مجله محیط زیست و مهندسی آب
سال پنجم شماره 4 (زمستان 1398)

In this research, projection of precipitation in the three distinct 20-years future periods (i.e. 2021-2040, 2041-2060, and 2061-2080) was performed using the LARS-WG6 statistical downscaling model. For this purpose, two scenarios of the IPCC fifth assessment report (namely RCP4.5 and RCP8.5) and MPI-ESM-MR general circulation model, which is known to be a CMIP5 coupled models were utilized. The precipitation trends were analyzed in the base and future periods using the Mann-Kendall method for both seasonal and annual time scales. Sen’s estimator method was used to estimate the slopes of trend lines. The results showed that winter precipitation will be increased during the three considered future periods. Moreover, in the spring and autumn, according to the RCP8.5 scenario, precipitation will be decreased in all future periods. The precipitation in December and January would be increased in all three future periods using both scenarios. March, July, September, and October will also experience a decline in precipitation in the three future periods, according to both scenarios. The mean annual precipitation in the future period of 2061-2080 would be decreased based on both scenarios. The highest reduction in precipitation would occur in the period 2061-2080 belonged to the RCP8.5 scenario in which the amount of reduction in mean annual precipitation is equal to 10.4%. In addition, based on the RCP4.5 scenario, the highest increase in the average annual precipitation during the future period of 2041-2060 was equal to 8.1%. There was no significant trend in precipitation series at 5% level. The slope of the trend lines in the base period and the future periods, based on the scenario RCP8.5, was found to be negative in all seasons. While in the future period, based on the RCP4.5 scenario, the trend line slope was positive for in all seasons.

The study of the temperature mechanism and temperature advection along with the thickness layer and its effect on the rainfall level of an area is one of the most important subjects in the field of atmospheric science. The present study was carried out with the aim of studying the temperature advection and recognition of thickness layer in relation to spring rainfall in Iran. For this purpose, a daily rainfall database with a spatial resolution of 15 × 15 km2 was used in the period 1961–2013. After extraction of precipitation days, the corresponding pressure data was extracted using the programming capabilities in the Grades environment, and with the help of cluster analysis, representative days and spring weather patterns were identified in the Matlab environment. To determine the day of precipitation, three criteria of daily rainfall of 1 mm or more, minimum two-day continuity, and minimum 50% coverage were considered. Sea level pressure maps of 700 and 500 hPa were extracted along with temperature advection and thickness of the atmosphere. The results showed that five effective patterns were identified on Iran's spring general rainfall mechanism. The strongest amount of temperature advection from the Siberian high pressure occurred in the eastern and north-eastern parts of the country and reduced to the west and south of its intensity. Generally, from the east to the west and from the north to the south, there was a milder temperature advection during spring rainfalls in Iran. In addition, the most severe temperature advection occurred at sea level due to high-pressure thermal systems. At higher altitudes and higher levels, the temperature advection had a milder state than the sea level, and reduced the severity of the temperature advection due to the dynamic situation of the atmosphere, especially the blocking systemand Mediterranean deep trough.

The expansion of urbanization along with industrial and agricultural activities on the banks of the Alshar River and subsequent discharge of wastewater into water sources have caused water contamination by various pollutants. In this study, seasonal and annual changes in the long-term water quality changes in the Alshar River were evaluated. For this purpose, water quality data used were recorded at the Sarab Sayyed Ali hydrometric station located at the outlet of the Alshar River from 1970 to 2018. For analysis, 11 water quality variables were selected. Man-Kendall test was used to examine the trend of changes. The results showed that the patterns were similar for changes in parameters at both annual and seasonal scales, with decreasing concentrations of HCO3, Na, pH and SAR and increasing concentrations of Mg, Ca, TH, TDS, EC, Cl, and SO4. In the annual period, the trend of change of all qualitative parameters except Na was statistically significant at 99% level. During the summer seasons, there were more intense upward and slower downward trends, with the strongest increase in concentration during this season. However, in the winter, the results were in contrary with the summer. In most of the qualitative parameters, the decreasing and increasing trends were higher in spring than in autumn. The reason for this could be attributed to the fact that winter snow melting from the altitudes occurs in the spring, causing increased surface currents and a relative decrease in concentrations.

Hospital wastewater is one of the most infectious and dangerous wastewaters that may contain large amounts of pathogenic microorganisms, dangerous pollutants of various hormones. More than 80 different types of drugs have been found that are not completely eliminated in biological processes and reach the receiving water. In this study, one of the important hospitals of Tehran, in a crowded area with high volume of referrals, was investigated. The purpose of this study was to investigate the possibility of drugs, especially sedative drug compounds, in hospital treated wastewater. For this purpose, instant sampling was carried out three times from the effluent of the hospital wastewater treatment plant and the samples were conditioned using solid phase extraction (SPE) method. The extracted materials were measured by HPLC equipped with UV and FLD detectors, resulting in the identification of various sedatives (including Diazepam, Oxazepam, Lorazepam, Alprazolam Clonazepam, Chlordiazepoxide, and Bromazepam). The mean concentration of sedatives in the January sampling showed that the highest concentration observed for Lorasepam with a mean of 0.15 ng/l and the lowest one for Chlordiazepoxide with a mean of 0.02 ng/l. The highest and lowest concentrations measured in February were 0.15 and 0.02 ng/l for Lorasepam and Chlordiazepoxide respectively.

In this study, the performance of moving-bed sequencing batch reactor with intermittent aeration strategy (IA-MBSBR) was evaluated for treatment of livestock wastewater in simultaneous nitrification-denitrification process. The statistical design and analysis were employed to optimize independent variables such as sludge retention time (SRT), temperature, and aeration rate using response surface methodology (RSM) through Box-Behnken design (BBD). The effect of variables was investigated on chemical oxygen demand (COD) removal and SND efficiency ( ). The analysis of variance (ANOVA) was conducted to confirm the suitability and significance of the quadratic models. Based on the results, a very high regression coefficient was achieved between the variables and the responses: COD removal and SND efficiency were R2 = 0.9788 and R2 = 0.9600, respectively indicating an excellent evaluation of experimental data by polynomial regression model. Long SRT reduced the negative effect of low temperature, but lowered COD removal and ESNDin high temperature. Further, appropriate aeration rate was vital for the SND to reach equilibrium between the nitrification and denitrification processes. The optimal conditions obtained from the models were SRT= 20 d, temperature = 19.16 °C and aeration rate= 0.1 , which results in COD removal and ESND of 92.9 and 91.3%, respectively. It was found that an alternating anaerobic/aerobic conditions with step-filling mode is an effective, economic, and environmentally-friendly strategy for the biological treatment of livestock wastewater in the moving-bed sequencing batch reactor.

Estimation of sediment load in rivers is one of the most important and applicable issues in studies and design of river and water engineering projects. Therefore, identification and suggestion of suitable methods for estimating suspended sediment load should be done based on relevant research. These methods include artificial neural network models, neurophysics, sedimentation rate curve as well as multivariate regression model. In this study, the efficiency of these methods was investigated in predicting discharge rate of suspended sediments of Gharachai River watershed. Daily time series data of measured flow discharge and sedimentation of bridge station of Gharachai River were used. The statistical period used in this model was two years (2016-2017). Independent variables used to enter the network include runoff and suspended load at the Gharachai River Doab Bridge station. The dependent variable, which is the network output, was the suspended load. After modeling with each compound and calculating RMSE and R2 values, the best combination was selected. The results showed that the neurophasic method based on discharge and sediment inputs and artificial neural network models based on discharge inputs were more accurate than multivariate regression and sedimentation rate curve. For values ​​higher the long-run mean of the statistical series, the values ​​simulated by the ANN model and for values less the mean and annual sediment load were also closer to the observed values. While for maximum values, no significant difference was found between ANN models, neurophysics, and linear regression.

Analysis of existing drought management policies in some countries, including Iran, indicates that decision-makers mainly react to drought episodes through a crisis-management approach, instead of developing a comprehensive and long-term policies. One of the comprehensive programs is the drought risk management model in the member state of the European Union (EU), which is based on the EU Water Framework Directive (WFD). In the present study, the above-mentioned document along with the experiences of different countries faced with the drought crisis was analyzed in order to prepare a drought management plan for the country. This study is an applied research, which was performed through library studies based on scientific and international resources. The results showed that in the process of drought management, creation of organizational capacity is the main factor to evaluate drought and its various effects on the community. This can only be achieved through the establishment of a Drought Independent Committee. On the other hand, drought management should be seen as a risk management process that emphasizes permanent monitoring of resources and observes climate change in the monitored area, rather than the onest of disaster as a crisis management. Drought management has been accepted by the international community in terms of risk management instead of crisis management. The proposed plan presented in this study is based on active drought management (risk management) that provides appropriate plans and preparedness for drought response, by offering long-term planning and forecasting.