| 1. |
- Fensholt, Rasmus, et al.
(author)
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Greenness in semi-arid areas across the globe 1981-2007 - an Earth Observing Satellite based analysis of trends and drivers
- 2012
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In: Remote Sensing of Environment. - : Elsevier BV. - 0034-4257. ; 121, s. 144-158
-
Journal article (peer-reviewed)abstract
- Semi-arid areas, defined as those areas of the world where water is an important limitation for plant growth, have become the subject of increased interest due to the impacts of current global changes and sustainability of human lifestyles. While many ground-based reports of declining vegetation productivity have been published over the last decades, a number of recent publications have shown a nuanced and, for some regions, positive picture. With this background, the paper provides an analysis of trends in vegetation greenness of semi-arid areas using AVHRR GIMMS from 1981 to 2007. The vegetation index dataset is used as a proxy for vegetation productivity and trends are analyzed for characterization of changes in semi-arid vegetation greenness. Calculated vegetation trends are analyzed with gridded data on potential climatic constraints to plant growth to explore possible causes of the observed changes. An analysis of changes in the seasonal variation of vegetation greenness and climatic drivers is conducted for selected regions to further understand the causes of observed inter-annual vegetation changes in semi-arid areas across the globe. It is concluded that semi-arid areas, across the globe, on average experience an increase in greenness (0.015 NDVI units over the period of analysis). Further it is observed that increases in greenness are found both in semi-arid areas where precipitation is the dominating limiting factor for plant production (0.019 NDVI units) and in semi-arid areas where air temperature is the primarily growth constraint (0.013 NDVI units). Finally, in the analysis of changes in the intra-annual variation of greenness it is found that seemingly similar increases in greenness over the study period may have widely different explanations. This implies that current generalizations, claiming that land degradation is ongoing in semi-arid areas worldwide, are not supported by the satellite based analysis of vegetation greenness. (c) 2012 Elsevier Inc. All rights reserved.
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| 2. |
- Helldén, Anders, et al.
(author)
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Adverse drug reactions and impaired renal function in elderly patients admitted to the emergency department : a retrospective study
- 2009
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In: Drugs & Aging. - : Wolters Kluwer. - 1170-229X .- 1179-1969. ; 26:7, s. 595-606
-
Journal article (peer-reviewed)abstract
- BACKGROUND: Adverse drug reactions (ADRs) are common in elderly patients. There are various reasons for this, including age- and disease-related alterations in pharmacokinetics and pharmacodynamics as well as the common practice of polypharmacy. The decline in renal function in elderly patients may also predispose them to pharmacological ADRs (type A, augmented). Patients receiving home healthcare may be at even higher risk.OBJECTIVES: To study ADRs as a cause of acute hospital admissions in a defined cohort of elderly patients (aged >or=65 years) registered to receive home healthcare services, with special reference to impaired renal function as a possible risk factor.METHODS: This was a retrospective study of 154 elderly patients aged >or=65 years admitted to the emergency department of a university hospital in Stockholm, Sweden, in October-November 2002. Estimated creatinine clearance (eCL(CR)) was calculated from the Cockcroft-Gault formula, and estimated glomerular filtration rate (eGFR) by the Modification of Diet in Renal Disease (MDRD) equation. ADRs were defined according to WHO criteria. All medications administered to patients at admission and at discharge were collated. These and other data were collected from computerized hospital records.RESULTS: ADRs were judged to contribute to or be the primary cause of hospitalization in 22 patients, i.e. 14% of 154 patients registered to receive home healthcare. Eleven of the 22 patients were women. All but one ADR were type A. Excessive doses or drugs unsuitable in renal insufficiency were present in seven patients in the ADR group compared with only four patients in the group without ADRs (p = 0.0001). Patients with ADRs did not differ significantly from those without ADRs in relation to age, plasma creatinine, eCL(CR), weight or number of drugs prescribed at admission. However, women with ADRs were significantly older than women without ADRs (mean +/- SD age 88.8 +/- 5.7 years vs 82.5 +/- 8.0 years, respectively; p = 0.014) and had significantly lower mean +/- SD eCL(CR) values (25.5 +/- 10.8 and 37.1 +/- 17.1 mL/min, respectively; p = 0.035). Median MDRD eGFR was significantly higher than median eCL(CR) (59 [range 6-172] mL/min/1.73 m2 vs 38 [range 5-117] mL/min, respectively; p = 0.0001).CONCLUSIONS: In elderly patients registered to receive home healthcare, 14% of hospital admissions were primarily caused by ADRs. One-third of these ADRs were related to impaired renal function, generally in very old women. These ADRs may be avoided by close monitoring of renal function and adjustments to pharmacotherapy (drug selection and dose), particularly in very elderly women.
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| 3. |
- Helldén, Anders, et al.
(author)
-
Fluconazole-induced intoxication with phenytoin in a patient with ultra-high activity of CYP2C9
- 2010
-
In: European Journal of Clinical Pharmacology. - : Springer Science and Business Media LLC. - 0031-6970 .- 1432-1041. ; 66:8, s. 791-5
-
Journal article (peer-reviewed)abstract
- PURPOSE: The cytochrome P450 enzyme CYP2C9 metabolizes several important drugs, such as warfarin and oral antidiabetic drugs. The enzyme is polymorphic, and all known alleles, for example, CYP2C9*2 and*3, give decreased activity. Ultra-high activity of the enzyme has not yet been reported.METHODS: We present a patient with Behçet's disease who required treatment with high doses of phenytoin. When fluconazole, a potent inhibitor of CYP2C9, was added to the treatment regimen, the patient developed ataxia, tremor, fatigue, slurred speech and somnolence, indicating phenytoin intoxication. On suspicion of ultra-high activity of CYP2C9, a phenotyping test for CYP2C9 with losartan was performed.RESULTS: The patient was shown to have a higher activity of CYP2C9 than any of the 190 healthy Swedish Caucasians used as controls.CONCLUSIONS: Our finding of an ultrarapid metabolism of losartan and phenytoin may apply to other CYP2C9 substrates, where inhibition of CYP2C9 may cause severe adverse drug reactions.
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| 4. |
- Hellden, Anders, et al.
(author)
-
Renal function estimations and dose recommendations for dabigatran, gabapentin and valaciclovir : a data simulation study focused on the elderly
- 2013
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In: BMJ Open. - London, UK : BMJ. - 2044-6055. ; 3:4, s. e002686-
-
Journal article (peer-reviewed)abstract
- Objectives The thrombin inhibitor dabigatran is mainly excreted by the kidneys. We investigated whether the recommended method for estimation of renal function used in the clinical trials, the Cockcroft-Gault (CG(old)) equation and the estimated glomerular filtration rate (eGFR) modification of diet in renal disease equation 4 (MDRD4), differ in elderly participants, resulting in erroneously higher dose recommendations of dabigatran, which might explain the serious, even fatal, bleeding reported. The renally excreted drugs gabapentin and valaciclovir were also included for comparison. Design A retrospective data simulation study. Participants Participants 65years and older included in six different studies. Main outcome measure Estimated renal function by CG based on uncompensated (old Jaffe' method) creatinine (CG(old)) or by MDRD4 based on standardised compensated P-creatinine traceable to isotope-dilution mass spectrometry, and the resulting doses. Results 790 participants (432 females), mean age (SD) 77.6 +/- 5.7years. Mean estimated creatinine clearance (eCrCl) by the CG(old) equation was 44.2 +/- 14.8ml/min, versus eGFR 59.6 +/- 20.7ml/min/1.73m(2) with MDRD4 (p<0.001), absolute median difference 13.5, 95% CI 12.9 to 14.2. MDRD4 gave a significantly higher mean dose (valaciclovir +21%, dabigatran +25% and gabapentin +37%) of all drugs (p<0.001). With MDRD4 58% of the women would be recommended a full dose of dabigatran compared with 18% if CG(old) is used. Conclusions MDRD4 would result in higher recommended doses of the three studied drugs to elderly participants compared with CG, particularly in women, and thus increased the risk of dose and concentration-dependent adverse reactions. It is important to know which method of estimation of renal function the Summary of Products Characteristics was based on, and use only that one when prescribing renally excreted drugs with narrow safety window. Doses based on recently developed methods for estimation of renal function may be associated with considerable risk of overtreatment in the elderly.
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| 5. |
- Helldén, Johan, et al.
(author)
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Åtgärdslösningar : – erfarenheter och tillgängliga metoder
- 2006
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Reports (other academic/artistic)abstract
- Efter en kraftigt ökande aktivitet inom området förorenad mark finns ett stort behov av kunskap och erfarenheter hos de många aktörer vilka förväntas fatta beslut om åtgärdsalternativ. Projektets särskilda strategi för att bemöta detta har varit att inventera och bygga på de erfarenheter som finns från efterbehandlingar och att kombinera detta med en beskrivning av olika åtgärdsmetoder. I en första fas gjordes en inventering och sammanställning där målet var att få en översiktlig bild av hur saneringar bedrivits. I den översiktliga sammanställningen ingår 226 objekt vilket uppskattas till ca en sjättedel av totala antalet anmälda saneringar till tillsynsmyndighet. Till sammanställningen utvaldes ett antal saneringar som genomförts av SPI Miljösaneringsfond AB, SPIMFAB, totalt 90 fall, där de 10 % största schakt och sortering/ transport-saneringarna samt ett antal in situ-saneringar ingick. Kommuner, statliga eller andra privata beställare står för de resterande 136 fallen. Varje objekt beskrivs i tabellformat i bilaga 1. Som stöd till tolkning av de beskrivna fallen eller som ett läromedel i allmänhet finns en omfattande genomgång och beskrivning av olika åtgärdstekniker. Fokus för teknikbeskrivningarna ligger i första hand på de metoder som använts i Sverige och beskrivningarna refererar till fallstudier i angränsande kapitel.Sjutton utvalda fall analyseras fördjupat baserat på rapporter och intervjuer med inblandade parter. Projekten omfattar olika behandlingsmetoder, och tar upp såväl lyckade som problemfyllda projekt. Fallstudierna refererar till inhämtat rapportmaterial där åtgärdstekniken beskrivs, och fokuserar på i vilken grad uppställda åtgärdsmål har uppfyllts, samt på att identifiera framgångskritiska faktorer som styrt resultatet. Baserat på tillgängligt material i SPIMFAB:s databas har även statistik tagits fram som visar vad som styr resultat och ekonomi i ett stort antal saneringar. För att få en uppfattning om vad som händer med mottagna massor på behandlingsanläggningar genomfördes även en enkätundersökning till tillståndsgivna anläggningar. Fallstudierna visar att mer än hälften av SPIMFAB:s in situ-projekt fick slutföras genom bortgrävning av massor. En förklaring verkar vara att det under de första åren generellt funnits liten erfarenhet av metoderna och att appliceringen av in situ-teknik baserats på för vaga förundersökningar. De in situ-saneringar som varit lyckosamma har föregåtts av grundliga kartläggningar av förorenings- och markförhållanden. För såväl SPIMFAB:s projekt som övriga gäller att schakt och sortering/transport som åtgärdsstrategi dominerat stort. Den näst vanligaste strategin har varit in situ-saneringar med vakuumextraktion/markventilering. Även ett flertal andra in situ-metoder har använts med gott resultat, exv stimulerad nedbrytning med bakterietillsatser, eller olika former av barriärer och filter.Marksanering är en verksamhet som i hög grad styrs av plastspecifika förutsättningar vilket kräver flexibla problemlösningar. Projektets fallstudier ger en rad exempel på olika problem av vitt skilda slag som kan uppstå. Den klart största andelen jord som tas emot på behandlingsanläggningarna är oljeförorenadjord som behandlas biologiskt genom kompostering. Enligt behandlingsanläggningarna ger metoden goda resultat och det finns stor efterfrågan efter behandlade massor för sluttäckningar eller som konstruktionsmaterial på deponier. Behovet av sådant material verkar vara en stark drivkraft för att ta emot förorenade massor för behandling. En inte oansenlig andel av de behandlade massorna återanvänds även som konstruktionsmaterial utanför behandlingsanläggningen. Efterbehandling är i sig själv en miljöfarlig verksamhet och kan leda till en konflikt mellan olika nationella miljömål. Med utgångspunkt från tillgänglig litteratur om livscykelanalys (LCA) föreslås hur enkla index för s k eko-effektivitet kan användas för att värdera och styra val av saneringsåtgärder. I ett exempel visas även hur energiåtgång kan översättas till utsläpp av koldioxid och viktas mot sanerad mängd jord. Denna typ av index bör kunna användas som kriterier i upphandlingar av saneringsåtgärder. För att förbättra möjligheten att redovisa miljövinster och eventuella förluster samt styra val av åtgärder föreslås att data från miljörapporter från efterbehandlingsverksamhet sammanställs som en del av de ordinarie regionala och nationella årliga rapporterna. Ett sammanfattande intryck av det insamlade materialet är att en hel del branschmognad och tekniketablering skett de senaste 10 åren. Biologisk behandling dominerar som metod och genomförs nu framgångsrikt på ett stort antal behandlingsanläggningar. Jordtvätt och in situ markventilering är två metoder som haft en hel del bakslag men där aktörerna dragit lärdomar och blivit säkrare i sitt genomförande. Ett stort antal andra metoder som etablerats i omvärlden har emellertid varit svårare att etablera i Sverige (exempelvis termisk desorption, stimulerad gasfasavdrivning, kemisk oxidation, övervakad naturlig nedbrytning, filtertekniker et c). Följden av att det finns få alternativa åtgärdslösningar bidrar till att hålla priserna uppe och ger begränsande möjligheter att välja lösningar med avseende på minsta negativa miljöeffekt. Behandlingsanläggningarnas stora behov av täckmassor till avslutning av deponier är exempel på en betydande faktor som idag främjar ex situ-behandling. En generell åtgärd för att stimulera branschutvecklingen vore att organisera systematisk återkoppling och kvalitetsutveckling. Detta kan göras genom att bygga vidare på den inventering och sammanställning som gjorts i detta projekt. Enklare standardformulär kan iordningställas, vilka ifylls och rapporteras till tillsynsmyndigheten för sammanställning. Formulären föreslås innehålla uppgifter liknande de i bilaga 1. Som för andra industriella verksamheter bör även marksanering följas upp vad gäller miljörapportering. Faktorer som exv energiåtgång är således parametrar som bör finnas med i myndighetens sammanställning. Uppgifterna sammanställs och återrapporteras till bransch och samhälle, där de kan användas som aktuellt beslutsunderlag för olika förbättringsåtgärder.
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| 6. |
- Helldén, Ulf
(author)
-
A coupled human-environment model for desertification simulation and impact studies
- 2008
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In: Global and Planetary Change. - : Elsevier BV. - 1872-6364 .- 0921-8181. ; 64:3-4, s. 158-168
-
Journal article (peer-reviewed)abstract
- This paper presents the development of a system dynamic model to simulate and analyze desertification. The human-environment coupled model integrates socio-economic drivers with bio-physical drivers of biomass production, land degradation and desertification. It is based on the UN and GEF definitions of desertification. It illustrates the concept of desertification through differential equation and simulation output graphics. It is supplemented with a causal loop diagram demonstrating the existing feed-back mechanisms. The model relates population pressure and dynamics over time to the growth and availability of biomass resources. The human population stock is described as a function of growth rate, death rate and resources dependent in and out migration of people. The relative growth rate of the stock of resources is modeled as a function of climate and exploitation pressure affecting soil erosion and water availability. The model is applied for the Sahelian desertification syndrome using input data to illustrate and simulate a 150 years period (1900-2050) in Kordofan, Sudan. The model indicates that it is difficult to generate irreversible desertification. (C) 2008 Elsevier B.V. All rights reserved.
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| 7. |
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| 8. |
- Helldén, Ulf, et al.
(author)
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CASE STUDIES OF DESERTIFICATION MONITORING. -A DISCUSSION OF EU INITIATIVES
- 2005
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In: Proceedings: Local & Regional Desertification Indicators in a Global Perspective. ; , s. 195-203
-
Conference paper (peer-reviewed)abstract
- The word “desertification” was introduced in 1949 by the French scientist Aubreville in his report “Climats, forêts et désertification de l´Afrique tropicale”. The concept, however, was discussed earlier by European and American scientists in terms of increased sand movements, desiccation, desert and Sahara encroachment and man made deserts. Desertification, at the beginning of last century, meant the spreading (expansion) of deserts or desert-like (non productive or very low productive) conditions from existing deserts into non-desert areas close to the desert margins. The symptoms of the phenomena were often related to sand movement and encroachment into oasis and desert margins. Aubreville also stated in 1949 that there are real deserts being born, under our very eyes, in the 700-1500 mm annual rainfall areas. At that time, one school favored the idea of a postglacial long term climate change (desiccation) as a major driving force causing desertification. Others stressed the importance of human impact. The human impact was expressed in terms of bad management of the natural resources including over cutting, overgrazing, over cultivation and misuse of water. Since then, different concepts of desertification have developed and been discussed over and over again by scientists, politicians and the international aid and development society. Important international events were UNCOD in Nairobi 1977, UNCED in Rio de Janeiro 1992 followed up by the UNCCD adopted in 1994 and entering into force in 1996. The choice of land degradation mitigation strategies and the degree of resulting control success varies with the prevailing concepts of causes and consequences. These concepts are dependent on the monitoring approach used. This is exemplified through a discussion of a few desertification monitoring case studies followed by a presentation of a recent EU integrated assessment, monitoring and modelling initiative, DeSurvey (2005-2010). The initiative is targeting desertification affected areas in Europe, Africa, China and South America. It probably constitutes the largest ever international research project to exclusively focus on desertification surveillance and assessment. Conclusion: The causes, consequences and methods of control of desertification cannot be generalized but are site specific. Every site and case needs its own diagnosis, based on an integrated and systemic survey approach, before the right cure can be identified and implemented. The DeSurvey consortium aims at developing a generic survey, monitoring and modelling system for such an approach.
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| 9. |
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| 10. |
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| 11. |
- Helldén, Ulf, et al.
(author)
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Desertification and global climate change – Little Ice Age desertification in Iceland?
- 1999
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In: Proceedings of the 2nd International Conference on Land Degradation.
-
Conference paper (peer-reviewed)abstract
- 1. INTRODUCTION Geographers at the University of Lund have been active in research on desertification/ land degradation and environmental change monitoring of African drylands since the mid 1970’ies and of Asian drylands since the beginning of the 1990’ies. The results obtained so far do not confirm the concept of desertification as a mainly man made phenomena but indicate that the importance of climate variability and change has been underestimated (Helldén 1991). To learn about the importance of climatic fluctuations versus human impact on land degradation in arctic and sub-arctic environments, Iceland was selected for further studies. Iceland is not an arid, semi-arid or dry sub-humid region. Therefore the land degradation it is suffering cannot be called "desertification" in the strict sense as defined by the UN. On the other hand there is no doubt that land degradation has led to the creation of extensive desert like conditions in many areas of Iceland. In this sense, “desertification” is an Icelandic reality indicating the introduction and spread of desert like conditions in landscapes where there should not be any. 2. RESULTS There are few areas in Europe that have suffered such a severe and extensive land degradation as Iceland, leading to the creation of long lasting desert like conditions. It is estimated that when Iceland was settled, in 874 , at least 60% of the country was vegetated and that forests covered 15-25% of the country’s area (Bergþórsson 1998, Þórarinsson 1961, Einarsson 1963, Þorsteinsson 1973). The vegetative cover is now about 27%. There is almost no forest (The Agricultural Ministry 1986, IGI/LMÍ 1993, Arnalds et al.1997). The scientific and political societies in Iceland often relate the land degradation problems to human over use of the rangelands, starting with the introduction of cattle and sheep rasing at the time of the settlement 874 AD. They consider overgrazing and overuse of the woodlands for fuelwood and charcoal production to be the most important processes opening and exposing the landscape for soil erosion with growing desert patches and deserts as a consequence. Most farmers, on the other hand, seem to believe that the desert patches and deserts are natural phenomena. The initiation and expansion of the phenomena is supposed to be related to climatic events possibly enhanced by the traditional winter grazing habit, no longer practiced. Our observations and preliminary results indicate that the importance of climate may have been underestimated as a possible and important cause of land degradation and desertification in Iceland. Cold and dry periods have probably favoured the development and expansion of desert patches and deserts. The Little Ice Age, especially during the second half of the last century, seems to have offered favourable conditions for frost processing and events of severe wind erosion. The second half of the last century is also characterized by an outstanding high population pressure and most likely a correspondingly high grazing pressure in the study area. Time series photos of erosion remnants development during a covering a 32 years period indicate that the erosion processes creating deserts may be supprisingly slow.
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| 12. |
- Helldén, Ulf, et al.
(author)
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Desertification and Theories of Desertification Control: A discussion of Chinese and European concepts
- 2003
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In: Proceedings of the China-EU Workshop on Integrated Approach to Combat Desertification. ; , s. 94-104
-
Conference paper (peer-reviewed)abstract
- The word “desertification” was introduced in 1949 by the French scientist Aubreville in his report “Climats, forêts et désertification de l´Afrique tropicale”. The concept, however, was discussed earlier by European and American scientists in terms of increased sand movements, desiccation, desert and Sahara encroachment and man made deserts. Desertification, at the beginning of last century, meant the spreading (expansion) of deserts or desert-like (non productive or very low productive) conditions from existing deserts into non-desert areas close to the desert margins. The symptoms of the phenomena were often related to sand movement and encroachment into oasis and desert margins. Aubreville also stated in 1949 that there are real deserts being born, under our very eyes, in the 700-1500 mm annual rainfall areas. One school favored the idea of a postglacial long term climate change (desiccation) as a major driving force causing desertification. Others stressed the importance of human impact. The human impact was expressed in terms of bad management of the natural resources including over cutting, overgrazing, over cultivation and misuse of water. Since then, different concepts of desertification have developed and been discussed over and over again by scientists, politicians and the international aid and development society. Important international events were UNCOD in Nairobi 1977, UNCED in Rio de Janeiro 1992 followed up by the UNCCD adopted in 1994 and entering into force in 1996. Mitigation approaches and control success or failure varies with concepts of causes and consequences. This is exemplified through a discussion of recent and relict desertification and mitigation cases in Europe, China and Africa. Conclusion: The causes, consequences and methods of control of desertification cannot be generalized but are site specific. Every site and case needs its own diagnosis, based on an integrated and systemic research approach, before the right cure can be identified and implemented.
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| 13. |
- Helldén, Ulf
(author)
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Desertification, fact or fiction?
- 1994
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In: Our Planet. -The United Nations Environment Programme Magazine for Sustainable Development. - 1013-7394. ; 6:No. 5, s. 33-33
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Journal article (peer-reviewed)
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| 14. |
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| 15. |
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| 16. |
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| 17. |
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| 18. |
- Helldén, Ulf
(author)
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LU-CDM, A Conceptual Model of Desertification
- 2008
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Reports (other academic/artistic)abstract
- This paper presents a generic system dynamic model to simulate and analyze a desertification system and its stability for different desertification syndromes. The study is one of many desertification related modelling approaches carried out by different project partners within the frames of DeSurvey (A Surveillance System for Assessing, Monitoring and Modelling Desertification; 2005-2010). DeSurvey is an EU FP6 Integrated Project (IP) on desertification considering the inter-action and importance of socio-economy, climate and landscape vulnerability to land degradation. The human-environment coupled model integrates socio-economic drivers with bio-physical drivers of land degradation and desertification. It is based on the UN and GEF definitions of desertification. It illustrates the concept of desertification through differential equations, simulation output graphics and through causal loop diagrams demonstrating the existing feed-back mechanisms. It may be useful for land use system stability/equilibrium condition analysis and for sustainable strategic land policy and management decision support. The model relates population pressure and dynamics over time to the removal and availability of biomass resources. The population stock is described as a function of growth rate, death rate and resources dependent in and out migration of people. The relative growth rate of the stock of resources is modeled as a function of climate and exploitation pressure affecting soil erosion and water availability. Biomass recovery from serious degradation/desertification events follows the logistic growth function modified by population pressure, erosion and water availability conditions. The conceptual desertification model is applied for the Sahelian syndrome using input data to illustrate and simulate a 150 years period (1900-2050) in Kordofan, Sudan. The model indicates that it is difficult to generate irreversible desertification in a system where there is an open market and free population mobility unless serious climate change and/or extremely serious soil erosion creates long term wasteland conditions leading to ultimate land abandonment
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| 19. |
- Helldén, Ulf, et al.
(author)
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National Drought Impact Monitoring- A NOAA NDVI and precipitation data study of Ethiopia
- 1988
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Reports (other academic/artistic)abstract
- This is a study on the potential of NOAA satellite data for operational early warning and food security monitoring at a national level. Ethiopian NOAA NDVI 15-day composites (1981-1985) are analysed and compared to precipitation data including time series records from more than 200 stations. Anomaly analyses are introduced and the regional distribution of the 1984 drought is clearly identified. A strong relationship betwen satellite vegetation index anomalies and precipitation anomalies is demonstrated. It is concluded that NOAA NDVI GAC data can be used as an essential input to a national early warning and food security monitoring system if restricted to the drylands of Ethiopia.
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| 20. |
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| 21. |
- Helldén, Ulf, et al.
(author)
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Regional desertification: A global synthesis
- 2008
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In: Global and Planetary Change. - : Elsevier BV. - 1872-6364 .- 0921-8181. ; 64:3-4, s. 169-176
-
Journal article (peer-reviewed)abstract
- The paper presents results on the use of NOAA AVHRR data for desertification monitoring on a regional-global level. It is based on processing of the GIMMS 8 km global NDVI data set. Time series of annually integrated and standardized annual NDVI anomalies were generated and compared with a corresponding rainfall data set (1981-2003). The regions studied include the Mediterranean basin, the Sahel from the Atlantic to the Red Sea, major parts of the drylands of Southern Africa, China-Mongolia and the drylands of South America, i.e. important parts of the desertification prone drylands of the world. It is concluded that the suggested methodology is a robust and reliable way to assess and monitor vegetation trends and related desertification on a regional-global scale. A strong general relationship between NDVI and rainfall over time is demonstrated for considerable parts of the drylands. The results of performed trend analysis cannot be used to verify any systematic generic land degradation/desertification trend at the regional-global level. On the contrary. a "greening-up" seems to be evident over large regions. (C) 2008 Elsevier B.V. All rights reserved.
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| 22. |
- Helldén, Ulf
(author)
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Ökenspridning-ett lokalt problem?
- 1995
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In: Naturvetenskapliga forskningsrådet. Årsbok 1995 “Det evigt rinnande vattnet”. ss 131-142.. ; , s. 131-142
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Journal article (peer-reviewed)
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| 23. |
- Hill, Joachim, et al.
(author)
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Remote Sensing and Geomatics Strategies for Desertification and Land Degradation Monitoring and Assessment
- 2005
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In: Proceedings: Local & Regional Desertification Indicators in a Global Perspective. ; , s. 113-124
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Conference paper (peer-reviewed)abstract
- During the past 10 years, the European Commission has funded numerous dedicated research projects in the field of land degradation and desertification which focussed on data collection in specific field sites, detailed methodological studies, assessment and monitoring experiments, and the development of specific modelling concepts. Although substantial scientific progress has been achieved and some projects succeeded to link a considerable number of field sites and case studies across the Mediterranean basin, the scientific community has, apart from few initiatives not been able to provide unifying concepts for assessing land degradation processes on at least scale as required by political decision makers. Major fields of remote sensing and geomatics related research are in the development and application of methodologies to assess and monitor desertification and land degradation processes, especially in the European Mediterranean. While initial efforts were mostly confined to the evaluation of potential spatial indicators of degradation and how these could be inferred from spatial data sources, current approaches focus on methodological improvements, their multi-temporal application, and the development of remote sensing based environmental process models. In this context, an increasing integration with different disciplines is of utmost importance to proceed from purely descriptive approaches towards the definition of alternative management strategies to support the prevention or mitigation of land degradation. In this context, the GeoRange project focused on the implementation of integrated assessment concepts for multifunctional Mediterranean rangelands. These are based on retrospective data sets, where long time series of medium resolution satellite images have been set up and quantitatively analysed with respect to proportional vegetation cover as the target indicator of rangeland condition. Trend analyses were then calculated to characterize the development of vegetation cover with time, and interpretation frameworks were defined to interpret the resulting statistical parameters with regard to different problem regimes, such as wild fires, grazing and others. While the integration of remote sensing derived information into ecological process models has triggered widespread applications using medium and high resolution imagery, increasing emphasis is attributed to the synoptic, integrated assessment of larger spatial units, and the provision of dedicated information products for administrations and policy-makers. In the frame of the GMES initiative of the European Commission, the Ladamer project aims at the small-scale assessment of the degradation status of large areas, and the identification of degradation ‘hot spots’. In order to meet these prerequisites, the remote sensing interface, which so far has been based on limited data series obtained from earth observation satellites must now be extended to accommodate small scale multi-year observations from global monitoring satellites; this approach also forms the backbone of the remote sensing component of the recently launched Integrated European Project DeSurvey. An alternative approach is followed by the DesertWatch project which has recently been launched by the European Space Agency (ESA). This program is primarily triggered to derive land use changes in desertification-affected European countries based on the analysis of Earth observation satellite data from three distinct time steps (1984-1994-2004). Its complementarity to the Ladamer Project suggest that both projects should establish linkages to optimise their impact.
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| 24. |
- Janin, E., et al.
(author)
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Corrosive adsorption of Sn on the Pt(110)(1 x 2) surface
- 2002
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In: Surface Science. - 0039-6028 .- 1879-2758. ; 515:03-feb, s. 462-470
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Journal article (peer-reviewed)abstract
- Room temperature deposition of Sn on the Pt(110)(1 x 2) surface has been studied by scanning tunnelling microscopy and core level photoelectron spectroscopy. At low coverage Sri is found in three different configurations; as mobile adatoms in the valley of the missing-row reconstruction, as 1D-Pt-Sn-Pt- alloy chains forming local Pt3Sn(110)2 x 2 regions and finally as 3D alloy islands. At higher coverage these islands form a platinum rich alloy film, which is dissolved in the crystal upon annealing to 600 degreesC.
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| 25. |
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| 26. |
- Töttrup, Christian, et al.
(author)
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Long term NOAA-AVHRR GIMMS-NDVI - rainfall relationships and trends 1981 to 2003 for entire DeSurvey area of interest
- 2007
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Reports (other academic/artistic)abstract
- The paper presents results of a study on the use of the NOAA AVHRR data for desertification monitoring on a regional-global level. It is based on processing of the GIMMS 8 km global NDVI data set. Time series of annual integrated NDVI and standardized annual NDVI anomalies from the 1981-2003 periodic means were compared with a corresponding rainfall data set (i.e. 1981-2003) as well as a historical rainfall set (1901-2002). Both sets were derived from 2.5 degrees and 0.5 degrees global gridded climate data respectively. The areas studied include the Mediterranean basin (Southern Europe and Northern Africa), the Sahel from the Atlantic to the Red Sea, major parts of the drylands of Southern Africa, China and the drylands of South America, i.e. important parts of the desertification prone areas of the world (Cf. fig. 1) It is concluded that the suggested methodology is a robust and reliable way to assess and monitor desertification on a global, national and regional scale. The results of the applied methodology indicate a strong general relationship between NDVI and rainfall over time. The results of performed trend analysis cannot be used to verify any systematic generic land degradation/desertification trend at the regional-global level in any of the regions studied. On the contrary, a “greening-up” seems to be evident over the past 20 years in several of the regions when interpreting the NDVI as a proxy for biomass cover and seasonal vegetation growth. This is most obvious in the African Sahel region south of the Sahara.
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| 27. |
- Wu, Weicheng, et al.
(author)
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Assessing woody biomass in African tropical savannahs by multiscale remote sensing
- 2013
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In: International Journal of Remote Sensing. - : Informa UK Limited. - 1366-5901 .- 0143-1161. ; 34:13, s. 4525-4549
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Journal article (peer-reviewed)abstract
- Woody biomass production is a critical indicator in evaluation of land use management and the dynamics of the global carbon cycle (sequestration/emission) in terrestrial ecosystems. The objective of the present study was to develop, through a case study in Sudan, an operational multiscale remote-sensing-based methodology for large-scale estimation of woody biomass in tropical savannahs. Woody biomass estimation models obtained by different authors from destructive field measurements in different tropical savannah ecosystems were expressed as functions of tree canopy cover (CC). The field-measured CC data were used for developing regression equations with atmospherically corrected and reflectance-based vegetation indices derived from Landsat ETM+ (Enhanced Thematic Mapper Plus) imagery. Among a set of vegetation indices, the normalized difference vegetation index (NDVI) provided the best correlation with CC (R-2 = 0.91) and was hence selected for woodland woody biomass estimation. After validation of the CC-NDVI model and its applicability to Moderate Resolution Imaging Spectroradiometer (MODIS) data, time-series MODIS NDVI data (MOD13Q1) were used to partition the woody component from the herbaceous component for sparse woodlands, woodlands and forests defined by the Food and Agriculture Organization (FAO) of the United Nations Land Cover Map. Following the weighting of the estimation models based on the dominant woody species in each vegetation community, NDVI-based woody biomass models were applied according to their weighted ratios to the decomposed summer and autumn woody NDVI images in all vegetation communities in the whole of Sudan taking the year 2007, for example. The results were found to be in good agreement with those from other authors obtained by either field measurements or other remote sensing methods using MODIS and lidar data. It is concluded that the proposed approach is operational and can be applied for a reliable large-scale assessment of woody biomass at a ground resolution of 250m in tropical savannah woodlands of any month or season.
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