مجله پژوهش آب ایران
پیاپی 45 (تابستان 1401)

Daily streamflow prediction is very important for many hydrological applications in providing information for optimal use of water resources. Developing an efficient predictive technique for both long- and short-term streamflow is a challenge in hydrology which is crucial for resource planning and management. This is because streamflow is influenced by various dynamic nonlinear processes, such as rainfall, runoff yield and confluence, evaporation, topography, and anthropic activities. In addition, streamflow forecasting has attracted more attention because of reservoir operations and irrigation management decisions. Over the past decades, researchers have carried out different attempts to forecast daily streamflow. Artificial intelligence modeling has been widely used for streamflow forecasting in recent years because of the availability of long-term gauging data, the ever-increasing computational power.In this study, according to the nonlinear, random distribution, complex characteristics of hydrological parameters such as streamflow, an integrated method including decomposition technique based on the ensemble empirical mode decomposition (EEMD) combined with model tree (MT) was carried to forecast daily streamflow. To assess the validity of the proposed ensemble EEMD-MT model, a hydrometry gagging station, Gachsar station located on Karaj river, was considered for a 28 years period (1984-2012) at daily scale. Accordingly, a total of 9672 daily streamflow time series dataset given from Gachsar gagging station is employed for developing ensemble EEMD-MT model for daily steamflow forecasting. Among total daily streamflow dataset, 75% as calibration dataset were selected to construct the model and remaining of them were selected as validation dataset. One of the important steps in hydrological molding is to determine the optimum number of time delays from the river flow. In this way, two popular metrics, partial autocorrelation function (PACF) and auto-correlation function (ACF) for the time series dataset were calculated to detect the important input variables which have the highest effect on the target variable for modeling. In this study, for Gachsar station, three antecedent values were selected as the input paramater to simulate daily streamflow. Then, all input and output variables should be decomposed by EEMD into several intrinsic mode functions (IMFs) and one residual. IMFs, then, were modeled by MT model separately and all the forecasted results related to each IMF were aggregated. MT and adaptive neural-fuzzy inference system (ANFIS) as the benchmark models are compared with an ensemble EEMD-MT model. Several evaluation metrics such as correlation coefficient, root mean square error, relative square error, mean absolute error, and relative absolute error are considered to check the accuracy of the standalone and proposed ensemble models for streamflow forecasting at Gachsar station. The results obtained from the proposed standalone and ensemble models showed that the accuracy of EEMD-MT method compared to MT method increased by about 7.5% and modeling error for this station in the term of RMSE error index decreased by 6.8% in the validation phase. At this station, the MT with the combination of EEMD algorithm has the best accuracy (R = 0.96) in predicting the daily streamflow of Karaj river. According to the scatter plots, MT model shows an under-predicted performance in the validation stage for Gachsar station, although this drawback improved by considering decomposition process of streamflow integrating with EEMD algorithm. This reflects that a hybrid-based AI approach is a robust and useful tool for simulating daily streamflow over the mountainous region. However, most of the models could not successfully predict the extreme (high and low) flow events. The reason is the developed models are not predominantly trained on extreme events. This can be overcome in the future by the flexibility to incorporate auxiliary information and soft data, such as expert knowledge, into the algorithmic framework, which could provide more flexibility in simulation and assist water managers and dam operators. In summary, this research presents a novel study of testing various AI-based algorithms for streamflow prediction and gives a comprehensive comparison among popular AI methods in hydrologic simulation. The authors believe this unique feature of the AI methods, especially the EEMD-MT algorithm, is to be able to be further employed in the study region and provide more flexibility by adding desired decision variables for reservoir management. However, the proposed methodologies in this study are universally applicable to other mountainous regions, and are flexible to incorporate and test for other hydrologic time series data, such as flood records.

The purpose of this study is to evaluate the balancing strategies of groundwater resources in order to adapt to climate change. Accordingly, the simulation of two parameters of precipitation and temperature in Hashtgerd region with three climatic models HadGem2Es, EC-ERATH and GFDL-CM3, was performed using three emission scenarios RCP2.6, RCP4.5 and RCP8.5. Groundwater resources are one of the most important sources of water supply in arid areas, especially in areas facing surface water shortages. This shortage, along with climate stress, has made the water resource utilization system complex. The complexities of water resources systems along with unplanned exploitation of groundwater resources and the strong dependence of operators on it have made the development of a systemic approach in water supply and demand management for development clear. Due to the decline in groundwater aquifers, management of abstraction from these resources and control of abstraction is very important and many aquifer equilibrium scenarios have been proposed to achieve this goal.

Hashtgerd study area with code 4105 is in the division of National Water Resources Management Company-Ministry of Energy located in the west of Alborz province with an area of 1170.6 square kilometers, and with alluvial aquifer with an area of 410.7 square kilometers (Figure 2). This study area is located in the northern half of the Namak Lakebasin. Kordan river, the most important surface water source of this region, originates from the northern part and after passing through the central areas of the plain, it leaves the southern part. Most of the water resources in this area are exploited by wellsAfter climatic simulation, exponential down scaling was performed using LARS-WG v6 model. After evaluating the effect of climate change in the region, in order to evaluate the quantitative status of the aquifer, simulations were performed using the MODFLOW model and the prediction of the future situation under climate change conditions was analyzed.

The results of climatic simulation showed that the simulated values in comparison with the observational data indicate an increase in average precipitation and a decrease in temperature in most months of the year. The difference between the values obtained at the statistical level of 95% indicates a significant difference and appropriateness of simulation results. On the other hand, the quantitative results of the quantification of the aquifer indicate the continuation of the aquifer decline trend and the extracted results show that the highest rate of decline is recorded in the RCP 8.5 release scenario and the lowest rate is recorded in the RCP 2.6 scenario. The rate of aquifer drop in RCP 2.6 scenario was obtained in three models between 7.8 to 8 meters, in RCP 4.5 scenario between 7.9 to 8.8 meters and in RCP 8.5 scenario between 8.5 to 9.7 meters. After evaluating the future situation, aquifer equilibrium scenarios were analyzed in order to adapt to climate change in the region using 5 evaluation strategies by evaluating the relative improvement of the aquifer. The results of balancing strategies showed that in the scenario of drinking water supply through Taleghan dam and replacement of water from wells in the region, it was determined that 20 million cubic meters of water should be allocated for Hashtgerd drinking water supply and replace 20 million cubic meters of water extracted from wells. It becomes. Accordingly, in this scenario, while transferring water and considering the return water coefficient of drinking consumption of 60%, it was determined that a volume equivalent to 32 million cubic meters of water is taken less than the aquifer. The results obtained from the application of various balancing strategies in Hashtgerd aquifer indicate that the aquifer decline continues during the forecast period until the end of the 2024-2025 water year. Examination of the simulation scenarios shows that S1 solution, which is a 15% reduction in water abstraction from the aquifer, has shown the highest efficiency in all three scenarios of climate diffusion in the aquifer. 5. and RCP2.6 will occur at 4 and 3.2 m, respectively. The results also showed that the highest degree of uncertainty in the results of the aquifer level is related to S1 solution and shows a difference of 1.15 meters in the results of diffusion scenarios. The results of this study indicate the importance and necessity of developing strategies for balancing groundwater resources in all study areas of the country, which will be more acute in the event of climate change.

Although Iran has 1.1% of the world's land area, it has only 0.34% of the available water resources. On the other hand, in most parts of Iran, precipitation is not evenly distributed. The average annual rainfall in Iran is about 250 mm and is one of the arid and semi-arid regions of the world and drought is one of its main climatic characteristics. Drought can be defined as a period of time with abnormally dry climatic conditions that cause serious hydrological imbalances due to prolonged lack of sufficient rainfall. Drought is a natural, temporary and reversible phenomenon in any climate, which is more pronounced in arid and semi-arid regions. According to different definitions, the drought phenomenon is divided into four different categories based on the damages that drought causes to different sources such as river flow, groundwater level, soil moisture, agricultural products and people's living conditions. These four categories are named meteorological, hydrological, agricultural and socio-economic drought, respectively. Recognizing the drought phenomenon and quantifying it by using drought indicators, suitable for the conditions of each region, is one of the main ways to adapt and control this phenomenon and is also a suitable tool for managers and policy makers in different sectors to be able to reduce drought damages as much as possible with coherent planning. One of the main sources of fresh water needed by human societies is groundwater resources, which are the largest reserves of fresh water on earth after glaciers. Groundwater resources are used for different purposes. For example, more than 90% of cities and about 70% of the needs of the agricultural sector worldwide are supplied from these sources. Droughts and precipitation occurrance are the most important factors that affect groundwater resources in the long run. In arid and semi-arid regions, groundwater depletion and quality play a key role. As a result of the drought phenomenon, the amount of groundwater consumption also increases. Severe droughts have occurred in different provinces of Iran in recent years. This shows that it is important to study the drought in this country to prevent the environmental crisis and the damages caused by it. Occurrence of drought in Damghan city, located in Semnan province, has caused the development of deserts, especially in its southern regions, and in the crisis of groundwater and surface water shortages, agricultural lands, gardens and livestock are in danger in this regard and the damages caused through this has economically reduced the quantity and quality of products. Investigation and monitoring of drought are important tools for drought management, which could determine its beginning and end, areal extent and severity by using climatic and hydrologic parameters. Knowledge of the occurrence of drought is essential to design environmental and executive planning to raise awareness of this issue and mitigate its negative and harmful effects as much as possible and make the right decisions for the study area.

The objectives of the present study are summarized as follows:A) Understanding the general situation of Damghan city in terms of long-term rainfall characteristicsB) Examining the trend and characteristics of drought and determining the various indicators of meteorological drought in the regionC) Investigating the correlation between drought indicesD) Finding the most suitable drought index in the regionE) Analysis of the relationship between drought and rainfall changes with groundwater level in the region.In the current research, meteorological drought of Damghan region is studied by using drought indices. For this purpose, monthly precipitation data of Damghan, Hossein Abad, Khourzan, Ghousheh, Mabad, and Astaneh stations were obtained for a common statistical period (1997-2019). After studying annual precipitation trend for each station, duration and maximum drought were determined using SPI, DI, PN, CZI, MCZI and ZSI indices. To investigate the performance of these indices and select the best-fitted index for Damghan region, the minimal theorem of precipitation was used.

Based on the results, the best-fitted index for Damghan township was DI, which showed proper performance in both prediction of severe drought and wet years. In the next step, using Spearman correlation between precipitation and drought indices, the PN index had acceptable performance in prediction of severe droughts, but could not predict wet years. To compare the indices for prediction of fluctuations of groundwater level, the 3, 6, 9, 12, 18 24 an 48-month moving averages were used. Finally, the SPI index was selected as the best-fitted index for predicting groundwater level in Damghan region.

The flood risk analysis is of great importance in designing and planning to reduce flood damages. Flood is a multidimensional phenomenon that is described with correlated characteristics. Therefore, it is necessary to analyze all its characteristics simultaneously to obtain a more accurate estimate of the risk of its occurrence. In this paper, bivariate and trivariate flood frequency analysis were done in Bazoft watershed of Chaharmahal and Bakhtiari Province, Iran. For this purpose, three characteristics of flood, including flood volume (V), flood duration (D), and flood peak discharge (P) were extracted from 98 events recorded in the hydrometric station of this watershed. Nested copula functions were used to analyze the dependency structure of these three variables. Six copula functions of Clayton, Joe, Frank, t-Student, Gaussian and Gumbel were used to join the two and then the three variables. Finally, according to the obtained joint distributions, the primary, secondary and conditional joint return periods were calculated. Based on the Kolmogorov-Smirnov test, the most appropriate marginal distributions for the data of flood volume, peak flood discharge and flood duration were determined as Log-gamma, Weibull and Log-normal, respectively. The two variables of peak discharge and flood volume are the best pair to create a bivariate distribution, which were then joined with the third variable, the flood duration. Compared to the corresponding empirical copula, the Frank copula is specified as the best for PV pair (NSE = 0.996) and the Gumbel copula (NSE = 0.978) is the best option for PVD variables. Comparison of the flood variable quantiles for the univariate, bivariate and trivariate return periods corresponding to the AND and OR modes in the Bazoft watershed showed that the value of the secondary return period was less than the corresponding AND mode of that period and greater than the corresponding OR mode. Also, by comparing the period of joint conditional return period, it can be seen that the conditional return periods of the second type (i.e. the return period of the occurrence of one flood variable provided that two other flood variables occur) is greater than the values of the first type (i.e. the return period of two variables provided the third variable occurs).

When using a surface drip irrigation, the infiltrated water in the soil forms a wetted zone around an irrigation dripper. The knowledge of the soil water distribution and wetting patterns around the irrigation emitter is an important factor for designing and managing drip irrigation systems, for precise delivery of water and nutrients in the crop root zone and for matching the wetting pattern with the root growth pattern. The soil wetting pattern depends on soil hydraulic properties (soil texture, structure, hydraulic conductivity, water table) and irrigation management (Irrigation method, discharge rate, irrigation frequency, the total volume of applied water, emitter spacing and position above or below the surface). In recent years, using pulsed management in drip irrigation systems has increased because of its positive effects on the soil water distribution and consequently plant growth and development. Pulsed drip irrigation refers to irrigating for a short period of time and then waiting for another short period and repeating this on-off cycle until the entire irrigation depth is applied. In the present study, the effects of different pulsed managements with different off-time durations on the soil water distribution and wetting pattern dimensions in a clay soil was investigated, and the performance of the HYDRUS-2D model in simulating soil water distribution under pulsed drip irrigation was evaluated.

The treatments included three pulsed drip irrigation scenarios where irrigation water was applied in two (P2), three (P3), and four (P4) cycles with two on-off time duration periods were taking either the on and off times equal (T1) or considering the off-time duration periods as three times that of the on-time duration (T2). A soil container of internal dimensions (90 cm length, 90 cm width and 120 cm depth) was used in the experiments. One sides of this container are plexi-glass sheets to monitor advancing soil wetting pattern at different times during the experiments and the other sides are metal plates. The soil texture used in this study was clay. The duration of the experiment for all treatments was three hours, so the volume of water was constant for all treatments. The gypsum blocks that were calibrated before were used to measure the soil moisture within the wetting pattern. The measurements were recorded by a reader every half an hour after the start of the experiment in each treatment. The HYDRUS-2D model were used for simulating the soil water content under different pulsed treatment. It was calibrated and validated by the soil moisture measurements using inverse modeling. In order to statistically analyze the results of applying different irrigation pulses on the soil moisture distribution and wetting pattern the t-test analysis was used at a significance level of 5%. The simulated values of soil water content by the HYDRUS-2D model were compared with the corresponding measured values using some statistical criteria including root mean square error (RMSE), mean absolute error (MAE), and model efficiency (EF).

In the present study, the effect of different pulsed management and off-time duration on soil moisture distribution in a clay soil under a drip irrigation system was investigated. The performance of HYDRUS-2D numerical model was also evaluated to simulate moisture distribution in a clay soil under pulsed drip irrigation system. The results showed that increasing the number of pulses, increased the depth and width of the soil wetting pattern by 8 and 12%. Also, increasing the off-time duration, increased soil wetting pattern dimensions (depth and width) around an irrigation dripper in a clay soil by 13.5% and 20%, respectively. Pulsed irrigation improves soil water content distribution that it does not exceed from field capacity despite the heavy soil texture. Therefore, it can be concluded that better conditions in terms of aeration and oxygenation are provided for the crop roots under pulsed drip irrigation management. Also, evaluating the simulation of soil water content distribution and soil wetting pattern dimensions with the measured ones showed that the HYDRUS-2D model has a good accuracy in estimating soil wetting pattern dimensions (R2=0.95) and simulation of soil water content distribution (RMSE=0.018) in a heavy soil under pulsed drip irrigation. Therefore, the HYDRUS-2D numerical model can be used to simulate soil wetting pattern and soil moisture distribution for the design, management and scheduling of the drip irrigation systems with pulsed management.

The sharp decline of surface freshwater and groundwater resources in recent decades in most parts of the country are the most important issues of Iran today. One of the serious problems of the plains of Iran is the lowering of the water level of the wells the drying of the Qanats and the salinization of their water followed by the salinization of valuable soil of agricultural lands especially in dry and arid areas. Therefore appropriate strategies for exploiting unconventional water resources such as saline groundwater and seawater and agricultural drains can help reduce the negative effects of depletion of water resources. In this study one of the ways to exploit saline water resources was investigated. Due to its location in an arid and semi-arid region Iran has a high potential in the solar energy. Desalination of saline water by evaporation and condensation with the help of solar energy for the use of plants (distillation irrigation) is one of the simplest methods to produce fresh water that can be used in agriculture.

In this study by implementing plastic and polycarbonate structures the effect of material and size of different distillation surfaces in the distillation irrigation method on the yield and water use efficiency of tomato plants were investigated. This research was conducted in the research farm of Shahrekord University and from June to October 2016. Experiment in 7 treatments and 4 replications as a factorial experiment in a completely randomized design with two types of distillation surface materials including transparent plastic plate (P) and polycarbonate plate (PC) with two transparent walls and three external surface sizes (0.48 72 0. and 0.96 square meters) were done. The salt water used was also supplied from the salt water spring of Ardal city of Chaharmahal and Bakhtiari province. To compare the results a treatment with subsurface drip irrigation (fresh water irrigation) was also considered as a control treatment. In this experiment the parameters of fruit number fruit weight shoot weight and dryness fresh water volume produced in each treatment ion leakage rate leaf surface temperature and water use efficiency were measured.

The results showed that P3 treatment (plastic plate with external surface of 0.96 square meters) had the highest amount of fresh water production during the experiment (21 liters). In contrast PC3 treatment (polycarbonate plate with external surface of 0.48 square meters) produced the lowest freshwater (16.5 liters). Transparency of the plastic treatments and consequently more light passing into the structure than polycarbonate treatments can be the reason for the difference in fresh water production. The maximum light transmission through the transparent plastic and double-walled polycarbonate is about 91 and 80% respectively.Due to the production of the highest amount of fresh water in P3 treatment the highest number of fruits heavier fruits and heavier and drier plants were also observed in this treatment. In contrast the lowest amount of fresh and dry plants in PC3 treatment and the lowest number and weight of fruit were observed in PC3 P1 and P2 treatments which did not show a significant difference. The lowest amount of ion leakage and leaf surface temperature were observed in the control treatment which indicates that this treatment was not under water stress.Among other treatments the lowest amount of ion leakage was observed in P3 treatment which produced the highest amount of fresh water. The highest amount of ion leakage and leaf surface temperature were also observed in PC3 treatment this treatment had the lowest amount of sweet water production. Therefore it can be said that this treatment was under water stress. The lowest amount of fruit and plant material production in this treatment is also shows this issue. The highest water use efficiency in terms of fresh weight of fruit was about 11 g/l in P3 treatment which is not statistically significant with PC1 and PC2 treatments. The lowest value is related to PC3 treatment with a value of about 4 g/l which is not significantly different from P2 treatment. The control treatment had the lowest water use efficiency compare than the other treatments because it receives water based on its water requirement and part of the water is also lost by gravity. The P3 treatment with transparent plastic produces more fresh water and its water use efficiency is higher than the other treatments.

Biochar it is a carbon-rich organic compound that produced during the Pyrolysis process and improve the physical and chemical and biological characteristics of the soil. and improves the above characteristics. There has been little research on the effect of time on the use of Biochar on soil physical properties. With a biochar of microbial decomposition and its long shelf life in the soil, Biochar increases the surface of the soil organic matter for a long time and improved soil properties, especially in the dry and semi dry.land The aim of this study was to investigate the role of time in the application of rice straw and predominant from those moisture content of (FC, PWP and PAWC) and saturated hydraulic conductivity (KS) in clay loam soil.

This study was conducted at Shahrekord University, located in the center of Chaharmahal va Bakhtiari province with a geographical location of 32 degrees 21 minutes north latitude and 50 degrees 53 minutes east and 2074 meters above sea level in 2019. In this study, the surface soil of the research farm of Shahrekord University was used from zero to 30 cm deep. A factorial experiment with two corrective factors in the level Zero (control C), 0.5 (B1), 1 (B2), 2 (B3) weight percentage and correction of rice straw at zero level (C), 0.5 (D1), 1 (D2), 2 ( D3), weight percentage and time factor in four levels of 2 (T1), 3 (T2), 6 (T3) and 9 (T4) months after the addition of modifier to soil in a completely randomized design with three replications were tested in the greenhouse. To produce Biochar The need for rice straw and the putting up in the electric furnace for 2 hours at 400 ° C. In this study field capacity, permanent wilting point, Plant available Water Capacity and saturation hydraulic conductivity, were measured during each time after the test treatment and the pot in the greenhouse.Soil moisture coefficients (FC, PWP and PAWC) were calculated through compressive plates using the formula existing between the coefficients. The hydraulic conductivity of the soil saturation was calculated by the fixed load method.

The results showed that the main and mutual effect of factors has meaningful effects on the studied character. The results of this study showed that the FC and PAWC had an increasing trend at some levels and decreasing trend at some levels. Adding Biochar (at different levels) reduced PWP and increased in KS. Adding rice straw and straw increased in the FC, PWP, PAWC and KS. The results showed that the effect of time by increasing Biochar, FC and PAWC over a short period of time, but decreased within six or nine months. PWP decreased over time by adding Biochar, and the addition of the Biochar in the long run increased the KS. Regarding the effect of time on rice straw and rice stretch, the results showed that the addition of straw and rice to the soil in 2 and 3 months increased the FC, PWP and KS and increased PAWC in the long run. In general, with these results, it can be said that the use of Biochar over time has improved the physical properties of the examined and can be used as a soil modifier. The results showed that the main and mutual effect of factors has effects on the studied character. By adding Biochar, such as field capacity (16%), available water (60%) and soil saturation hydraulic conductivity (68%) increased in the first time. The feature, such as the permanent wilt point decreased by (13%) compared to the control at the first time. Add rice Straw characteristics such as field capacity (12%), available water (39%) and soil saturation hydraulic capacity (40%) compared to control at first time, increased, and characteristics such as permanent wilting point (6%), Compared to the control at the first time. By comparing the comparison of the mean Rin FC, PAWC and KS and the lowest PWP were observed in B3T1 treatment. Improving soil moisture coefficients in water stress conditions will also help plant growth and can be used biochar to this purpose. Biochar was one of the best methods for managing and modifying soil and to increase soil organic matter stability and improve the physical characteristics of the soil.

The entry of pollutants from agricultural land into water bodies is one of the most environmental issues connected to the tile drainage systems. Also leaching of drain water may cause the required nutrients for crop growth becomes out of reach. Thus, applying Best Management practies (BMPs) to relief the side effects of agricultural tile drainage systems is crucial. Over the past few decades, several BMPs have been introduced and studied with the aim of manage and control the volume and pollutants amount of tile drain water in agricultural lands, of which Controlled Tile Drainage (CTD) is one of them. Due to difficulty and costly nature of long-term monitoring programs, which is often used to assess impacts of applying BMPs on non-point source pollution, the AnnAGNPS model developed by USDA is a reliable alternative to simulate an effect of applying CTD at the watershed scale. AnnAGNPS, a comprehensive computational model that evolved from AGNPS, was designed for evaluating non-point pollutant loadings in agricultural watersheds and river basins. Briefly, AnnAGNPS is a distributed parameter simulation model that subdivides a watershed into small, homogeneous subwatersheds called “cells.” Cells are interconnected by stream channels called “reaches” In this study, an impact assessment of applying CTD on Total Suspended Sediment (TSS), Total Nitrogen (N total), Dissolved Nitrogen (N dissolved) and Surface Runoff were evaluated by AnnAGNPS at the Qharesu Watershed.

Qharesu watershed with an area of about 1670 square kilometers is one of the watersheds of Golestan province, which is surrounded by the Gorganrud watershed area from the north and east, Nekarud watershed in the south and the Gorgan Bay from the west. Finally, it is discharged into this bay. An average meteorological data of 5 statistical years of 2016 to 2020, used as a model input data in order to further adapt to the climatic conditions of the region in future, when tile drainage system is operated. The surface runoff data and suspended sediment load were also obtained from the Siah-Ab hydrometric station (outlet point of Qharesu watershed). Calibration and validation of the model performed by runoff and TSS observation data, in which the degree of confirmity between observation data and model output data performed by using three indices of Nash-Sutcliffe, RSR, and PBIAS.Two tile drain depth scenarios were examined in detail to mimic tile drainage control: The depth of 0.2m (CTD0.2) as an extensive controlled drainage and the depth of 0.6m (CTD0.6) as the recommended depth in the growing season for controlled drainage. The depth of the drainage base considered 1.1m as a reference condition as well.

The results showed that the model is reliable for simulating the studied parameters. The indices of E, RSR and PBIAS for runoff were 0.85, 0.48 and -2.6 for the calibration period and 0.76, 0.44 and -10.9 for the validation period respectively. These numbers were 0.73, 0.43 and -31.7 (calibration) and 0.66, 0.54 and -29.1 (validation) for sediment data.The AnnAGNPS model predicted a slight decrease in runoff and total nitrogen and a moderate decrease in dissolved nitrogen at the outlet of the Qharaesu River under the CTD0.6 scenario (during the growing season). Also, the increase in sediment load due to CTD0.6 was almost negligible. Based on the model results, Controlled drainage to a depth of approximately 0.6m below ground level is a suitable equilibrium point for reducing nitrogen and sediment loads at the watershed scale. Considering the importance of the outlet point of Gharesu, which is discharged to Gorgan bay, and since a significant part of tile drainage system in this watershed has not been impelemented yet, applying controlled tile drainage system is possible at a lower cost and more comfortable. Therefore, the possibility of applying CTD0.6 scenario should be on the agenda of authorities.

In the wake of global and regional climate change and heightened human activities, runoff from some rivers in the world, especially in the arid and semi-arid regions, has significantly decreased. During the past decades, due to the climate warming and the significant regional precipitation variation coupled with strong human activities such as the drastic agricultural and industrial development, soil and water conservation projects and water conservancy projects, more attention has been given to assess the impacts of climate change and human activities on runoff change. These variations in runoff have been an urgent challenge for water resources planning and management. In response to this challenge, one of the tasks for researchers is to identify the different roles of climate change and human activities on the nonstationarities in runoff. Both deterministic rainfall–runoff models and statistical methods have been proposed to assess the impacts of climate change or human activities on runoff. Climate change and human activities are the two main factors affecting runoff change in basins and the separating their impacts is of great importance for land use planning, water resources management and social, economic and political activities. Identifying and evaluating these factors and their contribution to reducing surface runoff is important for the sustainable development of water resources and for reviewing past and future calculations, plans and designs.

In this study, the contribution of the impacts of climate change and human activities on runoff reduction in Karkheh basin has been separated by hydrologic sensitivity analysis method. Hydrological sensitivity can be described as the percentage change in mean annual runoff in response to the change in mean annual precipitation and potential evapotranspiration. The Kaekheh basin is an important transboundary river basin whose environmental and economic significance, as well as future food security and hydropower production challenges, have been recognized nationally and internationally. The area of the Karkheh basin up to the Jelogir hydrometric station is approximately 40,000 square kilometers, of which about 55.5% are in mountainous areas and about 44.5% are plains and foothills. The common time period between the studied variables including daily streamflow in the hydrometric station and the air temperature and precipitation in the synoptic stations from 1990 to 2020 was considered. streamflow naturalization was done by adjusting agricultural water withdrawals, associated return flows and operational reservoir upstream of the Jelogir station. The Thiessen polygon method was used to estimate the average rainfall in the basin. Also, the arithmetic mean method was used to estimate the average air temperature and potential evapotranspiration at the basin. Hargreaves method was used to estimate potential evapotranspiration in synoptic stations. The trend in the annual values of precipitation, runoff, air temperature runoff and potential evapotranspiration from 1990 to 2020 was determined by Mann-Kendall test. Also, change points in the annual runoff were detected through Pettitt’s test and the precipitation–runoff double cumulative curve method. The Pettitt’s test is a non-parametric approach to determine the occurrence of a change point. It has been commonly used to detect changes in the hydrological series as well as climatic ones. The double cumulative curve is the plot of the accumulated values of one variable against the accumulated values of another related variable for a concurrent period.

The results show that runoff shows a decreasing trend at the significance level of 0.01, while no significant trend is observed in the amount of precipitation. The average annual air temperature and evapotranspiration show the potential of increasing trend at the significance level of 0.01. The rate of the annual runoff, potential evapotranspiration and air temperature trend is equal to -1.96, 2.71 and 0.062 mm per year, respectively, at a confidence level of 99%. The results show that the change-point in the annual runoff series based on the Pettitt’s test and the precipitation–runoff double cumulative curve method occurred in 1999. Therefore, the pre-change period and post-change period are before and after 1999, respectively. The average annual runoff in the post-change period has decreased by 34.4% compared to the pre-change period. The results of hydrologic sensitivity analysis method show that climate change and human activities have reduced runoff by 36.2% and 63.8% in the Karkheh basin, respectively. The results of this study can provide a reference for the development, utilization and management of the water resources and environment protection. The results of the present study can supply a reference to regional water resources management and planning. Water and soil conservation is not the sole purpose and means of development, at the same time, a practically possible proposition in term of increasing the produced runoff can be put forward for local managers to reasonably arrange the local actions, synthetically considering the sustainable development in the regional water resource and ecological environment.

Soil salinity and sodicity is a world-wide problem of irrigated farmlands that threaten soil quality and crop productivity in arid and semi-arid regions. Soil salinity refers to the accumulation of salt in the plant root zone which reduces plant growth. The use of saline and sodic groundwater for irrigation purposes deteriorates soil quality, causing clay dispersion, and reduction in hydraulic conductivity and plant available water. It also negatively affects plant physiological parameters such as reduction of grain yield, shoot and root length, biomass, rate of photosynthesis, leaf water potential, and increases proline content. Therefore research on possible amendments for the soils in these systems is necessary. Different organic and inorganic amendments are used to address salinity problems in agricultural soils. Common organic amendments include animal manures, agricultural residues, green wastes and biochars, and the inorganic amendments include gypsum, zeolite and super absorbents. In this study, the application of biochars produced at pyrolysis temperatures of 300 and 500 °C and their feedstocks as well as a superabsorbent (SA) on the leaching of salts through the soil columns were investigated.

The experiment was carried out in the Irrigation Laboratory, Department of Irrigation, College of Agriculture, Isfahan University of Technology, Iran, in 2018. The experiment was conducted as a completely randomized design with three replications. A saline-sodic soil (0–30 cm layer) was sampled from the Rodasht Soil Salinity Research Center, located in the east of Isfahan, Iran. The soil was classified as Typic Haplosalids, soil texture was silt loam and comprised 610, 180 and 210 g kg-1 silt, sand and clay, respectively. Five combinations of sugarcane bagasse, rice husk, cow manure, and pine wood were considered and pyrolyzed at 300 °C and 500 °C under oxygen-limited conditions (continuous inflow of nitrogen) for 2 hours (slow pyrolysis) in a pyrolysis chamber. A control with no amendment (CT), a super absorbent (Stockosorb) (SA), feedstocks (BWM, RWM, WM, BWMR and BWR), and their biochar produced at 300 and 500 °C were considered. The five combinations were pyrolyzed at two temperatures of 300 and 500 °C to obtain the biochar samples. Then the feedstocks and their biochars, as well as the SA sample, were applied to the saline-sodic soil and incubated in sealed plastic bags at a water content of 80% of the soil plastic limit, and room temperature (25 ± 1°C) for 40 days. After the incubation, the amended soils were packed into soil columns (PVC pipes) of 15 cm diameter and 50 cm height, and leached with 4 pore volumes (PV) of irrigation water. The PV was determined using the porosity and volume of the soil column. A constant water height of 5.0 cm was held on the soil surface by a mariotte bottle. The saturated hydraulic conductivity (KS) of the soil and the leachate electrical conductivity (EC) were measured during the leaching period at every 1/3 PV leaching. After leaching, the soil samples were carefully collected from the columns. Then the soluble ion concentrations (Mg2+ and Ca2+) were determined.

At a given period, there was a lower EC of the leachate for the BWR (sugarcane bagasse, rice husk and pine wood) treatment compared to the other amendments. The KS of soil increased significantly with the application of all amendments, which could be related to the improvement of soil structure, and increased porosity and leaching of sodium. The lowest KS was observed in control, which could be related to exchangeable sodium between the solution and the soil exchange sites, and soil dispersion. The biochar treatments had less Mg2+/Ca2+ ratio than their feedstocks and subsequently, the soil aggregate stability increased in the biochar treatments. Soil quality is influenced by the physical properties of amendments that are applied to the soil. It is important to consider the pH and EC of biochar for soil amendment. The BWR combination had the lowest EC and pH compared to other combinations. Also, the BWR had the highest C/N ratio compared to other combinations, subsequently, the KS increased. Overall, this study suggested that the use of BWR300 (the biochar of BWR compound produced at pyrolysis temperature of 300 °C) and SA amendments might be suitable for the improvement of saline-sodic soils in arid and semi-arid regions. Further experiments are needed to determine the rates of amendments for different soil types and water qualities in the long–term periods and large-scale applications in saline-sodic conditions.