- B. Hurk van den (1)
- A.F.G. Jacobs (1)
- E. Meijgaard van (1)
- K. Metselaar (1)
- E.J. Moors (1)
- M. Reichstein (1)
- S.I. Seneviratne (1)
- R. Stockli (1)
- A.J. Teuling (1)
- L.H. Ulft van (1)
- E.L. Wipfler (1)
- S.J. Zwart (1)
Seasonal evaluation of the land surface sheme HTESSEL against remote sensing derived energy fluxes of the Transdanubian regions in Hungary
Wipfler, E.L. ; Metselaar, K. ; Dam, J.C. van; Feddes, R.A. ; Meijgaard, E. van; Ulft, L.H. van; Hurk, B. van den; Zwart, S.J. ; Bastiaanssen, W.G.M. - \ 2011
Hydrology and Earth System Sciences 15 (2011)4. - ISSN 1027-5606 - p. 1257 - 1271.
aardoppervlak - evapotranspiratie - remote sensing - klimaatverandering - modellen - hongarije - land surface - evapotranspiration - climatic change - models - hungary - terrestrial water storage - era-40 reanalysis - balance closure - climate models - field - atmosphere - hydrology - impact - basin
The skill of the land surface model HTESSEL is assessed to reproduce evaporation in response to land surface characteristics and atmospheric forcing, both being spatially variable. Evaporation estimates for the 2005 growing season are inferred from satellite observations of the Western part of Hungary and compared to model outcomes. Atmospheric forcings are obtained from a hindcast run with the Regional Climate Model RACMO2. Although HTESSEL slightly underpredicts the seasonal evaporative fraction as compared to satellite estimates, the mean, 10th and 90th percentile of this variable are of the same magnitude as the satellite observations. The initial water as stored in the soil and snow layer does not have a significant effect on the statistical properties of the evaporative fraction. However, the spatial distribution of the initial soil and snow water significantly affects the spatial distribution of the calculated evaporative fraction and the models ability to reproduce evaporation correctly in low precipitation areas in the considered region. HTESSEL performs weaker in dryer areas. In Western Hungary these areas are situated in the Danube valley, which is partly covered by irrigated cropland and which also may be affected by shallow groundwater. Incorporating (lateral) groundwater flow and irrigation, processes that are not included now, may improve HTESSELs ability to predict evaporation correctly. Evaluation of the model skills using other test areas and larger evaluation periods is needed to confirm the results.
Contrasting response of European forest and grassland energy exchange to heatwaves
Teuling, A.J. ; Seneviratne, S.I. ; Stockli, R. ; Reichstein, M. ; Moors, E.J. - \ 2010
Nature geoscience 3 (2010)10. - ISSN 1752-0894 - p. 722 - 727.
anemometer (co)sine response - balance closure - climate-change - heat-wave - flux measurements - water-vapor - summer - transpiration - impact - deforestation
Recent European heatwaves have raised interest in the impact of land cover conditions on temperature extremes. At present, it is believed that such extremes are enhanced by stronger surface heating of the atmosphere, when soil moisture content is below average. However, the impact of land cover on the exchange of water and energy and the interaction of this exchange with the soil water balance during heatwaves is largely unknown. Here we analyse observations from an extensive network of flux towers in Europe that reveal a difference between the temporal responses of forest and grassland ecosystems during heatwaves. We find that initially, surface heating is twice as high over forest than over grassland. Over grass, heating is suppressed by increased evaporation in response to increased solar radiation and temperature. Ultimately, however, this process accelerates soil moisture depletion and induces a critical shift in the regional climate system that leads to increased heating. We propose that this mechanism may explain the extreme temperatures in August 2003. We conclude that the conservative water use of forest contributes to increased temperatures in the short term, but mitigates the impact of the most extreme heat and/or long-lasting events.
Towards closing the surface energy budget of a mid-latitude grassland
Jacobs, A.F.G. ; Heusinkveld, B.G. ; Holtslag, A.A.M. - \ 2008
Boundary-Layer Meteorology 126 (2008)1. - ISSN 0006-8314 - p. 125 - 136.
energiebalans - graslanden - fotosynthese - aardoppervlak - warmtestroming - energy balance - grasslands - photosynthesis - land surface - heat flow - balance closure - heat-flux - eddy-correlation - boundary-layer - storage terms - forest - land - cases-99 - carbon - area
Observations for May and August, 2005, from a long-term grassland meteorological station situated in central Netherlands were used to evaluate the closure of the surface energy budget. We compute all possible enthalpy changes, such as the grass cover heat storage, dew water heat storage, air mass heat storage and the photosynthesis energy flux, over an averaging time interval. In addition, the soil heat flux was estimated using a harmonic analysis technique to obtain a more accurate assessment of the surface soil heat flux. By doing so, a closure of 96% was obtained. The harmonic analysis technique appears to improve closure by 9%, the photosynthesis for 3% and the rest of the storage terms for a 3% improvement of the energy budget closure. For calm nights (friction velocity u * <0.1 m s¿1) when the eddy covariance technique is unreliable for measurement of the vertical turbulent fluxes, the inclusion of a scheme that calculates dew fluxes improves the energy budget closure significantly.