نشریه مدل سازی و مدیریت آب و خاک
سال دوم شماره 4 (زمستان 1401)

Decreased fertility, destruction of aggregates and erosion are the most common forms of soil degradation. Soil erosion is carried out by erosive agents, which remove the soil from its origin place. Among the measures to control unauthorized erosion are measures that prevent water erosion agents, which are called watershed management. Given the 60-year history of watershed management measures in the country, the evaluation of these measures has received less attention. The purpose of this study is to investigate watershed management measures to reduce erosion and sedimentation in Doholkooh Watershed.

Considering that before the implementation of watershed management measures, erosion and sedimentation of the study area was calculated using the Modified PSIAC (MPSIAC) model, in new studies for the accuracy of the work (evaluation of the executive effects on the rate of erosion and sedimentation), the same model (MPSIAC) was used. In this model, nine effective factors in erosion are considered, each of which has a score depending on its severity and weakness, and finally, by considering these scores, the amount of sediment in the area is considered.

The results showed that due to the implementation of watershed management plans, the average specific sedimentation of the watershed has increased from 6.7 to 5.18 t ha-1. As a result, the average of special sedimentation at the watershed level has decreased and the area covered by the upper classes of special sedimentation has also been reduced. During the 11-year statistical period after the implementation of the project, the total erosion of Doholkooh Watershed was reduced from 28393.7 t y-1 to 16679.5 t y-1 (40% reduction) and the total sediment of the watershed was also reduced from 15647.6 t y-1 to 12103.5 t y-1 (21% reduction). During the implementation process in some sub-watersheds, confinement operations were not performed properly, in which the amount of litter decreased and the amount of bare soil increased, which resulted in a high volume of runoff in these sub-watersheds. Surface erosion has increased compared to the past and other areas have decreased.

Given that the purpose of watershed management operations is to stabilize the soil and provide suitable conditions for plant growth, the implementation of extensive biological operations and exclosure management in the basin had a positive effect on reducing erosion and sedimentation of the watershed and was able to prevent soil particles from separating slowly. Also, the soil particles that were separated from their place, after a path, finally, were collected inside the canals behind the constructed dams, and by accumulating sediments behind the constructed structures, its transfer to the canals was prevented.

Ecological services are the benefits that humans derive from ecosystems and include four categories of provision, regulatory, cultural, and supportive services. Each of these four categories includes a wide range of ecosystem services. In fact, climate control services include hydrological cycles, water supply and biochemicals, land-based processes and various biological processes. In this regard, to reduce the degradation rate and improve the condition of the Chehl-Chai Watershed in the northeast of Iran, several watershed management measures have been implemented.

The present study has investigated the extent of changes of supporting service (soil aggregate stability), provisioning (crops and fruits production, timber, and biomass production), regulating (control of soil erosion, runoff control, and carbon sequestration), and cultural (Increase of interaction and sustainability of local communities, increase of landscape aesthetics and tourist attraction and increase of knowledge and educational values) as a result of implementation of restoration measures in Chehl-Chai Watershed of Golestan Province. After quantifying the amount of services, prioritization of measures was done using TOPSIS method to identify and propose the most effective management option to improve services in the study area.

The results showed that the effect of watershed management measures on the ecosystem services improvement is not the same for all services, whereas it is highest for the regulating services and decreases towards the provisioning, supporting, and cultural services, respectively. Furthermore, the watershed management measures on improvement of the watershed services of treatment sub-watershed showed a statistically significant difference at the level of 5% (p<0.05). The results of applying TOPSIS method in the treatment sub-watershed showed that walnut orchards have provided the best effectiveness according to the indicators and criteria considered in the study. In other words, watershed management measures, through increasing the vegetation cover have led to more preciptation absorption, reduction of surface runoff and soil erosion in sloping lands and enhancement of landscape aesthetics as well as improvement of stakeholders participation level, social relationships, and income generation through conducting training and extension programs.

Among the employed measures, horticultural activities (planting walnut trees) have had the most success and if additional measures are taken and expanded, the success rate can be improved to a more desirable level. The watershed management measures are economically viable and can be implemented by the people. Therefore, in order to optimally manage water and soil resources and make watershed management more effective in improving the services of Chehelchai watershed, horticultural activities intercropped with forage and medicinal plants are recommended. In addition, the criteria, indicators and procedures applied in this study to quantify the effectiveness of watershed measures on ecosystem services can be consulted in developing a methodology or guideline for monitoring and evaluation of watershed management measures.

General atmospheric circulation models show an increase in greenhouse gas concentrations. These models predict global climate change by simulating the earth's climate. General atmospheric circulation models are not accurate enough for hydrological and water resources studies due to the large temporal and spatial scale of the simulated climate variables compared to the case model. Therefore, they must be scaled. There are different methods for exponential downscale of large-scale variables, and general atmospheric circulation models. In this research, the SDSM model is used to downscaling climatic data.

Boroujerd Synoptic Station with an altitude of 1629 meters above sea level is located at latitude 33◦ 55′ East and longitude 48◦ 45′ North. Boroujerd city is located at the foot of the highest wall of the Zagros at an altitude of 1550 to 1571 meters above sea level and the highest point is in the Garin mountain range with an altitude of 3623 meters in the west and its lowest area is in Silakhor plain with an altitude of 1500 meters. In this study, the CanESM2 climate model under three scenarios RCP26, RCP45, and RCP85 in three time periods 2040-2021, 2060-2041, and 2080-2061; and SDSM model version 4.2 were used for downscale (micro-scale) exponential climatic data. For calibration and validation of the SDSM microscale model, R2 and RMSE calibration indices were used. In this study, 30% of the data were used for validation and 70% of the data were used for calibration.

In the SDSM model, the maximum and minimum temperature values are better predicted than the precipitation values, and the simulated data are closer to the observational values. In all scenarios and periods, the precipitation trend is decreasing. The largest decrease in precipitation is related to January in the period 2021-2040 and the RCP8.5scenario, with a decrease of 69.22 percent. The temperature in all scenarios and periods had an increasing trend compared to the base period. The highest increase in the minimum temperature data is related to the RCP4.5 scenario in October for the period 2061-2080 and it was equal to 4.90 ° C, respectively, and in the maximum temperature data related to the RCP4.5 scenario in October for the period, 2061-2080 was predicted to be equal to 7.02 ° C. Calibration of SDSM model for Boroujerd station for each of the minimum and maximum temperature and precipitation showed the mean values of coefficient of determination 0.99, 0.98 and 0.67, respectively.

The highest decrease in rainfall is related to January in the period 2040-2021 and the RCP8.5 scenario, with a decrease of 69.22%. Also, the SDSM exponential downscale (microscale) model for the minimum and maximum temperature parameters predicted an upward trend. Calibration of SDSM model for Boroujerd synoptic station shows the efficiency of SDSM model in microcompalation of parameters. As a result, we will face a decrease in hydrological reserves in future periods.

Atmospheric conditions such as climate change, ocean temperatures, changes in the jet stream, and changes in the local landscape are all factors that contribute to drought. Drought not only threatens agriculture but also causes a series of ecological, social, and economic damages. Therefore, it is necessary to have valid and appropriate indicators that can evaluate and measure drought efficiently. Drought monitoring by meteorological and hydrological indicators has always been of interest to researchers. Decreasing or increasing precipitation has a direct effect on river flow rate and groundwater level.

Drought monitoring was performed for 10 meteorological stations and 10 hydrometric stations in the western basin area of Urmia with different distribution functions to identify the best distribution function for fitting data based on standardized precipitation index (SPI) as meteorological drought index and standardized streamflow index (SSI) as hydrological drought index. SPI and SSI values were measured with four cumulative functions, i.e., Gamma, Weibull, logarithmic normal, and Gaussian normal functions. Some performance criteria such as MAE were used to evaluate the efficiency of the functions. This research has been conducted on an annual scale for 31 years from 1989 to 2019. Drought continuity zoning was done through the Inverse distance weighting (IDW) method based on drought continuity.

The results of the SSI showed that the cumulative gamma function had the best performance for fitting data for nine stations. Only at the Merakand station, the Weibull cumulative distribution function provide a better fit for the data. Babarood station with 99% correlation and MSE of 0.017 had the best fit among other stations. In order to understand the drought conditions of the region, according to the selected indicators and based on positive values for wet conditions and negative values for drought conditions, the stations have been studied. Finally, a zoning map of drought continuity is presented.

The SSI and SPI indicators are directly related to each other. The SPI is better for predicting the onset of drought and the SSI is better for measuring the severity and persistence of drought. During the last three decades (1998-2000), Urmia basin has witnessed the highest severity of hydrological drought. Based on the zoning map of the northwest region, especially the upper Chihriq station, it has always enjoyed more favorable conditions and has experienced a milder drought than other regions. However, the extent of severe drought changed from the western part in 1998 to the eastern part in 2000. the severity of drought in 1998 was less than in 2000. In 2000, the drought intensity reached the highest value just in the Merakand station.

Watershed management projects with different objectives require some kinds of prioritization due to the natural condition prevailing in the watershed, including socio-economic issues, technical and financial constraints. The main purpose of the paper is to provide and apply the concept and techniques of multi-criteria decision-making (MCDM) under a fuzzy environment in the prioritization and selection of projects in portfolio management. In order to priority watershed management practices and evaluate the ecological potential of Ferizi and Rig-Sefid watersheds (Chenaran city, Khorasan Razavi province), the Fuzzy-TOPSIS method has been used as a powerful tool in multi-criteria decision making.

In this study, the preference weights of the criteria were identified using fuzzy AHP. Then, the weights are embraced in fuzzy-TOPSIS to improve the gaps of projects (alternatives) to achieve the organizational objectives as well as interactions between projects. The hybrid Fuzzy-AHP and Fuzzy TOPSIS methods made it more systematic and helpful for the decision maker to choose the best alternative from watershed management practices. In this respect, there are three phases performed in this study, the first phase of data is collected via questionnaire by experts. Next, determining criteria weights via Fuzzy-AHP was the main purpose of the second phase. In the third phase, the output obtained from Fuzzy-AHP with regard to criteria weights is used as input to be applied in fuzzy-TOPSIS for defining the optimal alternative and capturing the complex relationships between the assessment criteria and alternatives.

The comparison of the prioritization with the Fuzzy-TOPSIS method in this study and studies in 2010 indicate their similarity to some items, while in the second category priorities, the differences are more than the third and fourth priorities. The results indicate that multi-criteria decision models suggest the best location due to the usage of several criteria quantitatively and qualitatively with respect to objectives. In addition, it can be provided valuable information on prioritizing executive operations for integrated watershed management. It is also revealed that in the Fuzzy-TOPSIS technique, calculating the weights of criteria is essential and they can adjust the rating for other projects. Therefore, Fuzzy-TOPSIS will additionally help to select the optimal management project for the decision-making process.

It was found that many researchers applied many kinds of MCDM methods to help the decision makers understand and have more concentration on the high rank of criteria and also provide the ranking of the best alternatives in different problems and situations.

Due to river dynamic nature, the morphological characteristics of rivers are always changing and these changes can have negative effects on structures built along rivers, agricultural lands, etc. Rivers have been one of the most important factors in the geomorphological processes of the land and the erosion cycle, and so far, extensive studies have been conducted on the morphological changes of rivers and the factors affecting them. The instability of the river channel and its sediments not only destroys the marginal lands and facilities adjacent to the river bank, but also the sediments caused by erosion in some cases include a significant amount of the total sediments that the river flows.

The morphology of a part of Qarachai river in Markazi province of Khondab city from the top of Shaveh village to the bottom of Farab village, with a length of 12 km has been studied. First, the location of the Qarachai River watershed and the study area have been determined using digital topographic maps and ArcGIS10.2 software. Then satellite images and aerial photographs of the study area, which are the most important tools for studying changes in river paths, have been collected in two time periods. In the following, the aerial photos scanned in Photoshop software are photomosaic and are referenced in ArcGIS10.2 software using fixed points such as villages, bridges, etc., using aerial photographs of the year. 1968 Satellite images of Landsat sensor of 2021 have been digitized in two time periods in ArcGIS10.2 software environment.
 

Changes in wavelength and valley length in the two time periods studied in the study section of the river show that in the study area, the morphology of the river has not undergone major changes and the curvature of the study area has not changed much. The study of changes in wavelength and valley length and arc length in the two periods studied shows that the average wavelength in 1968 is about 413.25 and in 2021 is about 387.63. The wavelength in 1968was longer than in 2021. The changes compared to the 53-year period are about 6.2% and very small. As the wavelength decreases, the distance between the windings also decreases. The changes in the length of the valley relative to the meanders. The average length of the valley in 1968 is about 224.46 and in 2021 is about 12.21. Changes in the two timelines are about 5.5% and are very small.

The general pattern of the river from 1968 to 2021 has not changed significantly and is always twisting. The number of windings during 53 years is the same as 23 windings. The fact that the number of meanders is constant indicates that there is no change in the morphological pattern of the river. The results of extraction and statistical comparison of geometric parameters of this part of the river such as wavelength, sine coefficient, width to depth ratio, etc. show that the sine coefficient of the river from 1.5 to 1.3 The wavelength and radius of the tangent circles on the twists and turns have also increased. The average curvature coefficient in the 40s is about 1.11 and in 2021 is about 1.08. According to the division table of rivers, this period studied by Khondab river has a sinusoidal state and has not changed much in two time periods.

Urban development and land use pattern changes strongly affect the ecosystem service of carbon sequestration and storage. To integrate the concept of this climate regulation service into land use issues, we need to have information about its spatio-temporal distribution, so that with the help of mapping and quantification, protection and development sites can be selected with the continued provision of this service by the ecosystem. The current research was conducted with the aim of investigating the process of carbon sequestration and carbon storage ecosystem service changes in the process of urban growth and development and its valuation to improve the spatial planning of the land.

The study area is the coastal strip of Bandar Abbas City with a coastline length of 69 km. To comprehensively conduct the research, the smallest hydrological unit in the region where this city is located was selected which included three sub-watersheds. The total area of the region is equal to 272806 ha. At first, the land cover-land use map for the years 2000 and 2020 was prepared, and the future changes were predicted with different scenarios. Then, using the InVEST carbon storage and sequestration model, spatial distribution and changes in carbon storage and economic value were obtained.

The results showed that the largest area of the study watershed is the barren and range lands, which during the study period have decreased and man-made uses, water levels, and agriculture have increased. Modeling calculations showed the carbon sequestration capacity from 3741321.08 t in 2000 to 3763695.92 t in 2020 with an increase of 22374.82 t positive carbon sequestration. The reason for that was the growth of agricultural lands. Correspondingly, the economic value of this increase in deposition power during the study period was calculated as 874393.08 $.

It is expected that with the future usage scenarios, the positive growth of sequestration and subsequent financial benefit in terms of carbon sequestration will continue. But various factors can cause changes or disturbances in ecosystems and ultimately in ecological functions, that climate change is one of the most important factors and causes changes in the structure and functioning of ecosystems. As a result, services should be checked depending on climatic factors and land use changes, because the influence of climatic factors creates new states of the possible future situation, and uncertainty of land use scenarios and conflicts between ecosystem services can cause a change in the nature and change in the direction and size of services being provided by the ecosystem. Along with quantification, the economic value of service can provide valuable spatial principles for urban development and environmental awareness.

Climate changes and global warming have caused changes in weather patterns and the occurrence of serious events in different regions of the earth. Therefore, it is necessary to predict destructive floods, especially in coastal areas, to announce flood warnings and control them. Satellite precipitation estimation systems often generate data with global coverage that can provide information in areas where data from other sources are not available. Satellite retrieval and estimation systems, rain gauges, and radar networks complement each other regarding coverage and rainfall monitoring capabilities. Satellite precipitation estimation systems often produce data with global coverage. One of the main advantages of satellite-based precipitation products is the ease of real-time data availability and high spatial-temporal resolution. Currently, various satellite precipitation products such as GPM, TRMM, GSMap, CMORPH, CHIRPS, etc. are available to the public.

In this study, the southwest coastline of Caspian Sea, Gilan province is considered as the study area and the accuracy of four satellite-based products namely CHIRPS, GPIM-IMERG, PERSIANN CDR, TRMM-3B42V7 is compared in order to estimate the heavy precipitation from 2017 to 2021. Estimates are performed using categorical indices including PC, CSI, BIAS, and HSS and statistical criteria of correlation coefficient (Corr) and normalized root mean square error (nRMSE).

Evaluations and statistical criteria are conducted by comparing estimated satellite precipitation with ground stations through definitive indicators as well as the height of each station and the average of all stations respectively. The results show that in the PC index in eight stations, all of which are located at an altitude of fewer than 40 m above sea level and on the Caspian coast, the product IMERG scores higher than other products. The weakest performance in the PC index at the threshold of more than 5 mm belongs to TRMM and PERSIANN-CDR, which have the lowest scores jointly in eight stations. According to the results obtained from CSI, IMERG product had better performance in all stations except the Manjil station. Additionally, evaluation of the height of stations and the results obtained from this index demonstrate the fact no relationship was found between station height and product performance. In the Bias quality index, in IMERG and CHIRPS products, the bias of each station is directly related to its height, so that in higher stations, rainfall is overestimated, and vice versa in lower altitudes, the precipitations have been underestimated less than the amount of observation.

The IMERG product has performed better than the other three products in all categorical indices and correlation criteria. Finally, to evaluate and analyze heavy precipitation in the coastal strip of Gilan province and studies related to precipitation estimation, it is suggested that the IMERG product be used as a priority. The analysis carried out in this study, from the collection of satellite precipitation bases in estimating heavy precipitation in coastal areas, reveals the need to study and investigate this issue as much as possible in future research.