Javad ramezani moghadam; Mostafa Yaghoubzadeh; Ahmad Jafarzadeh
Abstract
Introduction & Background: Assessment of climate change impacts on hydrology is relied on the information of climate changes in adequate scale. Due to outputs of GCMs (General Circulation Models) that are the most confident tools for simulating climate change impacts but are available in coarse resolution. ...
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Introduction & Background: Assessment of climate change impacts on hydrology is relied on the information of climate changes in adequate scale. Due to outputs of GCMs (General Circulation Models) that are the most confident tools for simulating climate change impacts but are available in coarse resolution. Downscaling process which is classified to several methods such as transfer function, weather generator and weather typing is performed for improving of GCMs projection and using them in local scale. Meanwhile feature selection is the main essential step in downscaling with transfer function. Because the main goal of downscaling is the improvement of GCMs projections, several researches examined vary approaches for feature selection. This study aims to assess performance of downscaling daily precipitation under four different selection methods such as PCA, CA, SRA and ParCA using comprehensive comparison tests.
Materials and Methods: Measured daily rainfall for Ardebil (with cold semi-arid climate) and Birjand (arid climates) were collected for the period from 1977 to 2004. The CanESM2 (Canadian Earth System Model) outputs were used as GCM for simulating of climate change impacts on precipitation pattern. So of CanESM2 outputs (large scale predictors) and measured daily precipitation (local scale predictants) were considered as input and target for downscaling respectively. The Artificial Neural Network (ANN) which widely has been used in climate change researches was selected as downscaling method. Despite of the most of literature have used only efficiency criteria for distinguishing from different approaches in downscaling, this study reveals performance of feature selection methods based on either them or statistical tests. The comparison tests between measured and downscaled rainfall such as assessment criteria, statistics characteristics comparison, contingency table event for wet and dry series diagnostics and Violin plot were used as tools for skill assessment of feature selection approaches.
Results and Discussion: Results showed that although different methods of predictor selection had includes various subsets, predictors such as relative humidity at surface and zonal velocity component at 500-hPa pressure levels in Birjand and mean temperature at 2m, mean sea level pressure and rotation of the air in Ardebil are the most descriptive features which have more relationship with measured daily precipitation. The efficiency criteria of comparing measured and downscaled precipitation indicated that CA method is superior to other in Birjand station and SRA’s results were better than those of other in Ardebil station. Value of RMSE, R and NSE was achieved 1.2 mm/day, 0.55 and 0.25 in Birjand and 1.75 mm/day, 0.14 and 0.013 in Ardebil respectively. The examination of measured and downscaled statistical characteristics reveals that CA has the better influence on downscaling than those of others in Birjand station. In this comparative test most of downscaled statistical components such as mean, median and skewness under CA have more similarity to measured values. But in Ardebil, with cold and arid climate, performance of SRA to downscale was the same as performance of CA to it. Also both SRA and CA were better than ParCA. The skill assessment of different methods to fit measured and downscaled variability by violin plot showed that generally ParCA outperformed other method in Birjand station. The comparison of violin plots, in Ardebil, revealed that no one of predictor selection methods has acceptable accuracy for fitting measured variability. Outcomes of contingency table event showed although all feature selection methods have not remarkable capability for distinguishing from the measured wet and dry series in Ardebil station, performance of ParCA and SRA were acceptable in Birjand station. The values of CSI for ParCA and SRA were calculated 0.25 and 0.22 in Birjand and it shows that more of 20 percent of ParCA and SRA’s diagnostics was correct.
Conclusions: By assessing of results, it can be inferred that generally downscaling of daily rainfall in Birjand station is outperforming Ardebil. In other expression daily downscaling of precipitation in arid climate has better results than cold and arid climate. Also different tests have various results about feature selection methods. In Ardebil, SRA in efficiency criteria test and both SRA and CA in statistics characteristics have better performance than others. But in this region no methods have remarkable performance in violin and dry and wet tests.
Javad ramezani moghadam; yaser hosseini; Mohammad Reza Nikpour; atieh abdoli
Abstract
Introduction: The largest share of water consumption in Iran is related to the agricultural sector. Therefore, in order to save water resources, priority is given to reducing irrigation water consumption. On the other hand, reducing of water quality and salinization are the main problems which are commonly ...
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Introduction: The largest share of water consumption in Iran is related to the agricultural sector. Therefore, in order to save water resources, priority is given to reducing irrigation water consumption. On the other hand, reducing of water quality and salinization are the main problems which are commonly found in the areas with limited water resources. One of the most important effects of salinity is the reduction of yield and its inhibitory effects on plant growth and metabolism. Also, increasing salinity can reduce potassium, calcium and magnesium ions. One of the significant points regarding the effects of salinity stress is a significant decrease in the hydraulic conductivity of the roots, which leads to a decrease in the water use efficiency index. According to the food and agriculture organization (FAO), more than 40 percent of Iran's irrigated lands are affected by salinity stress, which is generally found in dry and semi-arid areas. Therefore, studying the combined effect of stress caused by salinity and water stress can be used to provide management solutions for irrigation and crop production.
Materials and Methods: This study was conducted in greenhouse laboratory at University of Mohaghegh Ardabili, Ardabil, Iran during August to November 2016. In this research, the effects of saline water on cherry tomato yield under water stress conditions were investigated. The applied treatments included irrigation with saline water (in two levels: S1=4ds/m and S2=7ds/m) and water stress (in three levels, irrigation at 40, 50 and 65% field capacity, respectively, I1, I2,I3). The experimental design used in this research was a completely randomized block design with four replications. On the other hand, in order to compare the plant yield under water stress and salinity conditions with non-stress conditions, control treatment with salinity characteristics less than 1ds/m and irrigation without water stress were used in three replications. In this experiment, cherry tomatoes were cultivated in the pots with diameter and height of 26 and 27 centimeters, respectively. The moisture meter (Model: PMS-714) was also used to measure soil moisture and determine the irrigation time. The most important parameters included cherry tomato yield, total evapotranspiration and water use efficiency index. It should be mentioned that analyses of the results were done by MSTATC software (Version: 2.10).
Results and Discussion: The results of this study showed that the interaction between two factors of water and salinity stress on the parameters was not significant, but the effects of salinity stress on yield, total evapotranspiration and water use efficiency (in two levels: 2% and 5%) are significant. Also, the greatest effect of salinity stress on cherry tomato yield was observed, so that by increasing the amount of irrigation water salinity from 4 to 7 ds/m, the yield was decreased by 27%. Also, the performance in salinity treatments of S1 and S2 decreased by 27.2% and 46.7%, respectively, compared to the controled treatment. Probably the reason for the yield reduction caused by decreasing in plant evapotranspiration and plant growth and metabolism. In addition, water use efficiency index in treatments of S1 and S2 decreased by 3.4% and 22.3%, respectively, compared to the controlled treatment. As it can be seen, the differences in water use efficiency between the control and S1 treatments were not significant. In this study, the average values of Ky (plant response coefficient to salinity and water stresses) were achieved 1.39, which was higher than the value that was reported by FAO for tomato plant under water stress conditions (equal to 1.05). This can be due to the significant effect of saline irrigation water on the yield of the tomato plants. Finally, based on the results of this research, it can be said that although salinity decreased yield significantly at 1% confidence level, in the coming years, with severe water resource constraints and increased costs for its preparation, this yield loss can be economical and feasible.
Conclusions: In this research, the effect of saline water on cherry tomato yield under water stress conditions was investigated. According to the results of this study, with increasing salinity of irrigation water from 4 to 7 ds /m, total evapotranspiration decreased by 10%. On the other hand, due to salinity stress, tomato yield was decreased to 27% in the most salinity levels of irrigation water compared to control treatment; one of the main reasons of which could be the reduction of total evapotranspiration in the growing season. In the end, the important point to note is that although, based on the results of this study, utilization of irrigation saline water decreased the yield, total evapotranspiration and water use efficiency by 27%, 8.9% and 19.2%, respectively compared to the control treatment, but in the near future, by increasing the water production costs and the quantitative reduction of water resources, even use of saline water is economically feasible and justifiable.
