Environ Monit Assess (2011) 178:247–256 DOI 10.1007/s10661-010-1686-y

Changes in the area of inland lakes in arid regions of central Asia during the past 30 years

Jie Bai · Xi Chen · Junli Li · Liao Yang · Hui Fang

Received: 5 November 2009 / Accepted: 23 August 2010 / Published online: 10 September 2010 © Springer Science+Business Media B.V. 2010

Abstract Inland lakes are major surface water flexible than those of other two types. Accord- resource in arid regions of Central Asia. The area ing to comprehensive analyses, different types of changes in these lakes have been proved to be inland lakes presented different trends of area the results of regional climate changes and recent changes under the background of global warming human activities. This study aimed at investigating effects in Central Asia, which showed that the the area variations of the nine major lakes in increased human activities had broken the balance Central Asia over the last 30 years. Firstly, multi- of water cycles in this region. temporal Landsat imagery in 1975, 1990, 1999, and 2007 were used to delineate lake extents auto- Keywords Arid region · Central Asia · Inland matically based on Normalized Difference Water lake · Lake variations · Climate change · Index (NDWI) threshold segmentation, then lake Human activities area variations were detailed in three decades and the mechanism of these changes was ana- Introduction lyzed with meteorological data and hydrological data. The results indicated that the total surface Lakes act as the essential components of the hy- areas of these nine lakes had decreased from drological cycle, which would have affected on 91,402.06 km2 to 46,049.23 km2 during 1975–2007, many aspects of ecosystems and human activities. accounting for 49.62% of their original area of Lakes remain sensitive to the natural changes, 1975. Tail-end lakes in flat areas had shrunk dra- so as to serve as an important proxy of global matically as they were induced by both climate climate change and regional environment varia- changes and human impacts, while alpine lakes re- tions (Mason et al. 1994). Especially for the lakes mained relatively stable due to the small precipita- in the arid areas of Central Asia, which provide tion variations. With different water usage of river sparse but valuable water resources for the fragile outlets, the variations of open lakes were more environments and human beings. Mapping high- precision lakes and detecting their changes are of great significance to understand the relevance of lake variations to climate changes, and they J. Bai (B) · X. Chen · J. Li · L. Yang · H. Fang are also crucial to evaluate the impacts of the Institute of Ecology and Geography, CAS, economic development to ecological balances. 818 South Beijing Road, Urumqi 830011, Xinjiang, People’s Republic of “Middle Asia” was defined as Turkmenistan, e-mail: [email protected] Uzbekistan, Tajikistan, and Kyrgyzstan by Russian 248 Environ Monit Assess (2011) 178:247–256 researchers. While the term “Central Asia” in- shrinkage of lake extents had been proven to cluded not only the four “Middle Asia” countries, cause serious environmental issues (Tatyana and but also Kazakhstan, northwest part of China and Igor 2000; Lioubimtseva et al. 2005; Lioubimtseva Mongolia as well (Cowan 2007; Lioubimtseva and and Henebry 2009). Accurate lake mapping Henebry 2009). However, in majority of Chinese and lake dynamics in spatial–temporal variability research, Central Asia was defined as the four were vital to the assessment of water resource “Middle Asia” republics, Kazakhstan and Xinjiang management and regional environment changes of China (Chen 2008), and this definition was used (Lehner and Doll 2004; Ouma-and-Tateishi 2007; in this paper. Central Asia covers one-third of the Alejandra et al. 2008). arid area of the world (Chen 2008), where the Many studies about the lake variation in Central rivers and lakes are the major sources of surface Asia had been reported (Micklin 1988; Savvaitova water resources and supply most of the water for and Petr 1992; Boomer et al. 2000; Saiko and Zonn human use in the oasis of Central Asia. There are 2000;Stanevetal.2004; Kezer and Matsuyama more than 6,000 lakes with a total surface area of 2006;Maetal.2007), while most of them just 12,300 km2 (Savvaitova and Petr 1992), and most focused on lakes in local basin and lake changes of them are endorheic lakes. These inland lakes over the wide region were relatively few. As the are highly responsive to climatic variations and inland lakes in Central Asia were numerous and human activities (Friedrich and Oberhänsli 2004). some lakes are hindered by remote locations and The supplied rivers, where headwaters origi- difficult terrains, it was a great challenge for map- nated from snow melting in the mountains, pro- ping and detecting the lakes with field survey and vided water for upstream storages to support manual digitization. Remote sensing provided a agricultural irrigation, and downstream water feasible tool to analyze the status and variations flowed into the terminal lowland lakes. With the over a long-term time period (Harris 1994;Ma increase in population, expansion of agricultural et al. 2007). Lake delineation with remote sensing land in the basin and increased water diversion, imagery had been studied widely such as thresh- more water in the plains of arid regions had been old segmentation method (Braud and Feng 1998), used for agricultural irrigation, and less water water indices method (McFeeters 1996;Xu2006; had drained into the terminal lakes. Since the Ouma and Tateishi 2006), variants of component 1960s, a lot of inland lakes in this region had analysis method (Lira 2006), and step-wise iter- been drying up (e.g., Aral Sea, Issyk-Kul, Ebinur, ative classification algorithm (Luo et al. 2009). and Bosten), and some of them even had been These studies had made the lake mapping more disappeared (e.g., , Manas and Taitema; effective and efficient. Micklin 1988; Savvaitova and Petr 1992; Boomer There were three different types of inland et al. 2000; Saiko and Zonn 2000; Kezer and lakes (closed lake, open lake, and alpine lake), Matsuyama 2006). The decline of lake levels and as showed in Table 1. The objective of this paper

Table 1 The main lakes Lake Country Elevation (m) Type Depth (m) in Central Asia Maximum Average Aral Sea Kazakhstan and 53 Closed 67 16.1 Uzbekistan Balkhash Kazakhstan 342 Closed 26.5 5.8 Alakol Kazakhstan 348 Closed 54 22.1 Ebinur China 189 Closed 2.8 1.4 Issyk-Kul Kyrgyzstan 1,608 Alpine 702 278 Sayram China 2,073 Alpine 92 46.1 Zaysan Kazakhstan 386 Open 13 7 Bosten China 1,048 Open 16.5 8.15 Sasykkol Kazakhstan 347 Open 4.7 3.32 Environ Monit Assess (2011) 178:247–256 249 is to mapping the dynamics of lake area of nine inhomogeneous distribution, and most areas are typical inland lakes in Central Asia using Land- severe drought. The annual precipitation is about sat satellite imagery, and their spatio-temporal 1,000 mm in mountainous regions, while less than changes are also analyzed with related meteoro- 100 mm in low-lying desert regions. Though the logical data. precipitation is less, the potential evaporation is more than 900–1,500 mm per year (Qin 1999), forming an extensive semi-arid and arid region Materials and methods in the world. Most of lakes are concentrated on the northwest grassland of Kazakhstan and Study area the southern mountain regions, and mainly are separated into three types, closed lake, alpine The spatial extents of study area was from lake and open lake. About 20 larger closed lakes N55◦25,E46◦29 to N34◦20,E46◦29 (Fig. 1). Lo- with total areas more than 1,000 km2 are dis- cating in the mid-latitudes of the north-western tributed in the basins of Aral Sea, Ili River and hemisphere, this area is under the control of con- Irtysh River, whose water supplies mainly come tinental climate, with a cold winter and a hot from snowmelt water and precipitation, and their dry summer. Water resources in this area have area are approximately 50% of total lake area in

Fig. 1 Location of the study region, Central Asia 250 Environ Monit Assess (2011) 178:247–256

Central Asia. Alpine lake is mainly located at in Fig. 2). The Shuttle Radar Topographic Mission the Tienshan Mountains and the Altai Mountains (SRTM) DEM data with a spatial resolution of with average elevation more than 1,500 m, and 90 m was used (Jarvis et al. 2008). most of them are supplied with the glaciers and In order to analyze the relationships between snowmelt water during the dry seasons. lake area variations and climate changes. An- nual precipitation data during 1970–2000 were collected from the Asian Precipitation-Highly- Satellite imagery and precipitation data Resolved Observational Data Integration To- wards Evaluation (APHRODITE) of the Water + Landsat MSS, TM, ETM imagery during 1975– Resources, which had a raster format and its 2007 were used as remote sensing data source for spatial resolution of 0.25◦ × 0.25◦ (Xie et al. investigating lake extent variations in the study 2007; Yatagai et al. 2009; http://www.chikyu.ac.jp/ area. The Landsat data was downloaded from precip/). USGS GLOVIS, and date preprocessing was pro- ceeded with ENVI software. According to the previous studies, lakes in Central Asia were com- Methods of delineating lake features paratively stable in spring and autumn seasons as they were less affected by glacier melting wa- In the electromagnetic spectrum, water absorbs ter and agricultural irrigation, so 102 scenes of almost all of incident radiations in the near- the cloud-free satellite images were acquired in and mid-infrared bands, while shows a strong these two seasons. Most of selected images were reflectance in visible bands. Based on the spectral cloud-free or nearly cloud-free and had been geo- analysis, NDWI is used to extract the water body referenced with the topographic maps (as shown by McFeeters (1996). It is a band ratio index

Fig. 2 Landsat images selection at best month Environ Monit Assess (2011) 178:247–256 251 between the green and near infrared (NIR) spec- ations of the local segmentation were made to get tral bands, which would not only enhance water the best segmentation threshold. As different lake features, but also depress vegetation, bare lands elements were processed with different thresh- and other environmental information (Xu 2006). olds, this algorithm made the lake delineation NDWI is defined as more accurate and more efficient. The method above gave a minor modification of the algo- RGreen − RNir rithm based on Luo et al. (2009) and the NDWI NDWI = (1) RGreen + RNir was applied to threshold segmentation instead of global classification. The flow diagram showing Where RGreen is the top of atmospheric data processing was in Fig. 3. reflectance of the green band, and RNir represents The main advantage of this method was that that of the near-infrared band, which are corre- different segmentation thresholds were applied sponding to band 2 and band 4, respectively, in on different types of lakes, so it made the re- Landsat TM/ETM+ imagery. sults more reasonable. The raster results of lakes After the geometric correction and atmospheric were converted to vector layers with the ArcGIS correction, the images were used to extract the software, and the analyses of lake change were lake extents with a segmentation algorithm of based on vector processing. As lake areas were step-wise iterative based on NDWI (Luo et al. concerned, a uniform projection was important 2009). The algorithm firstly segmented the satel- to lake mapping in large regions. Here Lambert lite image into lake pixels and background pixels Azimuthal Equal Area Projection was used to with global segmentation of NDWI map. Sec- make the lake areas of projected lake layers equal ondly, the results of global lake were processed to those of original layers. Then lake layers of with the method of regional label, so as to take the same time period were merged and duplicate each lake element as an individual object. Thirdly, lakes in the overlapped regions were removed, so each lake was segmented locally with their sur- as to form an integrated lake layer over the whole rounding background pixels. A buffer was built study area. At last, lake area between two time on each lake and its size was approximately equal periods were compared and the attributes of area to that of the lake, and the threshold was easily changes were counted with lake-related spatial determined within the buffer through local his- analyses. In this paper, the mapping accuracy was togram analyses. If the change in lake extents was evaluated by overlaying NDWI map with vector greater than 5% after the local segmentation, iter- layer, and it was found that they were matched

Fig. 3 Flow chart depicting processes involved in extraction of lake areas information 252 Environ Monit Assess (2011) 178:247–256

Fig. 4 Selected Landsat TM (a), and the extraction results of water information overlying NDWI map in Landsat TM (b)

(a) (b)

perfectly and the mapping accuracy was less than of Zaysan, Sayram, and Sasykkol lakes expanded 1 pixel (Fig. 4). by 4.2%, the other six lakes in this region lost approximately 52.1% of their area from 1975 to 2007. Water boundaries in four periods showed Results and discussion that the surface area of the lakes in the eastern part of Central Asia was larger than that of those Changes in lake surface area in the western part. The trend of decreased lake area had spread from east to west. As the largest Table 2 showed the dynamic changes in surface inland lake of Central Asia, the endorheic Aral area of nine Central Asian lakes during the pe- Sea had shrunk by 75% of its surface area, which riod from 1975 to 2007. The total surface area of was the largest loss of surface area among nine the nine lakes decreased from 91,402.06 km2 to lakes. At the beginning of 1990, the Aral Sea split 46,049.23 km2, with 49.62% shrinkage compared into a small northern sea (named Maly) and a with the area in 1975. Although the total area large southern sea (named Bolshoi) as the water

Table 2 The changes in Lake name Area in 1975 Change (%)* Area in 2007 lake area extracted from (km2) (km2) satellite images in Central 1975–1990 1990–1999 1999–2007 1975–2007 Asian during the past Aral Sea 59,262.35 −32.90 −28.18 −49.57 −75.70 14,400.15 30 years Balkhash 17,199.72 −2.18 −0.36 −0.08 −2.61 16,750.22 Ebinur 603.50 −10.59 0.78 1.69 −8.37 553.00 Alakol 2,992.47 −3.48 0.96 1.83 −0.76 2,969.76 Issyk-Kul 6,252.23 −0.61 −0.29 0.24 −0.66 6,211.21 Sayram 458.17 0.48 −0.25 0.50 0.72 461.48 Zaysan 2,832.79 1.79 3.18 0.79 5.85 2,998.60 Bosten 1,055.83 −11.70 15.16 −10.69 −9.18 958.90 Sasykkol 745.00 −0.14 0.04 0.22 0.12 745.91 Total 91,402.06 −22.05 −15.47 −23.54 −49.62 46,049.23 Environ Monit Assess (2011) 178:247–256 253 recorded (Nezlin et al. 2004). The water moved Central Asia, the Aral Sea accounted for 64.84% 100–150 km away from the original coastline, and of total lake area in 1975, but decreased to 31.27% a salty bed with area 4,500 km2 was formed. in 2007, with a sharp decrease of 75.7% (see In terms of the variations of surface area since Fig. 5). Balkhash Lake, in the east of the Aral 1975, the inland lakes in Central Asia could be Sea, covered an area 18.82% of the total lake classified into three types. The first type was area in 1975, but shrunk by 2.26% in 2007. Alakol defined as the closed lake, which was mainly lo- Lake and Ebinur Lake experienced surface area cated on the low-lying plains of Central Asia (in- decreases with 3.48% and 10.59% from 1975 to cluding Aral Sea, Balkhash, Alakol, and Ebinur 1990, and then expanded 2.47% and 2.79% from lakes). Changes in the surface area in this type 1990 to 2007. Ebinur Lake had shrunk by 8.37% of lake were consistently decreased. These lakes while Alakol Lake had no obvious changes from were located at the base of a great tectonic basin 1975 to 2007. below 500 m elevation, with only water supply The second type was categorized to alpine lake, from river runoff feeding by the glacial and snow- which was mainly located above 1,500 m elevation melting but no outlet. Both the surface area and with an average water depth greater than 90 m. water level decreased in these inland lakes. As With less anthropogenic disturbances, alpine lake the largest landlocked lake in the eastern part of was in a natural environment and the changes in

Fig. 5 The spatial changes in mean annual precipita- zones were marked on the histograms. Histograms in the tion (mm year−1) in Central Asia during 1970–2000 were vertical direction showed the precipitation distribution at defined by gauge-based precipitation analyses. Five mete- different elevations, and those in the horizontal direction orological stations at different elevations and precipitation showed the precipitation distribution at different latitudes 254 Environ Monit Assess (2011) 178:247–256 surface area were mainly affected by climate vari- the surface area of these lakes had decreased. ations. The changes in lake surface area in high Despite the general decrease in precipitation in mountains were smaller than those on the plains. most regions of Central Asia, the opposite trend During the period 1975–2007, the high mountain was found in Tienshan Mountains, Altai Moun- lakes and Issyk-Kul experienced tains, northern Xinjiang, western Tarim basin and slight changes in their surface area, with 0.7% and Yanqi basin during the period 1980–2000, and sur- −0.66%, respectively. face area of Boston, Zaysan, Ebinur, and Alakol The third type of lake was termed open lake lakes which were local in these basins showed an (including Zaysan, Bosten, and Sasykkol lakes). increased trend after 1990s. As these lakes had outlets, the changes in surface The distribution of precipitation was different area were much more complicated than those of depending on altitude. Five meteorological sta- the other two types. The surface area of Zaysan tions, located at different elevations, showed the Lake, in the lower western region of the Altai variations of annual average temperature and pre- Mountains, had expanded by 5.85% from 1975 cipitation. The total annual precipitation in moun- to 2007. The , located in the central tainous regions was higher than that in low desert Tienshan Mountains, had fluctuant surface area regions. Zhaosu meteorological Station, at an el- and decreased by 9.1% during 1975–2007. The evation of 1,851 m, had an average precipitation surface area of Sasykkol Lake was basically in the of 503 mm year−1, while Kungrad meteorological constant. Station, at an elevation of 60 m, had an average precipitation of 140 mm year−1. Sayram Lake which located in the west Tienshan Mountains was Causes of the changes in inland lake surface area an alpine lake, and supplied by snow-melt water in Central Asia from the mountains. The meteorological data in Wenquan meteorological Station nearby Sayram Climate changes in Central Asia Lake represented that the annual increscent of temperature was 0.022◦ and that of precipitation The climate changes affected the river runoff was 2.9 mm (histograms in Fig. 5). With the in- which supplied the inland lakes, and then creases in precipitation and runoff water of snow- influenced the changes in inland lake areas over melt, the lower evaporation rate of the lake water the long term. Most inland lakes in arid regions and less human activities made the surface area of were supplied by seasonal snow-melt water and this lake remained steady. rainfall, so they were sensitive to the volume of water flowing into the lake and evaporation losing Impact of human activities on changes in lake area from the lake surface. A rain-gauge-based analysis of annual precipi- In arid regions, the changes in lake surface area tation had been constructed for Central Asia dur- caused by human factors were mainly from agri- ing 1970 to 2000. Over most of Central Asia, the cultural water consumption and construction of climate change was featured as decreased precip- reservoirs, which was a significant withdrawal of itation (Fig. 5). About 40% of Central Asia was water which would otherwise flow into the termi- in the area of decreased precipitation, and 22% nal lakes. was in the area of increased precipitation. The The Aral Sea had two transnational supplied spatial distribution of precipitation became rela- rivers of Amu Darya and Syr Darya, and nearly tively reduced by 20–50% in the eastern part of 75% of available water was used for agriculture Central Asia (including Kazakhstan, Uzbekistan (Aladin and Plotnikov 1993). The irrigated area and Turkmenistan), while it was going plentiful in in this basin had expanded by 54.17% from 1960 the western part from 1970 to 2000. The Aral Sea, to 1999, and the water flow into this lake had Issyk-Kul, Balkhash, and Ebinur basins which decreased by 67.67% (Saiko and Zonn 2000), were situated at Western Tienshan Mountains had which resulted in a great reduction in discharge significant decreases in annual precipitation, and to the sea and the surface area of lakes shrank Environ Monit Assess (2011) 178:247–256 255 significantly. As for the Bosten Lake, its area was parameters, lake levels and water supplies. The controlled by both of the feeding water of Kaidu alpine lake was less intervened by human activi- River and outlet river of Konqi River and Tarim ties and the lake variation was mainly caused by River. The annual discharge of the Kaidu River the climate change, and the lake surface area kept reduced by 7.04% from 1970s to 1980s, and then stable during the observed period. The terminal increased by 17.80% in the wet periods of 1990s end lake at the downstream part of the basin was (Gao et al. 2005). With the changes in runoff affected by both of climate changes and human inputting lake, the lake area grew by 15.16% from activities, and water area had decreased by 56.7% 1990 to 1999, and then reduced by 10.69% in since 1975. For the open lake at the midstream of the wet seasons as total 22.76 × 108 m3/yr water basin, the outflow and increased water diversion redirected to aliment the Konqi River and Tarim broke the water balance and the changes in lake River at the downstream from 2000 to 2006. area were mainly affected by human activities. The construction of reservoirs and dams were The analysis based on satellite images in this two other types of human interference that research indicated that both climate change and affected both of the runoff into the lakes and human activities had importance effects on the the outlets from them. The key supplied river of changes in lake surface area in Central Asia, Balkhash was Ili River, which accounted for 73% but anthropogenic effects are more dominated of the total inflow and decreased by 77% of the in plain lakes. The future research would focus pre-1969 mean values after Kapchagay Dam con- on the quantitative analyses of the relationship struction (Kezer and Matsuyama 2006), causing among the changes in inland lake surface area, cli- a sharp reduction in the level and area of lake. mate change and human activities over long time Zaysan was the outlet lake of the Irtysh River, and scales and assess the natural and anthropogenic the lake level raised 6 m and the area increased impacts on the changes in the surface area of since it became a part of the Buqtyrma Reservoir inland lakes. at the downstream. Acknowledgments Financial support for this work was provided by a Key Directional Program of the Knowledge- Conclusion innovation Project of the Chinese Academy of Sciences (KZCX2-YW-307), Natural Science Foundation of China (No.40730633), Western Doctoral Support Project The present study showed that more than half (No.0874071). 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