A detailed spatial geodatabase of aufeis (or
The aufeis coverage varies from 0.26 % to 1.15 % in different sub-basins
within the Indigirka River watershed. The digitized historical archive
(Cadastre, 1958) contains the coordinates and characteristics of 896 aufeis
fields with a total area of 2064 km
Most present and historical aufeis fields are located in the elevation band
of 1000–1200 m. About 60 % of the total aufeis area is represented by
just 10 % of the largest aufeis fields. Interannual variability of aufeis area for the period of
2001–2016 was assessed for the Bolshaya Momskaya aufeis and for a group of
large aufeis fields (11 aufeis fields with areas from 5 to 70 km
The combined digital database of the aufeis is available at
Aufeis (
The main hydrological role of aufeis is the seasonal redistribution of the
groundwater component of river run-off, whereby the winter groundwater
discharge is released to summer streamflow through the melting of aufeis
(Surface water resources, 1972). In most cases, the share of the aufeis
component in a river's annual streamflow accounts for 3 %–7 %, reaching
25 %–30 % in particular river basins with an extremely large proportion of
aufeis (Reedyk et al., 1995; Kane and Slaughter, 1973; Sokolov, 1975). The
most significant water inflow from aufeis melt takes place in May–June
(Sokolov, 1975). For example, the share of the aufeis flow accounts for more
than 11 % of total annual streamflow of the Indigirka River (gauging
station Yurty, 51 100 km
It is important to understand how climate change may impact aufeis formation because warming has been observed in this region, causing the transformation of permafrost (Romanovsky et al., 2007), glaciers' reduction (Ananicheva, 2014) and hydrological regime changes (Bring et al., 2016; Makarieva et al., 2018a). Aufeis is formed by a complex connection between rivers and groundwater. Many studies have reported the increase of minimum flow in Arctic rivers (Rennermalm et al., 2010; Tananaev et al., 2016), including those where aufeis is observed in abundance (Makarieva et al., 2018a). A widely accepted hypothesis for permafrost regions is that a warming climate increases the connection between surface water and groundwater that in turn leads to the increase of streamflow, both in cold seasons and in annual flow (Bense et al., 2012; Ge et al., 2011; Walvoord et al., 2012; Walvoord and Kurylyk, 2016). Variation and changes in aufeis extent can be assessed using remote sensing techniques, whereby aufeis dynamics can serve as an indicator of groundwater change that is otherwise difficult to observe (Topchiev, 2008; Yoshikawa et al., 2007).
The understanding of how aufeis responds to a warming climate varies. Alekseev (2016) suggests 3- to 11-year up and down cycles of aufeis maximum annual size, which may vary up to 25 %–30 % in comparison with long-term average values. However, the same author (Alekseev, 2016) states a general tendency of a decrease of aufeis volume for the last 50–60 years in some aufeis-affected areas of Russia, such as the Baikal region, South Yakutia, the Kolyma region and the eastern Sayan Mountains, following the increase of global and local air temperature.
Some authors suggest that degradation of permafrost in the discontinuous and
sporadic permafrost regions will lead to the decrease of the number of
aufeis fields and even an almost complete disappearance. Meanwhile, in the
zone of
continuous permafrost in North-east Siberia, a climate warming of
2–3
In Alaska as well, no significant changes were documented in the area and volume of aufeis over the past few decades or even a century (Yoshikawa et al., 2007). Yoshikawa et al. (2007) suggested that the formation and the melting of ice are less dependent on climate and more so on the source (spring) water properties such as temperature and volume.
In 1958, Simakov and Shilnikovskaya (1958a) compiled and published a map
inventory of aufeis of the North-east USSR (scale
The aim of this study is to update the inventory of aufeis in North-east Russia using Landsat images, as well as to develop an electronic
catalogue, which will contain data on historic and current locations and
characteristics of aufeis. Here we present work that has been completed for
the Indigirka River basin (down to the Vorontsovo gauging station, 305 000 km
The new database, which includes geographic information system (GIS) formatted files, is freely available (Makarieva et al., 2018b) and can be used both for scientific purposes and for solving practical problems such as engineering construction and water supply.
The study region is the Indigirka River basin, which is located in
North-east Siberia and covers an area of 305 000 km
Geographical location of the Indigirka River basin.
The climate of the study area is distinctly continental with annual average
and lowest monthly air temperature varying from
The Indigirka River basin is located in the zone of continuous permafrost. Permafrost depth can reach 450 m in the mountains, up to 180 m in river valleys and intermountain areas, with taliks found in riverbeds and fractured fields. The hydrogeological regime is affected by the active layer, which varies from 0.3 m to over 2 m (Explanatory note to the geocryological map of the USSR, 1991). The river run-off regime is characterized by high snowmelt freshet, summer–autumn rainfall floods and low winter flow. In winter, small- and medium-sized rivers completely freeze. Freshet starts in May–June and lasts for approximately 1.5 months. Meltwater from aufeis, glaciers and snow patches adds to the river discharge in summer.
In total, about 10 000 aufeis fields with a total combined area of about
14 000 km
The inventory map (scale
The Cadastre contains data on 7448 aufeis fields of different size and over 2000 boolgunyakhs (frost mounds). Of the total number of aufeis fields, 7006 are plotted based on air-photo interpretation data and another 442 based on geological reports from field data. It should be noted that aufeis was identified based on geomorphologic features, meaning that in some cases only the areas or river valleys with aufeis were identified but not aufeis itself.
In the Cadastre (1958) and our digitalization, the following characteristics of the aufeis are presented: location (the name of the river, the distance from the mouth or source), size (maximum length, average width and area) and the dates of ice recording in aerial images (ranging from 8 June 1944 to 27 September 1945). Areas of the aufeis were evaluated via planimetry.
Only very large aufeis fields (
A section of the Cadastral map of the North-east USSR from 1958 (sheet 7, upper reaches of the Indigirka River – the basins of the rivers Suntar, Agayakan and Kuydusun).
Here, we developed the GIS database of aufeis in the Indigirka River basin
up to the cross section at the Vorontsovo gauging station based on the
Cadastre (1958) and topographic maps. Our compilation contains data on 896
aufeis fields. The aufeis fields are presented as point objects in our database. The areas
are specified for only 808 aufeis fields. The total area of all the aufeis fields
within the specified area accounts for 2063.6 km
In the Cadastre, the dates of ice recording for 592 aufeis fields (66 %) are presented, based on aerial images within the study area. The average seasonal date of recording is 2 August, ranging from 8 June to 27 September. The dates of ice recording for the remaining 34 % of the aufeis were not described, meaning that aufeis detection could be carried out based not on the visible ice presence at the aerial images but on geomorphological features of river valleys. Therefore, the Cadastre might contain data on old aufeis glades, where the aufeis itself was absent.
Spatial positioning of the Cadastral map of aufeis was conducted using the
location description by Russian topographic maps with the scale of
The locations of the remaining aufeis were determined with the spatially positioned map of the Cadastre. Additionally, 11 aufeis fields were found which were absent in the Cadastre but present in the topographic maps. Aufeis areas were estimated using digitalization of the maps. Areas of the remaining aufeis were estimated with the Cadastre. It was not possible to estimate the area of 88 aufeis fields, as they were not drawn on the topographic maps, and only their location, but not area, was stated in the Cadastre.
Aufeis location and area are relatively easy to determine using Landsat
and/or Sentinel-2 images, received immediately after snow cover melt.
Snow and ice are known to be characterized by relatively high reflectance in
the visible and near-infrared spectral bands and its significant decrease in
the mid-infrared band. The Normalized Difference Snow Index (NDSI) is based on this
pattern and is calculated according to the formula (Hall et al., 1995):
Landsat-based detection of aufeis required some additional data to exclude other surface types with similar spectral characteristics, such as snow-covered areas and turbid water. It is problematic to separate floodplain lakes from aufeis using late spring satellite images because many of these lakes are still ice-covered in May–June. Morse and Wolfe (2015) recommended creating a mask of water surface using midsummer images (when all water bodies are not already covered by ice), to exclude them from further analysis.
Aufeis detection in the Indigirka River basin was carried out based on the
Landsat-8 OLI satellite images, from 2013 to 2017, downloaded from the United States
Geological Survey web-service (
Preprocessing of the images was performed with the use of the Semi-Automatic Classification Plugin module (QGIS 2.18). It includes the calculation of surface reflectance and atmospheric correction using the Dark Object Subtraction (DOS1) image-based algorithm described by Chavez (1996).
The Aufeis detection algorithm was realized in ArcGIS with the help of the ModelBuilder application. Apart from the Landsat images, the digital terrain model GMTED2010 (Danielson and Gesch, 2011) with a spatial resolution of 250 m was used to build a network of thalwegs within the study basin. This is essential for semi-automated separation of the aufeis from snow-covered areas in late spring Landsat images. Indeed, almost all aufeis is located either at streams or thalwegs, or in immediate proximity to them. On the contrary, snow cover in late spring mainly remains on mountain ridges and other elevated locations, i.e. relatively far from thalwegs. Based on the preliminary analysis of aufeis location in relation to the network of thalwegs created, we found that a 1.5 km wide buffer zone around the thalwegs covers almost all aufeis. So, snow- and ice-covered areas, which are located outside this buffer, are excluded from further analysis.
The process of aufeis detection using Landsat images consisted of the following
steps:
detection of snow-ice bodies with a NDSI threshold of 0.4; creation of a water mask with threshold values of the Normalized Difference
Water Index (NDWI; taken equal to 0.3) and reflectance in the
near-infrared band (taken equal to 0.04); extraction of the detected snow–ice bodies by the buffer zone around
thalwegs (1.5 km wide); conversion to vector format, area calculation and removal of objects smaller
than five Landsat pixels (0.45 ha).
The suggested algorithm allows successful aufeis detection if an image is
predominantly snow-free. At the end of May and early June, many aufeis fields in
mountain regions are still covered by snow. Their detection required later
images, obtained in mid-June.
Morse and Wolfe (2015) suggested a new spectral index, MDII, for automatically distinguishing snow bodies from ice ones. However, here some of the high-elevation aufeis fields were partially covered with snow at the image acquisition time. Instead of automatic processing, the outlining of high elevation aufeis was conducted manually when snow cover was present, with separation of aufeis from adjacent snow-covered areas.
Further, during melt season, the aufeis often divides into several
neighbouring areas. When assessing the number of aufeis fields with satellite data,
it is therefore necessary to aggregate the areas into one aufeis field if they
are located at a distance
As a result of semi-automated processing of Landsat images, aufeis with a
total area of 1253.9 km
The structure of the GIS dataset of aufeis according to Landsat images is presented in Table 2.
The structure of the GIS database of aufeis using Cadastre (1958).
The structure of the GIS database of aufeis using Landsat images (2013–2017).
Cross-verification of aufeis data collection using the Cadastre (1958) and satellite imagery was performed in two steps. In the first step, we found the closest aufeis field in the Landsat-derived dataset for each aufeis field from the Cadastre data if the distance between them was less than 5000 m. The determination of search radius was based on a preliminary analysis of the aufeis locations by the Cadastre in relation to the Landsat-based dataset. As a result, the cross index (identifier of the closest aufeis in the Landsat-derived dataset) and minimum distance (m) to the closest aufeis were determined for aufeis from the Cadastre. For the Landsat-based dataset, the cross index is the key field for the reference to the dataset from the Cadastre.
In the second step, a full manual verification was performed to find the mistakenly interrelated aufeis. For example, if the closest aufeis fields from the Cadastre and from the Landsat-based dataset were at a distance of less than 5000 m but in different thalwegs, they were considered to be different (unrelated) aufeis fields.
In total, 260 aufeis fields from the Cadastre were not verified by Landsat images.
For them, the NoData value (
The results of the comparison are presented in Table 3. In total, 634 aufeis
fields from the Cadastre were found by the Landsat images. They correspond to 611
aufeis fields identified with the images, meaning that in 23 cases, one aufeis field in
an image corresponds to two aufeis fields in the Cadastre. But 262 aufeis fields from the
Cadastre were not detected by the satellite images. Those are mainly small
aufeis fields, which melt by the middle of June. However, among them there are also
43 large aufeis fields over 1 km
Data correlation of aufeis based on the Cadastre (1958) and the Landsat images.
Difference between aufeis location according to the Cadastre and
satellite data:
A little over half of the aufeis detected by Landsat images is included in
the Cadastre: a total of 602 aufeis fields detected (the total area of 250.4 km In some cases a single aufeis field, according to the Cadastre, corresponds
to two or more aufeis fields in a satellite image. Aufeis is characterized by significant interannual variability, which
results in possible formation of new aufeis in areas where it was previously
not observed (Alekseev, 2015; Pomortsev et al., 2010; Atlas of
snow and ice resources of the world, 1997).
Total aufeis area evaluated based on satellite images appeared to be 1.6
times smaller than stated in the Cadastre (1958). First and foremost, such
a difference can be explained by the fact that it was not the area of the
aufeis itself but instead the aufeis glades that were reported in the
Cadastre (1958), and this corresponds to the maximum aufeis area during one
or several seasons. With the satellite data, the areas of the aufeis
itself were assessed, and when mid-June images were used, the aufeis area
was significantly smaller than the typical annual maximum.
Aufeis area distribution according to the Cadastre and satellite data is shown as Lorenz curves (Fig. 4). In both cases, the shape of the curves signifies a high degree of irregularity which is similar: 10 % of the largest aufeis fields make up 61 % and 57 % of their total area according to the Landsat and the Cadastre data, respectively.
Lorenz curves illustrating aufeis area distribution according to the Cadastre and Landsat data.
The cross-verification of the Cadastre and satellite data shows that almost
60 % of aufeis fields that are unconfirmed in the Landsat imagery and that
are therefore only present in the Cadastre have an individual aufeis area of less
than 0.25 km
Aufeis area distribution:
In general, aufeis distributions by elevation as assessed using the Cadastre and Landsat data are quite similar, although there are some differences that are elevation-specific (Fig. 6). Most aufeis is located in the elevation band of 1000–1200 m. At lower elevations (up to 800 m) the number of aufeis fields according to Landsat data is higher than stated in the Cadastre. At the elevations of 1400–2000 m, more aufeis is identified in the Cadastre data than in the satellite images. This can be explained by the fact that many aufeis fields located at high altitudes often have a small area, so they could have been missed during the analysis of the satellite data. Further, they could have been covered with snow at the image acquisition time, which would increase the possibility of them being missed.
Aufeis distribution by elevation within the Indigirka River basin.
The elevation band of 200–300 m is characterized by the location of large aufeis fields. Though less than 2.5 % and 5.0 % of aufeis fields by the Cadastre and Landsat images are situated here, they represent about 11 % and 13 % of aufeis area from the datasets respectively (Fig. 7).
Aufeis area distribution by elevation within the Indigirka River basin.
In the Indigirka River basin, there are several zones with a high density of aufeis: in the southern part (the Suntar and Kuidusun River basins) as well as in the central part (Chersky Range slopes) (Fig. 8). The largest aufeis fields identified by satellite images are located in the Syuryuktyakh River basin on the north-east slopes of the Chersky Range. Meanwhile, aufeis is almost absent in the northernmost (lowland) part of the Indigirka basin.
Aufeis in the Indigirka River basin according to the Cadastre and Landsat images. Black outlines represent the zones where aufeis area interannual variability was assessed.
We analysed the aufeis coverage for six river basins with available
streamflow data. The headwater part of the Indigirka River, with the gauge
near the Yurty village (area 51 100 km
Aufeis area coverage (percentage) in the sub-basins within the Indigirka River watershed by the Cadastre and Landsat data.
The assessment of aufeis area interannual variability was conducted in two
areas: for the Bolshaya Momskaya aufeis, which is located in the Moma River
channel (area in the Cadastre is 82 km
Cloudless images from Landsat-5 (TM), Landsat 7 (ETM
Aufeis area changes, 2001–2017.
Both areas are located at low elevations (Bolshaya Momskaya 430 to 500 m and Syuryuktyakh 200 to 500 m), which contributes to the relatively early and intensive aufeis melt in spring. The aufeis fields reach their maximum area by the beginning of May. Using the available satellite images it is impossible to make a reliable conclusion on aufeis area increase or decline because the acquisition dates vary significantly from year to year. However, it is possible to make some conclusions based on the available data, detailed below.
In 2002–2017 the Bolshaya Momskaya aufeis did not reach the maximum area
stated in the Cadastre (82 km
The area of the largest aufeis field in the Syuryuktyakh River basin in May 2014
was 78.0 km
The most important uncertainty in the obtained results relates to our ability to draw a conclusion on the long-term trend of total aufeis area comparing the historical and satellite-derived datasets. The total area of aufeis estimated by Landsat images is 38 % less than according to the Cadastre. Is it possible to confirm that such a significant reduction in the aufeis area really occurred? Considering this issue, it is important to emphasize some limitations of the methodology and the datasets created.
The main limitation of the historical aufeis dataset is that the Cadastre provides an area of aufeis glades but not the aufeis itself. Simakov and Shilnikovskaya (1958a) noted that the areas of aufeis glades match the average annual maximum of the ice-covered area. Alekseev (2005) states that the assessment of the stages and patterns of the development of aufeis glades based on the analysis of their landscape and geomorphological features is difficult due to the lack of research on temporal aspects of mutual transitions of landscape facies and their factorial dependencies. However, studying the aufeis landscapes in the central part of the Eastern Sayan Mountains, Alekseev (2005) assumed that the vegetation community which is a typical indicator of aufeis development may persist for 200–300 years after the beginning of aufeis processes attenuation.
The satellite-derived assessment of the aufeis area has the following main source of uncertainty. It is often impossible to determine the maximum area of aufeis by satellite images, since it is observed at the beginning of the snowmelt season, when aufeis is still covered with snow. In late spring and the beginning of summer, the area of aufeis may already have significantly reduced in comparison with the maximum values, due to melting and mechanical destruction.
Maximum intensity of aufeis melt in the studied region is observed in June
when spring flood river streams actively erode the aufeis surface.
Sokolov (1975) reported the results of the observations at the Anmyngynda aufeis
carried out in 1962–1965. This aufeis is located in the upstream area of the
Kolyma River basin (723 m a.s.l.) and may be used as being representative of
the mountainous part of the studied region. In 1962–1965, the aufeis area
changed from 5.1 to 6.2 km
Some aufeis in the mountainous regions could be missed by satellite images, since it can be covered with snow until the end of June. However, its contribution to the total area is non-significant.
Taking into account all the above-described limitations, and also that more than 600 aufeis fields that were missing in the Cadastre were found by Landsat images, we conclude that it is not correct to make a conclusion about long-term trends of aufeis area based on the entire dataset created. Following Pavelsky and Zarnetske (2017), we decided to examine only several of the largest aufeis fields in order to identify the long-term trend.
We selected the 38 largest aufeis fields with an area
The combined digital database of the aufeis is publicly
available and can be downloaded from
The research conducted here is the first step of the study aimed at the
development of a GIS database of the aufeis of North-east Russia.
Historical data of the Cadastre (1958) and topographic maps were used to
create a geodatabase of aufeis in the Indigirka River basin (up to the
Vorontsovo gauge, with the area of 305 000 km
The recent total aufeis area is 1.6 times smaller than stated in the Cadastre (1958).
More significant changes occurred in 38 large and giant aufeis fields
(area
The analysis of large and giant aufeis seems to indicate that there has been a significant decrease in aufeis area over the period of the last 70 years. Additional analysis of historical aerial photography data could help to clarify the issue of the aufeis area decline trend from the middle of the 20th century to the present. One of the further study goals will be to find out the extent to which these changes are climate-derived and to identify their impact on river streamflow.
OM and NN designed the study. The historical aufeis dataset from Cadastre and topographic maps was compiled by AO. Identification of aufeis based on Landsat data and the cross-referencing between historical and satellite-based aufeis data collection were performed by AS. The initial draft of the paper was written by OM and NN, with contributions by AO (Sect. 3.2) and AS (Sects. 3 and 4). All authors contributed to the final form of the paper.
The authors declare that they have no conflict of interest.
The authors are grateful to David Post, Anna Liljedahl and an anonymous reviewer for valuable comments and assistance with English. Edited by: Kirsten Elger Reviewed by: Anna Liljedahl and one anonymous referee