Abstract
stimating water and energy fluxes at the land surface is difficult and the resulting uncertainty is an important source of error in many hydrological and meteorological models. To understand the fluxes and feedback mechanisms in land surface hydrology, it is important to measure as many fluxes and states as possible at one location. Understanding and quantifying these flux processes through observation can help to improve both meteorological and hydrological models. Water budgets are often used to determine the size of water fluxes across catchment boundaries. This research project focuses on the water budget of a man-made (polder) water system in Cabauw, The Netherlands. The Cabauw Experimental Site for Atmospheric Research (CESAR) is a hotspot for meteorological and hydrological observations in The Netherlands. The most important feature is the 213-m-high observation tower which provides vertical profiles of many quantities, such as wind and temperature, which can be used for boundary layer modeling studies. An X-band polarimetric precipitation radar is located on top of the tower. An extended meteorological station, dedicated fields for measuring energy fluxes, radiation and precipitation and remote sensing equipment are located around the tower. Cabauw is a FLUXNET site and often used for satellite ground validation. In addition to the extensive meteorological observations, hydrological measurements are required to understand the water and energy fluxes and study the water budget of the 0.5 km2 polder area around the site. This “catchment” can be divided into two nested catchments of 0.3 and 0.2 km2. It is part of a polder area, and drained by small, man-made channels. The area is flat and at an elevation of one meter below mean sea level. Water is supplied upstream. Downstream of the inlet a V-notch weir has been installed. At the outlets of the first and second sub-catchment Rossby-weirs have been installed. Discharge is derived from water levels recorded with pressure sensors and a stage-discharge relationship obtained in the laboratory. In April 2009 a magneto-strictive sensor has been installed upstream of the V-notch weir to measure water levels directly. Accurate discharge data are available since May 2007. Soil moisture data are obtained from a TDR-system of 36 sensors which has been installed in November 2003. Precipitation sums and actual evapotranspiration rates are provided by the KNMI (Royal Netherlands Meteorological Institute). Our intention is to continue this hydrological field study over a period of several years for modelling purposes. In Cabauw the most important water budget terms are precipitation, evapotranspiration, inflowing and outflowing discharge and change in storage. Possibly upward seepage from a nearby river should be added to this budget. In winter precipitation is the largest input term and outflowing discharge the largest output term. In summer inflowing discharge is the largest input term and evapotranspiration the largest output term. A detailed analysis of the water budget terms over several years will be presented.
http://www.cesar-observatory.nl/
| Original language | English |
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| Publication status | Published - 2012 |
| Event | Fall Meeting of the American Geophysical Union, San Francisco, USA - Duration: 3 Dec 2012 → 7 Dec 2012 |
Conference/symposium
| Conference/symposium | Fall Meeting of the American Geophysical Union, San Francisco, USA |
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| Period | 3/12/12 → 7/12/12 |