Presentation on theme: "INTERACTIONS BETWEEN CLIMATE AND DESERTIFICATION M.V.K. Sivakumar Agricultural Meteorology Division World Meteorological Organization M.V.K. Sivakumar."— Presentation transcript:
INTERACTIONS BETWEEN CLIMATE AND DESERTIFICATION M.V.K. Sivakumar Agricultural Meteorology Division World Meteorological Organization M.V.K. Sivakumar Agricultural Meteorology Division World Meteorological Organization
Presentation Use of the term “desertification” Problem of desertification Human impact on drylands - Overgrazing - Biomass burning - Soil erosion - Irrigation Impact of dryland climates on soils, ecosystems, water balance and land use Climate change and desertification Recommendations
Use of the term “Desertification” The term desertification was employed by French forester Aubreville in He used the term to refer to the replacement of tropical rainforest by secondary savanna and scrub in those parts of Africa where forest was being cleared and burned to provide land for cultivation. “true deserts are being born in front of us at present time, in regions where the rainfall ranges from 700 mm to more than 1500 mm per year”
Use of the term “Desertification” UNEP’s definition in 1990 attributed all desertification to human activity: “land degradation in arid, semi-arid and dry sub-humid areas resulting from adverse human impact” UNCCD (1995) definition of desertification allows a role for “various factors, including climatic variations and human activities”.
Hence we should look at two-way interactions between climate and desertification Look at ways in which human activities modify the surface characteristics and atmospheric composition of drylands and consider how these may influence local and regional dryland climates. Evaluate the impact of dryland climates on soils, ecosystems, water balance and human land use in the dryland regions.
Problem of desertification Total land area of the earth – 145 m km 2 Drylands occupy 6.31 billion ha (Bha) or 47.2% of the total land area (UNEP, 1992). - Africa 2 Bha - Asia 2 Bha - Australasia 0.68 Bha - North America 0.76 Bha - South America 0.56 Bha - Europe 0.30 Bha
GLASOD estimates of desertification (Oldeman and Van Lynden 1998) Type of degradationArea (Bha) Water erosion0.478 Wind erosion0.513 Chemical degradation0.111 Physical degradation0.035 Total1.137
Estimate of annual rate of land degradation in mid latitude drylands Land UseTotal land area (Mha) Rate of desertification Mha y -1 % of total y -1 Irrigated land Rangeland Rainfed cropland Total
Human Impact on drylands - surface and atmospheric conditions Locally severe overgrazing can aggravate the impact of drought and desertification by modifying soil microclimate, altering soil-water- plant relationships and exposing bare soil to erosion. Biomass burning contributes significantly to gross global emissions of trace gases and particulates from all sources to atmosphere. Forest and woodland clearing leads to accelerated soil erosion. Expansion of irrigation leads to waterlogging and salinisation, important agents of desertification.
Impact of Human Activities in Drylands on Climate Human induced changes in dryland surface conditions and atmospheric composition directly affect the energy budget of the surface and atmosphere column. Perturbations in energy balance may affect near- surface and surface temperature in many ways.
Impact of Human Activities in Drylands on Climate (contd.) Impact of Human Activities in Drylands on Climate (contd.) Human influence on local and regional precipitation levels has been more difficult to identify. Climatic consequences associated with surface changes in drylands are local as well as often regional. It is difficult to detect a global-scale climate impact.
Overgrazing in rangelands Widely considered to be a major cause of desertification in rangelands due to depletion of grass and shrub cover and ensuring the accelerated loss of top soil Attributed to a combination of overstocking and poor land management Aggravated by periodic droughts
Hypothetical impact of overgrazing and reduced grazing, on rainfall in drylands (After Krebs and Coe 1985)
Biomass burning and atmospheric emissions Includes wild and prescribed fires in forested areas as well as annual burns of savanna, burning of agricultural waste and use of fuelwood as energy source Common practice in the tropics and subtropics Affects Africa all year round, but particularly prevelant in the dry season Emissions from biomass burning are considerable and contribute significantly to gross global emissions of trace gases and particulates from all sources to atmosphere.
Estimates of gross global atmospheric emissions from all sources and biomass burning (Cachier 1992) Gas or aerosol All sources (10 12 g/yr) Biomass burning g/yr (%) CO 2 8,7003,70042 CO1, CH NH
Estimates of biomass burning Biomass burning from savanna fires annually affect an area about 100 times larger than that from which forest is cleared. 80% of the biomass burning now occurs in the inter- tropical zone, of which nearly half is from agricultural burning and use of wood for fuel. Most of the fires are deliberately started by humans.
Biomass burning by region (Adopted from Andreae 1993) Region% Africa42.6 South America26.5 Asia12.5 Australia and Oceania6.6 Central America and Mexico 6.8 North America4.2 Europe0.8
Emissions from biomass burning Biomass burning contributes significant amounts of trace gases and particulates to the atmosphere. Estimates of smoke emissions from tropical America, Africa, Asia and Australia range between 25 and 79 x g/yr. For a comparison, smoke emissions from fossil fuel burning range between 22.5 and 24 x g/yr, the dominant source of smoke in the Northern Hemisphere (Ghan and Penner 1992).
Agriculture’s contribution to air pollution Public attention tends to focus on the more visible signs of agriculture’s impact on the environment, whereas it seems likely that the non-visible or less obvious impacts of air pollution cause the greatest economic costs Pretty et al. 2001
Effects of biomass burning Soot, dust and trace gases are released by biomass burning during forest, bush or rangeland clearance for agriculture. Biomass burning results in globally important contributions to the atmospheric budget of several trace gases (Crutzen and Andreae 1990). Ozone from biomass burning makes up 38% of all tropospheric ozone. About 50% of all nitrogen in the biomass is released as N 2 during burning, causing sizeable loss of fixed nitrogen in tropical ecosystems in the range of 10 to 20 x g/yr. Trace gases and particulates can modify atmospheric chemistry.
Climate change itself, however, may cause temperatures to rise in the dry season, increasing fire risks and thus increasing pollution from biomass burning in some areas Lavorel et al. 2001
Forest and woodland clearing and accelerated soil erosion If the soil surface is left bare through clearing for agriculture, the erosive impact of early season convective rains can increase erosion by a factor of 50 or above the normal long-term disturbed rate. Accelerated soil erosion affects the C pool and fluxes because of breakdown of soil aggregates, exposure of C to climatic elements, mineralization of organic matter in disrupted aggregates and redistributed soil, and transport of sediments rich in SOC downslope to protected areas of the landscape.
Rates of erosion in selected countries (kg/m 2 /yr) CountryNaturalCultivatedBare soil China< Cote d’Ivoire Nigeria India
Impact of drought and removal of vegetation on sand and dust transport It has been estimated that in the arid and semi-arid zones of the world, 24% of the cultivated land and 41% of the pasture land are affected by moderate to severe land degradation from wind erosion The world-wide total annual production of dust by deflation of soils and sediments was estimated to be 61 to 366 million tonnes. For Africa alone, more than 100 million tonnes of dust per annum is blown westward over the Atlantic.
Model to show relationship of drought, human activities and desertification to increasing duststorm activity
Anthropogenic land disturbances and wind erosion Human-induced change is by far the most significant factor in the alarming increase of dust storms in some regions. According to previous studies, wind erosion in the semi-arid regions of America, Africa, Australia, the Near East and many parts of Central Asia could only reach threatening proportions when man disturbed the ecosystem balance. Past policies on land-use and the promotion of farming systems that were unsustainable were the root cause of most disasters.
Increasing frequency of sand and dust storms In recent years, there is evidence that the frequency of sandstorms is increasing. Annual frequency of strong and extremely strong sandstorms in China - 5 times in the 1950s - 8 times in the 1960s - 13 times in the 1970s - 14 times in the 1980s - 20 times in the 1990s. Every year desert encroachment caused by wind erosion buries 210,000 hectares in China ( PRC, 1994).
Wind erosion in the Sahel Rapid population growth of 3% during recent decades, has increased demand for food and farmers have tried to enhance production by extending cropping to more marginal areas. Consequently, over- exploitation has resulted in land degradation, or desertification, on a large scale. The amount of dust arising from the Sahel zone has been reported to be around or above 270 million tons per year which corresponds to a loss of 30 mm per m 2 per year or a layer of 20mm over the entire area.
Impacts of dust storms on climate Dust particles exert a radiative influence on climate directly through reflection and absorption of solar radiation and indirectly through modifying the optical properties and longevity of clouds. Dust particles can cause cooling in two ways. Directly, through radiative influence and indirectly by acting as condensation nuclei, resulting in cloud formation. Dust storms have local, national and international implications concerning global warming. Climatic changes in turn can modify the location and strength of dust sources.
Impact of irrigated agriculture on surface conditions in drylands About 30% of all irrigated lands are considered to be degraded to varying degrees. Inadequate drainage and ineffective leaching of the soil, can cause problems of water logging and salinisation which are becoming increasingly frequent. A secondary and equally incidious problem is the dispersion of sodic soils leading to a reduction in soil infiltration capacity and permeability. Salt-affected lands are reflected as saline seeps in dryland agriculture and secondarily salinized irrigated lands (Tanji 1995).
Extent of salinisation in the world Total area of saline soils is 397 million ha and of sodic soils 434 million ha at global level. Of the current 230 million ha of irrigated land, 45 million ha are salt-affected soils (19.5 percent) Of the almost million ha of dryland agriculture, 32 million are salt-affected soils (2.1 percent) to varying degrees by human-induced processes.
Impact of saline soils on local climate Albedo over salt pans and dry salt lakes is higher (60%). Greater contrast in surface temperatures - day temp 40 ° C on sand vs 24 ° C on salt crust - night temp 0.4 ° C on sand and 8 ° C on salt Nocturnal air flow convergence and daytime divergence Changes in airflow could accelerate wind erosion and dust deflation.
Two-way interactions between climate and desertification W ays in which human activities modify the surface characteristics and atmospheric composition of drylands and consider how these may influence local and regional dryland climates. Evaluate the impact of dryland climates on soils, ecosystems, water balance and human land use in the dryland regions.
Impact of dryland climates on soils High temperatures and low precipitation 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. Evapotranspiration greatly exceeds precipitation leading to accumulation of salts on soil surface. Soils with natric horizon are easily dispersed. Low moisture levels lead to limited biological activity. Structural crusts/seals formed by raindrop impact which could decrease infiltration, increase runoff and generate overland flow and erosion.
Marked seasonality and a tendency towards drought limits the productive capacity of the land.
Impact of dryland climates on ecosystems Climate exerts a strong influence over dryland vegetation type, biomass and diversity. Rainfall influences vegetation production, which in turn controls the spatial and temporal occurrence of grazing and favours nomadic lifestyle. Dryland plants and animals display a variety of physiological, anatomical and behavioural adaptations to moisture and temperature stresses brought about by large diurnal and seasonal variations in temperature, rainfall and soil moisture.
Impact of climate on the hydrological cycle Dryland precipitation is highly variable in time and space, leading to corresponding variability in runoff, soil moisture, and streamflow in the drylands of the world. Dryland rivers exhibit a high variability of volume and discharge. One reason is the influence of ENSO. Owing to the infrequent and short-lived nature of rainfall, runoff in most drylands is < 10% of rainfall
Impact of climate on human land use Rainfall variability and other dryland climate characteristics greatly influence vegetation productivity, carrying capacity of the land, susceptibility of the land to erosion, surface water availability and aquifer recharge. Operations affected include crop planting dates, rangeland management strategies, subsistence strategies among peasant farmers, water management in irrigated agriculture etc.,
“An increasing body of observations gives a collective picture of a warming world and other changes to the climate system” Present Climate Intergovernmental Panel on Climate Change, 2001
Agriculture’s contribution to global greenhouse gas and other emissions GasCarbon dioxide MethaneNitrous oxide Nitric oxides Ammonia % of total anthropog. sources Main effects Climate change Acidifi- cation Acidification. Eutrification Agric. Source Land use change, deforest. Ruminants Rice prod. Bio Burning Livestock Fertilizer Bio Burning Biomass Burning Fertilizer Livestock Fertilizers Bio Burning Expected Changes to 2030 Stable or declining Rice: stable or declining Livestock: rising 60% 35-60% increase Livestock: rising 60%
Role of drylands in greenhouse gas build-up Difficult to assess, but drylands are likely to contribute between 5 to 10 per cent of overall greenhouse gas build- up. These values are small at the global level, but are significant at the regional or national level. Many drylands have relatively small anthropogenic emissions of carbon dioxide.
Why Climate Change can be of Significance to the Drylands ? Most dryland ecosystems are already affected by increasing resource demands and unsustainable management practices and human-induced climate change adds an important new stress. Most systems are sensitive to both the magnitude and rate of climate change. Successful adaptation depends upon advances in technology, institutional arrangements, availability of financing and information exchange. Vulnerability increases as adaptive capacity decreases.
Recommendation for the Meeting and for the Working Groups to discuss Recommendation for the Meeting and for the Working Groups to discuss Establish CONASTAC Network to provide an integrated approach to study the contribution of agriculture to the state of climate. The integrated approach would help address the issue in a holistic manner and would contribute significantly to the IPCC process. Participating scientists in the network would benefit from exchange of information and experiences. Means to disseminate information on the web would help highlight the issue and help interest more scientists to participate in the work of the network.