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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 114, D07102, doi:10.1029/2008JD010537, 2009
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Variation of hydrological regime with permafrost coverage over Lena
Basin in Siberia
Baisheng Ye,1 Daqing Yang,2 Zhongliang Zhang,3 and Douglas L. Kane2
Received 3 June 2008; revised 18 November 2008; accepted 4 February 2009; published 2 April 2009.
[1] We use monthly discharge and permafrost data to examine the relationship between
discharge characteristics and basin permafrost coverage for the nested subbasins of
the Lena River in Siberia. There are similarity and variation in streamflow regimes over
the basin. The ratios of monthly maximum/minimum flows directly reflect discharge
regimes. The ratios increase with drainage area from the headwaters to downstream within
the Lena basin. This pattern is different from the nonpermafrost watersheds, and it
clearly reflects permafrost effect on regional hydrological regime. There is a significant
positive relationship between the ratio and basin permafrost coverage. This relationship
indicates that permafrost condition does not significantly affect streamflow regime
over the low permafrost (less than 40%) regions, and it strongly affects discharge regime
for regions with high permafrost (greater than 60%). Temperature and precipitation have
similar patterns among the subbasins. Basin precipitation has little association with
permafrost conditions and an indirect relation with river flow regimes. There exists a good
relation between the freezing index and permafrost extent over the basin, indicating that
cold climate leads to high coverage of permafrost. This relation relates basin thermal
condition with permafrost distribution. The combination of the relations between
temperature versus permafrost extent, and permafrost extent versus flow ratio links
temperature, permafrost, and flow regime over the Lena basin. Over the Aldan subbasin,
the maximum/minimum discharge ratios significantly decrease during 1942–1998 due to
increase in base flow; this change is consistent in general with permafrost degradation
over eastern Siberia.
Citation: Ye, B., D. Yang, Z. Zhang, and D. L. Kane (2009), Variation of hydrological regime with permafrost coverage over Lena
Basin in Siberia, J. Geophys. Res., 114, D07102, doi:10.1029/2008JD010537.
1. Introduction
[2] River runoff is the primary freshwater source to the
Arctic Ocean. Fresh water discharge from the northernflowing rivers plays an important role in regulating the
thermohaline circulation of the world’s oceans [Aagaard
and Carmack, 1989]. Both the amount and the timing of
freshwater inflow to the ocean systems are important to
ocean circulation, salinity, and sea ice dynamics [Aagaard
and Carmack, 1989; Macdonald, 2000]. Recent studies
report significant changes in arctic hydrologic system,
particularly cold season and annual discharge increases over
large Siberian watersheds. These changes indicate hydrologic regime shifts due to large-scale climate variations,
1
States Key Laboratory of Cryospheric Sciences, Cold and Arid Regions
Environmental and Engineering Research Institute, Chinese Academy of
Sciences, Lanzhou, China.
2
Water and Environment Research Center, Civil and Environmental
Engineering Department, University of Alaska Fairbanks, Fairbanks,
Alaska, USA.
3
Department of Resources and Environment, Lanzhou University,
Lanzhou, China.
Copyright 2009 by the American Geophysical Union.
0148-0227/09/2008JD010537$09.00
permafrost changes, and human impacts [Peterson et al.,
2002; Yang et al., 2002; Ye et al., 2003; McClelland et
al., 2004].
[3] In the cold regions, hydrological regime is closely
related with permafrost conditions, such as permafrost
extent and thermal characteristics. Ice-rich permafrost has
a very low hydraulic conductivity and commonly acts as a
barrier to deeper groundwater recharge or as a confining
layer to deeper aquifers. Because it is a barrier to recharge,
permafrost increases the surface runoff and decreases subsurface flow. Permafrost extent over a region plays a key
role in the distribution of surface-subsurface interaction
[Lemieux et al., 2008; Carey and Woo, 2001; Woo et al.,
2008]. Permafrost and nonpermafrost rivers have very
different hydrologic regimes. Relative to nonpermafrost
basins, permafrost watersheds have higher peak flow and
lower base flow [Woo, 1986; Kane, 1997]. In the permafrost
regions, watersheds with higher permafrost coverage have
lower subsurface storage capacity and thus a lower winter
base flow and a higher summer peak flow [Woo, 1986;
Kane, 1997; Yang et al., 2003].
[4] It is difficult to accurately determine changes in
permafrost conditions. Our understanding of permafrost
change and its effect on hydrological regime is incomplete.
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Figure 1. The Lena River watershed and hydrological stations (A through K) used in this study. Also
shown are the reservoir location on the Vilui River and the permafrost distribution [Brown et al., 1997,
2001] over the Lena basin.
For instance, there are uncertainties regarding the impact of
ground ice melt and its contribution to annual flow changes
over large Siberian rivers [McClelland et al., 2004; Zhang et
al., 2005a]. Permafrost condition and streamflow characteristics vary within large watersheds in Siberia. Examination
and comparison of hydrological regimes between subbasins
with various permafrost conditions can improve our understanding of impact of permafrost changes on cold region
hydrology. This paper examines the relationship between
hydrological regime and permafrost coverage over nested
subbasins within the Lena River in Siberia. It analyzes
monthly discharge data, with a focus on the ratio of the
maximum to minimum discharge (Qmax/Qmin) and its
relation with permafrost condition, because this ratio
reflects the hydrological regime. The objective of this study
is to quantify the impact of permafrost on streamflow
regime and change, and to specifically define a relationship
between basin permafrost extent and streamflow conditions
over the Lena watershed. We also examine relationship
between basin air temperature and precipitation and their
effect on permafrost extent and basin streamflow regimes.
The result of this study will shed light on our knowledge of
cold region hydrology and its change due to climate impact
and human influence.
2. Basin Description, Data Sets, and Method
of Analysis
[5] The Lena River originates from the Baikal Mountains
in the south central Siberian Plateau and flows northeast and
north, entering into the Arctic Ocean via the Laptev Sea
(Figure 1). Its drainage area is about 2,430,000 km2, mainly
covered by forest and underlain by permafrost. The Lena
River contributes 524 km3 of freshwater per year, or about
15% of the total freshwater flow into the Arctic Ocean
[Yang et al., 2002; Ye et al., 2003]. Relative to other large
rivers, the Lena basin has less human activities and much
less economic development [Dynesius and Nilsson, 1994].
There is only one large reservoir in the Vilui subbasin. A
large dam (storage capacity 35.9 km3) and a power plant
were completed in 1967 near the Chernyshevskyi
(112°150W, 62°450N). This reservoir is used primarily for
electric power generation: holding water in spring and
summer seasons to reduce snowmelt and rainfall floods
and releasing water to meet the higher demand for power in
winter [Ye et al., 2003]. Various type of permafrost exists
in the Lena basin, including sporadic, or isolated permafrost
in the source regions, and discontinuous and continuous
permafrost in downstream regions (Figure 1) [Brown et al.,
1997]. Approximately 78– 93% of the Lena basin is underlain by permafrost [Zhang et al., 1999; McClelland et al.,
2004].
[6] Since the late 1930s hydrological observations in the
Siberian regions, such as discharge, stream water temperature, river ice thickness, dates of river freezeup and breakup,
have been carried out systematically by the Russian Hydrometeorological Services and the observational records
were quality-controlled and archived by the same agency
[Shiklomanov et al., 2000]. The discharge data are now
available from the R-ArcticNet (v4.0), a database of PanArctic River Discharge during 1936 – 2000 [Lammers et al.,
2001]. In this analysis, long-term monthly discharge records
collected at 9 stations (A – H and K) along the main stem
and 2 tributary stations (I and J) were used (Figure 1).
Relevant information of these stations is given in Table 1.
[7] Permafrost data and information were obtained from
the database of the digital permafrost map compiled by
International Permafrost Association (IPA) [Brown et al.,
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Table 1. List of Hydrologic Stations Used in This Studya
Station Code
(see Figure 1)
A
B
C
D
E
F
G
H
I
J
K
Station Name/Location
Kachug
Zhigalovo/Upper Lena
Gruznovka/Upper Lena
Ust’-Kut/Upper Lena
Zmeinovo/Upper Lena
Krestovskoe/Upper Lena
Solyanka/Upper Lena
Tabaga/Upper Lena
Verkhoyanskiy Perevoz/
Aldan subbasin outlet
Vilyuy/Vilui valley outlet
Lena At Kusur
Latitude
(°N)
Longitude
(°E)
53.97
54.82
55.13
56.77
57.78
59.73
60.48
61.83
63.32
105.88
105.13
105.23
105.65
108.32
113.17
120.7
129.6
132.02
1936
1969
1912
1936
1936
1936
1933
1936
1942
63.95
70.68
124.83
127.39
1936
1934
Annual Runoff
Drainage Area
(1000 km2)
%
km3
mm
%
1990
1977
1990
1986
1990
1999
1999
1999
1999
17
30
42
71
140
440
770
897
696
0.7
1.3
1.7
2.9
5.8
18.1
31.7
36.9
28.6
2.9
3.8
6.2
10.1
35.4
131.3
213.5
221.0
166.0
164.0
124.6
148.0
141.9
253.1
298.5
277.2
246.4
238.5
0.5
0.7
1.2
1.9
6.7
24.8
40.4
41.8
31.4
1998
2000
452
2430
18.6
100.0
46.7
528.6
103.3
217.5
8.8
100.0
Data Period
a
Stations A – H are listed from upstream to downstream.
1997, 2001]. The shapefiles were derived from the original
1:10,000,000 printed map. The IPA permafrost map was
categorized as continuous (90 – 100%), discontinuous (50 –
90%), isolated (10 – 50%), and sporadic (0 – 10%). The
coverage of permafrost (CP) in a basin has been determined
differently [McClelland et al., 2004; Zhang et al., 1999].
Most studies consider permafrost existence [Smith et al.,
2007; McClelland et al., 2004] and determined the total
coverage of permafrost (4 types of permafrost) [McClelland
et al., 2004]. In this study, basin and subbasin permafrost
areas are determined by overlaying the permafrost map to
the river network map. Basin/subbasin boundaries and
drainage areas are derived from 1 km DEM data, the USGS
GTOPO30 data set [Bliss and Olsen, 1996]. The drainage
areas from the 1km DEM match well to those reported by
the Pan-Arctic River Discharge Database [Lammers et al.,
2001], with the relative errors being less than 15% for the
subbasins. The coverage of permafrost in a basin is defined
as the weighed average of the 4 different types of permafrost. Considering the ranges of permafrost coverage, we
take the mean coverage as representative coverage for every
permafrost type, i.e., 95%, 70%, 30% and 5% permafrost
coverage in continuous, discontinuous, isolated and sporadic
areas, respectively. Variations from the mean CP are ±5%,
±20%, ±20% and ±5% for continuous areas, discontinuous
areas, isolated areas, and sporadic permafrost, respectively.
[8] The methods of analyses include calculation of
monthly mean discharge and hydrographs for the nested
subbasins within the Lena watershed, determinations of
ratio of monthly high to low flows, and examination of
the relation between the ratio and permafrost coverage over
the nested subbasins. We compare the ratio between pre-dam
and post-dam periods to quantify and discuss reservoir
impact on streamflow regime and change. We conduct trend
analysis to define the long-term changes in hydrographs and
use the Student t test to determine the statistical significance
of the trends. Furthermore, we compare the ratio trends
among the subbasins to understand the regional differences
in streamflow characteristics and changes. We also use
monthly precipitation (P) and temperature (T) data [Jones,
1994] for the Siberian regions and calculate the basin mean
values for the upper Lena, Aldan and Vilyuy subbasins.
Based on these data, we carry out analyses of basin precip-
itation and temperature and their relationships with basin
permafrost extent and streamflow regime.
3. Results
3.1. Hydrographs
[9] Figure 2 shows the mean monthly discharge at the
9 stations from the upper to lower Lena basin. They
generally have similar runoff regimes, i.e., high discharge
in summer and low flow in winter. However, the difference
among them is very obvious. The large difference is seen in
the peak flow, both in rate and timing. Lena river peak
discharge is mainly related to snowmelt [Yang et al., 2007;
Ye et al., 2003], as it varies over the basin. The mean peak
flow is about 210 m3/s at the Kachug station located in the
upper basin (station A in Figure 1), due to increasing drainage
area, it gradually grows to 74,000 m3/s at the basin outlet
(the Kusur station, K in Figure 1). The monthly peak flow
occurs in May in the upstream source regions (stations A– D)
and in June over the downstream regions (stations E– H
and K), because early snowmelt in the source regions and
later melt downstream [Yang et al., 2003, 2007].
[10] As expected, the minimum discharge increased with
drainage area in the Lena basin. The lowest monthly flow is
about 22 m3/s at the Kachug station (A in Figure 1) and it
gradually increases to 1100 m3/s at the basin outlet (K in
Figure 1). The lowest flow occurs in February in the
headwaters (stations A – E), in March over the middle
streams (F – G), and in April in downstream (stations H
and K). This pattern, early low flow in the source regions
and late low flow in lower basin, is related with the timing
of snowmelt and hydraulic routing of flow. Also, the timing
of snowmelt usually dictates the timing of discharge recession. Usually early (late) snowmelt is associated with early
(late) peak and subsequently early (late) low flow. Figure 2
clearly illustrates the variation of hydrographs over the Lena
basin. The difference in hydrographs reflects basin climatic
and physical characteristics, particularly permafrost conditions. Among other measures, the high and low flows
determine the hydrograph shape. The ratio of monthly
maximum discharge (Qmax) to minimum discharge (Qmin)
is a direct measure of hydrograph shape and hydrologic
regime [Woo, 1986; Kane, 1997]. This ratio can also
indicate streamflow regime changes caused by reservoir
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Figure 2. Monthly hydrographs at selected stations along the main river valley.
regulation [Ye et al., 2003; Yang et al., 2004a, 2004b]. Ice
jams in the northern regions affect hydrograph in spring. In
this study, we use monthly maximum and minimum discharge to determine both the hydrograph shape and the
calculation of the ratio. We did not use any daily (maximum
and minimum) discharge. This may help to eliminate or
smooth the ice jam effect on flow regime analysis.
[11] Calculations of the Qmax/Qmin for the 9 stations in
the Lena basis show variations from upstream to downstream. The mean Qmax/Qmin are about 13– 16 in the source
regions (stations A– E), and increases from 21 in middle
upper Lena (station F) to 74 at the outlet station (stations K).
The ratio increases with drainage area (Figure 3). This
positive relationship is different from nonpermafrost
regions/basins, where the ratio decreases with basin area.
3.2. The Relationship Between Qmax/Qmin Ratio and
Coverage of Permafrost (CP)
[12] The permafrost distribution varies from sporadic in
the source regions to continuous permafrost over the Lena
basin (Figure 1). The extent of permafrost gradually
increases from 20% in the headwaters to 86% in downstream regions (Figure 3). The Qmax/Qmin ratios are low
(10 – 20) for CP less than 40%, and moderate (20 – 30) for
CP interval of 60– 75%, and high (about 70– 80) for CP
greater than 86%. The ratios change with CP over the basin,
i.e., increasing with the CP from upstream to downstream.
[13] Dam regulation can significantly alter streamflow
regime [Ye et al., 2003; Yang et al., 2004a, 2004b]. It is
therefore critical to use pre-dam and natural flow data for
regional hydrology analyses. Using the flow data from the
upper Lena without dam regulation and the pre-dam data for
the basin outlet, we conducted regression analysis between
the Qmax/Qmin and CP. The result reveals a significant
relationship (significant at 99%, Figure 4). This relationship
clearly indicates the effect of permafrost distribution on
discharge process. Permafrost regions/basins have low infiltration and limited subsurface storage capacity [Woo,
1986; Kane, 1997; Woo et al., 2008]. Relative to nonpermafrost or low permafrost basins, high permafrost basins
Figure 3. The mean ratio of Qmax/Qmin and coverage of permafrost (CP) versus drainage areas. The
ratio for Kusur (station K) is for pre-dam data.
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Figure 4. The ratios of Qmax/Qmin versus coverage of permafrost (CP) at the nine stations from the
upper Lena to basin outlet without reservoir regulation. Two additional stations (the Aldan and Vilui
subbasins in Lena basin) and one additional basin (the Yasachnaya Kolyma River) in East Siberian are
also shown. The ratios of Qmax/Qmin are showed at the Vilui subbasin and Kusur at Lena basin outlet
with reservoir regulation since 1967. Note: the Y axis is in logarithm scale.
have higher maximum discharge and lower minimum discharge, hence higher ratio of Qmax/Qmin. Figure 4 shows
that the permafrost condition does not significantly affect
streamflow regime over the low permafrost regions (i.e., CP
< 40%), and it strongly affects discharge regime for regions
with high permafrost coverage (i.e., CP greater than 60%).
It is useful to determine this threshold of permafrost impact
to regional hydrology, particularly in regions undergoing
climate warming and permafrost degradation. Further analyses over broader regions are necessary to refine and verify
the relation and threshold.
[14] The Qmax/Qmin– CP relation has been derived for
the nested basins from the upper Lena to the basin as a
whole. To test the relationship, two independent subbasins
within the Lena watershed (i.e., the Aldan and Vilui subbasins, stations I and J in Figure 1) have been included in
Figure 4. These two tributaries have very high CP, 92%
and 95% for the Aldan and Vilui, respectively. There is a
reservoir in the upper Viliu valley, with a storage capacity of
36 km3, or about 77% and 7% of annual discharge at Vilui
outlet and Lena basin mouth. Operation of this dam has
changed streamflow regimes [Ye et al., 2003]; it reduced the
peak flows by about 30% and enhanced low flows by about
27 times at Vilui outlet (station J in Figure 1). Because of
these changes, the ratio of Qmax/Qmin sharply decreases
from 536 to 38 at the Vilui outlet (station J in Figure 1) and
from 75 to 45 at the Lena outlet (K in Figure 1), respectively
(Figure 4).
[15] The Qmax/Qmin ratios are high, 75 for the Aldan
(Station I) and 536 for the Vilui (Station J) during the pre-
dam period. The higher ratio for the Vilui is due to
continuous permafrost and very low winter flows in the
northern parts of the Lena basin. The ratios and CP of these
two subbasins are generally consistent with the relationship,
showing higher Qmax/Qmin ratios with higher CP. Furthermore, we include the Yasachnaya Kolyma watershed in
eastern Siberia for a comparison. This basin has high
permafrost extent (about 94%) and fits well with the curve
derived from the Lena basin (Figure 4). These results may
indicate a general applicability of the relation over the
northern basins. It is, however, important to recognize the
limitation of this relation. The Qmax/Qmin ratios can be
very high due to very low base flow over continuous
permafrost regions. For instance, winter base flow is extremely low in the very cold Arctic coast watersheds with
almost 100% permafrost coverage, such as the Yana and
Olenka basins near the Lena River.
3.3. Qmax/Qmin Ratio Changes Over Time
[16] It is difficult to survey permafrost change over large
regions. It is easy to calculate the ratio of Qmax/Qmin over
a basin where discharge data is available. The relationship
between the Qmax/Qmin ratio and CP directly links streamflow regime with basin permafrost coverage. The changes in
the ratio over time and space perhaps can, therefore, reflect
basin permafrost changes.
[17] Figure 5 shows the time series of Qmax/Qmin ratio
during 1935 –2000 at 3 tributary stations and at the Lena
river outlet. The ratio at the Tabaga station (H) in the upper
Lena varies from 16 to 48, with a mean of 28. The ratio does
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Figure 5. The ratio of Qmax/Qmin (a) at stations of Tabaga in upper Lena and Verkhoyanskiy Perevoz
in Aldan without dam regulation and (b) at Viluy in Vilui and Kusur at Lena outlet during 1935– 2000.
not show any trend, although it is obviously lower during
1980 – 1998, with a mean of 26 due to higher Qmin. The
ratio in the Aldan subbasin ranges from 24 to 177, with a
mean of 75. It has significantly (95% confidence) decreased
by 54 (75%) during 1942– 1998 due to a strong increase
in Qmin. There are no dams in this tributary. The decrease
of the ratio is mainly due to increases in winter flows [Ye et
al., 2003]. The ratio for the Vilui tributary varies between 6
and 1,000. It has sharply decreased since 1966 when the
dam went operational. The mean ratios are 531 and 15 for
pre- and post-1967, respectively. The drop in ratio is caused
by the operation and regulation of the Vilui reservoir around
1967 [Ye et al., 2003], i.e., enhancing winter flows and
reducing summer flows downstream of the dam. The ratio at
the Lena river outlet varies from 24 to 164, with a mean of
60. It decreases over time, with the total trend of 58
(nearly 95%) at 99% confidence during 1935 – 2000. This
decrease is mainly caused by reservoir regulation in the
Vilui valley.
[18] Over the Lena basin, the Qmax/Qmin ratio has a very
strong decreasing trend for the Aldan valley. This change in
ratios depends on the max and min discharge. Monthly flow
data (Figures 6a and 6b) show that peak flow did not change
much, and the low flows during November to April increased significantly by 50– 117%, (99% significant level)
over the study period and the total trend was 114% for the
Qmin during 1942 – 1999 (Figures 6a and 6b). Low flow
changes are particularly strong during 1976– 1999, with a
step rise from 200– 400 m3/s to 600 – 800 m3/s in April.
There are large fluctuations in the low flow records over the
study period. It is important to note the consistency in the
interannual variation of low flow among the months, i.e.,
high flows in early winter translating to high flows in late
winter.
[19] In addition, regression analyses of the low flows
show high correlations (R2 = 0.73 to 0.94) between the
consecutive months during November to April (Figure 7).
This result is expected, as the winter hydrology is dominated by discharge recession.
[20] The ratio of monthly flows between consecutive
months, or monthly recession coefficient (RC), is a quantitative measure of recession processes. The mean monthly
recession coefficients for this subbasin ranges from 0.62 in
early winter (December/Nov) to 0.92 in later winter (Apr/
March), indicating fast (slow) recession in early (late)
winter (Figure 7). The time series of recession coefficient
over the study period shows significant increases (at 99%
confidence) in most winter months, except an insignificant
decrease for December/November (Figure 8). Increasing
RC over time suggests decreases in recession rate. Dis-
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Figure 6. (a) The maximum monthly discharge and (b) the monthly discharge during low-flow months
during cold season at Aldan station during 1942 – 1999.
charge recession is generally a process of storage release.
Studies report significant permafrost changes in this region,
including warming of ground temperatures and deepening
of active layer depth [Pavlov, 1994; Frauenfeld et al., 2004;
Zhang et al., 2005b; Romanovsky et al., 2007]. There seems
to be a general coherency between hydrology and permafrost changes over this region, which deserves more research attention.
4. Discussion
[21] In addition to permafrost conditions, other factors,
such as geography, geology, and climate also influence
streamflow regimes in the northern regions. Data availability is a limitation for most arctic research, including this
study. To understand the climate effect on permafrost and
basin hydrology, we have obtained monthly precipitation
and temperature data from CRU [Jones, 1994] for the
Siberian region and calculated the basin mean values for
the upper Lena, Aldan, and Vilyuy subbasins. Using these
data, we examine precipitation and temperature patterns
over the subbasins and their relationships with basin permafrost extent and streamflow regime.
[22] Results of analyses of basin precipitation data show
little association of precipitation with permafrost conditions
(Figure 9), this is because temperature mostly controls
large-scale permafrost distribution [Nelson and Outcalt,
1983]. We discovered similar precipitation patterns over
the 3 subbasins within the Lena watershed (Figure 10a),
although the discharge patterns differ among the subbasins.
This association of precipitation with flow regime is reasonable, as in the northern regions and watersheds, snowfall
accumulates over winter season and snowpack melt in
spring produces the highest floods.
[23] Monthly mean temperatures also have similar patterns among the subbasins (Figure 10b). To relate temperature with permafrost conditions, previous studies use
various temperature indexes, including seasonal and yearly
means and the freezing index (FI). FI is defined as the
cumulative degree days of negative temperature over a year.
This index is often used to calculate the freezing depth
[Nelson and Outcalt, 1983, 1987]. Calculations of the FI,
using basin mean monthly temperature data, show a range
from 140 to 175°C for the 3 tributaries.
[24] There is a good relation between the FI and permafrost extent (coverage of permafrost, CP), i.e., CP increase
with FI for the 3 tributaries (Figure 11a). This result, as
expected, indicates cold climate leads to high coverage of
permafrost. This relation is very important, as it relates
basin thermal condition with permafrost distribution. Our
analyses have already established the relationship between
permafrost extent and flow regime. The combination of
relations between T-CP and CP ratio links temperature,
permafrost, and flow regime over the Lena basin.
[25] In addition, the Qmax/Qmin ratio increases with the
FI (Figure 11b) over the Lena basin. This is reasonable, as
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[26] This study found significant winter flow increase
over the Aldan subbasin. Other analyses also reported base
flow rise over the large northern watersheds, such as the
Lena basin [Ye et al., 2003] and Yukon river [Walvoord and
Striegl, 2007]. Base flow changes are likely related with
changes in subsurface processes and frozen ground conditions in northern regions. Liu et al. [2003] documented
significant of winter discharge in the source areas of the
Songhuajiang river with high permafrost extent in the
northeast China, and related this change to the warming
of ground temperatures and deepening of active layer depth.
Studies show that active layer increase affects runoff
characteristics in a small headwater catchment (Mogot
River) in the southern mountainous region of eastern Siberia
[Yamazaki et al., 2006] and in the Kuparuk River basin
[McNamara et al., 1998]. McNamara et al. [1998] reported
a long recession to the slow drainage of water from a
thawing active layer in northern Alaska. These changes in
base features may be due to changes in storage capacity and
amount in the thawed active layer [Woo et al., 2008].
[27] There is little direct measurement of basin storage
capacity and amount over the northern regions. It is therefore difficult to accurately determine their changes over
time. The basin storage capacity is a measure of groundwater reservoir. A large storage capacity leads to a slow
recession. For a given storage capacity, a large storage
amount results in a fast recession. Over the Aldan subbasin,
the recession slows down from early winter to early spring
(Figure 7) maybe due to decrease in storage amount over
winter. River discharge increased over the Aldan basin in
winter during 1940 – 1999 (Figure 6b), suggesting storage
amount did increase over time. This increase should lead to
a fast recession, but, in fact, recession slows down in most
winter months (Figure 8). This may imply the increase of
basin storage capacity. In addition, Ye et al. [2003] found
that discharge increase in November is the strongest over
the winter months over the Lena basin. This suggests more
storage of water in November over the basin and a fast
recession. However, RC decreased in December/November,
this may imply that the negative effect of increased storage
amount on RC may overcome positive effect of increased
storage capacity. More research is necessary to investigate
the linkage between changes in subsurface storage and river
streamflow.
Figure 7. The relationship of discharge between the
consecutive months in low-flow periods at Aldan during
1942 – 1999.
rivers in cold regions have very low base flows and very
high peak flows, consequently high Qmax/Qmin ratio. It is
important to mention that monthly T data have been used in
this analysis for the determination of FI over the subbasins.
There might be uncertainties in the FI calculations particularly during the early and late winter periods when the
monthly T is close to 0C. Daily T data can better define the
FI, but the data was not available to this study for the Lena
basin. It is expected that the relationship of T with CP and
Qmax/Qmin ratio may improve when daily T data are used
in future analyses.
5. Conclusions
[28] Monthly discharge regimes vary over the Lena basin,
although it is generally high in summer and low in winter.
The ratios of Qmax/Qmin are a direct measure of hydrologic regime. They increase with drainage area from the
headwaters to downstream within the Lena basin. This
pattern is different from the nonpermafrost watersheds.
The ratios also change with basin permafrost coverage,
suggesting that permafrost affects regional hydrology. Regression analysis between the Qmax/Qmin ratio and basin
permafrost coverage reveals a significant relationship at
99% confidence. This relationship quantifies the effect of
permafrost distribution on discharge process. It shows that
permafrost conditions do not significantly affect streamflow
regime over the low permafrost (less than 40%) regions, and
it strongly affects discharge regime for regions with high
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YE ET AL.: STREAMFLOW REGIME VERSUS PERMAFROST COVERAGE
Figure 8. The monthly recession coefficient between the consecutive months in low-flow period at
Aldan during 1942 –1999.
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YE ET AL.: STREAMFLOW REGIME VERSUS PERMAFROST COVERAGE
Figure 9. The basin annual precipitation versus CP for the
three tributaries (Upper Lena, Aldan and Vilui) in the Lena
River basin.
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(greater than 60%) permafrost coverage. It is important to
define this relation of permafrost impact to regional hydrology, as this knowledge will be useful for further investigation into permafrost effect on basin hydrology over the large
northern regions. Temperature and precipitation have similar
patterns among the subbasins. Basin precipitation has little
association with permafrost conditions. There is a reasonable relation between the FI and permafrost extent over the
basin, indicating that cold climate leads to high coverage of
permafrost. This relation relates basin thermal condition
with permafrost distribution. The combination of the relations between T-CP and CP-Qmax/Qmin links temperature,
permafrost, and flow regime over the Lena basin.
[29] The variations in the Qmax/Qmin ratios reflect
hydrologic regime changes. Trend analyses of the ratios
show different results over the Lena basin. The ratios
significantly decrease in the Vilui valley and at the Lena
basin outlet due to dam regulation. In the unregulated upper
Lena regions, the ratios do not show any trend during
Figure 10. (a) The basin monthly mean precipitation and (b) the temperature for three tributaries in
Lena River.
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YE ET AL.: STREAMFLOW REGIME VERSUS PERMAFROST COVERAGE
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Figure 11. The freezing index (FI) for October to April versus (a) CP and (b) Qmax/Qmin ratio for
three tributaries (Upper Lena, Aldan and Vilui) in Lena River basin.
1936 – 1998. This may imply that the permafrost changes in
the region were not sufficient enough to affect hydrological
processes. In the Aldan tributary without regulation, the
ratios significantly decrease due to increase in base flow
during 1942 –1998. This change is consistent with permafrost degradation over the eastern Siberia. This consistency
to some extent verifies permafrost influence on basin
streamflow process and change. Our efforts continue to
refine this relationship for various climate and permafrost
conditions in the high latitude regions.
[30] Acknowledgments. This study was supported by National Basic
Research Program of China (2007CB411502), Innovation Project of CAS
(KZCX3-SW-345), USA NSF grants 0230083, 0612334 and 0335941 and
International Partnership Project of CAS (CXTD-Z2005-2).
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D. L. Kane, Water and Environment Research Center, University of
Alaska Fairbanks, 306 Tanana Loop, Fairbanks, AK 99775-5860, USA.
([email protected])
D. Yang, Water and Environmental Research Center, Civil and
Environmental Engineering Department, University of Alaska Fairbanks,
306 Tanana Loop, Fairbanks, AK 99775-5860, USA. ([email protected])
B. Ye, States Key Laboratory of Cryospheric Sciences, Cold and Arid
Regions Environmental and Engineering Research Institute, Chinese
Academy of Sciences, 320 Donggang West Road, Lanzhou 730000, China.
([email protected])
Z. Zhang, Department of Resources and Environment, Lanzhou
University, 222 Tianshui South Road, Lanzhou 730000, China.
([email protected])
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