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Abstract
Aims: Conversion of orchards and agricultural lands in urban areas to residential and commercial areas has made a wide range of hydrological changes in urban watersheds. The aim of this research is to provide an Urban Distributed Hydrological Balance Model (UDHBM) to investigate the urban runoff in some parts of Tehran, including Tajrish and Elahiye.
Methods: To reach this goal, at first, we broke down the runoff amount of upstream mountain and urban areas from measured values. The HEC-HMS Model has been used to determine the volume of net runoff and flood produced in metropolitan areas. The annual water balance model considering rainfall, evaporation and other necessary inputs, have been made after defining the amount of flood in metropolitan areas. In the next step, a sensitivity analysis has been carried out on the main factors affecting the model to obtain a better understanding of the behavior of the model by changing these factors.
Findings: Results of this sensitivity analysis showed that this model has the most sensitivity to the rain factor and soil hydraulic conductivity. The results of comparing estimated values and urban runoff observations show minimum root-mean-square error and maximum correlation coefficient of 89% with a significance level of 5%.
Conclusion: This means that the UDHBM model has a good ability to calculate the runoff volume based on water balance for each land usage including residential houses and buildings, streets, parks and urban green spaces.
 

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In recent years, changes in catchments water balance due to land use management have become the main concern of water resources authorities in Iran. Due to rapid population growth and land use changes, especially construction of Taleghan dam, Taleghan catchment has undergone rapid changes such as urban development, declining of rangelands, and deterioration of environment and erosion of soil resources by cultivating the hilly lands along the slopes for wheat or barely production. The extent of rangeland area shrinkage is substantial: from 83% during the early stages of dam construction down to 35% by the end of the study period. The ‘good’ rangeland area decreased to 5.90% from 34.49% while the poor rangeland increased from 19.04 to 23.35% during the period of 1987 to 2007. These changes could potentially have devastating impacts on water balance of the catchment. The main objective of this research was to examine the effects of land use changes on water balance of the Taleghan catchment before and after the dam construction. The Soil and Water Assessment Tools (SWAT) model was applied for predicting water balance in the middle and outlet of the catchment. The main input data for simulation of SWAT are Digital Elevation Model (DEM), soil type, soil properties, and hydro-climatological data. Comparing the water balance for 1987's land use for the middle station (Joestan) and the outlet station (Galinak) showed that surface runoff was 21% of the precipitation for the upper part of the catchment and 33% at the outlet. Total groundwater and lateral flows were 37 and 19%, respectively. The water balance at the outlet was predicted for two other scenarios of 2001 and 2007. The results showed 7.3% increase in surface runoff and 11.3 and 11% decrease in the lateral flow and groundwater flow, respectively. These results indicated progressive increase in surface runoff and decline in interflow and groundwater flow.Therefore, one of the main challenges facing development planners is the control of the accelerated degradation of the natural resources that has been taking place during the last decade.

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The authors of the present paper studied some aspects of hydro and agrometeorological phenomena in terms of humidness, dryness and crop growing periods over India. Revised water balance model is used to obtain the above and the results are examined during the two half centuries i.e 1901 to 1950 and 1951 to 1995 in delineating the climate change impacts over India. Palmer Drought Severity Index (PDSI) for All India is related to aridity and humidity indices to understand the dry and wet spells over India. The paper also holds its stand on the analysis and the trends of thermo and hygric components such as precipitation, maximum and minimum temperatures, water need, actual evapotranspiration and soil moisture for All India. The return rates of All India maximum and minimum rainfall and temperatures are obtained for different time intervals using Extreme Value Analysis, that might be useful in assessing the impact and thereby to plan over the risk management for the better environmental and thus the human sustainability.

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In this study, the relative humidity of the gases in the PEM fuel cell was changed and its effect on electro-osmotic flow was investigated. ‎By changing the humidity on both sides of the fuel cell and using the water balance equations, the values of the electro-osmotic flow, ‎electro-osmotic coefficient and net drag in different humidity levels were found. Results showed that variations of the electro-osmotic ‎flow changed linearly by anode and cathode humidity to the special humidity and after that not much variation was seen. In addition, the ‎results revealed that humidity change at anode had more desirable effect than the cathode. For example, at 70% anode humidity and 35% ‎cathode humidity with the current of 5A, the value of electro-osmotic flow was obtained as 2.66639E-06 mol/cm2.s, while in the former ‎‎35% and the latter 70% with the same current, this value was recorded as 2.56418E-06 mol/cm2.s. In addition, results showed that the‎‏ ‏variations of the electro-osmotic coefficient changed linearly by humidity. It was determined the current change of fuel cell has not so ‎effect on the curves of electro-osmotic coefficient. The electro-osmotic coefficients varied between 0.636001 and 1.632476, which were ‎in a good agreement with the values obtained in other related papers. In addition, the variations of the net drag in respect of humidity were ‎investigated, too. It was determined that the net drag changed linearly by the cathode humidity with positive slope, but its variations by ‎the anode humidity were linearly with negative slope.‎

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Accurate estimation of Evapotranspiration (ET), as a key component in the hydrological cycle, is essential in agricultural water management. In the current study, an approach based on the Bayesian Model Averaging (BMA) was used to combine eight ET empirical models, namely, Blaney-Criddle, Makkink, Penman, FAO-Penman-Monteith, Priestly-Taylor, Thornthwaite, Turc and Wang to improve the accuracy of ET estimations compared to individual models. The results of eight models and 247 combinations of them (without replacement) were compared to the results of the Water Balance (WB) model as the reference of comparison. This study was performed using warm season (April-September) data of 2005-2014 from Gorganrood-Gharesoo Basin, north of Iran. The performance of the eight models and all possible combinations were evaluated based on four statistical metrics i.e. Root Mean Square Error (RMSE), Kling-Gupta (KGE), Coefficient of Determination (R²), and Bias. Then, the best-performing combination, (BMA-Best), was determined. Based on the WB method, the BMA-Best combination had better performance than the single models according to most of the metrics. In a few cases in which individual models showed slightly better performance than BMA-Best combination, the differences were not statistically significant. On average, the BMA-Best combination increased the R² by more than 50% and decreased RMSE by more than 70%. According to results of the current study, BMA provides a more reliable estimation of ET and it is recommended for use rather than the individual models. Moreover, the BMA-best combination mostly consisted of energy-based ET models, suggesting that these models have a better performance in climatic conditions of the study area.