sima rahimi bondarabadi; Bahram Saghafian; Tayeb Raziei
Abstract
Introduction
Monitoring of hydrological droughts is one of the basic needs of water resources management in watersheds, especially in the field of water agriculture. Drought is divided into three major groups: meteorology, agriculture and hydrology. Hydrologic drought can be studied in different ways. ...
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Introduction
Monitoring of hydrological droughts is one of the basic needs of water resources management in watersheds, especially in the field of water agriculture. Drought is divided into three major groups: meteorology, agriculture and hydrology. Hydrologic drought can be studied in different ways. One of the common methods is the use of low flow indexes and threshold level approach.
Materials and methods
In this research, the minimum flow indices (Q75, Q90 and Q95) extracted from the flow continuity curve and minimum flow series (10 and 30 days) as well as the amount of flow deficit for hydrological drought monitoring in the Caspian Sea Basin were investigated and evaluated. For this purpose, 40 hydrometric stations with 41-year statistics (1970-2011) were selected. In the next step, the data of the studied stations were evaluated in terms of homogeneity, independence and randomness. Then, with the help of hierarchical cluster analysis and step-by-step regression, hydrological homogenous areas were determined and regional analysis of these indicators was done.
Results and discussion
In order to investigate the characteristics of the minimum current in the Caspian Sea Basin, first, the continuous flow curve was drawn for each of the stations, and then, three indices Q75, Q90 and Q95 were calculated for each of the stations. For the spatial comparison of the minimum flow, the specific minimum discharge or qs (minimum discharge value divided by the area) was used. qs75 index varies between 0.0006 and 13 m3s-1per km2. The value of qs75 is less (drier) in the eastern parts and in the western parts of the region, the amount of dryness of the stream is less than other places. Examining the spatial distribution maps of these three indicators shows that the trend of their spatial changes is almost similar and they all indicate that the western regions of the Caspian Sea Basin are more humid than the eastern and central regions. In the next step, to examine the minimum flow indicators, a series of minimum flows of 10 and 30 days was prepared. By comparing distribution parameters with the help of scoring method, Log-Pearson type 3 distribution was selected as the best distribution in most stations. After choosing the most appropriate distribution, the values of the 10-day and 30-day minimum indices with different return periods were calculated. Examining the average indicators shows that the minimum discharge value of 10 days with a value equal to 0.01 m3s-1 in Vatana Station (12-035) located in the east of the basin and the highest with a value of 19.2 m3s-1, it is at Rudbar Station (17-034) in the western region of the basin. Regarding the average minimum discharge of 30 days, the lowest value is equal to 0.20 m3s-1 and the highest value is equal to 8.52 m3s-1in these two stations. In order to investigate the temporal changes of hydrological drought intensity, the annual time series of 10-day and 30-day low flow at each station were plotted in relation to the year of their occurrence, in order to determine the trend of changes in the drought situation in different years. Examining the time trend of the minimum flow indicators on the graphs, shows a decrease in the value of the indicators in recent years and a negative trend of the indicators. In other words, the graphs in almost all stations show hydrological droughts (reduction of minimum flow indicators) during recent years. In order to determine the length of minimum flow periods, 10 and 30 day moving averages of discharge were compared with Q90 index value in different stations. The results show that the persistence of drought in the central parts of the Caspian Sea Basin (Pulor, Razan, Karsang, Tange Lavij, Pol Zoghal and Zowat sub-basins) is more than the rest of the regions, these sub-basins are located in Mazandaran Province. The lowest duration of drought (between 22 and 25 days) is related to the sub-basins of Shalman, Pol-e-Sazman, Pashaki, Astana and Tutkabon in the eastern part of the Caspian Sea Basin and in Gilan Province. The eastern parts of the basin have also experienced a drought period between 28 and 30 days.
Conclusion
Results indicate that the years 1990 to 2010 have undergone severe and long droughts in most of the stations. The review of the spatial distribution of indexes shows better conditions in the western parts of the study area compared to the eastern sections in terms of dryness. However, the duration of hydrological droughts in the central study area is longer than in other parts of the basin. Investigating the time trend of the indexes also shows the increase in the frequency and duration of hydrological droughts in recent years. A comparison of different indexes shows that all of them have similar results in the region. The results of cluster analysis divided the area into three distinct homogenous units (in 0.01 significant level). The result of the regional analysis showed that in the eastern homogeneous region, the influencing factor on low flow indexes is elevation, while in the central and western regions, the drainage area and density have a greater impact.
Sima Rahimi Bondarabadi; Saeed Jahanbakhsh; Behrooz Sari Saraf
Abstract
Any change in the concentration of greenhouse gases will upset the balance between the components of the climate system. But, the change in the concentration of these gases and how they will affect in the future is unknown. To study the effects of climate change on different systems in the future, climate ...
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Any change in the concentration of greenhouse gases will upset the balance between the components of the climate system. But, the change in the concentration of these gases and how they will affect in the future is unknown. To study the effects of climate change on different systems in the future, climate variables must first be simulated under changes in greenhouse gases (climate scenarios). There are several ways to do this, the most reliable of which is the use of climatic models. AOGCMs can simulate climate parameters globally in large scale, while these may not be suitable for small scales. One of the most important downscaling methods is dynamic methods that are based on increasing the resolution and analysis of planetary climate models. Here, in this research, climate change status in Karkheh River Basin where a major basin for water and agricultural yields is studied. For this purpose, the PRECIS model was used. PRECIS is an exponential dynamics downscaling model used to estimate the temperature and precipitation rates for the period of 2070 to 2100 under A2 and B2 scenarios. According to the results of climate change assessment under scenario A2, precipitation would increase up to 11% and up to five degree centigrade would rise in average maximum and minimum temperature while concerning B2 scenario, an increase in precipitation up to 7% and a rise in temperature rise up to three degree centigrade are estimated. However, under both the scenarios, despite, the fall’s precipitation is higher than the winter’s precipitation.
Sima Rahimi Bondarabadi
Abstract
Increasing the greenhouse gases not only has impacts on the weather parameters, but also, has impact on water resources, agriculture, environment, health and economy. Climate change has significant effects on water resources by changing the hydrological cycle. There are several simulation methods for ...
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Increasing the greenhouse gases not only has impacts on the weather parameters, but also, has impact on water resources, agriculture, environment, health and economy. Climate change has significant effects on water resources by changing the hydrological cycle. There are several simulation methods for investigating the effects of climate change on different systems in the future, like climate models. The AOGCM model is able to simulate global climate in an area of some ten dousant km2, but, while they are not suitable for regional scale. For this reason, downscaling methods such as dynamic methods are used. These methods are based on high resolution and analysis of climate models. In this research, the impact of climate change was investigated on the low flow of Karkheh Basin as one the most important basins due to its water product and agricultural point of view. For this purpose, the PRECIS which is exponential dynamics and downscaling model, was used to estimate the temperature and precipitation in the period of 2070 to 2100 under A2 and B2 scenarios. The SWAT model, a comprehensive and continuous hydrological model was also used to estimate the flow discharge for the watershed. After calibration and validation of the SWAT model, the amount of rainfall and temperature used as input for PRECIS model under different climate scenarios and finally the daily flow rate was estimated for sub-basins. Then the indices of low flow rates (Q75, Q90 and Q95) and low flow series frequency analysis of 10 and 30 days were assessed. Results showed that rainfall and flow rate have negative and temperature have positive trend. In general, the results of PRECIS model indicated that this model has a good estimate of temperature and precipitation in the region, but, it is not strong for rainfall in autumn and spring, due to the local nature of the precipitation. The climate change assessment under scenario A2, indicated the rise of low flow rate by 70 percent, and this increase of low flow was more in the northern parts of basin, while under the scenario B2 the low flow rate droped by 50 percent for the period of 2080. But, low flow distribution had no change compared to base period.Thus, sever droughts would happen in the central and some northern parts of basin. It can be concluded that under different scenarios, climate change has different impact on the low flow rate. Therefore, due to the different impacts of climate change on low flow rate under different scenarios, uncertainties of scenarios as well as regional economic and social status should be considered in the management plans.
sima rahimi bondarabadi
Abstract
The increase of greenhouse gases caused imbalance in the amount of air and water in the Earth, which called climate changed. Increasing the greenhouse gases not only impact on the weather parameters, but also impact on water resources, agriculture, environment, health and the economy as well. For the ...
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The increase of greenhouse gases caused imbalance in the amount of air and water in the Earth, which called climate changed. Increasing the greenhouse gases not only impact on the weather parameters, but also impact on water resources, agriculture, environment, health and the economy as well. For the effects of climate change on different systems in the future, first the climatic variables which are affected under the greenhouse gases should be simulated (different climate scenarios). There are several simulation methods where the climate model methods are most suitable. The AOGCM model is able to simulate global climate in large scale, while not suitable for small and regional scale. So, it is necessary to identify the variations (climate) in small scale. For this reasons it is necessary to use the downscaling methods such as dynamic methods which are based on high resolution and analysis of climate models. This method is suitable and appropriate for Iran since it suffers from lacks of observed data as well as lack of long term and enough stations in the country. In this study, PRECIS model (a dynamical downscaling climate model) was evaluated for simulation of precipitation and temperature. In general, the results of PRECIS model indicate this model can be a good estimate of temperature and precipitation in the region. Although for the rainfall in autumn and spring, due to the local nature of the precipitation, the model is not very strong. Also, comparison of spatial and point evaluation of the model showed that areal evaluation is appropriate as opposed to a point.
Saeed Jahanbakhsh; Behrouz Sari Sarraf; Abdolmohammad Ghafouri Roozbahani; Sima Rahimi Bandarabadi
Abstract
Hydrologic drought can be studied in different ways. One of the common methods is the use of low flow indexes. In this study for the purpose of determine of the identity of aspects of low flow, the homogenous zones, the extraction of regional regression models, and finally, the study of low flow trends ...
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Hydrologic drought can be studied in different ways. One of the common methods is the use of low flow indexes. In this study for the purpose of determine of the identity of aspects of low flow, the homogenous zones, the extraction of regional regression models, and finally, the study of low flow trends of Karkheh river basin, applied the data of 13 hydrometric stations during the statistical period of 1960-2000. After qualitative and quantitative controlling and the retrieval of missing data used flow duration curves for indexes such as Q75, Q90 and Q95. Also frequency analysis of 10-day, and 20-day low flows was carried out for indexes such as Q10,5, Q10,50, Q10,100, Q30,5, Q30,50, Q30,100 and some more indexes. Afterwards, some other factors like physiographic, climatic, geologic and vegetation cover were applied as influential parameters in the regional analysis. These factors were used in cluster analysis and stepwise regression estimations. Final step was the trend analysis of times series of the indexes. Results indicate that among the indexes being calculated, Q10,100 and Q95 had the minimum quantities, whose amounts reduced as the return periods increased. On the hand, the time spans of 1998-1999, 1999-2000, 2000-2001 have undergone severe and long droughts in most of the stations. The review of the spatial distribution of indexes show better conditions of the south-eastern parts of the study area compared to the northern and southern sections in terms of dryness. Results of cluster analysis divided the area into two distinct homogenous units (in 0.01 significant level). In the area No. 1, the elevation factor, in the area No. 2, the drainage density, and in general, the factors such as the mean of area and drainage density have the highest effects. The Spearman statistic, and Mann-Kendall findings also indicate that the low flow in upper basin have negative trend during the statistical period.
