Background & State-of-the-art
There is growing evidence that land-use changes and the increased concentration of CO2 in the atmosphere will in turn impact water resources. Characteristic for both is that the hydrological consequences are manifested on longer time scales and at larger spatial scales (catchment scale). Accordingly, the Water Framework Directive within the EU prescribes that water management strategies must be developed at catchment scale - instead of according to administrative bounds.
So far, the vast majority of the hydrological process understanding has been obtained at small scales (<10 km2) and thus 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. Recent studies have shown that basic climatic and hydrological fluxes are inaccurately determined at catchment scale which has led to problems with closure of the water balance.
In a recent national water resources assessment it was necessary to introduce empirical correction factors to simulated net precipitation to obtain a closure of the water balance at catchment scales. Despite using state-of-the-art hydrological modeling techniques the estimate of the groundwater resources is uncertain. Moreover, research focused on water quality problems have to a large extent been focused on contamination by point sources. Thus, the investigations have been done at small scales and as a result the findings have not been derived for large scales. Furthermore, global climate change research networks which monitor, analyze and forecast the impact on ecosystems do not address the scaling issue and provide only limited knowledge of the water cycle at catchment scale.
The international hydrological scientific community has recently proposed that large-scale hydrological observatories be established with long-term hydrological measurements of in- and outflow fluxes and fluxes between the different hydrological compartments. With the HOBE-project Denmark will contribute to this international research trend.