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Lake Area Change in the Kolyma River Basin – Chersky, Russia
Introduction
Thermokarst lakes are created through the degradation of ice-rich permafrost and
subsequent precipitation in areas of low relief with large quantities of unconsolidated sediments.
Change in the number and surface area of thermokarst lakes is thought to be an indication of
permafrost thaw with important positive and negative feedbacks on the global carbon budget
(Jones, Grosse, Arp, Jones, Anthony & Romanovsky, 2011). The need to document and
understand climate change feedbacks on thermokarst lakes, and in turn the carbon budget, is
reflected in papers by Andresen & Lougheed (2015), Roach, Griffith & Verbyla (2012), Jones et
al.(2011), and Marsh, Russell, Pohl, Haywood & Oncilin (2009). Each of these papers uses
modern satellite imagery and historical photographs in northern latitudes to look at hydrology
and thaw lake dynamics in their own unique way. Although these papers look at different
geographic areas, there is a consensus that climate variability associated with increased
temperatures is affecting the morphology of the land and causing rapid change to otherwise
stable ecosystems. Andresen & Lougheed (2015), focusing on ponds smaller than 1 hectare,
found a 30.3% decrease in the total surface area and a 17.1% decrease in the number of ponds.
This is contrasted with Jones et al. (2011), which found a 10.7% increase in the number of thaw
lakes larger than .1 hectares and a 14.9% decrease in the total surface area. These studies also
looked at the rate of lake thaw and drainage. Marsh et al (2009) found evidence of decreasing
rates of thaw lake drainage, whereas Jones et al. (2011) found stable rates of drainage. Roach et
al. (2012) assessed the effectiveness between three different methodologies for analyzing lake
area change, and found that density slicing performed the best overall. Density slicing is a

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simple method using threshold values to discriminate between water and non-water pixels. Given
the contradictory findings using differing methodologies, we further examine thermokarst lake
change dynamics by using Roach et al.’s density slicing on a region that has yet to be studied.
We find that from 1965 to 2011, the total number and surface area of lakes increased between
1965 and 2011. Small lakes increased in count and percentage of total area, while large lakes saw
the opposite: decreasing frequency and percentage of total area.
Methodology
This study focuses on a 559,791,625 m2 area of boreal forest near Chersky, Russia and
uses a pixel-based classification approach to assess how lakes have changed between 1965 and
2011. We follow a density slicing approach to classification, which is outlined in Roach et al.
(2012). Similar to other studies, we look at a 50-year timespan, using contemporary satellite
imagery from 2011 and a historical photograph of the same area from 1965. The contemporary
imagery includes panchromatic images taken by WorldView in July 2011 with a .5 m resolution.
The black and white historical photograph corresponding to the same area was taken in July of
1965 with a .6 -1.2 meter resolution. All imagery was obtained in raster format with one 1 band
of gray-scale values. The study area was limited to the geographic area that was captured by
imagery from both periods, without cloud or snow cover. The overlapping area in historical
photograph was georeferenced to the contemporary imagery. The study area was georeferenced
using 30 control points, starting in the northwest region. Many of the control points were placed
in the northwest or west side of the study region on buildings or along the river, which did not
visibly change over the period. The limited number of stable features within these images
resulted in imperfect overlap in the southeast region of the study area. We believe this explains
why a few of the lakes look slightly shifted in that area. We account for this by dividing lakes

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into size ranges and looking at the change within those size ranges, rather than using geospatial
analysis that may have counted the shift as a change in a lake’s size.
In order to identify and measure lakes within the study region, each pixel value was
reclassified according to a value threshold distinguishing between water bodies and land. Pixel
values in the contemporary imagery ranged from 0-716, 0-2047 and 0-1852. The threshold
between water and land was set at 200 or 190. The historical photograph’s pixel values ranged
from 0 - 255, and the water threshold was set at 125. These threshold values were identified
through trial and error on each image. We noticed that reclassifying according to these thresholds
picked up some pixels that were actually shadows and reclassified them as waterbodies. In other
cases, pixels within clear water bodies were not classified as water because of some reflection off
the water. This was especially problematic because a single lake could be identified as multiple
through vectorization. To correct for these errors, the Focal Statistics tool was used to smooth
each 15x15 pixel area, using the ‘majority’ method, which takes the value (1 or 2) that was the
most present in the 15x15 pixel-moving window. This effectively eliminated values that may
have been falsely identified.
Each raster image was then converted to a vector, so that we may analyze the lakes as
individual polygons. At this point, the three contemporary images were merged into one layer for
easier comparison to the historical image. The historical image was then clipped to the
contemporary extent. Following the example set by Roach et al. (2012), we eliminated all water
bodies with a surface area less than 30m2 and the rivers within the study area. In removing the
rivers, some lakes were also eliminated because they were connected through tributaries.
Although this resulted in the removal of a few large lakes, we believe this was necessary because
lakes clearly connected to the river are likely to fluctuate in size due to natural variation in the

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river height, rather than due to geomorphologic or precipitative changes over the study period.
The lakes that were removed from the contemporary study area through the removal of the rivers
are displayed in Map 4.
Once layers were created with only lakes disconnected from tributaries and over 30 m2,
we calculated the total lake area size in the contemporary and historical images. Following the
example of Jones et al. (2011), we found the number of lakes that fall into five different size
ranges, and calculated the percent of total area taken up by lakes in that size range. Table 1
displays the lake size ranges and the number of lakes falling in those ranges in each period.
Results
Map 3 displays the change in lake size between 1965 and 2011. We found that the total
lake area rose from 40,729,901 m2 in 1965 to 43,531,302 m2 in 2011. This 2,801,400 m2 increase
is coupled with two consecutive findings. Firstly, we find that the frequency of different types of
lakes is changing. The number of smaller lakes between 30 and 1,000 m2 increased by 3,907 and
lakes between 1,000 and 10,000 m2 increased by 160. Lakes in the largest three categories,
10,000 and 100,000, 100,000 and 400,000, and 400,000 and 4,000,000 m2 saw declines in
number of lakes by 9, 20, and 9 respectively. Secondly, percentage of total area saw declines
with a similar pattern, which you can see at Table 1. In Map 2, Map 1, and Map 4 you can see
the contemporary lake cover, historic lake cover, and the water bodies areas we omitted from our
study. The difference in some of the lake areas shown in the historic imagery versus the
contemporary imagery can be attributed to distortions created through georeferencing. Omitting
several large lakes due to their connection to the river system, as outlined in our methodology,
was a necessary concession. In hindsight, including these lakes in the contemporary analysis

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would have furthered our findings, as they would contribute to an increased total lake area. A full
list of our results in the form of maps and tables can be found in the appendix.
Discussion
Our study area saw a 2,801,400 m2 increase in the total surface area, even with large
lakes omitted in the contemporary imagery. This significant increase contrasts with the findings
in Andresen & Lougheed (2015) and Jones et al (2011), which saw decreases in total surface
area. This difference may be related our study area’s proximity to a large river. Our changes in
the number of lakes within each size range are consistent with the results in Jones et al. (2011).
Jones et al. also found increases in the number of small lakes and a decrease in the number of
large lakes. The increased frequency of lakes between 30 and 10,000 m2 could mean several
things. Thermokarst thaw could be draining larger lakes, causing horizontal flow of water into
smaller, more separate water bodies. In some cases, increased precipitation may have raised
water levels.
Although it is unfortunate that we needed to omit several large lakes, the trends found are
clear. We believe that had all lakes been included, the trend of increasing surface area would
have persisted. However, we may have seen less of a decrease in the number of large lakes had
they been included. We also recognize that a pixel-based approach has its limitations because the
original images we used had different value ranges, resulting in a lack of uniformity in how the
images were classified. Although we followed the guidelines of one study by limiting our study
to lakes larger than 30 m2, other studies, such as Andresen & Lougheed (2013), focused on
smaller ponds. However, our use of focal statistics led us to worry that dark patches of vegetation
may have been smoothed into small lakes, or small lakes may have been smoothed out of our

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study. We hoped to avoid studying these potential errors by setting a minimum lake area size of
30 m2.
Conclusion
Overall, we found an increase the number of smaller lakes, contributing to a net positive
change in the total surface area. This indicates that the Chersky area has undergone notable
hydrologic change that may indicate thermokarst thaw, drainage of large lakes, as well as
precipitation change. Incorporating topographic maps and precipitation data would yield results
that are more conclusive. On-site surveying would also expand this analysis by confirming the
accuracy of our waterbody classification and adding data on the depth of lakes to determine any
changes in volume that may have occurred.

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Appendix
**2011 Map area was cropped to 1965 extent
Map 1:
Map 2:

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Map 3:
Map 4

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Table 1: Frequency of Lakes within Each Size Range
Size Range (m) 1965 2011 Difference (2011-1965)
30 1000 81 3988 3907
1000 10000 158 318 160
10000 100000 193 184 -9
100000 400000 55 35 -20
400000 4000000 26 17 -9
Total Area 40,729,902 43,531,302 2,801,400
Table 2: Percent of Total Lake Area Taken by Each Size Range (1965-2011)
Size Range (m) % of Total Lake Area % of Total Lake Area Change in % (2011-1965)
30 1000 0.1 1.5 1.4
1000 10000 1.8 2.4 0.6
10000 100000 16.2 13.4 -2.8
100000 400000 27.4 15.8 -11.6
400000 4000000 54.5 35 -19.5

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References:
Andresen, Christian G., and Vanessa L. Lougheed. "Disappearing Arctic Tundra Ponds: Fine
-scale Analysis of Surface Hydrology in Drained Thaw Lake Basins over a 65 Year
Period (1948-2013)." Journal of Geophysical Research: Biogeosciences J. Geophys.
Res. Biogeosci. 120, no. 3 (2015): 466-79. Accessed March 31, 2016.
Curasi, Salvador, Michael M. Loranty and Susan M. Natali. “Water Track Distribution and
Effects on Carbon Dioxide Flux in an Eastern Siberian Upland Tundra Landscape” (In
Press) 1-23. Accessed March 31, 2016.
Jones, B. M., G. Grosse, C. D. Arp, M. C. Jones, K. M. Walter Anthony, and V. E.
Romanovsky. "Modern Thermokarst Lake Dynamics in the Continuous Permafrost Zone,
Northern Seward Peninsula, Alaska." Journal of Geophysical Research 116 (2011): 1-13.
Accessed March 31, 2016.
Marsh, Philip, Mark Russell, Stefan Pohl, Heather Haywood, and Cuyler Onclin. "Changes in
Thaw Lake Drainage in the Western Canadian Arctic from 1950 to 2000." Hydrol.
Process. Hydrological Processes 23, no. 1 (2009): 145-58. Accessed March 31, 2016.
Roach, Jennifer. "Comparison of Three Methods for Long-term Monitoring of Boreal Lake Area
Using Landsat TM and ETM+ Imagery." Canadian Journal of Remote Sensing 38, no. 4
(August 8, 2012): 427-40. Accessed March 31, 2016.
Imagery
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2. WV02_20110711010622_103001000B8FB000_11JUL11010622-P1BS-
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3. WV02_20110711010623_103001000B8FB000_11JUL11010623-P1BS-
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