The hydrological component of the Cabauw Experimental Site for Atmospheric Research (CESAR)
Creators: name: Bokhorst, Jantine
name: Uijlenhoet, Remko
name: Stricker, Han
name: Bokhorst, Jantine
Publisher: name: XVI International Conference on Computational Methods in Water Resources
Year: 2006

description: It is well recognized in the weather and climate modelling community that over 
shorter time scales (rainfall, surface runoff) and over longer time scales (latent 
heat flux, soil moisture storage) the parameterisation of the exchange processes 
from the atmosphere to the land surface and vice versa still needs considerable 
improvement. Over the past decade the atmospheric research site at Cabauw has 
already served as one of the prominent sites in intercomparison studies of land-
atmosphere interactions (PILPS, AMIP). From the latter study it was concluded that 
next to clouds and radiation interactions, the consistent description of the 
interactions between the atmospheric and terrestrial hydrologic processes remains to 
be achieved. However long-term time series of measurements of all the terms of the 
terrestrial water budget around validation sites are in general lacking. To further 
expand the opportunities at Cabauw for testing and validating land-atmosphere 
parameterisations, extra efforts are being put in the hydrological component. 
Ultimately, this will increase the confidence in the realism of such 
parameterisations.

Our goal is to improve the parameterisation of the hydrological component of land 
surface - atmosphere exchanges in regional climate models through: 1) monitoring the 
water budget of two nested polder areas around the Cabauw tower that are 
representative for the region; 2) upscaling of the hydrologic processes and their 
parameterisations to the scale of regional climate models, taking into account sub-
grid variability. In this contribution, we focus on the former. The concrete 
question we address is: Are we able to close the water budget for two selected areas 
around Cabauw? Since 1.5 years, we have been observing the components of the water 
budget in two nested areas of approximately 0.3 and 0.5 km2 around the Cabauw tower. 
We employ a combination of in situ measurements (groundwater level from divers, soil 
moisture storage from time domain reflectometry, water intake and discharge from 
weirs, evapotranspiration by eddy covariance and precipitation from rain gauges) and 
remotely sensed observations (scintillometry, weather surveillance radar). Here we 
present an analysis of the data collected thus far.

Our work is part of a larger effort, called the Cabauw Experimental Site for 
Atmospheric Research (CESAR). The CESAR observatory is located near the village of 
Cabauw, approximately 20 km SW of Utrecht (http://www.cesar-observatory.nl) and is 
operated by a consortium of major universities and research institutes. The overall 
purpose of CESAR is to enhance the possibilities of the Cabauw site and to set-up 
and operate an observational facility with a comprehensive set of remote sensing and 
in situ equipment for studies on atmospheric and land surface processes, monitoring 
of long-term tendencies in climate parameters, the development of new measurement 
techniques, the validation of satellite observations and climate models, and the 
training of young scientists.