About Urmia Lake Basin
A Short Viwe on Urmia Lake Basin
The Urmia Lake Basin is a generally mountainous territory containing two of the famous Iranian volcanic peaks (Sahand, 3707 m. and Sabalan, 4810 m.), and with several vast productive plains in the valleys and around the Lake. Most parts of the Basin are located at altitudes above 1280 m and up to 4886 m above mean sea level. The elevation of Lake’s water surface is varying between above 1270 and below 1280 m.
Fig.1: Topographical Plan of Urmia Lake Basin
Due to several tectonic events during different geological era, the geology of the basin is rather complicated. Major parts of folded sedimentary deposits were metamorphed under volcanic events and magmatic activities. Numerous thermal springs all over the basin demonstrates the extent of these volcanic activities. From a geological point of view the entire basin is categorized in 4 broad tectonic zones;
1) Colored mélange zone; a very small area in the far western border of the basin consisting of ultra basic, Gabro and Diorite-Radiolarite and limestone rocks.
2) Urmia-Hamadan zone; this zone is situated west of the basin and contains a collection of colored mélange and metamorphic rocks and Paleozoic platform sediments of generally Permian age.
3) Central Iran zone; this zone contains metamorphic rocks and platform Paleozoic sediments. This zone continues to the north of Lake Urmia and is limited from north and east by the fault of Tabriz-Sofian-Bostanabad.
4) Alborz-Azerbaijan zone; this zone is comprised of areas in the northeastern Azerbaijan, northeast of the Tabriz fault. Sabalan Volcano (4810 m), the vast extension of volcanic ash rocks, and salt domes in Aji Chai sub-basin are major geological features in this zone.
The complete geological tectonic description is shown in fig2.
Fig.2: Geological tectonic plan of Urmia Lake Basin
3- General climatology
Considering the latitude and altitude of the basin area, its general climate is very similar to the middle latitude, semi-high plains with cold winters and relatively temperate summers. Based on data from four example climatological stations, the most important climatic indicators of the LU basin are presented in table.
Table 1: Mean annual climatological indicators of example stations in the Urmia Lake Basin-
Though drought is a common occurrence in Iran, since around 2000 a persistent drought has seriously affected the hydrological status of the UL basin. During the period 1970-2010, the decrease in average annual precipitation in Tabriz was about 90 mm, about two fold of that in Urmia (50 mm) for the same period.
The records of the average annual temperature in the basin vary between 6.4ºCand 13.2ºC. The ambient air temperature is recorded in more than 50 meteorologicalstations. The following general conclusion can be drawn:
• At all stations, July 23-August 22 (Mordad) is the warmest month. However, At 20 stations, December 22-January 20 (Dey) is the coldest month, whereasin the other 29 stations Bahman (January 21-February 20) is the coldest month.The difference in average temperatures of the coldest and warmest monthsin the Basin varies -in different stations- between 25.8°C to 28.3°C.
Fig.3: Mean monthly maps of satellite-derived daytime and nighttime WST for Urmia Lake from 2007 to 2010
Average annual precipitation in the Basin has been varying between 203 and 688 mm during the period of 1964-1992. In the same period, the basin-wide average annual precipitation amounts to 372 mm. Precipitation in the selected station over the basin during 1971-2006 indicates the range of variation in average annual precipitation within the stations being between 160-620 mm/yr with an average of 340 mm/yr. During this period the maximum annual precipitation of a single station was 1125 mm in Sananeh station in 2006. Considerable part of the annual precipitation is in the form of snow. Precipitation regime in Urmia Lake Basin follows that of Mediterranean one with the maximum occurring in spring and little precipitation occurs during summer. The average monthly precipitation over the basin is presented as follow:
Table.2: Monthly precipitation distribution in the Urmia Lake Basin
The annual average evaporation (class A pan) in the Urmia Lake Basin is 1500 mm, and varies between 1000 mm (at Areshtenab Meteorological Station-1950 m above sea level) and 2100 mm (at Sahlan Meteorological Station-1400 m above sea level). The evaporation varies according to the geographical conditions (Latitude and altitude), as well as distance from the Lake. Closer to the Lake, evaporation is lesser which reflects the role of the lake in humidifying the environment. The mean annual evaporation of stations around the Lake varies between 1250 (Sharafkhaneh) to 2000 (Mahabad) mm/yr. The mean annual evaporation from the Lake surface is estimated at around 1000 mm/yr.
Monthly relative humidity varies between 42% and 85%, whereas the average annual relative humidity of the station vary between 57-76%.
Tabriz and Urmia synoptic stations are the closest stations to the Urmia Lake which measure the wind speed and direction. The maximum wind speed recorded at the Urmia station using the data of 1951-1985 is 60 knots (31 m/s) in January 1951 with a southwest direction, while the maximum wind speed recorded in Tabriz station is 52 knots (26 m/s). Statistical analysis of the wind data indicates that with a return period of 50 years, the strongest wind in Tabriz will have a speed of about 28.8 m/s with southeast direction and in Urmia will have a speed of 31.9 m/s with southwest direction. In the Urmia Lake Basin the maximum average dominant wind speed is 3.2 m/s with a south-west direction. In general, the strongest winds occur in the region with west and southwesterly directions.
4-Population and Ethnic status
Population within Urmia Lake Basin and the rate it increases is one of the main driving forces for increasing use of water resources and releasing contamination into the environment. Indeed increasing human uses of water resources is the main cause for decreasing inflows into the Lake and other wetlands.
The majority of the population within the Urmia Lake Basin is comprised of Turks. They are Shiite Muslims and speak in Turkish. However in the western and particularly southern parts of the Basin, higher proportion of the population is comprised of Kurds who usually are Sunni Muslims and speak in Kurdish. Kurds and Turks have their own cultural activities including music and dancing styles which are easily identified. Both Kurds and Turks are rich in music and singing arts. Dancing is an important part of the social ceremonies particularly among Kurds.
Table.3: Trends in population growth
5- Agricultural activities
Irrigated agriculture and horticulture for long have been the main occupation in the area. Rain-fed cultivation of cereals and to lesser extent peas is also a common practice in all parts of the basin. Main winter crop in the area is cereals (including wheat and barley). Summer crops include alfalfa, potato, tobacco, cotton and cash crops (tomato, eggplant, cucumber, sugar beet, etc). Hortilcuture is also an important activity particularly in the West Azerbaijan. Apple and grape are the dominant garden production, while other fruits such as peaches, plums, berries, are also largely produced. Land use of the Urmia Lake Basin has been studied in several cases during the last 3 decades. The studies conducted by Yekom consultants in 2002 (IIP) was on the basis of interpretation of satellite images and produced a map which could show the distribution of different land uses.
Agricultural sector is the main water user in the basin. Also it is releasing significant chemical residues into water resources. It is estimated that close to 90% of water resources are used in this sector. According to 2006 data, the volume of water used in agriculture is estimated at 5600 mcm/yr. This volume has been 1800 mcm/yr in 1979. Basin-wide average efficiency of water use for irrigation is estimated at 30%.
Impacts from agriculture on the environment and the Urmia Lake (including its satellite wetlands) are tremendous. Not only 90% of surface and ground water resources are used in this sector but also considerable amount of chemicals (estimatedly 200,000 Tons of fertilizer and 4,000 Tons of pesticides and herbicides) are applied annually. Residues of these chemicals when transferred to the water resources seriously impact theirqualify and ecological attributes. The traditional downslope ploughing of steep foot-hills for rainfed cultivation is also a very important factor for soil erosion in the farms and sedimentation in water resources (rivers and wetlands).
Table4: Land use within the Urmia Lake Basin and ecological zone (ha)