S.,Technical University of Delft |
And 4 more authors.
Hydrological Sciences Journal | Year: 2010
Characterizing the response of a catchment to rainfall, in terms of the production of runoff vs the interception, transpiration and evaporation of water, is the first important step in understanding water resource availability in a catchment. This is particularly important in small semi-arid catchments, where a few intense rainfall events may generate much of the season's runoff. The ephemeral Zhulube catchment (30 km2) in the northern Limpopo basin was instrumented and modelled in order to elucidate the dominant hydrological processes. Discharge events were disconnected, with short recession curves, probably caused by the shallow soils in the Tshazi sub-catchment, which dry out rapidly, and the presence of a dambo in the Gobalidanke sub-catchment. Two different flow event types were observed, with the larger floods showing longer recessions being associated with higher (antecedent) precipitation. The differences could be related to: (a) intensity of rainfall, or (b) different soil conditions. Interception is an important process in the water balance of the catchment, accounting for an estimated 32% of rainfall in the 2007/08 season, but as much as 56% in the drier 2006/07 season. An extended version of the HBV model was developed (designated HBVx), introducing an interception storage and with all routines run in semi-distributed mode. After extensive manual calibration, the HBVx simulation satisfactorily showed the disconnected nature of the flows. The generally low Nash-Sutcliffe coefficients can be explained by the model failing to simulate the two different observed flow types differently. The importance of incorporating interception into rainfall-runoff is demonstrated by the substantial improvement in objective function values obtained. This exceeds the gains made by changing from lumped to semi-distributed mode, supported by 1 000 000 Monte Carlo simulations. There was also an important improvement in the daily volume error. The best simulation, supported by field observations in the Gobalidanke sub-catchment, suggested that discharge was driven mainly by flow from saturation overland flow. Hortonian overland flow, as interpreted from field observations in the Tshazi subcatchment, was not simulated so well. A limitation of the model is its inability to address temporal variability in soil characteristics and more complex runoff generation processes. The model suggests episodic groundwater recharge with annual recharge of 100 mm year-1, which is similar to that reported by other studies in Zimbabwe. © 2010 IAHS Press.
Schaefer K.,University of Colorado at Boulder |
Lantuit H.,Alfred Wegener Institute for Polar and Marine Research |
Lantuit H.,University of Potsdam |
Romanovsky V.E.,University of Alaska Fairbanks |
And 3 more authors.
Environmental Research Letters | Year: 2014
Degrading permafrost can alter ecosystems, damage infrastructure, and release enough carbon dioxide (CO2) and methane (CH4) to influence global climate. The permafrost carbon feedback (PCF) is the amplification of surface warming due to CO2 and CH4 emissions from thawing permafrost. An analysis of available estimates PCF strength and timing indicate 120α85 Gt of carbon emissions from thawing permafrost by 2100. This is equivalent to 5.7α4.0% of total anthropogenic emissions for the Intergovernmental Panel on Climate Change (IPCC) representative concentration pathway (RCP) 8.5 scenario and would increase global temperatures by 0.29α0.21 °C or 7.8α5.7%. For RCP4.5, the scenario closest to the 2 °C warming target for the climate change treaty, the range of cumulative emissions in 2100 from thawing permafrost decreases to between 27 and 100 Gt C with temperature increases between 0.05 and 0.15 °C, but the relative fraction of permafrost to total emissions increases to between 3% and 11%. Any substantial warming results in a committed, long-term carbon release from thawing permafrost with 60% of emissions occurring after 2100, indicating that not accounting for permafrost emissions risks overshooting the 2 °C warming target. Climate projections in the IPCC Fifth Assessment Report (AR5), and any emissions targets based on those projections, do not adequately account for emissions from thawing permafrost and the effects of the PCF on global climate. We recommend the IPCC commission a special assessment focusing on the PCF and its impact on global climate to supplement the AR5 in support of treaty negotiation. © 2014 IOP Publishing Ltd.
Buckley T.R.,Landcare Research |
Gleeson D.,Landcare Research |
Howitt R.,Landcare Research |
Attanayake D.,Landcare Research |
And 2 more authors.
New Zealand Journal of Zoology | Year: 2011
We have analysed mitochondrial DNA and shell morphometric data from all species and subspecies of Placostylus land snails in New Zealand. These subspecies were originally described on the basis of shell morphology. The genetic data show that each of the three species P. bollonsi, P. hongii and P. ambagiosus are well differentiated and monphyletic for mitochondrial DNA, consistent with their species status. Variation among subspecies within each of the three species was minimal with sharing of haplotypes among subspecies. Morphometric analysis of shell shape characters shows large amounts of environmental plasticity. On the basis of these data we have synonymised all subspecies within each of the three Placostylus species. Consequently, the New Zealand fauna now consists of three Placostylus species, P. ambagiosus, P. hongii and P. bollonsi, and no subspecies. We recommend conservation of multiple populations within each species to ensure preservation of genetic variation. © 2011 The Royal Society of New Zealand.
Hoyer-Klick C.,German Aerospace Center |
Wald L.,MINES ParisTech |
Menard L.,MINES ParisTech |
Blanc P.,MINES ParisTech |
And 13 more authors.
30th ISES Biennial Solar World Congress 2011, SWC 2011 | Year: 2011
Southern and eastern Mediterranean regions are prone to production of electricity by solar systems. The solar resource is the "fuel" of such systems and its availability is a key economic parameter in system design. Even though the southern and eastern Mediterranean region is served by several commercial data providers, in a public domain, so far only coarse resolution (100 km) data or data with limited temporal coverage is available. For more rapid development of policies and to attract the industrial interest in this region a more enhanced and easy to access free information is needed. The project will bring high resolution (1 km), long term coverage of at least 15 years data on the available solar resources for the region covering the countries Syria, Jordan, Israel, Lebanon, Egypt, Libya, Tunisia, Algeria, Morocco, Palestine National Authority, Mauretania and Turkey. The resource data will be derived from Earth Observation satellite data, based on published and transparent methodologies and the data will be validated with existing ground measurements in the region. The database will be provided by SOLEMI and Helioclim-3 (SoDa) sources - Global Horizontal Irradiation (GHI) and Direct Normal Irradiation (DNI). The data will be made available via a distributed information system which will ensure the ease of access to the data. The free access to the data will include historical, annual and monthly averages, and more detailed data products and services will remain the domain of commercial data providers. This paper will show the first prototype of the user interface for an easy web access to the solar radiation as well as ancillary geographical data. With the presentation of this paper we aim to encourage potential users to give us feedback on the further development.
Bottazzi P.,University of Bern |
Bottazzi P.,University of Lausanne |
Crespo D.,Latin American Faculty of Social Sciences |
Soria H.,Latin American Faculty of Social Sciences |
And 5 more authors.
Development and Change | Year: 2014
Carbon sequestration in community forests presents a major challenge for the Reducing Emissions from Deforestation and Forest Degradation (REDD+) programme. This article uses a comparative analysis of the agricultural and forestry practices of indigenous peoples and settlers in the Bolivian Amazon to show how community-level institutions regulate the trade-offs between community livelihoods, forest species diversity, and carbon sequestration. The authors argue that REDD+ implementation in such areas runs the risk of: 1) reinforcing economic inequalities based on previous and potential land use impacts on ecosystems (baseline), depending on the socio-cultural groups targeted; 2) increasing pressure on land used for food production, possibly reducing food security and redirecting labour towards scarce off-farm income opportunities; 3) increasing dependence on external funding and carbon market fluctuations instead of local production strategies; and 4) further incentivising the privatization and commodification of land to avoid transaction costs associated with collective property rights. The article also advises against taking a strictly economic, market-based approach to carbon sequestration, arguing that such an approach could endanger fragile socio-ecological systems. REDD+ schemes should directly support existing efforts towards forest sustainability rather than simply compensating local land users for avoiding deforestation and forest degradation. © 2014 The Authors. Development and Change published by John Wiley & Sons Ltd on behalf of International Institute of Social Studies.
News Article | October 24, 2016
Following the ICAO deal to offset the global growth in aviation emissions and the Paris Agreement passing the 55 / 55 criteria for entry into force, a third major announcement has followed in as many weeks; the agreement of an addendum to the Montreal Protocol (agreed in 1987 to progressively eliminate the use of chlorinated fluorocarbons or CFCs, coming into force in 1989) which will bring the HFC family of gases into that process, leading to their eventual elimination from day to day use. Hydrofluorocarbons or ‘HFCs’ have been increasingly used this century as an alternative to ozone damaging CFCs in refrigeration systems.Though HFCs provide an effective alternative to CFCs, they are also powerful greenhouse gases. A snapshot of current greenhouse gas emissions to atmosphere highlights the HFC issue; today they represent approximately 1 Gt on a CO2 equivalent basis, or about 2% of the total GHG problem. While 2% is not insignificant, being just above the impact that aviation currently has on the climate issue, it is the longer term impact that the growth in use of these products has that is the main cause for concern. India alone could build upwards of 400 million refrigerators over the coming 20 years. But following seven years of negotiations, the 197 Montreal Protocol parties reached a compromise, under which developed countries will start to phase down HFCs by 2019. Developing countries will follow with a partial freeze of HFCs consumption levels in 2024, with some countries freezing consumption in 2028. By the late 2040s, all countries are expected to consume no more than 15-20 per cent of their respective baselines. A small group of countries is treated more leniently owing to the very high local temperatures experienced during much of the year. This is an important agreement, but I certainly didn’t expect to see the claim that came from UNEP (United Nations Environmental Programme) that the Kigali Amendment to the Montreal Protocol (as this was agreed at the 28th Meeting of the Parties to the Montreal Protocol at their meeting in Kigali, Rwanda) was the equivalent of shaving 0.5°C from the anticipated warming of the climate system. Secretary of State John Kerry rounded this up slightly and referred to the result as a 1°F achievement. The claim was reminiscent of the pre-Paris statement by the UNFCCC that the INDCs submitted had already reduced warming to 2.7°C, a story that carried right through the December COP and gave great confidence to the negotiators. Such a number could be arrived at with some big assumptions about the future but most commentators put the level of warming after the INDCs (and assuming they are delivered) at something around 3.8°C (which was at least less than 4+°C). The source of the 0.5°C figure is a series of academic papers, such as a 2013 paper from Scripps Institution of Oceanography (The role of HFCs in mitigating 21st century climate change, Y. Xu1, D. Zaelke, G. J. M. Velders, and V. Ramanathan). This paper notes that most HFCs now in use have relatively short lifetimes in the atmosphere in comparison with long-lived GHGs, such as CO2 and N2O (nitrous oxide) and are therefore referred to as short-lived climate pollutants (SLCPs). The global average lifetime, weighted by the production of the various HFCs now in commercial use, is about 15 years, with a range of 1 to 50 years. But the chemicals have very high global warming potentials (e.g. over 4000 for HFC-143a). Therefore, HFCs have a significant impact on radiative forcing in the years immediately after release into the atmosphere, but their impact on peak warming when that occurs depends more on the level of HFC emissions at that time rather than the emissions now or in the near term. As such, the warming that they induce is nearer term and tends to mean that we will reach a certain temperature earlier than we might have, even if the eventual peak warming remains the same. Peak warming is dictated primarily by cumulative CO2 emissions, with the approximate relationship of 2°C for every trillion tonnes of carbon (or 3.7 trillion tonnes CO2) emitted. Nevertheless, some significant warming numbers arise, although they are very dependent on the HFC demand projections and scenarios that are developed. Mitigation of the potential growth of HFCs is shown to play a significant role in limiting the warming to below 2°C this century and could contribute additional avoided warming of as much as 0.5°C by 2100. Using the lower limits of BAU increase of HFC, 0.35°C warming is shown to be avoided. Most importantly though, this paper emphasizes that HFC mitigation should not be viewed as an “alternative” strategy for avoiding the 2°C peak warming, but rather as a critical component of a strategy that also requires mitigation of CO2 and the other SLCPs. The focus of the study presented was on near-term warming over the next several decades to end of the century. For the longer-term (century and beyond), mitigation of CO2 would be essential for a significant reduction in the warming. A further feature of the Kigali Amendment was an agreement to provide adequate financing for HFCs reduction, the cost of which is estimated at billions of dollars globally. The exact amount of additional funding will be agreed at the next Meeting of the Parties in Montreal, in 2017. Grants for research and development of affordable alternatives to hydrofluorocarbons will be the most immediate priority. But this financing requirement may still cause problems, particularly if the US Senate requires oversight of the amendment, given it ratified the Montreal Protocol in the first place. With the ink barely dry on the Kigali documents, The Guardian was already reporting that in the view of some legal experts the US Senate will have to vote on the issue.