Distributed modelling of climate change impacts on snow sublimation in Northern Mongolia

Adv. Geosci., 21, 117–124, 2009 www.adv-geosci.net/21/117/2009/ © Author(s) 2009. This work is distributed under the Creative Commons Attribution 3.0 License. Advances in Geosciences Distributed modelling of climate change impacts on snow sublimation in Northern Mongolia F. Wimmer1 , S. Schlaffer1,* , T. aus der Beek1 , and L. Menzel1 1 Center for Environmental Systems Research, University of Kassel, Germany * now at: Dr.-Ing. K. Ludwig, Wasserwirtschaft-Wasserbau GmbH, Karlsruhe, Germany Received: 15 January 2009 – Revised: 25 March 2009 – Accepted: 28 April 2009 – Published: 12 August 2009 Abstract. Sublimation of snow is an important factor of the hydrological cycle in Mongolia and is likely to increase according to future climate projections. In this study the hydrological model TRAIN was used to assess spatially distributed current and future sublimation rates based on interpolated daily data of precipitation, air temperature, air humidity, wind speed and solar radiation. An automated procedure for the interpolation of the input data is provided. Depending on the meteorological parameter and the data availability for the individual days, the most appropriate interpolation method is chosen automatically from inverse distance weighting, Ordinary Least Squares interpolation, Ordinary or Universal Kriging. Depending on elevation simulated annual sublimation in the period 1986–2006 was 23 to 35 mm, i.e. approximately 80% of total snowfall. Moreover, future climate projections for 2071–2100 of ECHAM5 and HadCM3, based on the A1B emission scenario of the Intergovernmental Panel on Climate Change, were analysed with TRAIN. In the case of ECHAM5 simulated sublimation increases by up to 17% (26...41 mm) while it remains at the same level for HadCM3 (24...34 mm). The differences are mainly due to a distinct increase in winter precipitation for ECHAM5. Simulated changes of the all-season hydrological conditions, e.g. the sublimation-to-precipitation ratio, were ambiguous due to diverse precipitation patterns derived by the global circulation models. 1 Introduction Currently, the snowfall water equivalent in Northern Mongolia accounts for up to 20% of annual precipitation (Batima et al., 2005). The shallow snow cover prevails for at least one third of the year. In conjunction with cold and dry conditions, this leads to the sublimation of up to 50% of total snowfall (Zhang et al., 2008), i.e. 10% of total annual precipitation. Results from the Fourth Assessment Report, provided by the Intergovernmental Panel on Climate Change (IPCC), project an increase in precipitation by 10–20% for Northern Mongolia by the end of the 21st century (Cruz et al., 2007; Menzel et al., 2008). This raises the question how sublimation rates are affected by the projected change of climate conditions. Previous small scale investigations in Mongolia and Eastern Siberia provide observations of sublimation rates based on different methods (Zhang et al., 2004, 2008; Suzuki et al., 2006). Pomeroy et al. (1998) demonstrate that snow drift strongly enhances sublimation rates and specify an algorithm to simulate this effect with land surface models. The objective of this study is to provide spatially distributed simulations of sublimation for current climate conditions and future climate scenarios in Northern Mongolia. The hydrological model TRAIN (Menzel, 1997; Menzel and Lang, 2005) was used to assess how changing precipitation patterns affect snow sublimation. Spatial and temporal variability of sublimation in the Kharaa catchment (Sect. 2.1) was simulated on a 1 km×1 km grid with daily time steps using interpolated meteorological data for current conditions (1986–2006). Because of limited data availability in the model region, an interpolation technique for meteorological variables was developed, which is capable to select an appropriate method depending on the available data. Additional model runs were conducted with climate projections of two general circulation models (GCM) driven by the A1B emission scenario (IPCC, 2000). Finally, simulated current and future sublimation values were compared. Correspondence to: F. Wimmer () Published by Copernicus Publications on behalf of the European Geosciences Union. 118 F. Wimmer et al.: Distributed modelling of climate change impacts on snow sublimation in Northern Mongolia Snowfall (Ps ) is simulated as a fraction of precipitation (P ) depending on air temperature. Ps equals P if air temperature is below Ts (−0.4 ◦ C) and is zero if air temperature is above Tr (1.6◦ C). For temperatures in the interval [Ts,... , Tr ], Ps decreases linearly from P to zero. Daily snow melt (M) is estimated by the degree-day approach (e.g. Dyck and Peschke, 1995) (1) M = F × (T − Tm ) where F is a degree-day factor (1.8 mm d−1 K−1 ), T is air temperature and Tm is the threshold air temperature for snow melt (0◦ C). Sublimation of snow is calculated according to the Penman-Monteith equation (Monteith, 1965) with canopy resistance set to zero and aerodynamic resistance (ra ) derived from wind speed (u) in m s−1 at height z (Thom and Oliver, 1977): ra =  4.72 z 2 ln 1 + 0.54 u 0.125 h (2) Canopy height (h) is a parameter characterising the land cover type of the grid cell. The Penman-Monteith equation mainly depends on the vapour pressure deficit of the air and the energy available for sensible and latent heat flux, at the earth surface. The latter is the balance of the net radiation flux directed towards the 1. and Location stations (12) and posts (14) in the Kharaa 2Figure Material methodsand sea level of meteorological surface and the energy flux from the surface into the ground. radiation is parameterised using47° T , global and catchment and its surroundings. The catchment Net extends over an area from 50’ radiation N to 49° 2.1 Study region the surface albedo. In case of an existing snow cover, the surface albedo is 40’study N and 20’ tothe 107° 25’river E. catchment This was105° carried outEfor Kharaa modified to represent the albedo of snow (α s ). For T <Tm , it 2 (14 500 km ) north of the Mongolian capital Ulan Bator is computed depending on the number (N ) of days since the (Fig. 1). The climate in the study region is continental cold last significant snowfall (Ps >3 mm d−1 ) (Plüss, 1997): and dry, with cold winters and hot summers. Mean annual Fig. 1. Location and sea level of meteorological stations (12) and posts (14) in the Kharaa catchment and its surroundings. The catchment extends over an area from 47◦ 500 N to 49◦ 400 N and 105◦ 200 E to 107◦ 250 E. temperature is about −0.4◦ C while annual precipitation is about 330 mm. Runoff is mainly generated in the mountainous eastern part (Khentii Mountains). The major land cover types are grassland (60%), forest (26%) and cropland (11%). Grassland occurs throughout the catchment, except for the northern slopes of higher mountain ranges, which are covered with forest. Cropland and settlement areas are (...truncated)