N. Khalili Samani; A. Azizian
Abstract
Interduction: Spatial and temporal improper distribution of precipitation is one of the major problems in the water district. Increasing population and reduction per capita fresh water has made freshwater resources as a renewable to a semi-renewable source (1).
Rainfall is one of the climatic variables ...
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Interduction: Spatial and temporal improper distribution of precipitation is one of the major problems in the water district. Increasing population and reduction per capita fresh water has made freshwater resources as a renewable to a semi-renewable source (1).
Rainfall is one of the climatic variables that influence the ground water resources. The existence of models for predicting the annual precipitation and subsequent management of water resources in arid, semi-arid and also humid regions is useful . In this study, the simple regression models that relate the annual precipitation to the duration of 42.5 and 47.5 mm of precipitation from the beginning of autumn (t42.5 and t47.5, respectively) and mean annual precipitation (Pm), in Khuzestan (2), Kerman (3) and southern and western provinces of Iran (4) were evaluated using long-term daily precipitation data of Shahrekord and Yazd Weather stations and, if necessary, modified equations.
Materials and methods: In this study, long-term daily precipitation data of Shahrekord and Yazd Weather stations (1360-1392) from Meteorological Administration of Chaharmahal and Bakhtiari and Yazd were prepared, completed and used for analysis. At each station the duration of 42.5 and 47.5 mm of precipitation from the beginning of autumn (t42.5 and t47.5, respectively) for each year, annual precipitation and mean annual precipitation for subsequent calculations were extracted. Then, the homogeneity and adequacy of data were checked using RUN Test. Equations of 1 to 8 were used for predicting the annual precipitation using 70% of the data. The relationship between observed and predicted annual precipitation were evaluated. Then the coefficients of equations were corrected by 70% of the data set using SPSS Software in Shahrekord and Yazd Weather Stations. The remaining 30% of data were used to validate the modified models. Index of agreement (d) and normalized root mean square error (NRMSE), were used to evaluate the models. The NRMSE values close to zero and d values close to 1 indicate proper operation of the model.
Results and Discussion: Results showed that the models with straight and reverse relationships between t42.5 or t47.5 and Pm were not suitable to estimate the annual precipitation in Shahrekord. However, these models were relatively acceptable for Yazd. While the simple regression model using t42.5, t47.5 and the long-term Pm as independent inputs could be able to predict the annual precipitation of Shahrekord and Yazd stations with acceptable accuracy.
Conclusion : Using the relationship between t42.5, t47.5 and Pa (equations of 1, 3, 4 and 7) for estimating the annual precipitation in Shahrekord and Yazd stations, NRMSE values obtained greater than 0.3 and d index less than 0.7 (Fig. 3 and 4). Furthermore , the models included t42.5, t47.5 and Pm versus Pa (equations of 2, 5, 6 and 8), had not acceptable results (Fig. 5 and 6). By modifying the above mentioned equations (models of 10 to 14 for Shahrekord and 15 to 19 for Yazd) and comparison of measured and predicted annual precipitation by the modified models, the results showed that the linear and inverse relationship between t42.5, t47.5 and annual precipitation could not be an appropriate model for Shahrekord Station (Fig. 7-A and 7-B and 7-C) and results of the evaluation of these relationships for estimating of the average annual precipitation of Yazd were relatively acceptable (Fig. 8-A and 8-B and 8-C results in Yazd station). While the simple linear model including the relationship between those time periods (t42.5, t47.5 ) and the long-term average annual precipitation with corrected coefficients could accurately estimate the annual rainfall in the Shahrekord and Yazd stations (Fig. 7-d and 7-H for Shahrekord and 8-D, 8-H for Yazd station). In order to validate the above results, the models were evaluated with the remaining 30% of the data . Results showed in Figs. 9 and 10. The NRMSE values in Figs. 10-A, 10-B and 10-C, confirm the validity of the relationship between t42.5, t47.5 and annual precipitation.
M. Yektafar; M. Zare; M. Akhavan Ghalibaf; S. R. Mahdavi Ardakani
Abstract
Introduction: Desertification, is a complex phenomenon, which as environmental, socio-economical, and cultural impacts on natural resources. According to the United Nations Convention to Combat Desertification defination, desertification is land degradation in arid, semi-arid, and dry sub-humid regions, ...
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Introduction: Desertification, is a complex phenomenon, which as environmental, socio-economical, and cultural impacts on natural resources. According to the United Nations Convention to Combat Desertification defination, desertification is land degradation in arid, semi-arid, and dry sub-humid regions, resulting from climate change and human activities. Because of limiting access to qualified water resources in arid lands, it is necessary to use, all forms of acceptable water resources such as wastewater. Since irrigation with sewages has most effects on soil, in this research, desertification intensity of lands irrigated with sewages and natural lands of the area, where located near Yazd city, has been analyzed considering soil criterion of the Iranian Model for Desertification Potential Assessment (IMDPA). Several studies have done in Iran and in the world in order to provide national, regional or global desertification assessment models. A significant feature of the IMDPA is easily defining and measuring criteria, indicators, and ability of the model to use geometric means for the criteria and indicators.
Materials and Methods: In first step, In first step, in a random method, soil samples were taken in each of the defined land units with considering of the size of area. Next, all indices related to the soil criterion such as soil texture index, soil deep gravel percentage, soil depth, and soil electrical conductivity were evaluated in each land use (both irrigated lands and natural lands) and weighted considering the present conditions of the lands. Each index was scored according to the standard table of soil that categorized desertification. Then, geometry average of all indices were calculated and map of the desertification intensity of the study area were prepared. Thus, four maps were prepared according to each index. These maps were used to study both quality and effect of each index on desertification. Finally, these maps were integrated to prepare the final map that shows current status of desertification in the region by calculating geometric mean of all indices based on following formula:
QS = [EC * STI * SDI* SGI]1/4
Where:
QS: Soil criteria score; EC: Electrical Conductivity index; STI: Soil texture index; SDI: Soil depth index and SGI: Soil deep gravel percentage index.
Integrating of thematic databases and spatial analyst and mapping were done using ESRI Arc GIS v.10 software. Statistical analyses such as Mann-Whitney and t-statistic were done using SPSS v.21 software for comparing land irrigated with wastewater and natural land area.
Results and Discussion: Results show that in the land irrigated with wastewater, soil texture index with weighted average of 3.74 classified in severe desertification intensity class, and soil depth gravel percent, soil depth, and soil electrical conductivity indices with weighted average of 1.23, 1, and 1, respectively were classified in low desertification class. In general, soil criteria with weighted average of 1.21 classified in low desertification class. In natural lands of the area, soil depth gravel percent index (1) classified in low intensity class, soil depth index (3.06) grouped in severe class, and soil electrical conductivity (4) and soil texture (3.93) indices with were classified in very high desertification intensity classes.
Conclusion: In natural lands, soil criteria with weighted average of 2.89 classified in severe desertification class. General results show that in the lands irrigated with sewages, soils tissue index and in the natural lands, soil electrical conductivity index are the most effective indices in increasing of desertification intensity. Totally, soil criteria with the weighted average of 2.8, which are grouped in the very high desertification intensity class, are the main factors affecting desertification in total study area. Totally, soils tissue index is the most effective index of increasing in intensity of desertification in the total study area. However, the intensity of desertifcation in the land irrigated with wastewater is lower than the desrtification intensity in the natural lands of the study area, but this issue caused by losing of large amounts of good quality purified wastewater and converting of a large part of the area to wetland which can craates numerous environmental problems in the region in future. Finally, it can be concluded that the natural land of the study area, are not suitable for afforestation and agriculture in present condition, and if the land is irrigatted, salinity of the soil depths transferred up to the surface and can be cause some environmental problems in thi region.
F. Hazirei; Mohammad Zare Ernani
Abstract
Sand dunes movement is one of the critical processes of desertification. Mulching is one of the methods of sand movement control. Oil mulches have been used in Iran. Because of high cost and negative environmental impacts of oil mulches, changes in mulch type sand mulching methods is vital. Therefore, ...
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Sand dunes movement is one of the critical processes of desertification. Mulching is one of the methods of sand movement control. Oil mulches have been used in Iran. Because of high cost and negative environmental impacts of oil mulches, changes in mulch type sand mulching methods is vital. Therefore, in this research different combinations of clay and lime were used as stabilizer. Sandy soil from the Yazd-Ardakan plain is used as bed treatment and clay particles (taken from Meybod area) were used as mulch in this research. The treatments were prepared using different ratios of the above mentioned materials. One liter of water was added to the each mulch combination and was sprinkled on the plot of 100 cm (length) × 30 cm (width) × 4 cm (height) sand. A completely randomized design is used as research plan with three repeating. Physical parameters, such as thickness, compressive strength, impact resistance and abrasion resistance which are created by mulches, and wind erodibility of the treatment were measured. The measured data were analyzed using SPSS software. Results show that the measured compressive strength, impact resistance and abrasion resistance of the clay–lime mulch is increase in the ratio of 200 gr clay and 10 gr lime in one liter of water.
