Towards Improvement of the Land Surface Parametrization Using the Experimental Study Results.
Shutov, Vladimir A. (1)
(1) Valday Branch of State Hydrological Institute
The Land-surface Parametrization Schemes (LPS) for Global Climate Models (GCM) consist of submodels of processes such as evapotranspiration, soil moisture, snowmelt, overland flow as incorporated into these simulation models. The special experiments and long-term observation data can be successfully used for evaluation of the heat- and water balance components.
The author has an experience in the water cycle investigation at Valday and some other Russian regions for a long time. Therefore, our opinion on the sensitivity and drawbacks of existing LSPs may promote improvements of the GCMs. Analysis about significant problems in modern LPSs results in following issues:
1. The snow cover parameters such as surface albedo, bulk density, snow water content and its areal extent (snow covered area) are changing in time, for snow melt season particularly. These changes should be described (parametized) properly to the respective LPSs may be successive.
2. The snow water equivalent (SWE) is changing spatially being variable for different landscapes. There is particular variability in SWEs caused by rugged relief: some hollows with accumulated snow pack and, in opposite, the hilltops where the snow cover is blown. We proffer the method called "informative-mapping analysis" through which the timely persistent distributions of snow pack can be simulated and displayed using only landscape maps.
3. Analogically to the above mentioned, we must taken the spatial variability of soil water properties into account as responsible for infiltration and runoff. It is the most respective to those factors of seasonally frozen soils which are particularly unstable with thawing and spring surface runoff generation. The author estimated these conditions for such impermeable layer within upper soil, as well as the spatial distribution of this layer on the catchment at a spring.
4. Field measurements carried out with use of neutron probe testify that soil water contents within upper 1m soil layer vary from 76 to 343 mm for various soil texture (sands to loamy soil). Empirical non-linear relationship between soil water content and evapotranspiration obtained in research can serve to estimate the variability of latent heat flux. It is very notable that such variations appear to be of importance where soil texture is non-homogenous.
