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Iranian Water Researches Journal
Analysis of Hydrology Cycle in the Urmia Lake Basin with the WetSpass-M Model

 submission: 08/10/2019 | acception: 08/12/2019 | publication: 14/09/2020


Dariush Rahimi1*, Fatemeh Bashirian2, Saeed Movahedi3, Reza Zakerinejad4

1-University of Isfahan،d.rahimi@geo.ui.ac.ir

2-University of Isfahan،bashiryan.f@gmail.com

3-University of Isfahan،S.movahdi@geo.ui.ac.ir

4-University of Isfahan،R.zakerinejad@geo.ui.ac.ir



Introduction Urmia lake is the largest interior lake in Iran, known worldwide. This lake, as an effective ecosystem unit in northwestern Iran, highly contributive in the ecology of the region. The Urmia lake level has dropped between ۶ and ۷.۴۰ meters and has reduce the area of water zone leading to an increase in salty marsh since۱۹۹۵. By May ۲۰۱۷ it was ۳.۱۱ m lower than the ecological balance. Explanation of salty marsh, is due to successive droughts and an increase in water harvesting from the surface water together with ground water sources in depletion. This phenomenon in turn world promotes dust and salt storm occurrence, leading to the death of the lake ecosystem, compulsory migration and population health threats of more than ۱۰ million people. In order to optimal long-term planning and management of the available water resources, a better understanding of the temporal and spatial variations of water balance components, especially actual evapotranspiration, surface runoff, and groundwater recharge is essential. A review of various research findings shows that the WetSpass-M model is a suitable model for the spatial simulation of surface runoff, actual evapotranspiration and groundwater recharge in world basins. The main contribution of this paper were in analysis spatial distribution of annual components of hydrology cycle in the Urmia lake basin using WetSpass-M model during ۲۵ years (۱۹۹۲-۲۰۱۷). Materials and methods The method adopted in this study is analytic. Climatic, hydrological and land use data are applied in this analysis. Climatic and hydrological data are provided from meteorological stations, hydrometric station information and observed wells respectively. Here, the satellite images and field studies are applied to determine land use. This images are downloaded from the site (https://earthexplorer.usgs.gov). WetSpass-M model The original Wet Spass-M model is a quasi-steady state spatially distributed water balance model scripted in Avenue and used to predict hydrological processes at seasonal and annual time step. Since the model is a distributed one, the water balance computation is performed at a raster cell level. Individual raster water balance is obtained by summing up independent water balances for the vegetated, bare soil, open- water, and impervious fraction of a raster cell. The total water balance of a given area is thus calculated as the summation of the water balance of each raster cell. Precipitation is taken as the starting point for the computation of the water balance of each of the above mentioned components of a raster cell, the rest of the processes (interception, runoff, evapotranspiration and recharge) follow in an orderly manner. To validate the results of WetSpass-M model, Nash-Sutcliffe Efficiency coefficient and RMSE-Observations Standard Deviation Ratio coefficient were used. Results Urmia lake basin has been affected by many climate and human changes that have caused Lake Urmia crisis. In during the study period, runoff declined but temperature and evaporation increased. Land use has also changed a lot. These changes include dry farming and rangelands convert to settlement and increased area of irrigated farming. About ۳۰۴۳ km۲ of lake area has been reduced and added to salt marsh. The average depth of ground water has decreased ۷.۴ meters. The analysis of simulation results shows that WetSpass-M model works properly to simulate hydrological water budget components in the Urmia lake basin. According to its results, In ۱۹۹۲, the highest runoff occurred in the western part of the basin with the highest rainfall, and all groundwater in the southern and western parts of the basin was well recharge. In the year ۲۰۱۷ most of the runoff and groundwater recharge is confined to the southwestern part of the basin. In ۲۰۱۷, Lake Urmia experienced higher evapotranspiration than the year ۱۹۹۲. In ۱۹۹۲, ۵۸.۴۲% of the basin precipitation was spent on evapotranspiration, ۷.۲۰% for surface runoff, ۳۱.۱۸% for groundwater recharge and ۳.۲% for interception. In the year ۲۰۱۷, these changed to ۵۵.۴۹, ۱.۵۵, ۳۹.۷۷ and ۳.۱۹%, respectively. Among the simulated components during the study period, the runoff has the highest coefficient of variation and the lowest groundwater recharge. Also during the ۲۵-year statistical period, eastern parts of Urmia Lake including: Ajab Shir, Azarshahr, Maragheh and Shiramin had the highest coefficient of variation in all studied components. The southwestern parts of the basin are in better condition.


Urmia Lake Basin  Remote Sensing  Water Balance  WetSpass M Model 

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