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Geographical introduction to the Ükök catchment

The Republic of Kyrgyzstan is a mountainous, landlocked country in Central Asia. The mountain areas are mainly used as pastures, only the irrigated areas of the intermountain depressions and greater valleys in the north and southwest are suitable for large scale agriculture. The Ükök catchment is located in one of these basins, the Kochkor Basin, and the mountains further to the south, around 120 km south-east of the Kyrgyz capital Bishkek. The whole study area, including the mountain areas and the basin, has an area of 202,484m².

The Ukök river catchment is located in the Tesky Ala-Too mountains in Central Asia, a mountain range striking in east-west direction. The mountains underwent folding by the continental collision between India and Eurasia in the late Cretaceous [1]. The Central Tyan'-Shan' is still an active forming region between the stable Kazhak Platform and the Tarim Basin. Most common are Neoproterozoic to Ordovician deposits and Silurian to Cambrian granite intrusions. They are overlaid by carboniferous and Permian terrestrial deposits [2]. The modern topography is dominated by a continuous process of denudation and the neotectonic development since the late Oligocene [2][3]. A subsidence of the intermountain depressions and the uplift of mountainous areas are determining the relief.

The Ükök catchment is devided in three main parts. The gentle intermountain basin areas are located at an altitude around 1800 to 1900 m a.s.l. At its south border, the basin has a depth of around two to four kilometers, with a decreasing sediment thickness towards north [4]. The areas around the Chüy River are characterised by alluvial terraces [5]. In southern direction they are followed by steep alluvial-proluvial slope foods [5]. Differenciated from this area by a sharpe, the lower mountainous part between 2000 and 3000 ma.s.l. is characterized by erosional-gravitational processes.

The "V"-shaped Ükök valley is roughly running in east-western direction, with strongly divergent south and north exposed slopes. Erosional processes are more intensive on south-facing slopes, because they are steeper. Furthermore, due to the higher insolation, higher evaporation and lower soil moisture slow plant growth. Hence, the sparse vegetation cover is not protecting the soils from erosion. This valley asymmetry is determining the soils and plant composition in the whole Ükök catchment.

Several glacial landforms are coming across in the Ükök catchment; erosive forms as ridges, cols and "U"-shaped glacial valleys and accumulative forms, mainly lateral and ground moraines [3]. Also periglacial processes can be observed, foremost solifluction lobes, beginning at an altitude of 3000 m a.s.l.,with a higher quantity on northern slopes. The periglazial zone is located in a zone between 3000 and 3500 m a.s.l., the glazial zone above 3500 m a.s.l. Due to fluctuations in temperature and moisture, processes of chemical and physical weathering are active. Especially in steep areas, slope forming processes and mass movements occur [3] and the related accumulative landforms like talus cones are visible.

Topographic features and the connected diversity in climatic conditions are the most determining factors for soils and vegetation in the study area. The Ükök river catchment can be divided into five geoecological zones. These are the intermountain depression (arable land, settlements, infrastructure), the semi-desert, the dry steppe, the short grass steppe and the long grass steppe. There are also some azonal ecological units, e.g. wetlands.

Four main types of soil can be identified in Ükök catchment along a moisture, horizon depth and humus content gradient: Syrosems, Burozems, Kastanozems and Chernozems. Also some transiton zones can be observed, which are dark Kastanozems and Kastanozem–Chernozems.

The orography of the Tyan'-Shan' mountains is complex. That's why the climate divers vertically and horizontally and slopes with different aspects (and therefore insolation) have a various micro-climate [1]. In general, the climate is continental, which means that there is a temperature inversion between winter and summer and day and night [6].

On local scale, elevation is the most important factor characterizing the spatial distribution of precipitation, with a higher amount in higher elevations [7]. At an altitude of around 3000 m a.s.l. the cooling of air masses causes a line of maximum precipitation [8]. There is a big difference in precipitation between intermountain valleys and high mountain areas. Due to lower elevation and protection by the mountains, the basin receives lower precipitation, more single event rainfall and an earlier maximum in the year [8]. In Kochkor, the precipitation reaches it's maximum from June to August [9].

The Ükök catchment is drained by Ükök rive a right tributary of the Chüy river. The Ükök is mainly fed by glacier melt water from May to August, but also by snow melt water and rainwater. Hence, the lowest mean monthly discharge is from October to March with a minimum in January. From April to August the mean monthly discharge is getting gradually higher, reaching a maximum in the period of glacier melt in August.

Due to the fact that the period with the highest discharge is the period with maximum evaporation, the river regime is suitable for irrigation farming.

The village Kara Suu, a typical Soviet-style chequered village, according to villagers, founded in the late 1950s. Also the village of Isakeva and parts of Kochkor are located in the Ükök catchment. In 2011, Kara-Suu registered a population of 2802 people living in 592 households [10]. On the level of administration, Kara-Suu is part of the Ayyl Kennesh Akkyya (rural community), the Kochkor Rayon (district) and the Naryn Oblast (province). Kochkor is an important place for marketing local products.

The references cited in the geographical introduction can be found »here.