Estimation of water balance in and around the Mittivakkat Glacier basin, Ammassalik Island, southeast Greenland

Northern Research Basins Water Balance (Proceedings of a workshop held at Victoria. Canada, March 2004). IAHS Publ. 290, 2004 129 Estimation of water balance in and around the Mittivakkat Glacier basin, Ammassalik Island, southeast Greenland BENT HASHOLT & SEBASTIAN H. MERNILD Institute of Geography, University of Copenhagen, 0ster Voldgade 10, DK-1350 Copenhagen K, Denmark bhfsjgeogr.ku.dk Abstract The arctic alpine landscape on Ammassalik Island features catchments with varying glacier coverage. Climatic data from three stations were analysed, water balances were calculated, and the problems in estimating the water balance in this type of catchment are discussed. Potential évapotranspiration according to Makkink (1957) varies from 379 mm year' 1 to 400 mm year" 1 ; corrected precipitation varies between 1036 mm year" 1 and 1255 mm year" 1 ; and modelled runoff from 702 mm year" 1 to 1708 year" 1 on a 4-year average. Comparisons of modelled runoff with measured values indicate that the higher runoff values, based on corrected precipitation, are in the right order of magnitude. The high measured runoff values can partly be explained by excess runoff from glaciers in the area having a negative annual mass balance. Key words glacier; low arctic area; Sermilik; southeast Greenland; Tasiilaq; water balance INTRODUCTION Glaciology investigations were initiated by Milthers in 1933 in the Ammassalik region of Greenland; Milthers visited a number of glaciers and took stereoscopic pictures of the Mittivakkat Glacier. Fristrup (1961) followed up on this research as a contribution to the International Geophysical Year (IGY, 1957-1958); the first measurements of runoff and climate were carried out simultaneously by Valeur (1959). After a decade, in 1969 Fristrup started up research on the Mittivakkat Glacier again and a permanent station, the Sermilik Station, was built in 1970. The focus of these studies were glacier mass balance and glaciology; however, in 1972 measurements of sediment transport were carried out (Hasholt, 1976). The station had been used for teaching purposes and different projects related to the development of hydropower in the area. In the late 1980s the focus shifted toward process studies related to the catchments. In the early 1990s, grants from the Danish Natural Science Research Council made establishing automatic recording stations possible. Until then, only analog recording had been carried out during the stay of field crews, since the station was not permanently manned throughout the year. The aims of this paper are to describe the present monitoring programme at the Mittivakkat Glacier basin and its data, and to discuss the difficulties encountered when monitoring in this environment as well as their influence on the reliability of water balance calculations. Because of the difficulties in obtaining complete field data for all seasons, modelling and subsequent water balance calculations are considered important means to bridge the gaps.

130 Bent Hasholt & Sebastian H. Mernild LOCATION AND SETTING The Sermilik Station is located in the Mittivakkat Glacier basin, on Amraassalik Island, southeast Greenland at 65 41'N 37 48'W, approximately 15 km northwest of Tasiilaq (Ammassalik). The main catchment of interest is the one drained by the outlet from the southwestern most part of the Mittivakkat Glacier (Fig. 1). The glacier complex has several outlets and covers about 31 km 2 of the central western part of Ammassalik Island. The investigations cover only the parts of the glacier (20 km 2 ) that drains west to the Sermilik Fiord and south toward the fiord at the town of Tasiilaq (Fig. 1). The percentage of glacier area is largest for the proglacial valley, approximately 78%, and for the part draining through a string of lakes toward the outlet at Lake Kuutuaq it is approximately 20%> (Fig. 1). A M M A S S A L I K 0 Lake Kuutuaq 7 Station Nunatak The Sermilik Station imartivapqacitiai tsotias Field, - 9 T 0 VftgnsFjota $3* Ikkattoq iu i Immikkeerteq. Attpreq i s ''9Tunutie<t... Aarartiangaaq (Prœstefjeld) Meteorological Station, Tasiilaq n r \ V ;;U«nriflo»rjq ' VT.-."' "T^oqqartrvflkâjik. Fig. 1 The Ammassalik Island, South East Greenland, including the Sermilik Station, the Mittivakkat Glacier and the Meteorological Station in Tasiilaq (Ammassalik) (Source: Greenland Tourism).

Estimation of water balance in and around the Mittivakkat Glacier basin, Ammassalik Island 131 The relief is alpine with peaks around 1000 m a.s.l. A major part of the area west of the Mittivakkat Glacier has levels around 200-400 m a.s.l., crisscrossed by fissure valleys eroded by local glacial activity or nivation. The valleys run mainly in a westerly direction toward the coast at the Sermilik Fiord, whereas the valleys east of the glacier are shorter and lead to a larger north-south oriented valley ending in the fiord at Tasiilaq. To the south and east the bedrock under the glacier is the Ammassalik Intrusive Complex (AIC), and at the western margin and west of the glacier the bedrock is biotite-bearing garnet-granite gneiss (GGG) (Friend & Nutman, 1989). Bare bedrock dominates the area, and loose sediments are found as talus and debris flow deposits at the lower part of the slopes. In the valley bottoms morainic deposits or sediments of fluvial origin are found. A tidal delta is developed at the coast, at the outlet from the Mittivakkat Glacier river. At all other locations the coast is steep and rocky. Minor aeolian deposits are found at higher levels in the delta. The soil is a weakly developed podsol and located on morainic or fluvial deposits. Sporadic peat soils are observed, yet these are too shallow to qualify as histosols. The vegetation is sparse, with Betula and Salix shrubs covering lower areas that have not recently been covered by glacier or by part of active flood plains. The talus of south-facing slopes is often covered with lush grass and herbs. Larger areas of grass are found on a delta deposit east of Lake Kuutuaq (Fig. 1). Lichens and mosses cover the rocks, and the density of the coverage depends on the amount of time since the rocks became ice-free. INSTRUMENTATION AND DATA COLLECTION At the meteorological station at Tasiilaq (Fig. 1), standard synoptic climatic data has been obtained since 1897. To provide more useful information on the local climate and the orographic effects near the Mittivakkat Glacier, two local climate stations were established. Station Nunatak was established in 1993 on a nunatak 515 m a.s.l. located at the northern flank of the glacier, at the equilibrium line, and Station Coast was established in 1997 on a rock hill close to the coast about 25 m a.s.l. (Fig. 1). Station Nunatak records climate data at two levels; 2 m and 4 m above the ground (since August 1993), while Station Coast only records at 2 m above the ground (since May 1998). The two climate stations collect data every 3 h: wind speed, wind gust, wind direction, air temperature, ground temperature, relative humidity, incoming and outgoing short-wave radiation, net radiation and liquid precipitation (summer only, from June to September). Both stations are manufactured by Aanderaa, except for the raingauge at Station Coast, which is a Davis tipping bucket. Snow depth is recorded separately by an ultrasonic sensor (a Campbell SR50), initially located on the Mittivakkat Glacier and later, in August 1999, moved to Station Nunatak; both locations are at the equilibrium line. A second ultrasonic sensor is located at the Mittivakkat Glacier River, at Isco Island, in order to monitor the water level at the river during the summer season. During the winter season when the river is frozen, the sensor is used to monitor the accumulation of snow and ice in the valley. Discharge is measured using a current meter (Ott C31 and C2), and a stage-discharge relationship is established and used together with the water level measurements to calculate hourly

132 Bent Hasholt & Sebastian H. Memild discharge values for the summer period. Since 2002 an EnviroMon pressure transducer (DIVER) has been tested in a lake at the glacier terminus and in Lake Kuutuaq (Fig. 1). Satellite images and maps based on aerial photos of the catchments are available: a 5 m contour map (1:5000; 1972) covering most of the Mittivakkat Glacier and the coast, a 10 m contour map (1:20 000; 1981) covering only the Mittivakkat Glacier and a commercial hiking map (25 m contour, 1:100 000; 1981) of the whole area (Fig. 1). Based on these maps a digital elevation model (DEM, 100 x 100 m grid) has been produced. Daily photos are taken with an automatic camera from both the pro-glacial valley (Fig. 2) and a part of the Mittivakkat Glacier; these are used to follow the extent of snow coverage. The camera system was developed by Hinkler, Institute of Geography, University of Copenhagen, Denmark...... Fig. 2 An example of the photographic time lapse from the pro-glacial valley at Sermilik. The photos were taken at 12-noon every day from September 2002 to May 2003.

Estimation of water balance in and around the Mittivakkat Glacier basin, Ammassalik Island 133 WATER BALANCE COMPONENTS AND ESTIMATION The elements of water balance for a watershed depend upon watershed characteristics and processes. The usual formation of the water balance equation for a catchment with glaciers is: (P.ino\v Pyain) ~ Ea (Rsnow Ryain Pice Rgyowid) ~ (ASsnow ^ ASjce ASgyound) ~ T) ( 1 ) where P is the precipitation input from snow and rain (mm); Ea is the evaporation/sublimation output (mm); R is the baseflow and surface runoff from rain, snow and ice (mm); AS is changes in water storage within the catchment from snow, ice and groundwater (mm); and n is the balance discrepancy (error term). The error term should be 0 if the four major components (P, Ea, R and LSS) on the left side of the equation have been determined correctly. Precipitation Six-hour values of the precipitation and phase are available all year round from the meteorological station in Tasiilaq. A scheme for correction of liquid and solid precipitation on Greenland was developed by Allerup et al. (1998, 2000b) and applied to the precipitation data from the meteorological station. A correcting procedure was used that was valid for wind speeds under 8 m s" 1 and 15 ms" 1 for solid and liquid precipitation, respectively. For this procedure, the air temperature needs to be higher than -20 C and precipitation intensity, less than 15 mm h" 1. At the climate stations, Station Nunatak and Station Coast, the measured liquid precipitation (P ra i ) is used without correction because the orifice of the gauge is located about 50 cm above the ground, which is approximately the height of local roughness elements. The solid precipitation (P OT0,) is measured using an ultrasonic sensor; the amount is determined from the rise in the accumulation curves of the recorded snow depth (A5 S 0W ). When noise is removed, the rise in snow depth is multiplied with a variable density for snow as a function of air temperature (Brown et al, 2003) and with an hourly settling rate for the snow pack (Anderson, 1976), to estimate the water equivalent precipitation. Snowmelt and glaciermelt As a first approximation, a simple degree-day model, with a melt threshold at 0 C and a 3 mm/degree-day factor (both constant in time and space), has been applied to calculate the snowmelt (R sn0 w) and the glaciermelt (Ri Ce ). Furthermore, detailed studies of different energy balance models SMELT (Sand, 1990) and ENBAL (Liston, 1995; Liston & Hall, 1995a,b) have been applied to test the validity of the degree-day model. Potential évapotranspiration and actual évapotranspiration The potential évapotranspiration (Ep) (reference évapotranspiration) is needed to calculate the actual évapotranspiration (Ea). Due to its simplicity the Makkink (1957)

134 Bent Hasholt & Sebastian H. Mernild formula, using only incoming short-wave radiation and air temperature has been applied for calculation of the potential évapotranspiration. Furthermore, actual evaporation (sublimation) has been calculated using SnowTran-3D by Liston & Sturm (1998) for a single winter (from September 1997 to June 1998) (Hasholt et al, 2003) but in the present investigation the actual évapotranspiration has been calculated using a soil water budget method developed by Thornthwaithe & Mather (Mather, 1961). Storage terms Actual glacier storage (A5, ce ) has been measured using stakes and snow surveys, along transects with 100 m spacing to calculate the winter, summer and net balance (Knudsen & Hasholt, 1999, 2003). Internal accumulation like refreezing of meltwater within the snow cover and superimposed ice formation have not been calculated or included in the winter, summer and net balances. Soil moisture Soil moisture {L\S gwmd) has not been measured, due to the large areas of bedrock and thin till covers. The amount of water at field capacity used in calculations of actual évapotranspiration has been set to 50 mm for non-glacier and non-bedrock areas. Runoff Runoff (Rtotai) from the Mittivakkat Glacier stream has been calculated using yearly stage-discharge relationships found by regression analysis. On a monthly basis the water available for runoff from the three stations has been calculated using the Thornthwaithe-Mather method mentioned above, supplied with snow reservoir calculations that keeps track of the snow storage and the melting based on the simple degreeday model described above. RESULTS Figure 3 shows monthly average values: wind speed (2 m), air temperature (2 m), relative humidity (2 m) and liquid precipitation (summer precipitation) for Station Nunatak and Station Coast based on data from 1993 to 2002 and 1998 to 2002, respectively. The liquid precipitation at Station Nunatak is remarkably low, in spite of its higher altitude, between 35-37 mm month" 1 (Fig. 3). To elucidate the representivity ofthe air temperature from the shorter measurement periods (Station Coast and Station Nunatak), long-term records of air temperature and precipitation from the Tasiilaq meteorological station (1897-1997, except 1910-1911) are shown in Fig. 4. The decrease in temperature at Station Coast is confirmed by observations of temperature at Isco Island. Monthly and seasonal runoff values from the Mittivakkat Glacier

Estimation of water balance in and around the Mittivakkat Glacier basin, Ammassalik Island 135 -SN: Wind Speed SN: Air Temperature -SC: Wind Speed -SC: Air Temperature ISN: Precipitation - - SN: Relative Humity 3SC: Precipitation -SC: Relative Humity Fig. 3 Monthly average values: wind speed, air temperature, relative humidity and liquid precipitation (summer precipitation) from Station Nunatak (SN) and Station Coast (SC) at Sermilik. The average values from SN are based on data from 1994-2002 and SC on data from 1998-2002. 1897 1907 1917 1927 1937 1947 1957 1967 1977 1987 1997 EBB MST: Precipitation MST: Air temperature SN: Air temperature S C : Air Temperature Fig. 4 Yearly mean air temperature and sum precipitation from the Meteorological Station at Tasiilaq (MST) (1897-2002) (DMI), and air temperature from Station Nunatak (SN), Sermilik (1994-2002), and Station Coast (SC), Sermilik (1998-2002). Data at MST are missing in the period from September 1910 to August 1911. Table 1 Runoff from the Mittivakkat Glacier river (1999-2002) calculated by yearly stage-discharge relationships. Notice the different runoff periods. Year Runoff period Jun Jul Aug Sep Sum (mm) (mm) (mm) (mm) (mm) 1999 24 Jun-19 Sep 13 223 656 93 984 2000 8 Jun-17 Sep 304 683 682 341 2010 2001 26 Jul-21 Sep No data 61 305 132 498 2002 4 Jun-5 Sep 671 742 690 11 2130

136 Bent Hasholt & Sebastian H. Mernild Table 2 Water balance from cases 1 to 3 on a four-year average (1998-2002). Ta: Air temperature, P: Precipitation, Ep: Potential evaporation, SN: Snow water equivalent, SM: Soil moisture, Ea: Actual evaporation, M: Snow melt, R: Surplus water for runoff and Rgl: Water from glacier for runoff. Snow melt and glacier runoff are calculated by a simple degree-day model, with a melt threshold at 0 C and a 3mm/degree-day factor constant in time and space. In case 2 and 3 summer precipitation is based on precipitation measurements and winter precipitation on the rise in the accumulation curves of the recorded snow depth. Case 1 OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP YEAR Ta(C) 0.4-2.0 -AA -5.7-7.9-7.6-2.6 1.7 4.9 6.6 6.3 4.3-0.5 P(mm) 32.4 118.4 100.3 136.8 137.0 117.9 65.4 70.0 80.6 30.4 78.6 123.0 1090.8 Ep (mm) 11.1 2.3 0.7 1.0 4.9 19.3 43.5 62.2 79.4 82.5 53.7 28.5 389.1 P-EP (mm) 21.3 116.1 99.6 135.8 132.1 98.6 21.9 7.8 1.2-52.1 24.9 94.5 SN (mm) 0.0 116.1 215.7 351.5 483.6 582.2 604.1 446.0 5.0 0.0 0.0 0.0 SM (mm) 50.0 50.0 50.0 50.0 50.0 50.0 50.0 50.0 50.0 2.9 27.8 50.0 EA (mm) 11.1 2.3 0.7 1.0 4.9 19.3 43.5 62.2 79.4 82.5 53.7 28.5 389.1 M (mm) 0.0 0.0 0.0 0.0 0.0 0.0 0.0 158.1 441.0 0.0 0.0 0.0 R (mm) 21.3 0.0 0.0 0.0 0.0 0.0 0.0 165.9 442.2 0.0 0.0 72.3 701.7 Case 2 OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP YEAR Ta(C) -0.5-1.9-3.8-5.0-7.4-6.8-2.3 1.8 3.1 4.6 4.9 3.4-0.8 P(mm) 111.2 162.4 82.0 169.0 150.2 92.2 58.4 115.4 82.3 42.0 62.7 126.7 1254.5 Ep (mm) 11.4 2.4 0.7 1.0 5.5 20.2 44.2 62.5 74.8 77.4 51.3 27.7 379.1 P-EP (mm) 99.8 160.0 81.3 168.0 144.7 72.0 14.2 52.9 7.5-35.4 11.4 99.0 SN (mm) 99.8 259.8 341.1 509.1 653.8 725.8 740.0 572.6 293.6 0.0 0.0 0.0 SM (mm) 50.0 50.0 50.0 50.0 50.0 50.0 50.0 50.0 50.0 50.0 50.0 50.0 EA (mm) 11.4 2.4 0.7 1.0 5.5 20.2 44.2 62.5 74.8 77.4 51.3 27.7 379.1 M (mm) 0.0 0.0 0.0 0.0 0.0 0.0 0.0 167.4 279.0 258.2 0.0 0.0 R (mm) 0.0 0.0 0.0 0.0 0.0 0.0 0.0 220.3 286.5 258.2 11.4 99.0 875.4 Case 3 OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP YEAR Ta(C) -2.1-5.2-6.0-7.7-10.7-9.6-4.0 0.3 4.2 6.0 5.2 1.6-2.3 P(mm) 41.5 122.8 90.1 130.1 106.6 134.3 93.4 101.1 37.4 34.1 34.2 110.3 1035.8 Ep (mm) 9.2 1.1 0.3 0.5 3.2 15.7 42.2 69.3 86.9 89.1 56.6 25.5 399.6 P-EP (mm) 32.3 121.7 89.8 129.6 103.4 118.6 51.2 31.8-49.5-55.0-22.4 84.8 SN (mm) 32.3 154.0 243.7 373.3 476.7 595.3 646.5 618.6 191.1 0.0 0.0 0.0 SM (mm) 50.0 50.0 50.0 50.0 50.0 50.0 50.0 50.0 50.0 50.0 50.0 50.0 EA (mm) 9.2 1.1 0.3 0.5 3.2 15.7 42.2 69.3 86.9 89.1 56.6 25.5 399.6 M (mm) 0.0 0.0 0.0 0.0 0.0 0.0 0.0 27.9 378.0 136.1 0.0 0.0 542.0 R (mm) 0.0 0.0 0.0 0.0 0.0 0.0 0.0 59.7 378.0 136.1 0.0 84.8 658.6 Rgl (mm) 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 421.9 483.6 144.0 1049.5 River (1998-2002) are illustrated in Table 1; because of the different length of the observation periods it is not possible to compare all months, and the seasonal amount represents a minimum of the annual runoff. Three cases of water balance calculations in and around the Mittivakkat Glacier Basin, using different combinations of data, are presented in Table 2 for 1998-2002. The first case uses corrected precipitation and air temperature from the Tasiilaq meteorological station, potential évapotranspiration (Makkink, 1957) calculated using air temperature from Tasiilaq, and incoming short-wave radiation from Station Coast. This setup theoretically represents the conditions in a sheltered valley in the inner part ofthe island. The resulting actual annual évapotranspiration is 389 mm year" 1 ; this is

Estimation of water balance in and around the Mittivakkat Glacier basin, Ammassalik Island 137 equal to the potential évapotranspiration, 389 mm year" 1 (see Table 2), because of the abundance of water in the soil moisture reservoir. The calculated annual runoff is 702 mm year" 1 (Table 2). The second case uses calculated winter precipitation based on snow depth variations from Isco Island (from September to June) and summer liquid precipitation (from June to September) data from Station Coast. The potential évapotranspiration is also calculated by air temperature and incoming short-wave radiation from Station Coast. This setup represents a coastal location in an ice-covered fiord having only seasonal snowcover. The resulting actual évapotranspiration is 379 mm year" 1, equal to the potential évapotranspiration, because of the high amount of precipitation (1255 mm year" 1 ). The annual runoff is 875 mm year" 1 (Table 2). The third case uses winter snow depth variations and summer liquid precipitation data, air temperature, and incoming short-wave radiation from Station Nunatak. Calculations are carried out both for melting of seasonal snowcover alone and for melting of a glacier. The actual évapotranspiration is 400 mm year" 1, equal to the potential évapotranspiration, independent of soil moisture. The runoff from the rainfall and seasonal snowcover is (117 + 542 mm year" 1 ) 659 mm year" 1 and, from the glacier, 1050 mm year" 1, resulting in a combined runoff of 1708 mm year" 1 from the Mittivakkat Glacier Basin (Table 2). The calculation indicates a negative mass balance for the glacier. Known information about glacier storage is found in Table 3, where the water equivalent at the end of the accumulation period (winter balance), at the end of the ablation period (summer balance), and the annual net balance for the glacier are illustrated. Investigations by Knudsen & Hasholt (2003) illustrate an average annual negative net balance (1998-2002) of 765 mm (Table 3). DISCUSSION Previous use of data has mainly focused on relating processes connected to variations in climatic parameters e.g. studies of soil evolution (Jakobsen, 1990) and sediment transport studies (Nielsen, 1994; Hasholt et al, 2000). With the recent holistic basinrelated process approach, a description of the water balance is an important control of accuracy for quantification and description of the ongoing processes. The problems of monitoring the parameters in the water balance, their influence on reliability, and the accuracy of the results are discussed below. Table 3 Actual change in glacier storage (winter, summer and net balance) at the Mittivakkat Glacier, measured by stakes and snow surveys (Knudsen & Hasholt, 2003). Internal accumulation like refreezing of meltwater within the snow cover and superimposed ice formation are not included in the winter, summer and net balance. Balance Year Winter balance (mm) (From October to June) Summer balance (mm) (From June to October) 1998/1999 980-1750 -770 1999/2000 1230-2060 -830 2000/2001 1180-2140 -960 2001/2002 1280-1780 -500 Average 1998-2002 1168-1933 -765 Net balance (mm)

138 Bent Hasholt & Sebastian H. Mernild The most difficult parameter to monitor in this environment is probably precipitation. As mentioned in Allerup et al. (1997, 2000a), the measurements from the precipitation gauge need to be corrected for aerodynamic error due to wind speed effects, when the orifice of the gauge is significantly above the ground. This precipitation correction procedure for Greenland by Allerup et al. (1997, 2000a) has caused an increase in the annual precipitation from Tasiilaq of approximately 26% (1998-2002), including a minor contribution caused by wetting loss. This is not an unrealistic correction, because earlier research in Greenland had shown both lower (21%) and higher (97%) correction values (Allerup et al, 2000b; F. Vejen, April 2004, personal communication). However, the correcting procedure involves different calculations for liquid and solid precipitation, and in the case of an alpine relief, as in this study area, the type of precipitation can be rain below and snow above a certain elevation. To carry out the proper correction procedure, knowledge about the type of precipitation, air temperature, and wind-field is therefore needed. In the case of snow, winddrift and sublimation from wind-blown snow might further complicate the correct estimation of incoming precipitation (Hasholt et al., 2003). Here the precipitation data from Tasiilaq has been calibrated against the measured winter balance on the Mittivakkat Glacier. As mentioned previously, the liquid precipitation from the climate stations (Station Nunatak and Station Coast) is used without any correction; because the orifice is close to the ground, underestimation of the liquid precipitation is approximately below 5%. Surprisingly, the recorded summer precipitation is higher at Station Coast (187 mm, Table 2) than at Station Nunatak (106 mm, Table 2), implicating a negative orographic effect. Possible explanations are: existence of a local condensation layer and cloud formation close to the coast and an underestimation of the precipitation at the Nunatak, which may occur because the anticipated liquid precipitation actually falls as snow at this higher altitude. The common decrease in temperature at Station Coast and Isco Island, both located close to the ice fjord, might be explained by the fact that the ice cover has diminished and the wind blows more frequently from the fjord toward the land. The winter precipitation is available from Station Nunatak, from the equilibrium line at the glacier, and from the gauging station at Isco Island in the pro-glacial valley. As point values, the results are reliable for calculations for the snow water equivalent (SWE). An attempt has been made to measure the SWE directly using a snow pillow; however, the attempt failed. The snow courses earned out to determine the winter balance were measured in transects with 100 m spacing. The result is estimated to be correct within ±15%. However, larger errors might occur, especially in areas with many crevasses (Knudsen & Hasholt, 1999). The snow surveys can give a hint of the representativity of the Nunatak values for daily variation in the snowcover, but due to the strong winds occurring in this area (piteraqs, velocities up to 64 m s" 1 ), severe drifting can occur (Hasholt et al., 2003). The best estimate of areal distribution is obtained by snow surveys, which in this area are difficult and costly. The areal precipitation cannot be calculated in a simple way from a DEM, using an orography factor, because the measured summer precipitation and the calculated winter precipitation at Station Coast and Station Nunatak show a negative orographic effect (Table 2). The winter precipitation at Station Nunatak (930 mm from September to June, Table 2) contradicts the higher values found on the glacier based on the snow

Estimation of water balance in and around the Mittivakkat Glacier basin, Ammassalik Island 139 surveys (1168 mm, Table 3). Possible explanations for the low winter precipitation at Nunatak compared to the glacier are: the exposed station location at the nunatak, the windy conditions, and the removal of snow by drifting. Station Nunatak, therefore, seems only to represent a local area and the negative orography factor found is not considered representative for the area. A thorough validation and quality control of precipitation data is therefore needed. This implies a comparison between radiation, albedo and air temperature recordings; further validation is possible using daily images from automatic cameras overlooking the Mittivakkat Glacier and the pro-glacial valley (Fig. 2). The results should be tested against results from snow models and water balance calculations. Neither the potential nor the actual évapotranspiration have been measured regularly in this area. Measurements of potential évapotranspiration, using a shielded glass calibrated against open water pan evaporation, have shown that daily values of 3-5 mm can occur during the summer season. Similar results are found from Zackenberg (Soegaard et al., 2001). It has been demonstrated that sublimation from windblown snow can account for a loss of up to 10% of the winter precipitation for Ammassalik Island by SnowTran-3D (Hasholt et al, 2003). Because of the steep alpine relief, the resulting small fetch, and logistics difficulties, it is not appropriate to apply eddy correlation technique in this environment. Calculations of actual évapotranspiration using the Makldnk potential évapotranspiration and the Thornthwaithe- Mather soil moisture budget seems to be the best available estimate at the moment, although the Makkink values (from 379-400 mm year" 1, Table 2) are 100-200 mm year" 1 higher than empirical values applied in other studies in Greenland, e.g. Hasholt (1980) and Boggild et al. (1998). It is planned to apply more sophisticated budget models, including soil and vegetation parameters, at a later stage. Measurements of discharge in this area can be hampered by the harsh climatic conditions; a good example is freezing of the current meter. Also, transport of rocks and ice in the watercourses can damage the current meter. In case of high sediment concentrations in the water, it is very important that the bearings of the current meter are sealed, as is the case with the Ott current meter, because the friction caused by the sediment results in an underestimation of the velocity. Finding a safe, stable and accessible cross section can also be difficult. The quality of the stage-discharge relationship depends on the stability of the controlling cross section. An accuracy of the single discharge measurement of 5-10%o is assumed, depending on the geometry of the cross section. Stage can be recorded using float-type or pressure transducer types of gauges; both need installation inside the water and fixation to the bank. These are severe constraints in environments with freezing and ice-drift. The emergence of the ultrasonic sensor (Campbell SR50), with its rather low power consumption and no need for installation under the water surface, was a very welcome solution to a severe monitoring problem. Some problems, however, have occurred. The gold membrane on the emitting surface is often damaged by strong winds and requires annual replacement. Therefore, to avoid loss of important data, using two parallel sensors is recommended. The most reliable recordings can be obtained at the outlet from the lakes. Pressure transducers were deployed in two lakes in the 1980s as part of the hydro-power development programme carried out by GTO (Greenland Technical Organization).

140 Bent Hasholt & Sebastian H. Mernild Some problems have occurred with ice damaging the cables and formation of dew in the air-vent tube. Recently the EnviroMon pressure transducer (DIVER) has been tested in a lake at Kuutuaq and in a lake situated at the Mittivakkat Glacier margin. The results have been promising (Hasholt, 2002). This type of logger avoids the airvent tube problems, but needs to be compensated by using a special logger that records atmospheric pressure simultaneously. At Sermilik, where one of the main purposes has been to monitor glacial erosion and sediment transport, the location and stability of measuring cross sections poses a major problem. The pro-glacial river valley has a braided river drainage the individual channels are therefore moving rapidly in this case it is difficult, if not impossible, to locate sensors in the river or at the banks. Only two locations suitable for a discharge measurement cross-section and instrument placement have been found in the entire valley, in spite of intense reconnaissance. These discharge cross sections have been stable for about 30 years. In 2002, however, the large rock (weighing more than a tonne) where the equipment was placed was undercut by the Mittivakkat Glacier river and tilted slightly, destroying the stage-discharge relationship. Other problems in this environment are the development of icing and the freezing of the watercourse combined with snowfall and snow drifting. During the winter, the snow and ice covers the valley bottom up to a level 2-3 m above the summer level. During hot spells in winter (e.g. foehn situations), runoff might mn on the surface of the snow, at worst, damaging equipment that is not situated high enough, or at best, bypassing the measuring location. During the spring melt period water runs on the snow/icing surface initially, often following unpredictable courses. Later tunnels start to develop and in some places the water disappears below the surface. In some places the tunnels collapse and cause damming and rise of stage, all in a totally random pattern, which cannot be addressed using automatic recording alone. Therefore, periods with such conditions cannot be recorded properly without having observers on location. Less severe problems can occur during the freeze-up period because of the building up and break down of ice dams. It is not possible to predict the thaw and freeze-up period so accurately as to pinpoint the exact period when observers are needed. There is no obvious low cost solution to this problem; however, modelling the quantities of runoff that can occur during these periods is a possibility. But models have to be calibrated and validated against observed runoff data covering at least five years. The total average annual runoff cannot be calculated from the observations in Table 1; however, the runoff values must exceed the indicated sum, because measurements could only be carried out for part of the summer season for the reasons mentioned above. The runoff (Table 1 ) confirms the high values from the water balance calculations (Table 2) and the negative mass balance found from the glacier monitoring (Table 3). The results are almost in accordance with earlier data from Hasholt (1997), which shows that the runoff from a slightly glacierized basin south of Mittivakkat has runoff values much less than those from the Mittivakkat Glacier River (Table 1). SUMMARY AND PERSPECTIVES The data sets from the three stations demonstrate a major variation in climate and waterbalance within short distances in this alpine landscape. Measurements indicate

Estimation of water balance in and around the Mittivakkat Glacier basin, Ammassalik Island 141 that the precipitation at the ice-fiord (1255 mm year" 1 ) is higher than both at Tasiilaq (1091 mm year" 1 ) and at the Nunatak (1036 mm year" 1 ). The low values at the Nunatak are contradicted by results of snow surveys on the glacier and by runoff measurements around the glacier. The low values from the Nunatak are interpreted as a result of its exposure to wind and removal of snow by erosion. The high runoff values from the areas not supplied from glaciers indicate that the correction applied on the precipitation from Tasiilaq in some years is too low. The actual évapotranspiration resulting from the calculation (379^400 mm year" 1 ) is quite high compared to results from earlier estimates and measured results; a reduction will lead to 100-200 mm year" 1 higher runoff values. The high runoff values found show that the precipitation measurements underestimate the real amount of precipitation and that glaciers in this area can contribute significantly to the total runoff. In a study of circumpolar water balance it is therefore important to be able to cover the regional climatic variation, and to understand and quantify the impact of local glaciers. In order to do this, it is necessary to include basins in the same regional climatic setting having different percentage of glacier area in the monitoring and data collection. It appears that data from the Sermilik area can be collected with reasonable accuracy, and therefore fulfil the demands stated above. However, difficulties in monitoring the runoff occur during the thaw and the freeze-up periods water might bypass the measuring location, start developing tunnels, build up and break down ice dams it is believed that quantitative knowledge of water fluxes in these periods can be improved by using proper modelling and control calculations of the water balance. The project is part of a larger climate-landscape-interaction project aiming at a full understanding of the processes forming the landscape and a quantification of these processes by establishing water, ice, and sediment balances. A major part of the project's process recognition and data collection phase is finished, and it is now entering the modelling phase. It is planned to implement/develop the following models in the area: SnowTran-3D for calculation of snow distribution and snowmelt, a new glacier dynamic model (including erosion at the glacier sole), and an area-distributed, physically-based MIKE-SHE and MIKE 11 model system, developed by the Danish Hydraulic Institute (DHI), for calculation and illustration of runoff variation. The project period is 2004-2006. The data mentioned above will be utilized as drivers and for validation, together with new stations performing high resolution monitoring of glacier movement, glacier temperature profiles, and sediment transport as a supplement to the ongoing recording. Acknowledgements Previous recording has been sponsored by Danish Natural Science Research Council (SNF), Kommissionen for Videnskabelige Undersogelser i Gronland (KVUG) and the Institute of Geography, University of Copenhagen. The new project is also supported by SNF. REFERENCES Allerup, P., Madsen, H. & Vejen, F. (1997) A comprehensive model for correcting point precipitation. Nordic 28, 1-20. Hydrology

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