Multi-objective calibration of the land surface scheme TERRA/LM using LITFASS-2003 data

The turbulent sensible and latent heat fluxes simulated in the operational weather forecast model LM have been checked with data from the field experiment LITFASS 2003 (Lindenberg Inhomogeneous Terrain - Fluxes between Atmosphere and Surface: a Long-term Study) using both single site measurements and grid box aggregated fluxes. SCE-UA (single objective) and MOSCEM-UA (multi-objective) approaches were applied to calibrate the land-surface scheme TERRA/LM for 11 single sites and for the aggregated fluxes. A large variation is seen among the parameter sets found by calibration but no typical classification according to vegetation type is obvious. This is attributed to the calibrated parameter sets correcting for model deficiencies and data errors rather than describing the physical characteristics of the measurement site. The measured fluxes were combined into a time series of aggregated fluxes by the tile method. Calibration of TERRA/LM with respect to the averaged fluxes resulted in a range of parameter sets which all simulated the area-averaged fluxes in much better agreement with the observed fluxes than the standard parameter set of the operational model. A modified Nash-Sutcliffe measure as a coincidence criterion fell from 0.3 to a range between 0.15 and 0.28 for the latent heat flux and from 0.43 to between 0.26 and 0.36 for the sensible heat flux when the calibrated parameter sets were used instead of the standard parameters

Advantages of a topographically controlled runoff simulation in a soil-vegetation-atmosphere transfer model

Two methods to incorporate subgrid variability in soil moisture and runoff production into soil-vegetation-atmosphere transfer (SVAT) models are compared: 1) the variable infiltration capacity model approach (VIC), and 2) a modified "TOPMODEL'' approach. Because neither approach needs to track surface or subsurface flow within a catchment explicitly, they represent computationally efficient ways to represent hydrologic processes within the context of regional and global modeling. This study shows that, during low flow periods, the runoff simulation is superior when using the TOPMODEL-based equations, especially during the rising limb of the autumn hydrograph. A main drawback of the modified VIC-model approach, especially for regional and global application, is that, with five free parameters, considerably more model calibration is required. TOPMODEL, on the other hand, requires only the determination of one free parameter. However, a TOPMODEL approach does require extensive preprocessing of topographic data, and issues concerning resolution of the data used become relevant

Evaporation over a heterogeneous land surface - The EVA-GRIPS project

The representation of subgrid-scale surface heterogeneities in numerical weather and climate models has been a challenging problem for more than a decade. The Evaporation at Grid and Pixel Scale (EVA-GRIPS) project adds to the numerous studies on vegetation-atmosphere interaction processes through a comprehensive field campaign and through simulation studies with land surface schemes and mesoscale models. The mixture of surface types in the test area in eastern Germany is typical for larger parts of northern Central Europe. The spatial scale considered corresponds to the grid scale of a regional atmospheric weather prediction or climate model and to the pixel scale of satellite images. Area-averaged fluxes derived from point measurements, scintillometer measurements, and a helicopter-borne turbulence probe were widely consistent with respect to the sensible heat flux. The latent heat flux from the scintillometer measurements is systematically higher than the eddy covariance data. Fluxes derived from numerical simulations proved the so-called mosaic approach to be an appropriate parameterization for subgrid heterogeneity