HOBE – The Danish Hydrological Observatory

There is a growing need to improve the scientific understanding of the hydrological processes at catchment scale to quantify water resources and to assess hydrological consequences of natural and anthropogenic changes.

Several investigations have documented that our knowledge of the in- and outgoing water fluxes and the exchange of water between the different hydrological compartments in a catchment is insufficient due to both measurement limitations and lack of theoretical framework. As a result, the problem with closure of the water budget at catchment scale is a persistent issue.

In the past, most of the hydrological process understanding has been obtained at small scales (plot, field, small research catchments) and the issue of scale has not been considered in the design of experiments and in the theoretical analyses. Catchments are subject to a time-space variability of landscape characteristics and the hydrological processes occur and interact across a multitude of spatial and temporal scales. Therefore, the process understanding and associated parameters obtained at one scale cannot directly be applied at another scale. As a consequence, there is a disparity between the scale at which the current process understanding is based and the scale at which future hydrological consequences need to be addressed and water management strategies to be developed.

To address these challenges large-scale hydrological observatories have been established for long-term hydrological measurements of in- and outgoing fluxes as well as fluxes between the different hydrological compartments. Such observatories are necessary instruments for obtaining a better understanding of the catchment behavior and for improving the reliability of predictions of how catchments respond to external stresses. In Denmark a hydrological observatory – HOBE – was established in 2007 based on funding from the private VILLUM FOUNDATION (www.hobecenter.dk). The Skjern catchment located in the western part of Denmark was selected as the site for the hydrological observatory.

In the catchment state-of-the-art measurement techniques in combination with novel sensor technologies are used to measure and analyze the multi-scale spatial and temporal patterns of the land surface and subsurface systems, including system parameters, state variables, in- and outgoing water fluxes, and water fluxes between hydrological compartments. Fluxes of both water vapor and greenhouse gasses are measured above different vegetation types to understand the vegetative response to prevailing climatic conditions and hereby establish a better basis for assessing the effects of land-use or climate changes on these fluxes.

The project takes advantage of the recent developments within ground-based, air-borne and space-borne non-invasive geophysical, meteorological and remote sensing sensors. Also new instrumentation is used for easy and inexpensive measurements of water stable isotopes. The collected data form the basis for development of integrated and physically based models for different scales.

The collected project data are routinely imported in a user-friendly database. It consists of historical meteorological, hydrological, and geological data from the catchment. The database facilitates easy data-sharing among the scientists and students affiliated to HOBE and dissemination of data to interested national and international parties according to a data policy. Researchers from Denmark, Germany, Sweden, and Australia have been granted access to the data. Data from a soil moisture network in the HOBE area has been made available through the International Soil Moisture Network Database https://ismn.geo.tuwien.ac.at/ and the European Centre for Medium-Range Weather Forecasts (ECMWF).

HOBE has created widespread interest at the national level. The center is the pivotal point for hydrological research in Denmark and the research accomplishments have gained significant interest from professionals in the water administration.