Irrigation expansion and dynamics of desertification in the Circum-Aral region of Central Asia   总被引：2，自引：0，他引：2  

Tatyana A. Saiko  Igor S. Zonn 《Applied geography (Sevenoaks, England)》2000,20(4)

The aim of this paper is to examine the causes and dynamics of desertification in one of the world's worst disaster areas, the Aral Sea region. During the 1960s, a large-scale irrigation campaign aimed at achieving independence in cotton production was launched in Soviet Central Asia. From 1960, ever-increasing water withdrawal from the two inflowing rivers—the Amudarya and Syrdarya—has resulted in the dramatic decline of the level, area and volume of the sea. Desiccation was accompanied by the development and further acceleration of various desertification processes. The study reveals that, for different reasons, the predominant direction and trends of desertification have been changing during each of the four identified periods from 1961 to 1995. The main desertification processes recorded in the Circum-Aral region (‘Priaraliye’ in Russian) were a decline in the groundwater level, increased mineralization and chemical pollution of watercourses, soil salinization, the spread of xerophytic and halophytic vegetation, and deflation and aeolian accumulation, with the development of salt storms. Recent improvements in the situation are also discussed, along with their causes. Zonation of Priaraliye is carried out and an outlook for the future is given.  相似文献   

Reindeer pastoralism in modern Siberia: research and survival during the time of crash   总被引：1，自引：0，他引：1  

Igor Krupnik 《Polar research》2000,19(1):49-56

In many areas across Siberia, the reindeer herding economy of the native people went into a deep recession during the post-Soviet transition of the 1990s. However, as a larger cross-section of data indicates, the reindeer stock decline is not a universal phenomenon. Nor is the present-day crisis in native Siberian herding economies an unprecedented event, as pastoralists did suffer tremendously in "traditional times", due to the devastating epizootics and other natural disasters, and even more so, during the Soviet-induceed collectivizsation. While such a historical review by no means diminishes the scale of the present-day crisis in native herding economies, it helps to identify both the experience and traditional adaptations once used by the native Siberians during the previous times of hardship. Of those, the most efficient were: maintaining cultural and ecological diversity in local herding systems; the ability to shift quickly between nomadic population as the invaluable source of cultural knowledge, technological expertise, and of domestic reindeer stock for ultimate recovery. The modern situation in Siberia, in fact, favours increased local diversity and helps to produce a steady stream of new "winners" as well as new "losers." This new experience has to be comprehensively documented, to produce both a reliable general overview and a detailed summary of the specific regional and local transitions.  相似文献   

Unipolar outflows and global meridional circulations in rotating accretion flows     

Igor V. Igumenshchev † 《Monthly notices of the Royal Astronomical Society》2000,314(1):54-58

Using two-dimensional simulations of non-radiative viscous rotating black hole accretion flows, we show that the flows with α ∼0.1–0.3 self-organize to form stationary unipolar or bipolar outflows accompanied by global meridional circulations. The required energy comes, with efficiency ∼0.001–0.01, from the matter directly accreted on to the black hole. Observational implications are discussed.  相似文献   

Submesoscale features and their interaction with fronts and internal tides in a high-resolution coupled atmosphere-ocean-wave model of the Bay of Bengal   总被引：1，自引：1，他引：0  

Tommy G. Jensen  Igor Shulman  Hemantha W. Wijesekera  Stephanie Anderson  Sherwin Ladner 《Ocean Dynamics》2018,68(3):391-410

Large freshwater fluxes into the Bay of Bengal by rainfall and river discharges result in strong salinity fronts in the bay. In this study, a high-resolution coupled atmosphere-ocean-wave model with comprehensive physics is used to model the weather, ocean circulation, and wave field in the Bay of Bengal. Our objective is to explore the submesoscale activity that occurs in a realistic coupled model that resolves mesoscales and allows part of the submesoscale field. Horizontal resolution in the atmosphere varies from 2 to 6 km and is 13 km for surface waves, while the ocean model is submesoscale permitting with resolutions as high as 1.5 km and a vertical resolution of 0.5 m in the upper 10 m. In this paper, three different cases of oceanic submesoscale features are discussed. In the first case, heavy rainfall and intense downdrafts produced by atmospheric convection are found to force submesoscale currents, temperature, and salinity anomalies in the oceanic mixed layer and impact the mesoscale flow. In a second case, strong solitary-like waves are generated by semidiurnal tides in the Andaman Sea and interact with mesoscale flows and fronts and affect submesoscale features generated along fronts. A third source of submesoscale variability is found further north in the Bay of Bengal where river outflows help maintain strong salinity gradients throughout the year. For that case, a comparison with satellite observations of sea surface height anomalies, sea surface temperature, and chlorophyll shows that the model captures the observed mesoscale eddy features of the flow field, but in addition, submesoscale upwelling and downwelling patterns associated with ageostrophic secondary circulations along density fronts are also captured by the model.  相似文献   

Factors controlling high-frequency radiation from extended ruptures     

Igor A. Beresnev 《Journal of Seismology》2017,21(5):1277-1284

Small-scale slip heterogeneity or variations in rupture velocity on the fault plane are often invoked to explain the high-frequency radiation from earthquakes. This view has no theoretical basis, which follows, for example, from the representation integral of elasticity, an exact solution for the radiated wave field. The Fourier transform, applied to the integral, shows that the seismic spectrum is fully controlled by that of the source time function, while the distribution of final slip and rupture acceleration/deceleration only contribute to directivity. This inference is corroborated by the precise numerical computation of the full radiated field from the representation integral. We compare calculated radiation from four finite-fault models: (1) uniform slip function with low slip velocity, (2) slip function spatially modulated by a sinusoidal function, (3) slip function spatially modulated by a sinusoidal function with random roughness added, and (4) uniform slip function with high slip velocity. The addition of “asperities,” both regular and irregular, does not cause any systematic increase in the spectral level of high-frequency radiation, except for the creation of maxima due to constructive interference. On the other hand, an increase in the maximum rate of slip on the fault leads to highly amplified high frequencies, in accordance with the prediction on the basis of a simple point-source treatment of the fault. Hence, computations show that the temporal rate of slip, not the spatial heterogeneity on faults, is the predominant factor forming the high-frequency radiation and thus controlling the velocity and acceleration of the resulting ground motions.  相似文献   

Regional Flood Frequency Analysis Based on L-Moment Approach (Case Study Tisza River Basin)     

Igor Leščešen  Urošev  Marko  Dolinaj  Dragan  Pantelić  Milana  Telbisz  Tamás  Varga  György  Savić  Stevan  Milošević  Dragan 《Water Resources》2019,46(6):853-860

Water Resources - Floods are one of the most common natural hazards and as such, they are causing a great loss of human life as well as great economic damages. Flood frequency analysis (FFA) is...  相似文献   

Mobility and retention of heavy metals, arsenic and sulphur in podzols at eight locations in northern Finland and Norway and the western half of the Russian Kola Peninsula     

Marja Liisa Räisänen  Galina Kashulina  Igor Bogatyrev 《Journal of Geochemical Exploration》1997,59(3):175-195

The mobility and retention of heavy metals, arsenic and sulphur in podzols from eight areas located north of the Arctic Circle in Finland, Norway and Russia were determined by analyzing the < 2.0 mm fraction, using an ammonium acetate (pH 4.5) extraction in addition to a concentrated nitric acid digestion for the humus samples, and a hot aqua regia digestion for the mineral soil samples. Total C, H and N concentrations were determined in humus and mineral soil samples with a CHN analyser.Ni, Cu, Co and As were strongly enriched in the humus layer in the contaminated sites (Monchegorsk, Kurka, Zapoljarnij) when compared to their concentrations in the parent tills and in podzols from the background sites. In most study sites the illuvial layer showed a low capacity to retain the metals and As, the exception included a strongly eroded profile at Monchegorsk, where Ni was tightly fixed in the illuvial layer while Cu was mobile. In contrast to metals, airborne S was not accumulated in the humus layer, but was accumulated in the illuvial layer, more markedly at eroded sites than in places where the humus was covered as at Monchegorsk.  相似文献