Active layer depth as a key factor of runoff formation in permafrost: process analysis and modelling using the data of long-tem observations Lyudmila Lebedeva 1,2, Olga Semenova 2,3 1 St.Petersburg State University 2 Hydrograph Model Research Group 3 State Hydrological Institute, St. Petersburg, Russia

Objectives 1.Establishment of observations database for the period 1948 – To analyze the patterns of distribution of active layer depth in different landscapes 3.To assess the main factors determining active layer depth 4.To estimate physical properties of the soil strata and simulate the process of soil freezing and thawing in different landscapes 5.To simulate runoff using the same set of parameters as in active layer depth modelling

Fig.1. Sketch of the KWBS Study area Kolyma water-balance station (KWBS) Kolyma water-balance station (KWBS) – small research watershed (22 km 2 ) in the upper Kolyma river; observations since 1948 Watershed boundaries Meteorological Station Rain gauge Recording rain gauge Pit gauge Snow survey line Cryopedometer Evaporation plot Pan evaporation plot Snow evaporation plot Water balance plot Mean annual temperature – -11,6 0 C Precipitation – 314 mm/year Open wood, bare rocks Continuous permafrost High-mountain relief Representative for the North-East of Russia

KWBS instrumentation Measured parameters Observation period Temporal resolution Number of stations Stream flow1948–cont. Minute Daily 7 Meteorological observations 1948–cont.3h1 Precipitation1948–cont. Minute Pentad, decade in winter, daily in summer Decade Month Snow surveys1948–cont.Monthly (October – March), decadely (April…)5 Evapotranspiration1958–cont.Pentade4 Snow evaporation1958–cont.September – October, March – April (12-hourly)1 Pan evaporation1970–cont.Decade1 Energy balance1958–cont.Decade1 Soil freezing/thawing1958–cont.Once in 5 days5 Soil temperature at depths 0.1 – 3.2 m 1974–1981Daily1 Flow water chemistry1958–cont.Event based2

Hydrograph ModelR Deterministic distributed model of runoff formation processes Single model structure for watersheds of any scale Adequacy to natural processes while looking for the simplest solutions Minimum of manual calibration Forcing data: precipitation, temperature, relative humidity soil and snow state variables Output results: runoff, soil and snow state variables, full water balance

Landscapes The landscapes vary with altitude from stone debris to swamp forest Fig.2. The main landscapes of KWBS

Active layer depth in different landscapesUpper part of the slope: Lower part of the slope: clay slate rock debris rock debris absence of vegetation absence of vegetation peaty ground peaty ground swamp larch forest swamp larch forest

Soil properties The main parameters for simulation soil thawing and freezing processes in the Hydrograph model are physical soil properties Porosity, % Field capacity, % Heat capacity, J/m 3 *K Heat conductivity, W/m*K Peat Clay slate Crushed stone Crumbling rock

Slope aspect Slope aspect in mountain relief of KWBS controls both landscape and active layer depth because of different solar radiation income Fig.4. Direct solar radiation income during the year for north-and south-facing slopes Fig.2. The main landscapes of KWBS Fig.3. Domination of north- and south-facing slopes within KWBS Northern aspect Southern aspect

Active layer depth modelling Site 1 (subcatchment Severny): South-facing slope Absence of vegetation Rock debris Active layer depth up to 1.7 m m Site 2 (subcatchment Yuzhny): North-facing slope Sphagnum, shrubs Soil profile – peat, clay loam, clay slate Active layer depth up to 0.7 m Fig.5. Observed and calculated active layer depth in two landscapes, KWBS

Runoff modelling – slope scale Subcatchment Severny: 0.41 km 2 South-facing slope Sparse vegetation Thin soils and rock debris Subcatchment Yuzhny: 0.27 km 2 North-facing slope Moss, shrubs, open wood Soil profile – peat, clay loam, clay slate Fig.7. Observed and simulated runoff, Severny, 1981–1982Fig.8. Observed and simulated runoff, Yuzhny, 1981–1982

Runoff modelling at the Kontaktovy watershed (21,7 km 2 ) Different slope aspects, soil and vegetation were combined into 3 runoff formation complexes (RFC) For each RFC the set of parameters verified against active layer depth and runoff in subcatchments was used

Conclusions 1.Active layer depth has high variability and is determined mainly by landscape 2.The landscapes vary consecutively from stone debris with no vegetation in the top of the slope to swamp forest next to the stream body 3.The main parameters for computing water and heat dynamic in soils are its physical properties 4.Long-term observations accompanied with description of soil and vegetation properties may serve as a base for reliable estimation of the model parameters which can be transferred to the basins with limited data

Acknowledgements This study was conducted within the research grant provided by Russian-German Otto-Schmidt Laboratory for Polar and Marine research in 2010 The attendance to EGU 2011 was made possible with additional support of Russian-German Otto- Schmidt Laboratory for Polar and Marine research

Hydrograph Model Research Group

More results in the Canadian discontinuous permafrost environment on… Thu, 07 Apr, 11:30–11:45, Room 38 EGU “Parameterisation by combination of different levels of process- based model physical complexity” by Pomeroy, Semenova, Lebedeva and Fang Thank you for attention!