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PRESENTATIONS AND ABSTRACTS FROM THE INTERNATIONAL
WORKSHOP ON CLIMATE
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SESSION 2: Trends in Land Degradation
SESSION 3: Weather and Climate Information for Monitoring and Assessing Land Degradation
SESSION 4: Strategies for more Efficient Use of Weather and Climate Information and Applications for Reducing Land Degradation
SESSION 5: Case Studies on Successful Measures to Manage Land Use, Protect Land and Mitigate Land Degradation
SESSION 6: Improving Implementation of National Action Programmes (NAPs)
major attempts have been made over the past fifteen years to assess land
degradation at global scale. GLASOD (Global Assessment of Soil
Degradation) and Dregne and Chou (1992) covered the whole globe but
specifically addressed the drylands. NRCS (Natural Resources
Conservation Service) and the Millennium Ecosystem Assessment's LUCC
(Land Use and Cover Change) addressed the drylands only. Following the
UNCCD, these assessment defined land degradation in the drylands as
"desertification". Each of these assessments came up with a
different estimate of dryland degradation, i.e. in the extent of
desertification. The earlier assessments resulted in 70% and 20%, the
latest – in 10% of drylands being desertified. This large range is
partly due to differences in methodologies as well as in quality of data
and in their spatial coverage. Another drawback is that maps produced by
these assessments often carried misleading titles, what promoted a
common interchangeable use of the terms "drylands",
"desertification" and "desertification risk".
This rather poor state of the art is probably due to a prevailing disagreement about what precisely "land degradation" is. Adopting the conceptual framework of the Millennium Ecosystem Assessment (MA) project, land degradation can be viewed as a syndrome of impairment of terrestrial ecosystem services, culminating in persistent reduction in biological productivity, as expressed in primary production. This syndrome is of major significance in the drylands, which are defined by having an inherently low biological productivity; hence further lowering of their productivity is of serious consequences to their inhabitants. This syndrome may be partly responsible to the highest infant mortality and lowest GDP in drylands than in other major global ecological-societal systems.
Inasmuch as the global extent of desertification is controversial, some trends already emerge. Desertification peaks at the mid-section of the aridity gradient, i.e. at the semiarid drylands, and tails off towards the least and the most dry drylands. Assuming that human pressure on land resources increases with population density (which declines with aridity) and that the sensitivity of the land to human pressure increases with aridity, then a peak of degradation at medium aridity is expected. At the global scale, this peak in degradation also coincides with a peak in low indices of human well-being. Whereas it is difficult to establish desertification trends during the last several decades (except delimiting currently degraded land), MA projections for the coming 50 years are of increasing desertification driven by both socio-economic and climate change trends, and accelerating under a regionalized world, and environmentally reactive society.
A promising approach (developed by S.D. Prince) for assessing desertification is to identify regions with uniform environmental attributes, inspect time-series of their net primary productivity (NPP) detected by space-borne sensors, scale this NPP by the local rainfall and allocate and define those land units with NPP persistently lower than the maximal for this region as desertified. This approach already supported the proposed definition of land degradation (and in the drylands – desertification) as a persistent reduction in primary productivity. Next challenge is to determine where desertification is irreversible. This will require consulting information on past and current land uses in areas defined as desertified, and demonstrate that the reduced NPP is maintained after pressure has been removed.Top of Page
Combating Desertification and Promoting sustainable development: Assessing Current Land Degradation status and trends in the Asia Region by Ma Hong and Hongbo Ju. Institute of Forest Resource Information Technique, Chinese Academy of Forestry.
degradation, defined as lowering and losing of soil functions, is
becoming more and more serious worldwide in recent days, and poses a
threat to agricultural production and terrestrial ecosystem. It is
estimated that nearly 2 billion ha of soil resources in the world have
been degraded, namely approximately 22% of the total cropland, pasture,
forest, and woodland. Globally, soil erosion, chemical deterioration and
physical degradation are the important parts amongst various types of
land degradation. Asia is
the first big continent in the world.The total area of the Asia Region
is about 4 4,000,000 square kilometers, composition world land total
area 29.4%. Asia has the largest area under drylands.
has come to the forefront of global concerns, as demonstrated in the
number of international conferences and conventions, most recently, the
Convention to Combat Desertification. The Convention defines
desertification as a process of land degradation resulting from various
factors including both climatic variation and change and human
by the provisions of the United Nations Convention to Combat
Desertification (UNCCD), The Asian Regional Thematic programme Network
on Desertification Monitoring and Assessment, abbreviated as TPN1, was
launched in July, 1999 in Beijing, China. Many
countries and institutions have made achievement in this area. All of
the efforts and results will contribute to combat desertification, the
serious hazard to our planet.
Many countries and institutions have made achievement in this area. All of the efforts and results will contribute to combat desertification, the serious hazard to our planet.
The loss of biodiversity and a significant deterioration of soil productivity has been the result from a number of causes as agricultural practices, ecosystem fragility, human pressure and climate aggressivity. In tropical areas, sugar cane cultivation during the last three centuries and especially in the late 18th century, was the primary cause for forest cover removal to install unsustainable production systems. Much of this land had only shallow and fragile soils highly erosion prone due to the steepness of the slopes it occupied. Consequently it was observed a loss of significant amounts of topsoil from many areas, especially in the volcanic soils of Meso America occured. Although the worst affected areas are no longer in cultivation, the natural vegetation that has recolonised these areas is much poorer in species composition and accumulated biomass than the original vegetation
In arid and semiarid parts of the continent, low rainfall and frequent periods of drought stress generally produce poor stands of sparse vegetation, which provide ineffective protection to the soil from the erosive effects of rainfall. The same low rainfall reduces the rates of weathering that lead to soil formation, thus tilting the balance towards a shallower soil.
Argentina has significan soil erosion in La Rioja, San Luis and La Pampa Provinces. Overgrazing has been severe, causing erosion and river sedimentation. In the West, salination due to unsound irrigation practices become a serious problem.
The adoption of the EU Thematic Strategy for Soil Protection by the European Commission on the 22nd of September 2006 has given formal recognition of the severity of the soil and land degradation processes within the European Union and its bordering countries. The Strategy includes an extended impact assessment that has quantified soil degradation in Europe, both in environmental and economic terms. Available information suggests that, over recent decades, there has been a significant increase in soil degradation processes, and there is evidence that these processes will further increase if no action is taken. Soil degradation processes are driven or exacerbated by human activity. Climate change, together with individual extreme weather events, which are becoming more frequent, will also have negative effects on soil.
Soil degradation processes include:
· Erosion: the EEA estimates that 115 million ha, or 12% of Europe’s total land area, are affected by water erosion, and that 42 million ha are affected by wind erosion, of which 2% severely affected.
· Organic matter decline: soil organic matter (SOM) plays a major role in the carbon cycle of the soil. Indeed, soil is at the same time an emitter of greenhouse gases and also a major store of carbon containing 1,500 gigatons organic and inorganic carbon. Around 45% of soils in Europe have a low or very low organic matter content (meaning 0-2% organic carbon) and 45% have a medium content (meaning 2-6% organic carbon). The problem exists in particular in the Southern countries, but also in parts of France, the United Kingdom, Germany and Sweden.
· Compaction: estimates of areas at risk of soil compaction vary. Some authors classify around 36% of European subsoils as having high or very high susceptibility to compaction. Other sources speak of 32% of soils being highly vulnerable and 18% moderately affected.
· Salinisation is the accumulation in soils of soluble salts mainly of sodium, magnesium, and calcium. It affects around 3.8 million ha in Europe. Most affected are Campania in Italy, the Ebro Valley in Spain, and the Great Alföld in Hungary, but also areas in Greece, Portugal, France, Slovakia and Austria.
· Landslides often occur more frequently in areas with highly erodible soils, clayey sub-soil, steep slopes, intense and abundant precipitation and land abandonment, such as the Alpine and the Mediterranean regions. There is, to date, no data on the total area affected in the EU, but this problem can be due to population growth, summer and winter tourism, intensive land use and climate change.
· Contamination: due to more than two hundred years of industrialisation, Europe has a problem of contamination of soil due to the use and presence of dangerous substances in many production processes. It has been estimated that 3.5 million sites may be potentially contaminated, with 0.5 million sites being really contaminated and needing remediation.
· Sealing: on average the sealed area, the area of the soil surface covered with an impermeable material, is around 9% of the total area in Member States. During 1990-2000 the sealed area in EU15 increased by 6%, and the demand for both new construction due to increased urban sprawl and transport infrastructures continues to rise.
· Biodiversity decline: soil biodiversity means not only the diversity of genes, species, ecosystems and functions, but also the metabolic capacity of the ecosystem. Soil biodiversity is affected by all the degradation processes listed above, and all driving forces mentioned apply (equally) to the loss of soil biodiversity.
Though difficult to estimate, several studies demonstrate significant annual costs of soil degradation to society in the ranges of:
No assessments of costs of compaction, soil sealing and biodiversity decline are currently available. The total costs of soil degradation that could be assessed for erosion, organic matter decline, salinisation, landslides and contamination on the basis of available data, would be up to €38 billion annually for EU25. These estimates are necessarily wide ranging due to the lack of sufficient quantitative and qualitative data.These costs do not include the damage to the ecological functions of soil as these were not possible to quantify. Therefore, the real costs for soil degradation are likely to exceed the estimates given above.
On the other hand it must be highlighted that these costs of soil degradation do not take into account the effect of standards adopted in January 2005 under cross-compliance, nor the effect of other measures recently taken by Member States. Nevertheless, as changes in soil are very slow, it is likely that the current estimate of the extent of the problem is an appropriate reference. Evidence shows that the majority of the costs are borne by society in the form of damage to infrastructures due to sediment run off, increased health-care needs for people affected by contamination, treatment of water contaminated through the soil, disposal of sediments, depreciation of land surrounding contaminated sites, increased food safety controls, and also costs related to the ecosystem functions of soil. The Soil Thematic Strategy of the European Union paves the way towards adequate measures in order to reverse the negative trends in soil and land degradation in Europe and will have also an extensive impact at the global scale by promoting similar actions in the framework of internationally binding agreements related to land degradation, like the UNCCD, UNFCCC and CBD.Top of Page
The definition of land degradation in the United Nations Convention to Combat Desertification (UNCCD) gives explicit recognition to climatic variations as one of the major factors contributing to land degradation. In order to accurately assess sustainable land management practices, the climate resources and the risk of climate-related or induced natural disasters in a region must be known. Land surface is an important part of the climate system and changes of vegetation type can modify the characteristics of the regional atmospheric circulation and the large-scale external moisture fluxes. Following deforestation, surface evapotranspiration and sensible heat flux are related to the dynamic structure of the low-level atmosphere and these changes could influence the regional, and potentially, global-scale atmospheric circulation. Surface parameters such as soil moisture, forest coverage, transpiration and surface roughness may affect the formation of convective clouds and rainfall through their effect on boundary-layer growth. Land use and land cover changes influence carbon fluxes and GHG emissions which directly alter atmospheric composition and radiative forcing properties. Land degradation aggravates CO2-induced climate change through the release of CO2 from cleared and dead vegetation and through the reduction of the carbon sequestration potential of degraded land.
Climate exerts a strong influence over dry
land vegetation type, biomass and diversity.
and temperature determine the potential distribution of terrestrial
vegetation and constitute principal factors in the genesis and evolution
of soil. Precipitation also
influences vegetation production, which in
turn controls the spatial and temporal occurrence of grazing and favours
nomadic lifestyle. The
generally high temperatures and low precipitation in the dry lands lead
to poor organic matter production and rapid oxidation.
Low organic matter leads to poor aggregation and low aggregate
stability leading to a high potential for wind and water erosion.
The severity, frequency, and extent of erosion are likely
to be altered by changes in rainfall amount and intensity and changes in
wind. Impacts of extreme
events such as droughts, sand and dust storms, floods, heat waves, wild
fires etc., on land degradation are explained with suitable examples.
Current advances in weather and climate science to deal more
effectively with the impacts of different climatic parameters on land
degradation are explained with suitable examples.
frequency of occurrence of climate extremes (for example, heat waves,
droughts, heavy precipitation) is expected to increase during the next
century (Easterling et al., 2000). Here we examine the impact of climate
extremes on processes of land degradation including floods, mass
movements, soil erosion by both water and wind, and salinisation.
Extreme events vary in space, and in time at inter-annual to decadal
scales. However, the land degradation impacts of climate-driven extreme
events have lacked systematic study. Case studies of particular events
and their impacts on society are relatively common, but examples which
combine daily meteorological records spanning decades with individual
event impact records are rare.
Reference: Easterling, D.R., Meehl, G.A., Parmesan, C., Changnon, S.A., Karl, T.R., Mearns, L.O. 2000 Climate extremes: observations, modelling, and impacts. Science 289, 2068-2074.
impact of some meteorological parameters
to land degradation in Tanzania is analysed. The parameters used
were: rainfall, which is responsible for floods in case if it is in
excess and drought in case of deficit.In
recent years parts of Tanzania have experienced recurring droughts. The
devastating were those of 1983 - 1984 and 1993 – 1994.
According to Tanzania historical data, we have droughts every four years which affects 3629239 people. The most frequent hit areas are, central areas of Dodoma, Singida and some parts of Pwani, Shinyanga, Mwanza and Mara. These regions receive 200 –600mm of annual rainfall. Experience of the past twenty years 1980-2000 has shown that floods occurred 15 times and killing 54 people and affecting 800271 people. Flood prone regions are Tanga, Mbeya, Pwani, Morogoro, Arusha, Rukwa, Iringa, Kigoma and Lindi. The impact of El-Nino rains is discussed and the probability and the probability of rainfall exceeding specific thresholds is analysed. Wind erosion is discussed. The impact of climate change on Tanzania is analysed and its impact to land degradation.. Finally the impact of solar radiation, temperature and evaporation is discussed. The paper concludes that climate and weather contributes significantly to land degradation in Tanzania.
use of climate information must be applied in developing sustainable
practices as climatic variations contributes
to to land degradation and there is a clear need to consider carefully
how climate induces and influences land degradation. The paper
recommends that there is a need to: Make
an inventory of national land resources; assess potentials and
constraints in dryland farming, identifying agricultural options to
safely increase cropping intensity and yields, adopt more sustainable
forms of land use, including contingency crop planning in the case of
droughts., studying the reasons behind poor land use, encourage
pastorists to reduce their herds of stocks and finally encourage the use
of indigenous knowledge in land preservation.
The complexity of the notion ‘land’ and
its scale features leads to many different definitions of land and land
degradation. Desertification, soil degradation, erosion are components
of land degradation. A wealth of literature exists claiming that land
degradation is serious. These so-called doom papers are based on
‘hard’ facts: RS, GIS & computer models. However, there is also
a history of papers that raise the question ‘how serious is land
degradation?’ There are four spatial-temporal scales that should be
distinguished in a discussion on land degradation: the regional,
watershed, field and point scale. At each scale level one may use
different proxies for land degradation which will be discussed. It seems
that the common assessment by 'experts' of land degradation may very
well be overestimating the phenomenon. In the future they need to deal
better with the spatial and temporal dimensions of land degradation. A
major reason for the overestimation of land degradation is the
underestimation of the abilities of local farmers; many of them have
been able to adapt!
order to study land degradation at multiple scales it is necessary to
also study rainfall at multiple scales. Rainfall can be analyzed for
land degradation at five different scales, from the ‘small’ annual
scale to the ‘large’ rainfall intensity scale. Besides scales one
may also distinguish between average values and temporal and spatial
variations. For each of the scales one of more examples are be presented
of rainfall data and their interpretation with respect to land
the annual scale, isohyets, trend analysis, spatial analysis and
rainfall probabilities are given. The monthly scale is used to find a
possible shift in long and
short rains in a bi-model climate. The decadal scale is especially
suitable for calculating varying lengths of the growing season. At the
daily scale, size classes of showers, return period (design storm),
hydrological and agronomic modelling and dry spell analysis will be
discussed. At the rainfall intensity scale, erosivity in El Nino and La
and land meet at the soil surface. Rainfall is divided over several
Green water is that part of rainfall that is stored in the soil and
available to plants. Land
degradation decreases infiltration, water-holding capacity and
transpiration and enhances runoff and soil evaporation. These ago-physical processes decrease the
Green Water Use Efficiency (GWUE; the ratio transpiration /
precipitation). Special attention will be given how to estimate the
effects of land degradation on ‘computing soil moisture’ in order to
understand what farmers perceive as drought. Rain falling on the land may be
intercepted by vegetation, run off the ground surface, or infiltrate
into the soil, reflected in the rain water balance. Infiltrating water may be stored in the root zone or drain below the root
zone to groundwater and stream base flow, contributing what is nowadays
called ‘blue water’. These processes are reflected in the
infiltration water balance.
maximum amount of stored water in the root zone available for plant
a very important soil quality because it determines the potential
survival of plants in case of a dry spell.
stored in the root zone may be lost as evaporation from the soil surface
into the atmosphere or taken up by plants and lost as transpiration. This
is reflected in the soil water balance. GWUE in drylands in sub Saharan Africa ranges from 5-15%. In East Africa
it may reach 20% but in comparable climates in the USA the GWUE may be