Alireza Shokoohi; Reza Morovati
Abstract
The Lake Urmia is the 20th largest lake and the second hyper saline lake in the world. In recent years, the drying out of the Urmia Lake has attracted attention of many researchers. The main motivation of this study is to evaluate the role of drought in this disaster. For this purpose, Standardized Precipitation ...
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The Lake Urmia is the 20th largest lake and the second hyper saline lake in the world. In recent years, the drying out of the Urmia Lake has attracted attention of many researchers. The main motivation of this study is to evaluate the role of drought in this disaster. For this purpose, Standardized Precipitation Index (SPI) and Reconnaissance Drought Index (RDI) are employed. The data for analysis including precipitation and temperature was provided from two global databases: GPCC for precipitation and NCEP/NCAR for temperature. The study was performed at the time span of 1980-2010 and the results showed that the Lake Urmia basin has experienced a severely drought during 1999-2000. After this period and during eight subsequent years, the negative effects of this drought could not be reduced completely by near normal to wet condition of the basin. Moreover, another severely drought occurred at 2008. RDI value for the 1999 drought was found to be -2.23 which is related to the extremely dry condition. The value of SPI for the same region and same year was obtained as -2.13. This comparison for other severe and extreme cases shows that RDI is more sensitive than SPI at the tails of the phenomenon. It was also observed that after 2000, while the region, in terms of rainfall and drought conditions, is generally close to normal condition, the lake follows a continuous decreasing trend up to the present time. Therefore, one can conclude that in addition to drought, other factors contribute to the drying out of the lake. The results indicated that the anthropogenic effects are responsible to some percent in this disaster. Construction of reservoir dams for agricultural development and other activities for job creation purposes like constructing fish ponds has intensified this crisis. The span of these activities is concurrent to the periods which the drought indices show the fragile condition of the basin in terms of available water resources. This fact emphasizes the importance of drought monitoring as an inseparable part of an IWRM program to prevent a nationwide disaster.
Alireza Shokoohi; Asghar Azizian
Abstract
In recent years, Radar based DEMs due to ease of access and being free of charge are extensively used in hydrological modeling and deriving the geomorphological properties of watersheds. One of the most important questions on application of rainfall runoff models is the effect of DEMs from different ...
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In recent years, Radar based DEMs due to ease of access and being free of charge are extensively used in hydrological modeling and deriving the geomorphological properties of watersheds. One of the most important questions on application of rainfall runoff models is the effect of DEMs from different sources on simulation results. On this basis, this research focused on evaluation of the effects of DEMs derived from topographical maps at the scale of 1: 25000 and the SRTM DEM, on the performance of the KW-GIUH as a geomorphologic rainfall runoff model. The results showed that the SRTM DEM gives sub-watersheds' slope, the average slope of channels and the number of channels more than that was derived from topographic based DEM, while the overland flow length and average length of channels from the latter source are greater. The outcomes of the research showed that the Q-peak, hydrograph base time and the slope of hydrograph rising limb from Radar based DEM regarding different thresholds for artificial channel network derivation have a difference of about 1-12% with that was obtained from the model when using the topographic based DEM.
Ali Reza Eslami; Ali Reza Shokoohi
Abstract
According to diversity and complexity of hydrological processes, more information and data for analysis of this aspect of drought, is needed. Hence, to achieve an index using observed data, simplicity and robustness, which is also capable analysis of this kind of drought, can be valuable. In this research, ...
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According to diversity and complexity of hydrological processes, more information and data for analysis of this aspect of drought, is needed. Hence, to achieve an index using observed data, simplicity and robustness, which is also capable analysis of this kind of drought, can be valuable. In this research, an index that includes both environmental and hydrological drought aspects was introduced. The foundation of the proposed method using flow duration curve as a method of analysis of hydrological drought and low flows is proposed. Performance of the desired Index (FDCI), with a proposed new Streamflow drought index (SDI) has been compared. To implement the method, three areas (Chalus, Joestan and Frizi river) with different aspects of size, climates and length of records, which are located in various regions of Iran, were selected. The results showed that the correlation between the proposed index and SDI (R2= 0.98, S.E=0.02) is highly significant. The superiority of the proposed method is the use of all available historical data without changing the original data. Hence, the application of FDCI for the analysis of hydrological droughts in rivers located in the Mediterranean and semi-arid regions should be consider as a main result of this research.
