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121.
Motalleb Byzedi Bahram Saghafian Khosro Mohammadi Maaroof Siosemarde 《Environmental Earth Sciences》2014,71(6):2955-2972
Droughts are complex natural hazards that, to a varying degree, affect some parts of the world every year. The range of drought impacts is related to drought occurring in different stages of the hydrological cycle and usually different types of droughts such as meteorological, agricultural, hydrological, and socio-economical are the most distinguished types. Hydrological drought includes streamflow and groundwater droughts. In this paper, streamflow drought was analyzed using the method of truncation level (at 70 % level) by daily discharges at 54 stations in southwestern Iran. Frequency analysis was carried out for annual maximum series of drought deficit volume and duration. 35 factors such as physiographic, climatic, geologic and vegetation were studied to carry out the regional analysis. According to conclusions of factor analysis, the six most effective factors include watershed area, the sum rain from December to February, the percentage of area with NDVI <0.1, the percentage of convex area, drainage density and the minimum of watershed elevation, explained 89.2 % of variance. The homogenous regions were determined by cluster analysis and discriminate function analysis. The suitable multivariate regression models were ascertained and evaluated for hydrological drought deficit volume with 2 years return period. The significance level of models was 0.01. The conclusion showed that the watershed area is the most effective factor that has a high correlation with drought deficit volume. Moreover, drought duration was not a suitable index for regional analysis. 相似文献
122.
N. Mazaheri Kuhanestani B. Mokhtarzadeh Mohammadi D. H. M. Alderton S. H. Tabatabaei H. Bagheri 《Arabian Journal of Geosciences》2014,7(11):4779-4791
The Ni, Co, As, and Cu deposit of Gowd-e-Morad is located 20 km northwest of Anarak in Central Iran. In this hydrothermal deposit, mineralization occurs as veins in a fault breccia zone hosted by the Chahgorbeh (schist and metabasite) complex. The main ores are made up of Ni, Co, and Cu arsenides. Petrologic studies and results obtained from geochemical analyses have indicated that the Ni, Co, As, and Cu are derived from ultramafic rocks while Pb and Zn are likely to be derived from schist. Based on the geochemical evidence, particularly the high correlation between Ni, Co, and As, it is proposed that this deposit be categorized as a “five elements” mineral deposit. Fluid inclusion studies have shown homogenization temperatures (TH) in the range 113?206 ?C and salinity 3?13.5 % wt eq. NaCl. Therefore this “five elements” mineral deposit has been determined as a low temperature, epithermal deposit type. It is proposed that the low fluid temperatures are a result of an environment of formation which was distal to a volcanogenic source systems and the major influence of meteoric waters in the hydrothermal system. 相似文献
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The erosion features map is one of the basic maps in erosion and sediment studies and watershed management programs. Some methodologies of preparing erosion features map by using RS and GIS were compared in research which took place in the Jajrood sub-basin in north-east Tehran, Iran. In the first phase, four working units' maps were prepared by integration a) plant cover, geology and slope b) land use, geology and slope c) land use, rocks sensitivity to erosion and slope and d) land use, rocks sensitivity to erosion and land units' layers. In addition to these four working units' maps, three more maps were also evaluated in separating erosion features including e) land units f) sensitivity of rocks to erosion and g) image photomorphic units. The efficiency of these seven working units' maps was evaluated by 314 control points. For this purpose, by using erosion features of control points regarding field views, surface, rill, gully and channel erosion maps were prepared and compared by crossing them with working units' maps. Results showed that method "d" was better than "a", "b" and "c" in providing soil erosion features regarding economic and executive considerations. The accuracy of methods "e" and "f" was 53.0 and 42.9% and their Root Mean Squared Error was more than method "g" and methods "a" to "d". The coefficient of variation was highest for methods "e" and "f' and the least for method "e" and the greatest precision was related to image interpretation. 相似文献