This study presents thermokarst lake changes at seven different sites in the continuous and isolated permafrost zones in Mongolia. Lakes larger than 0.1 ha were analyzed using Corona KH-4, KH-4A and KH-4B (1962-1968), Landsat ETM + (1999-2001), and ALOS/AVNIR-2 (2006-2007) satellite imagery. Between 1962 and 2007, the total number and area of lakes increased by +21% (347 to 420), and +7% (3680 ha to 3936 ha) in the continuous permafrost zone, respectively. These changes correspond to the appearance of 85 new lakes (166 ha) during the last 45 years. In contrast, lakes in the isolated permafrost zone have decreased by –42% (118 to 68) in number and –12% (422 ha to 371 ha) in area from 1962 to 2007. The changes in lake area and number are likely attributed to shifts in climate regimes and local permafrost conditions. Since 1962, the mean annual air temperature and potential evapotranspiration have increased significantly in the northern continuous permafrost zone compared to the southern isolated permafrost zone. Due to ongoing atmospheric warming without any significant trend in annual precipitation, patches of ice-rich subsurface have thawed, and the number and area of lakes have accordingly developed in the continuous permafrost zone. Shrinking of thermokarst lakes in the isolated permafrost zone may be due to disappearing permafrost, deepening of the active layer, and increased water loss through surface evaporation and subsurface drainage.
Thermokarst lakes are common features in Arctic and sub-Arctic permafrost regions [
Most previous studies have investigated the dynamics of thermokarst lakes in the permafrost regions of Siberia, Canada and Alaska using remote sensing imagery with high and medium resolution [
The spatial and temporal extent of permafrost, as an impermeable ground layer, can have a first order effect on thermokarst lake dynamics. Smith et al. [
A similar geographical shift of permafrost zones from continuous in northern territories to sporadic in the southern region is seen in Mongolia. In addition, climatic gradients occur along latitude as well; it is, colder and wetter in the northern territory, and warmer and drier in the southern territory. Although this environmental gradient would be interesting for comprehensive analysis of the factors controlling dynamics of thermokarst lakes, which have extensively developed on the depressions and valleys in the Altai, Hangai, Hovsgol and Hentii Mountain regions [
The primary objective of this study is to provide quantitative information on the temporal and spatial changes of thermokarst lakes in Mongolia using a time series of high-resolution satellite imagery. The other objective is to address the effects of the long-term trends of hydro-climatic regimes and permafrost degradation on the areal changes of lakes.
Study sites are located in the southern fringe of Siberian permafrost regions in Mongolia. We selected four study sites in the northern continuous permafrost zone including Darkhad depression, Mungut river valley, Chuluut river valley, and Khongor-Ulun, while selecting three other sites Nalaikh depression, Galuut depression, and Erdene in the southern isolated permafrost zone (
1-7 respectively. A set of basic environmental characteristics at all study sites are summarized in
Permafrost exists in almost two thirds of Mongolia, predominantly in the Altai, Hangai, Hovsgol, and Hentii Mountain regions and the surrounding areas [
Mongolia has a typical continental climate. The lowest air temperatures often reach −34˚C in mid-January in the northern regions, while it reaches −20˚C in the southern regions [
of rainfall amount as well as vegetation, which changes from desert to grassland and boreal forest, within only several hundreds of kilometers over a south-to-north distance.
To estimate thermokarst lake changes at study sites, we used satellite imagery for three different time series: 1962-1968, 1999-2001 and 2006-2007. All images were acquired during the summer season. For this analysis we employed 14 Corona scenes, 7 Landsat Enhanced Thematic Mapper Plus (ETM+) images, and 7 Advanced Land Observing Satellite (ALOS) Advanced Visible and Near Infrared Radiometer type 2 (AVNIR-2) satellite data sets (
The oldest data (1960s) is especially useful in developing countries where aerial photographs in wide area coverage are rarely available. Beside the presented technical advantages, the high resolution Corona satellite images are also available at a reasonable price and provide an excellent opportunity for change detection studies. The Corona declassified images (1962-1968) were acquired from the US Geological Survey Earth
Study sites | Permafrost extent | Area (km2) | Above sea level (m) | Permafrost temperature (°C) | Ice-content (%) | Active layer (m) |
---|---|---|---|---|---|---|
Site 1 | Continuous | 576.3 | 1570 | −2.4 | >30 | 1.0 - 3.0 |
Site 2 | Continuous | 12.1 | 1767 | −1.2 | 10 - 20 | 2.0 - 2.8 |
Site 3 | Continuous | 9.5 | 1856 | −1.6 | 10 - 20 | 1.2 - 2.0 |
Site 4 | Continuous | 14.2 | 2377 | −1.4 | N/A | N/A |
Site 5 | Isolated | 0.2 | 1403 | −0.1 | 0-10 | 7.5 |
Site 6 | Isolated | 76.6 | 2445 | −1.0 | N/A | N/A |
Site 7 | Isolated | 0.8 | 2417 | −0.4 | N/A | 7.8 |
Study sites | Corona date | Corona KH-4, KH-4A, and KH-4B | Landsat date | Landsat ETM+ | ALOS date | ALOS/ AVNIR-2 |
---|---|---|---|---|---|---|
Site 1 | 1962/08/29 | DS009044048AF031 DS009044048AA036 | 1999/09/05 | LE71370241999248 | 2006/09/17 | AVNIR-2 |
Site 2 | 1968/08/29 | DS009044048AF024 DS009044048AA029 | 2000/09/07 | LE71370262000251 | 2006/08/29 | AVNIR-2 |
Site 3 | 1966/09/21 | DS1035-1006DF075 DS1035-1006DA076 | 1999/08/22 | LE71350271999234 | 2007/06/17 | AVNIR-2 |
Site 4 | 1968/08/11 | DS1104-1055DF009 DS1104-1055DA015 | 2000/09/10 | LE71420262000254 | 2007/09/01 | AVNIR-2 |
Site 5 | 1968/08/16 | DS1104-2135DF001 DS1104-2135DA005 | 1999/08/10 | LE71310271999222 | 2007/06/07 | AVNIR-2 |
Site 6 | 1964/06/10 | DS1006-2085DF054 DS1104-2085DA058 | 1999/08/22 | LE71350281999234 | 2007/09/27 | AVNIR-2 |
Site 7 | 1962/08/29 | DS009044032AF024 DS009044032AA030 | 2001/09/19 | LE71360292001262 | 2006/08/31 | AVNIR-2 |
Resources Observation Systems (USGS EROS) Data Center (http://earthexplorer.usgs.gov/). The images were taken by the KH-4, KH-4A and KH-4B satellite systems which were equipped with both forward and backward-looking cameras (
The Corona strips are known to contain significant geometric distortions, especially at the edges of an image along the track [
The Landsat ETM+ panchromatic images were obtained from the USGS Global Visualization Viewer (http://glovis.usgs.gov/) with limited cloud coverage conditions. The Landsat ETM+ images have spatial resolutions of 30 m (multispectral) and 15 m (panchromatic) over an area of 180 × 180 km. In this study, a total 7 Landsat ETM+ panchromatic images (band 8) from 1999 to 2001 were used (
In order, the ALOS/AVNIR-2 satellite images between 2006 and 2007 (
Firstly, we attempted the automated classification of lake areas based on the orthorectified
images. However, we abandoned the automated spectral approaches commonly used in digital image processing due to the issues where cloud shadows creating dark patches that were spectrally similar to water, and sun glint near the edges of these images creating bright small lakes were confused bright target such as meadows [
We visually delineated all lake areas from each satellite image that were above a minimum area of 0.1 ha (1000 m2). The shoreline of each lake was manually traced as a polygon area using ArcGIS 9.1 software. The areas of the extracted lake polygons were computed (
derstand the lake dynamics of individual lake size categories. Furthermore, we removed very large lakes (e.g., Dood Nuur (4810 ha) and Targan (1962 ha) in site 1 (
Since Mongolia has a sparse distribution of meteorological stations with weather records spanning more than 50 years, we used the reanalysis data to evaluate the correlation between thermokarst lake changes and hydro-climatic parameters. Mean annual air temperature (MAAT) at 2 meter height data from 1962 to 2007 was downloaded for the National Center for Environmental Prediction (NCEP) National Center for Atmospheric Research (NCAR) data. The horizontal resolution of the compiled NCEP/ NCAR precipitation data (2.5˚ × 2.5˚) was not sufficient to investigate rainfall. Therefore, the annual total precipitation (P) was downloaded from the high-resolution Asian Precipitation Highly Resolved Observational Data Integration Towards Evaluation (APHRODITE) data (0.5˚ × 0.5˚) from 1962 to 2007 (http://www.chikyu.ac.jp/precip/). In addition, the APHRODITE data is available until 2007, thus we only used satellite images from 1962 to 2007. The NCEP/NCAR and APHRODITE data were analyzed in the Grid Analysis and Display System (GrADS) software. In order to estimate water balance, we calculated annual potential evapotranspiration (PET) using the Thornthwaite Water Balance Model [
Contrasting changes in thermokarst lake dynamics were observed between the continuous and isolated permafrost zones in Mongolia. For the continuous permafrost zone (sites 1-4), the total number of lakes increased by 73 (or +21%), from 347 in 1962/68 to 420 in 2006/07 (
We observed spatially heterogeneous patterns in lake changes with identified increasing and decreasing lake number and areas for the continuous permafrost sites. The increase in both number and area of lakes in sites 1 and 4 can be explained by the formation of new lakes as results of permafrost thaw. While many new lakes were found in
site 1, where total of 53 lakes appeared in 142 ha in 1999/01 and 32 lakes appeared in 24 ha in 2006/07, only a few lakes appeared in site 4.
Permafrost zone | Study sites | 1962-1968 | 1999-2001 | 2006-2007 | |||
---|---|---|---|---|---|---|---|
Lake number | Lake area (ha) | Lake number | Lake area (ha) | Lake number | Lake area (ha) | ||
Continuous | Site 1 | 296 | 3350 | 350 | 3612 | 371 | 3651 |
Site 2 | 7 | 161 | 7 | 141 | 7 | 122 | |
Site 3 | 34 | 59 | 30 | 47 | 29 | 39 | |
Site 4 | 10 | 110 | 13 | 119 | 13 | 124 | |
Total | 347 | 3680 | 400 | 3919 | 420 | 3936 | |
Isolated | Site 5 | 2 | 7 | 1 | 5 | 1 | 1 |
Site 6 | 108 | 409 | 73 | 371 | 64 | 367 | |
Site 7 | 8 | 6 | 3 | 4 | 3 | 3 | |
Total | 118 | 422 | 77 | 380 | 68 | 371 |
of the satellite imagery for years 1962, 1999 and 2006. The new lakes appeared mostly in sizes less than 10 ha, while maximum size found was 113 ha. Such results consist of the local permafrost conditions (
The total changes of thermokarst lakes subdivided by lake area size are shown in
continuous permafrost zone. The next smallest size class of 1-10 ha also experienced a large change in both lake number (+47) and area (+215 ha) from 1962 to 2007. The number of lakes (10 - 100 ha) increased slightly (+3) from 1962 to 2007, however, their area decreased by 91 ha during the same time period. The large size class 100 - 1000 ha also expanded by 103 ha in the area of lakes since 1962, and the lake number actually increased in 1999/01 and remained stable in 2006/07.
As discussed above, the increases in number and area of thermokarst lakes have been widely reported in the continuous permafrost zone [
Lake size class (ha) | 1962-1968 | 1999-2001 | 2006-2007 | |||
---|---|---|---|---|---|---|
Lake number | Lake area (ha) | Lake number | Lake area (ha) | Lake number | Lake area (ha) | |
0.1 to 1 | 95 | 48 | 111 | 73 | 117 | 77 |
1 to 10 | 187 | 655 | 221 | 849 | 234 | 870 |
10 to 100 | 61 | 1928 | 63 | 1861 | 64 | 1837 |
100 to 1000 | 4 | 1049 | 5 | 1136 | 5 | 1152 |
permafrost zone. Our results differ from those of Jones et al. [
For the isolated permafrost zone, only two lakes were observed in 1962/68 in site 5 and one of them drained before 1999/01 (
In the isolated permafrost zone, there is a predominance of smaller lakes as shown in
ha (2006/07). Between 1962 and 2007, lake area decreased in all lake classes. In fact, fifty lakes completely disappeared in sites 5 - 7 (
Lake size class (ha) | 1962-1968 | 1999-2001 | 2006-2007 | |||
---|---|---|---|---|---|---|
Lake number | Lake area (ha) | Lake number | Lake area (ha) | Lake number | Lake area (ha) | |
0.1 to 1 | 81 | 25 | 42 | 21 | 34 | 20 |
1 to 10 | 30 | 104 | 29 | 98 | 28 | 96 |
10 to 100 | 6 | 112 | 5 | 110 | 5 | 108 |
100 to 1000 | 1 | 181 | 1 | 151 | 1 | 147 |
Shrinking and disappearing thermokarst lakes may become a common feature in the discontinuous, sporadic and isolated permafrost zones as a consequence of warming
climate and disappearing permafrost [
APHRODITE data for our study sites. The mean annual air temperature (MAAT) increased by 2.65˚C, 2.34˚C, 2.39˚C, and 0.79˚C in sites 1, 2, 3, and 4 respectively, in the
continuous permafrost zone between 1962 and 2007 (
isolated permafrost zone than sites 1 - 4 in the continuous permafrost zone (
We attribute the increase in area and number of lakes observed in the continuous permafrost zone to ongoing warming (
Study sites | MAAT (°C) | Total Annual P (mm) | Total Annual PET (mm) | Water Balance (P-PET) (mm) | ||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
∆T | r2 | p | ∆P | r2 | p | ∆PET | r2 | p | ∆P-PET | r2 | p | |
Site 1 | 2.65 | 0.33 | 0.001 | −13.4 | 0 | 0.443 | 81.5 | 0.41 | 0.001 | −94.9 | 0.17 | 0.001 |
Site 2 | 2.34 | 0.32 | 0.001 | −14.9 | 0 | 0.651 | 81.6 | 0.41 | 0.001 | −96.5 | 0.16 | 0.001 |
Site 3 | 2.39 | 0.33 | 0.001 | −100.5 | 0.21 | 0.006 | 94.9 | 0.47 | 0.001 | −195.4 | 0.4 | 0.001 |
Site 4 | 0.79 | 0.05 | 0.034 | −41.5 | 0.03 | 0.044 | 37.8 | 0.13 | 0.001 | −79.3 | 0.09 | 0.003 |
Site 5 | 0.91 | 0.15 | 0.011 | −49.1 | 0.06 | 0.007 | 4.63 | 0 | 0.721 | −53.7 | 0.03 | 0.049 |
Site 6 | 1.62 | 0.23 | 0.001 | −32.3 | 0.04 | 0.076 | 66.1 | 0.29 | 0.001 | −98.4 | 0.24 | 0.001 |
Site 7 | 0.35 | 0.01 | 0.322 | 27.8 | 0.13 | 0.017 | 14.6 | 0.01 | 0.093 | 13.2 | 0 | 0.859 |
The observed reduction in number and area of lakes in the southern isolated permafrost zone may be due to a combination of several factors including the air temperature, the potential evapotranspiration, and negative water balance, as well as permafrost disappearance [
This study provides the first baseline information of thermokarst lake changes across Mongolia, filling the gap in sub-Arctic lake inventories at regional scales such as the southern fringe of Siberian permafrost region. The time series data of high-resolution satellite imagery demonstrated useful in determining changes in the number and areal extent of thermokarst lakes greater than 0.1 ha in Mongolia from 1962 to 2007. We found contrasting changes of thermokarst lake dynamics in the continuous and isolated permafrost zones. Thermokarst lakes in the continuous permafrost zone have increased significantly in number and area while in the isolated permafrost zone we observed a decrease in both number and area over the 45 years of the study period. The dramatic increase in number of smaller lakes with sizes between 0.1 - 1 ha and 1 - 10 ha compared to larger lakes (10 - 100 ha and 100-1000 ha) in the continuous permafrost zone is likely as a result of permafrost degradation due to increasing temperature and evaporations. However, small lakes (0.1 - 1 ha) had a significant reduction in number in the isolated permafrost zone. The mechanism behind reduction of lake number and area may attribute to a combination of disappearing permafrost, deepening of the active layer and an increase water loss in this permafrost zone. Future research should focus on the temporal and spatial assessment of lake area changes across this region to better understand the detailed processes of lake area dynamics.
This research was supported by the Global Center of Excellence for Integrated Field Environmental Science Program at Hokkaido University in Sapporo, Japan. We thank all colleagues of the Permafrost Department, Institute of Geography and Geoecology, Mongolian Academy of Sciences who helped in this study. Finally, we also thank to C.G. Andresen of the Los Alamos National Laboratory for English revision, and one anonymous reviewer for the constrictive suggestions to improve this manuscript.
Saruulzaya, A., Ishikawa, M. and Jambaljav, Y. (2016) Ther- mokarst Lake Changes in the Southern Fringe of Siberian Permafrost Region in Mongolia Using Corona, Landsat, and ALOS Satellite Imagery from 1962 to 2007. Advances in Remote Sensing, 5, 215-231. http://dx.doi.org/10.4236/ars.2016.54018