Comparison of Evapotranspiration and Condensation Measurements between the Giant Mountains and the Alps

CARMEN DE JONG1, MARCO MUNDELIUS2 AND KRZYSZTOF MIGALA3 1 Geography Department, University of Bonn, Germany, 2 Institut fur Gewässerkunde und Binnenfischerei, Berlin, Germany, 3Institute of Geography, Department of Meteorology and Climatology, University of Wroclaw, Poland

12.1 INTRODUCTION

Several important parameters of the water cycle such as evaporation, transpiration and condensation have been largely neglected in mountain areas even though they form an important interface between ecology, hydrology and meteorology (de Jong in press). An accurate knowledge of these fundamental parameters is essential to further our understanding of possible climate variations as well as the redistribution of pollutants. Up-to-date, estimations and extrapolations of evaporation and transpiration in steep, high-altitude terrain do not adequately accommodate their spatial and temporal heterogeneity, nor are special components such as condensation considered (Gurtz etal. 1999). Diurnal and nocturnal dynamics of evaporation, transpiration (LeDrew 1975) and condensation should be measured in the field in order to produce a satisfactory basis for modelling and to contribute to our understanding of regional water fluxes.

Evapotranspiration, the process by which water is lost into the atmosphere by transpiration through the stomata of plants or freed directly from the surface by evaporation, is generally derived from meteorological variables at single Bowen Ratio stations and at meteorological stations. 'Although evapotranspiration data in mountain areas are almost non-existent, it is these losses rather than potential evaporation which are most significant for vegetation growth' (Barry 1992). Few studies have focused on direct and regionally distributed field measurements in the mountains (Calder etal. 1984, Cernusca etal. 1999, Korner etal. 1978, Graber etal. 1999, Staudinger and Rott 1981, Wright 1990). Our knowledge of these water fluxes is therefore usually reduced to modelling results, single station observations or derivations from the difference between long-term precipitation and discharge (Gurtz et al. 2003, Stewart and Rouse 1976). However, meteorological stations rarely cover spatial and temporal diversity of evapotranspiration since they are neither logistically feasible nor affordable in large enough numbers on steep slopes in mountain catchments. This is due, in particular, to the sensitivity, heavy weight and high costs of the equipment. For Bowen Ratio stations, in particular, it is the intensive maintenance of dew mirrors that is a limiting factor for remote, unstaffed stations. In addition, the Bowen Ratio method depends on the validity of the Monin-Obukhov Similarity Theory, which is not

Climate and Hydrology in Mountain Areas. Edited by C. de Jong, D. Collins and R. Ranzi © 2005 John Wiley & Sons, Ltd appropriate for this type of terrain since it is not flat and not horizontally homogeneous. Even so, the Bowen Ratio method has been applied as a common method in high mountain areas (Bernath 1990, Konzelmann et al. 1997). For the latter, data from stations placed only on the valley floor and at one higher elevation site are extrapolated linearly in order to regionalize evapotranspiration for a whole valley.

Furthermore, these methods are not developed to account for nocturnal variations of evapotranspiration. Nevertheless, it is essential to refer to continuous, highresolution field data to be able to validate model results. With the advance of low cost, electronic equipment, the development of alternative measuring systems is becoming increasingly feasible. A clear subdivision into potential evaporation, actual evapotranspiration and condensation is necessary. Studies based on field experiments in the Dischma valley, Switzerland, from 1995 to 1999 (de Jong et al. 2002, de Jong in press) show that these components are subject to very small scale temporal fluctuations according to local climatic conditions and regional aspects.

Condensation, a much-neglected component of the water cycle in nearly all environments, is the process by which fog or moist air is horizontally and/or vertically advected and deposited as water droplets or rime ice if the surface is super-cooled. It is not only an important exchange mechanism for water in the surface layer and roughness sublayer but also a potential pollutant source since it can promote the input of chemicals, such as SO2, from cloud water interception (Acker et al. 1999). There is evidence that high-elevation sites in Eastern Europe, such as the Black Triangle at the junction of Poland to the Czech Republic and former East Germany, receive greater amounts of atmospheric pollutants than surrounding low-elevation areas. Since the Giant Mountains (Karkonosze Mountains) form the first orographic barrier in this region, they are particularly prone to the absorption of contaminants through fog deposition. Long-term monitoring stations with passive cloud and fog collectors were installed in Mumlava, Karkonosze Mountains, in an attempt to assess horizontal and vertical fog deposition and pollutants (Migala and Szymanowski 1999, Sobik and Migala 1993). The results give evidence about average amounts and duration of fog for the study area presented in this paper. Investigations in the zone between 800 and 1200 m a.s.l. show that the pollution by fog droplets is 3 -4 times greater than that from normal precipitation (Pereyma et al. 1997), particularly in winter. The two main objectives of this presentation are to

• measure and compare evaporation, transpiration and condensation at hourly and weekly intervals in summer in two mountain catchments;

• explain the differences between evaporation, transpiration and condensation for a humid climate (Dischma, Alps, Switzerland) and a foggy climate (Giant Mountains, Poland);

Table 12.1 Comparison of physical, climatological, hydrological, geological and landuse characteristics for the catchment in the Giant Mountains, Poland and Dischma, Switzerland

Catchment

Szrenica, Giant Mountains, Poland

Dischma, Alps, Switzerland

Location

Polish/Czech boundary

Graubunden, E. Alps

Size (km2)

1.67

43

Length (km)

2.1

14

Altitude (m)

680-1435

1500-3100

Average Grad. (°)

16.5

30

Glaciers (km2)

None

Scaletta (0.66)

Chualp (0.3)

Geology

Mainly gneiss and slates, granite,

Mainly gneiss, some amphibolite

Soils

Syrosem, regosols, muirs, etc.

Regosols, podsols

Vegetation

Sub-alpine- (shrubs and grass)

Mainly alpine grass, dwarf shrubs, forest

and alpine

(spruce, larch, and pine)

Annual aver. snow covera

186 days"

225 days4

Mean rainfall (summer/annual)a (mm)a

450 (mid-May to July)/1420"

500 (mid-June to mid-Sept)/12004

Mean July temp (°C)a

10 (at 1110 m)"

12 (at 2000 m a.s.l)4

Mean discharge (summer/annual)a (mm)

_a

800/12004

Mean evapotranspiration (mm)a

a

300 (at 2000 m a.s.l)4

a(Migaia and Szymanowski, 1999). 4(wildi and Ewald 1986).

a(Migaia and Szymanowski, 1999). 4(wildi and Ewald 1986).

Comparison of évapotranspiration and condensation measurements between the Giant Mountains and the Alps 163

Figure 12.1 Mountain Szrenica catchment with experimental sites, Giant Mountains, Poland

12.2 STUDY AREAS

0 0

Post a comment