MEDIWA
Meteorological Drivers of Mass and Energy Exchange between Inland Waters and the Atmosphere (MEDIWA)
The correct quantification of the mass and energy exchange between inland waters and the boundary layer atmosphere is of great importance for both scientific research and practical issues of water management. For example, exact estimations of evaporation rates are essential for controlling and management of reservoirs as well as for a successful implementation of flooding projects in former mining areas. The water temperature and thermal stratification of a water body have a large influence on microbiological and hydro-chemical processes occurring in the water column and the waterbed. Thus, the knowledge about the heat balance and the heat exchange between the water body and the atmosphere are important in order to be able to efficiently use the possibilities of water management to control to and improve the water quality in a reservoir. In the same, information and data about the gas exchange occurring on the water surface are required for an optimal management of the hydro-chemical environment.
Exact direct measurements of mass and energy fluxes occurring at the water surface are possible, but highly expensive and extremely technically challenging. Therefore, mass and energy fluxes (e.g., evaporation rates) are typically determined using different models that are driven by meteorological and limnological variables being easier to measure. However, the reliability of such flux estimates significantly depend on (i) the complexity of the applied model, (ii) the parameterisation of the model equations and (iii) the representativeness and quality of input data. These dependencies lead to serious conflict situations in many cases as measurement data of environment variables that are required for the execution of complex and precise models are not available or are of insufficient quality. Thus, the mass and energy exchange of waters can be often only roughly estimated. However, it should also not be neglected that even highly complex models have still serious weaknesses and deficits in the simulation of processes occurring in natural waters. Therefore, the overall situation regarding the capabilities for modelling the mass and energy exchange of water bodies is to be classified as in need of improvement.
In order to enhance the capabilities to approximate and model mass and energy fluxes based on data and environment variables that are generally available, the exchange processes on the surface of natural waters are to be intensively investigated in the MEDIWA project. Based on the collected measurement data, new methods are to be developed to improve the reliability of models. Complex relationships are to be resolved and made describable by mathematic equations. The analysis how the spatial and temporal variations of meteorological variables affect the mass and energy balance of a water body is thereby a special subject of investigation.
In closed cooperation with the Landestalsperrenverwaltung des Freistaates Sachsen, the Technische Universität Dresden und the Helmholtz Centre for Environmental Research perform two long-term experiments performed at Bautzen reservoir (Saxony, Germany). The mass and energy exchange between the water surface and the atmosphere is to be measured under different meteorological and limnological conditions. These measurements will provide a well-founded data basis for processing the research tasks mentioned above. A floating outdoor laboratory will be utilised for direct measurements of fluxes and variables that are unaffected by land surfaces and are representative for the pure water-atmosphere-interaction. An eddy covariance measurement system and several automatically working meteorological, hydro-chemical and hydro-physical sensors will provide continuous measurement data with high temporal (half-hourly) resolution, which enable the direct observation and investigation of feedbacks and interrelationships between meteorological and limnological variables.
In addition to the extensive equipped outdoor laboratory, three further observation platforms with a simplified equipment are to be deployed and anchored on the water surface of the Bautzen reservoir. With the help of these platforms, the spatial alterations of meteorological basis parameters (e.g., air temperature, air humidity and wind speed), atmospheric turbulence signatures and limnologic variables will be measured along a transect parallel with the main wind direction. A sophisticated data set will be created, which makes it possible to separate influences that act on the mass and energy fluxes of a water surface from the environment of surrounding terrestrial sites from other effects and to investigate them in isolation. Laboratory tests and supplementary field measurements complete the measurement programme with regard on effects of surface films and micro-stratifications at the water surface.
The combination of experimental fieldwork, statistical analyses and model–based investigations as well as the nexus between limnological and micrometeorological research methods provide the methodical foundation of the MEDIWA project and help better to understand the processes occurring at the interface between water body and boundary layer atmosphere. In particular, processes can be studied being relevant on different scales of space and time. The measurements and the measurement data serve to enhance our knowledge as well as our abilities to qualitatively describe and quantitatively model the mass and energy exchange between inland waters and the atmosphere. Therefore, the research work of the MEDIWA project addresses both issues of fundamental research and practical interests of water supply and water management.