Variation of hydrological regime with permafrost … sources...hydrological regime and permafrost coverage over nested subbasins within the Lena River in Siberia. It analyzes monthly

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 betweendischarge characteristics and basin permafrost coverage for the nested subbasins ofthe Lena River in Siberia. There are similarity and variation in streamflow regimes overthe basin. The ratios of monthly maximum/minimum flows directly reflect dischargeregimes. The ratios increase with drainage area from the headwaters to downstream withinthe Lena basin. This pattern is different from the nonpermafrost watersheds, and itclearly reflects permafrost effect on regional hydrological regime. There is a significantpositive relationship between the ratio and basin permafrost coverage. This relationshipindicates that permafrost condition does not significantly affect streamflow regimeover the low permafrost (less than 40%) regions, and it strongly affects discharge regimefor regions with high permafrost (greater than 60%). Temperature and precipitation havesimilar patterns among the subbasins. Basin precipitation has little association withpermafrost conditions and an indirect relation with river flow regimes. There exists a goodrelation between the freezing index and permafrost extent over the basin, indicating thatcold climate leads to high coverage of permafrost. This relation relates basin thermalcondition with permafrost distribution. The combination of the relations betweentemperature versus permafrost extent, and permafrost extent versus flow ratio linkstemperature, permafrost, and flow regime over the Lena basin. Over the Aldan subbasin,the maximum/minimum discharge ratios significantly decrease during 1942–1998 due toincrease in base flow; this change is consistent in general with permafrost degradationover 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 theArctic Ocean. Fresh water discharge from the northern-flowing rivers plays an important role in regulating thethermohaline circulation of the world’s oceans [Aagaardand Carmack, 1989]. Both the amount and the timing offreshwater inflow to the ocean systems are important toocean circulation, salinity, and sea ice dynamics [Aagaardand Carmack, 1989; Macdonald, 2000]. Recent studiesreport significant changes in arctic hydrologic system,particularly cold season and annual discharge increases overlarge Siberian watersheds. These changes indicate hydro-logic regime shifts due to large-scale climate variations,

permafrost changes, and human impacts [Peterson et al.,2002; Yang et al., 2002; Ye et al., 2003; McClelland etal., 2004].[3] In the cold regions, hydrological regime is closely

related with permafrost conditions, such as permafrostextent and thermal characteristics. Ice-rich permafrost hasa very low hydraulic conductivity and commonly acts as abarrier to deeper groundwater recharge or as a confininglayer to deeper aquifers. Because it is a barrier to recharge,permafrost increases the surface runoff and decreases sub-surface flow. Permafrost extent over a region plays a keyrole in the distribution of surface-subsurface interaction[Lemieux et al., 2008; Carey and Woo, 2001; Woo et al.,2008]. Permafrost and nonpermafrost rivers have verydifferent hydrologic regimes. Relative to nonpermafrostbasins, permafrost watersheds have higher peak flow andlower base flow [Woo, 1986; Kane, 1997]. In the permafrostregions, watersheds with higher permafrost coverage havelower subsurface storage capacity and thus a lower winterbase 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 permafrostchange and its effect on hydrological regime is incomplete.

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 114, D07102, doi:10.1029/2008JD010537, 2009ClickHere

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1States Key Laboratory of Cryospheric Sciences, Cold and Arid RegionsEnvironmental and Engineering Research Institute, Chinese Academy ofSciences, Lanzhou, China.

2Water and Environment Research Center, Civil and EnvironmentalEngineering Department, University of Alaska Fairbanks, Fairbanks,Alaska, USA.

3Department of Resources and Environment, Lanzhou University,Lanzhou, China.

Copyright 2009 by the American Geophysical Union.0148-0227/09/2008JD010537$09.00

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For instance, there are uncertainties regarding the impact ofground ice melt and its contribution to annual flow changesover large Siberian rivers [McClelland et al., 2004; Zhang etal., 2005a]. Permafrost condition and streamflow character-istics vary within large watersheds in Siberia. Examinationand comparison of hydrological regimes between subbasinswith various permafrost conditions can improve our under-standing of impact of permafrost changes on cold regionhydrology. This paper examines the relationship betweenhydrological regime and permafrost coverage over nestedsubbasins within the Lena River in Siberia. It analyzesmonthly discharge data, with a focus on the ratio of themaximum to minimum discharge (Qmax/Qmin) and itsrelation with permafrost condition, because this ratioreflects the hydrological regime. The objective of this studyis to quantify the impact of permafrost on streamflowregime and change, and to specifically define a relationshipbetween basin permafrost extent and streamflow conditionsover the Lena watershed. We also examine relationshipbetween basin air temperature and precipitation and theireffect on permafrost extent and basin streamflow regimes.The result of this study will shed light on our knowledge ofcold region hydrology and its change due to climate impactand human influence.

2. Basin Description, Data Sets, and Methodof Analysis

[5] The Lena River originates from the Baikal Mountainsin the south central Siberian Plateau and flows northeast andnorth, entering into the Arctic Ocean via the Laptev Sea(Figure 1). Its drainage area is about 2,430,000 km2, mainlycovered by forest and underlain by permafrost. The LenaRiver 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 largerivers, the Lena basin has less human activities and muchless economic development [Dynesius and Nilsson, 1994].There is only one large reservoir in the Vilui subbasin. Alarge dam (storage capacity 35.9 km3) and a power plantwere completed in 1967 near the Chernyshevskyi(112�150W, 62�450N). This reservoir is used primarily forelectric power generation: holding water in spring andsummer seasons to reduce snowmelt and rainfall floodsand releasing water to meet the higher demand for power inwinter [Ye et al., 2003]. Various type of permafrost existsin the Lena basin, including sporadic, or isolated permafrostin the source regions, and discontinuous and continuouspermafrost in downstream regions (Figure 1) [Brown et al.,1997]. Approximately 78–93% of the Lena basin is under-lain 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 tempera-ture, river ice thickness, dates of river freezeup and breakup,have been carried out systematically by the Russian Hydro-meteorological Services and the observational recordswere quality-controlled and archived by the same agency[Shiklomanov et al., 2000]. The discharge data are nowavailable from the R-ArcticNet (v4.0), a database of Pan-Arctic River Discharge during 1936–2000 [Lammers et al.,2001]. In this analysis, long-term monthly discharge recordscollected at 9 stations (A–H and K) along the main stemand 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 byInternational Permafrost Association (IPA) [Brown et al.,

Figure 1. The Lena River watershed and hydrological stations (A through K) used in this study. Alsoshown are the reservoir location on the Vilui River and the permafrost distribution [Brown et al., 1997,2001] over the Lena basin.

D07102 YE ET AL.: STREAMFLOW REGIME VERSUS PERMAFROST COVERAGE

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1997, 2001]. The shapefiles were derived from the original1:10,000,000 printed map. The IPA permafrost map wascategorized as continuous (90–100%), discontinuous (50–90%), isolated (10–50%), and sporadic (0–10%). Thecoverage of permafrost (CP) in a basin has been determineddifferently [McClelland et al., 2004; Zhang et al., 1999].Most studies consider permafrost existence [Smith et al.,2007; McClelland et al., 2004] and determined the totalcoverage of permafrost (4 types of permafrost) [McClellandet al., 2004]. In this study, basin and subbasin permafrostareas are determined by overlaying the permafrost map tothe river network map. Basin/subbasin boundaries anddrainage areas are derived from 1 km DEM data, the USGSGTOPO30 data set [Bliss and Olsen, 1996]. The drainageareas from the 1km DEM match well to those reported bythe Pan-Arctic River Discharge Database [Lammers et al.,2001], with the relative errors being less than 15% for thesubbasins. The coverage of permafrost in a basin is definedas the weighed average of the 4 different types of perma-frost. Considering the ranges of permafrost coverage, wetake the mean coverage as representative coverage for everypermafrost type, i.e., 95%, 70%, 30% and 5% permafrostcoverage in continuous, discontinuous, isolated and sporadicareas, respectively. Variations from the mean CP are ±5%,±20%, ±20% and ±5% for continuous areas, discontinuousareas, isolated areas, and sporadic permafrost, respectively.[8] The methods of analyses include calculation of

monthly mean discharge and hydrographs for the nestedsubbasins within the Lena watershed, determinations ofratio of monthly high to low flows, and examination ofthe relation between the ratio and permafrost coverage overthe nested subbasins. We compare the ratio between pre-damand post-dam periods to quantify and discuss reservoirimpact on streamflow regime and change. We conduct trendanalysis to define the long-term changes in hydrographs anduse the Student t test to determine the statistical significanceof the trends. Furthermore, we compare the ratio trendsamong the subbasins to understand the regional differencesin streamflow characteristics and changes. We also usemonthly precipitation (P) and temperature (T) data [Jones,1994] for the Siberian regions and calculate the basin meanvalues 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 basinpermafrost extent and streamflow regime.

3. Results

3.1. Hydrographs

[9] Figure 2 shows the mean monthly discharge at the9 stations from the upper to lower Lena basin. Theygenerally have similar runoff regimes, i.e., high dischargein summer and low flow in winter. However, the differenceamong them is very obvious. The large difference is seen inthe peak flow, both in rate and timing. Lena river peakdischarge is mainly related to snowmelt [Yang et al., 2007;Ye et al., 2003], as it varies over the basin. The mean peakflow is about 210 m3/s at the Kachug station located in theupper basin (station A in Figure 1), due to increasing drainagearea, it gradually grows to 74,000 m3/s at the basin outlet(the Kusur station, K in Figure 1). The monthly peak flowoccurs in May in the upstream source regions (stations A–D)and in June over the downstream regions (stations E–Hand K), because early snowmelt in the source regions andlater 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 isabout 22 m3/s at the Kachug station (A in Figure 1) and itgradually increases to 1100 m3/s at the basin outlet (K inFigure 1). The lowest flow occurs in February in theheadwaters (stations A–E), in March over the middlestreams (F–G), and in April in downstream (stations Hand K). This pattern, early low flow in the source regionsand late low flow in lower basin, is related with the timingof snowmelt and hydraulic routing of flow. Also, the timingof snowmelt usually dictates the timing of discharge reces-sion. Usually early (late) snowmelt is associated with early(late) peak and subsequently early (late) low flow. Figure 2clearly illustrates the variation of hydrographs over the Lenabasin. The difference in hydrographs reflects basin climaticand physical characteristics, particularly permafrost condi-tions. Among other measures, the high and low flowsdetermine the hydrograph shape. The ratio of monthlymaximum discharge (Qmax) to minimum discharge (Qmin)is a direct measure of hydrograph shape and hydrologicregime [Woo, 1986; Kane, 1997]. This ratio can alsoindicate streamflow regime changes caused by reservoir

Table 1. List of Hydrologic Stations Used in This Studya

Station Code(see Figure 1) Station Name/Location

Latitude(�N)

Longitude(�E) Data Period

Drainage Area(�1000 km2)

Annual Runoff

% km3 mm %

A Kachug 53.97 105.88 1936 1990 17 0.7 2.9 164.0 0.5B Zhigalovo/Upper Lena 54.82 105.13 1969 1977 30 1.3 3.8 124.6 0.7C Gruznovka/Upper Lena 55.13 105.23 1912 1990 42 1.7 6.2 148.0 1.2D Ust’-Kut/Upper Lena 56.77 105.65 1936 1986 71 2.9 10.1 141.9 1.9E Zmeinovo/Upper Lena 57.78 108.32 1936 1990 140 5.8 35.4 253.1 6.7F Krestovskoe/Upper Lena 59.73 113.17 1936 1999 440 18.1 131.3 298.5 24.8G Solyanka/Upper Lena 60.48 120.7 1933 1999 770 31.7 213.5 277.2 40.4H Tabaga/Upper Lena 61.83 129.6 1936 1999 897 36.9 221.0 246.4 41.8I Verkhoyanskiy Perevoz/

Aldan subbasin outlet63.32 132.02 1942 1999 696 28.6 166.0 238.5 31.4

J Vilyuy/Vilui valley outlet 63.95 124.83 1936 1998 452 18.6 46.7 103.3 8.8K Lena At Kusur 70.68 127.39 1934 2000 2430 100.0 528.6 217.5 100.0

aStations A–H are listed from upstream to downstream.


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regulation [Ye et al., 2003; Yang et al., 2004a, 2004b]. Icejams in the northern regions affect hydrograph in spring. Inthis study, we use monthly maximum and minimum dis-charge to determine both the hydrograph shape and thecalculation of the ratio. We did not use any daily (maximumand minimum) discharge. This may help to eliminate orsmooth 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 down-stream. The mean Qmax/Qmin are about 13–16 in the sourceregions (stations A–E), and increases from 21 in middleupper Lena (station F) to 74 at the outlet station (stations K).The ratio increases with drainage area (Figure 3). Thispositive relationship is different from nonpermafrostregions/basins, where the ratio decreases with basin area.

3.2. The Relationship Between Qmax/Qmin Ratio andCoverage of Permafrost (CP)

[12] The permafrost distribution varies from sporadic inthe source regions to continuous permafrost over the Lena

basin (Figure 1). The extent of permafrost graduallyincreases from 20% in the headwaters to 86% in down-stream regions (Figure 3). The Qmax/Qmin ratios are low(10–20) for CP less than 40%, and moderate (20–30) forCP interval of 60–75%, and high (about 70–80) for CPgreater 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 istherefore critical to use pre-dam and natural flow data forregional hydrology analyses. Using the flow data from theupper Lena without dam regulation and the pre-dam data forthe basin outlet, we conducted regression analysis betweenthe Qmax/Qmin and CP. The result reveals a significantrelationship (significant at 99%, Figure 4). This relationshipclearly indicates the effect of permafrost distribution ondischarge process. Permafrost regions/basins have low in-filtration and limited subsurface storage capacity [Woo,1986; Kane, 1997; Woo et al., 2008]. Relative to non-permafrost or low permafrost basins, high permafrost basins

Figure 2. Monthly hydrographs at selected stations along the main river valley.

Figure 3. The mean ratio of Qmax/Qmin and coverage of permafrost (CP) versus drainage areas. Theratio for Kusur (station K) is for pre-dam data.


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have higher maximum discharge and lower minimum dis-charge, hence higher ratio of Qmax/Qmin. Figure 4 showsthat the permafrost condition does not significantly affectstreamflow regime over the low permafrost regions (i.e., CP< 40%), and it strongly affects discharge regime for regionswith high permafrost coverage (i.e., CP greater than 60%).It is useful to determine this threshold of permafrost impactto regional hydrology, particularly in regions undergoingclimate warming and permafrost degradation. Further anal-yses over broader regions are necessary to refine and verifythe relation and threshold.[14] The Qmax/Qmin–CP relation has been derived for

the nested basins from the upper Lena to the basin as awhole. To test the relationship, two independent subbasinswithin the Lena watershed (i.e., the Aldan and Vilui sub-basins, stations I and J in Figure 1) have been included inFigure 4. These two tributaries have very high CP, 92%and 95% for the Aldan and Vilui, respectively. There is areservoir in the upper Viliu valley, with a storage capacity of36 km3, or about 77% and 7% of annual discharge at Viluioutlet and Lena basin mouth. Operation of this dam haschanged streamflow regimes [Ye et al., 2003]; it reduced thepeak flows by about 30% and enhanced low flows by about27 times at Vilui outlet (station J in Figure 1). Because ofthese changes, the ratio of Qmax/Qmin sharply decreasesfrom 536 to 38 at the Vilui outlet (station J in Figure 1) andfrom 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 tocontinuous permafrost and very low winter flows in thenorthern parts of the Lena basin. The ratios and CP of thesetwo subbasins are generally consistent with the relationship,showing higher Qmax/Qmin ratios with higher CP. Further-more, we include the Yasachnaya Kolyma watershed ineastern Siberia for a comparison. This basin has highpermafrost extent (about 94%) and fits well with the curvederived from the Lena basin (Figure 4). These results mayindicate a general applicability of the relation over thenorthern basins. It is, however, important to recognize thelimitation of this relation. The Qmax/Qmin ratios can bevery high due to very low base flow over continuouspermafrost regions. For instance, winter base flow is ex-tremely low in the very cold Arctic coast watersheds withalmost 100% permafrost coverage, such as the Yana andOlenka basins near the Lena River.

3.3. Qmax/Qmin Ratio Changes Over Time

[16] It is difficult to survey permafrost change over largeregions. It is easy to calculate the ratio of Qmax/Qmin overa basin where discharge data is available. The relationshipbetween the Qmax/Qmin ratio and CP directly links stream-flow regime with basin permafrost coverage. The changes inthe ratio over time and space perhaps can, therefore, reflectbasin permafrost changes.[17] Figure 5 shows the time series of Qmax/Qmin ratio

during 1935–2000 at 3 tributary stations and at the Lenariver outlet. The ratio at the Tabaga station (H) in the upperLena varies from 16 to 48, with a mean of 28. The ratio does

Figure 4. The ratios of Qmax/Qmin versus coverage of permafrost (CP) at the nine stations from theupper Lena to basin outlet without reservoir regulation. Two additional stations (the Aldan and Viluisubbasins in Lena basin) and one additional basin (the Yasachnaya Kolyma River) in East Siberian arealso shown. The ratios of Qmax/Qmin are showed at the Vilui subbasin and Kusur at Lena basin outletwith reservoir regulation since 1967. Note: the Y axis is in logarithm scale.


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not show any trend, although it is obviously lower during1980–1998, with a mean of 26 due to higher Qmin. Theratio in the Aldan subbasin ranges from 24 to 177, with amean of 75. It has significantly (95% confidence) decreasedby 54 (�75%) during 1942–1998 due to a strong increasein Qmin. There are no dams in this tributary. The decreaseof the ratio is mainly due to increases in winter flows [Ye etal., 2003]. The ratio for the Vilui tributary varies between 6and 1,000. It has sharply decreased since 1966 when thedam went operational. The mean ratios are 531 and 15 forpre- and post-1967, respectively. The drop in ratio is causedby the operation and regulation of the Vilui reservoir around1967 [Ye et al., 2003], i.e., enhancing winter flows andreducing summer flows downstream of the dam. The ratio atthe Lena river outlet varies from 24 to 164, with a mean of60. It decreases over time, with the total trend of �58(nearly 95%) at 99% confidence during 1935–2000. Thisdecrease is mainly caused by reservoir regulation in theVilui valley.[18] Over the Lena basin, the Qmax/Qmin ratio has a very

strong decreasing trend for the Aldan valley. This change inratios depends on the max and min discharge. Monthly flowdata (Figures 6a and 6b) show that peak flow did not changemuch, and the low flows during November to April in-creased significantly by 50–117%, (99% significant level)

over the study period and the total trend was 114% for theQmin during 1942–1999 (Figures 6a and 6b). Low flowchanges are particularly strong during 1976–1999, with astep rise from 200–400 m3/s to 600–800 m3/s in April.There are large fluctuations in the low flow records over thestudy period. It is important to note the consistency in theinterannual variation of low flow among the months, i.e.,high flows in early winter translating to high flows in latewinter.[19] In addition, regression analyses of the low flows

show high correlations (R2 = 0.73 to 0.94) between theconsecutive months during November to April (Figure 7).This result is expected, as the winter hydrology is domi-nated by discharge recession.[20] The ratio of monthly flows between consecutive

months, or monthly recession coefficient (RC), is a quan-titative measure of recession processes. The mean monthlyrecession coefficients for this subbasin ranges from 0.62 inearly 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 coefficientover the study period shows significant increases (at 99%confidence) in most winter months, except an insignificantdecrease for December/November (Figure 8). IncreasingRC over time suggests decreases in recession rate. Dis-

Figure 5. The ratio of Qmax/Qmin (a) at stations of Tabaga in upper Lena and Verkhoyanskiy Perevozin Aldan without dam regulation and (b) at Viluy in Vilui and Kusur at Lena outlet during 1935–2000.


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charge recession is generally a process of storage release.Studies report significant permafrost changes in this region,including warming of ground temperatures and deepeningof active layer depth [Pavlov, 1994; Frauenfeld et al., 2004;Zhang et al., 2005b; Romanovsky et al., 2007]. There seemsto be a general coherency between hydrology and perma-frost changes over this region, which deserves more re-search attention.

4. Discussion

[21] In addition to permafrost conditions, other factors,such as geography, geology, and climate also influencestreamflow regimes in the northern regions. Data availabil-ity is a limitation for most arctic research, including thisstudy. To understand the climate effect on permafrost andbasin hydrology, we have obtained monthly precipitationand temperature data from CRU [Jones, 1994] for theSiberian region and calculated the basin mean values forthe upper Lena, Aldan, and Vilyuy subbasins. Using thesedata, we examine precipitation and temperature patternsover the subbasins and their relationships with basin per-mafrost 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 controlslarge-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 rea-sonable, as in the northern regions and watersheds, snowfallaccumulates over winter season and snowpack melt inspring produces the highest floods.[23] Monthly mean temperatures also have similar pat-

terns among the subbasins (Figure 10b). To relate temper-ature with permafrost conditions, previous studies usevarious temperature indexes, including seasonal and yearlymeans and the freezing index (FI). FI is defined as thecumulative 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 rangefrom �140 to �175�C for the 3 tributaries.[24] There is a good relation between the FI and perma-

frost extent (coverage of permafrost, CP), i.e., CP increasewith FI for the 3 tributaries (Figure 11a). This result, asexpected, indicates cold climate leads to high coverage ofpermafrost. This relation is very important, as it relatesbasin thermal condition with permafrost distribution. Ouranalyses have already established the relationship betweenpermafrost extent and flow regime. The combination ofrelations 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

Figure 6. (a) The maximum monthly discharge and (b) the monthly discharge during low-flow monthsduring cold season at Aldan station during 1942–1999.


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rivers in cold regions have very low base flows and veryhigh peak flows, consequently high Qmax/Qmin ratio. It isimportant to mention that monthly T data have been used inthis analysis for the determination of FI over the subbasins.There might be uncertainties in the FI calculations particu-larly during the early and late winter periods when themonthly T is close to 0C. Daily T data can better define theFI, but the data was not available to this study for the Lenabasin. It is expected that the relationship of T with CP andQmax/Qmin ratio may improve when daily T data are usedin future analyses.

[26] This study found significant winter flow increaseover the Aldan subbasin. Other analyses also reported baseflow rise over the large northern watersheds, such as theLena basin [Ye et al., 2003] and Yukon river [Walvoord andStriegl, 2007]. Base flow changes are likely related withchanges in subsurface processes and frozen ground con-ditions in northern regions. Liu et al. [2003] documentedsignificant of winter discharge in the source areas of theSonghuajiang river with high permafrost extent in thenortheast China, and related this change to the warmingof ground temperatures and deepening of active layer depth.Studies show that active layer increase affects runoffcharacteristics in a small headwater catchment (MogotRiver) 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] reporteda long recession to the slow drainage of water from athawing active layer in northern Alaska. These changes inbase features may be due to changes in storage capacity andamount 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 there-fore difficult to accurately determine their changes overtime. The basin storage capacity is a measure of ground-water reservoir. A large storage capacity leads to a slowrecession. For a given storage capacity, a large storageamount 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 overwinter. River discharge increased over the Aldan basin inwinter during 1940–1999 (Figure 6b), suggesting storageamount did increase over time. This increase should lead toa fast recession, but, in fact, recession slows down in mostwinter months (Figure 8). This may imply the increase ofbasin storage capacity. In addition, Ye et al. [2003] foundthat discharge increase in November is the strongest overthe winter months over the Lena basin. This suggests morestorage of water in November over the basin and a fastrecession. However, RC decreased in December/November,this may imply that the negative effect of increased storageamount on RC may overcome positive effect of increasedstorage capacity. More research is necessary to investigatethe linkage between changes in subsurface storage and riverstreamflow.

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 hydro-logic regime. They increase with drainage area from theheadwaters to downstream within the Lena basin. Thispattern is different from the nonpermafrost watersheds.The ratios also change with basin permafrost coverage,suggesting that permafrost affects regional hydrology. Re-gression analysis between the Qmax/Qmin ratio and basinpermafrost coverage reveals a significant relationship at99% confidence. This relationship quantifies the effect ofpermafrost distribution on discharge process. It shows thatpermafrost conditions do not significantly affect streamflowregime over the low permafrost (less than 40%) regions, andit strongly affects discharge regime for regions with high

Figure 7. The relationship of discharge between theconsecutive months in low-flow periods at Aldan during1942–1999.


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Figure 8. The monthly recession coefficient between the consecutive months in low-flow period atAldan during 1942–1999.


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(greater than 60%) permafrost coverage. It is important todefine this relation of permafrost impact to regional hydrol-ogy, as this knowledge will be useful for further investiga-tion into permafrost effect on basin hydrology over the largenorthern regions. Temperature and precipitation have similarpatterns among the subbasins. Basin precipitation has littleassociation with permafrost conditions. There is a reason-able relation between the FI and permafrost extent over thebasin, indicating that cold climate leads to high coverage ofpermafrost. This relation relates basin thermal conditionwith permafrost distribution. The combination of the rela-tions 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 ratiosshow different results over the Lena basin. The ratiossignificantly decrease in the Vilui valley and at the Lenabasin outlet due to dam regulation. In the unregulated upperLena regions, the ratios do not show any trend during

Figure 9. The basin annual precipitation versus CP for thethree tributaries (Upper Lena, Aldan and Vilui) in the LenaRiver basin.

Figure 10. (a) The basin monthly mean precipitation and (b) the temperature for three tributaries inLena River.


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1936–1998. This may imply that the permafrost changes inthe region were not sufficient enough to affect hydrologicalprocesses. In the Aldan tributary without regulation, theratios significantly decrease due to increase in base flowduring 1942–1998. This change is consistent with perma-frost degradation over the eastern Siberia. This consistencyto some extent verifies permafrost influence on basinstreamflow process and change. Our efforts continue torefine this relationship for various climate and permafrostconditions in the high latitude regions.

[30] Acknowledgments. This study was supported by National BasicResearch Program of China (2007CB411502), Innovation Project of CAS(KZCX3-SW-345), USA NSF grants 0230083, 0612334 and 0335941 andInternational 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, ChineseAcademy 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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Variation of hydrological regime with permafrost … sources...hydrological regime and permafrost coverage over nested subbasins within the Lena River in Siberia. It analyzes monthly