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Rheinischen Friedrich-Wihelm-Universitêt Bonn (2007)

Integrated desertification assessment in Southern Mongolia

Begzsuren, Shurentuya

Titre : Integrated desertification assessment in Southern Mongolia

Auteur : Begzsuren, Shurentuya

Université de soutenance : Rheinischen Friedrich-Wihelm-Universitêt Bonn

Grade : Doktor der Agrarwissenschaften 2007

Résumé
The Bulgan soum in southern Mongolia is a part of the Gobi Three Beauty National Park. The territory is composed of arid and semi-arid desert, encompassing 720 000 ha. A desertification threat, which was virtually unknown for many years, has become a serious environmental problem in the last 20 years. Climatic variations, low variable rainfall, and dust storms overlaid by unsustainable human land-use practices, primarily poorly managed livestock grazing, are contributing to accelerated desertification. The primary objective of this study is to assess desertification based on soil, vegetation, climate and socio-economic indicators including modified soil adjusted vegetation index (MSAVI), topsoil grain size index (GSI), shrinkage of groundwater sources, and extent of sand movement. Those were directly derived from Landsat MSS, TM, and ETM remote sensing images for the growing season months for the years of 1973, 1990, 1991, 2002 and 2005. The results show that the MSAVI is highly correlated to aboveground plant biomass and indicates a general decrease in vegetation biomass, while GSI manifests topsoil coarsening over the last 25 years. In terms of climatic indicators, the historical climate records for the Bulgan soum show warming of approximately 0.7°C over the period 1970 to 2002. Drought occurs once every 2-3 years according to the SPI and Pedi indices (with 50% probability). The frequency of dust storms in the 1987-2002 period was about twice that during the period 1970-1986. There was however, no dust haze after 1994. Plant biomass was largely controlled by low variable rainfall, by dust storms, and temperature. Climate change scenarios, based on results from time series forecasting, indicate future warming by 0.05°C per year (with 37% probability) and by 0.4 dust storm frequencies per year (with 31% probability). It results in a decline of plant biomass of 2 kg ha-1 yr
- 1 (with 26% probability) that will likely to exacerbate desertification In terms of the socio-economy of the herders, Chi-square tests show degradation classes to be associated with wealth groups, and the greater the livestock numbers, the greater the degradation. Large family size (triggers large stock numbers), older age, former herding households and decreased livestock moves were the causes of desertification. A time trend forecasting analysis projects an increase in livestock numbers (7000 standard stock units per year), particularly goats. In general, land degradation in the study area increased from 1990 to 2005, and 94% of the area is considered to be degraded to varying degrees. The slightly degraded class covered 12%, the moderate class 44% and the severely degraded class 38% of the Bulgan soum in 2005. Sand encroachments occurred in 35% of the landscape, which have increased by 19% since 1973. 1.7% of total groundwater bodies in 1973 completely disappeared in 2005. Furthermore, the area affected by desertification has increased ; the rate of desertification has also accelerated from 1% in the 1990s to 2% in 2005.

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