Distributed Biosphere Hydrological Model

Water resource management become one of the answers for anticipating the projection effects of climate changes. As been reported by Intergovernmental Panel on Climate change, by 2050 drought-affected areas will likely increase in some water-stressed regions while flood risks are likely to increase in some wet areas [2]. Hydrological studies are has being conducted by many researchers to encounter those possibilities of hazards.

Advance studies in hydrology proceed to comprehensive analysis on biosphere frame. The subject in biosphere environment itself is the exchanges of energy, water, and carbon within global system. Land Surface Parameters (LSPs) are utilized to describe global atmospheric general circulation models, which carried out the three generations of models [1]. First generation was based on simple aerodynamic bulk transfer formulas and often uniforms prescriptions of surface parameters (albedo, aerodynamic roughness, and soil moisture availability) over the continents. The second has explicitly recognized the effects of vegetation in the calculation of the surface energy balance. The latest models use modern theories relating photosynthesis and plant water relations to provide a consistent description of energy exchange, evapotranspiration, and carbon exchange by plants.

Back to the hydrology studies, those land surface models are being utilize by the pairing with hydrology models in order to improve the land surface representation, enhance the streamflow prediction capabilities, and provide improved estimates of water and energy fluxes into the atmosphere [2]. The third generation of land surface model is preferable on such studies, since it incorporates the canopy photosynthesis-conductance model to describe the simultaneous transfer of CO2 and water vapor into and out of the vegetation.

Wang et al. has conducted study of biosphere hydrological model by implementing geomorphology-based Distributed Hydrological Model (GBHM) coupled with Simple Biosphere model 2 (SiB2), a realistic land surface model. In the analysis process, this study describes the water moisture transfer from the atmosphere to river in surface and subsurface. The big river basin system is discrete into several model grids, which then divided to a number of geometrically symmetrical hillslope. From there, SiB2 is used to describe the transfer of turbulent fluxes between the atmosphere and land surface for each model grid. The GBHM simulates both surface and subsurface runoff using grid hillslope discretization, and then simulates flow routing in the river network.

When evaluated by the Southern Great Plains experiments (SGP97 and SGP99), the model shows an acceptable results to reproduces point scales of fluxes, predict discharges (peak and base flows) at the stream gauge, and predict the basin scale surface soil moisture evolution in spatially distributed manner [2]. This simulation is actually needs a soil characteristic data for each soil layer that the researcher made. It is consider impractical when we want to implement an immediate simulation while we do not have soil data.

However, the soil data issue been abandon by the utilizing of Moderate Resolution Imaging Spectroradiometers (MODIS) LST Version 5 to evaluate water and energy budget modeling for river basins. In other study, a distributed biosphere hydrological model (WEBDHM) was used to investigate the water and energy cycles in the upper Tone River Basin where flux observations are not available [3]. The MODIS V5 LST products were used to evaluate the model’s performance in representing energy processes in the basin, which shows reasonable accurate results.

The studies of distributed biosphere hydrological model give us an understanding model by examining process in biosphere frame. Assumed from the land use map on the papers, the example cases that have been mentioned are implemented in the sub basins that located at considerably rural area. The similar study that conducted in ‘urban sub basin’ area have not been found yet. It will be interesting to analyze such simulation in urban condition, since the value of ground heat flux will be much higher in urban surface compare in the condition of permeable soil that mostly found in rural area -consider also other land surface parameter value differences in the energy balance.

References:
1. Sellers, P. J., et al. Modelling the exchanges of energy, water, and carbon between continents and the atmosphere. Science Magazine Vo.275. (2007)

2. Wang, L., et al. Development of a distributed biosphere hydrological model and its evaluationwith the southern great plains experiments (SGP97 and SGP99). Journal of Geophysical Research. (2009), doi:10.1029/2008JD010800,2009

3. Wang, L., et al. Assessment of a distributed biosphere hydrological model against streamflow and MODIS land surface temperature in the upper Tone River Basin. J. Hydrol. (2009), doi:10.1016/j.jhydrol.2009.08.005