Applied Methods

Dam breach and flood routing models for glacier lake hazard assessments
Within the HighNoon project, the hazard situation of moraine dammed proglacial lakes in the Indian Himalayas is assessed. Overtopping flow can erode glacier lake dams leading to a partial or complete moraine dam failure with subsequent flooding of the downstream valleys. To analyze such dam failures and outburst floods, the dam break and flood routing models BASEMENT and FLO-2D are applied.

BASEMENT is a new erosion based dam break model developed at the ETH Zurich. This two-dimensional hydraulic model is based on the shallow water equations which are solved with an explicit Finite-Volume method. Erosion and transport of dam material due to overtopping flow are calculated with empirical sediment transport equations. Thus, sediment transport laws are used to calculate the vertical incision in earthen dam structures. The lateral widening of the dam breach is considered with a geometrical approach. If a critical slope angle is exceeded due to vertical erosion, gravitational induced sidewall failure takes place and sediment material moves downwards.

The software BASEMENT is designed for the numerical simulation of natural hazards and environmental flows. Unstructured meshes can be used for the hydraulic and sediment calculations and are advantageous for applications on field studies with irregular site geometries.


FLO-2D is a commercial hydraulic programme developed by J. O'Brien (U.S.A). It is a two-dimensional flood-routing model for channel and unconfined overland flow. The model simulates pure water, hyperconcentrated and debris flows and estimates the probable range of flow velocity and inundation depth. FLO-2D assumes volume conservation (i.e. the total inflow and outflow volumes plus storage and losses from infiltration and evaporation are accounted for). Flood wave progression over the flow domain is computed on the base of topographic data, flood hydrographs, flow parameters and resistance to flow. FLO-2D is a finite difference model using the continuity equation to describe general constitutive fluid and the equation of motion. When simulating sediment-laden flows with FLO-2D, the yield stress and viscosity have to be specified.


JULES
JULES, the Joint UK Land Environment Simulator, (JULES (Cox et al, 1998, Cox et al, 1999, Essery et al., 2003) is a land surface model designed to represent the exchange of heat, water and carbon between the land surface and atmosphere. The model runs on a grid, for HighNoon modelling at 0. 5 degree resolution.

In the HighNoon study a version of JULES based on JULES 2.1.2 is used. This version includes a multi-layer snow model including snow hydrology and a prognostic snow albedo scheme. In addition the model is coupled to the Total Ruonff Integrating Pathways (TRIP) (Oki and Sud, 2009) which simulates riverflow. The model is initialised by spinning up soil moisture, snow cover and river storage over the 1960-1970 period.

References

  • Cox, P. M., C. Huntingford, and R. J. Harding, 1998: A canopy conductance and photo-synthesis model for use in a GCM land surface scheme. J. Hydrology, 212- 213, 79-94
  • Cox, P. M., R. A. Betts, C. B. Bunton, R. L. H. Essery, P. R. Rowntree, and J. Smith, 1999: The impact of new land surface physics on the GCM simulation of climate and climate sensitivity. Clim. Dyn., 15, 183-203
  • Essery RLH, Best MJ, Betts RA, Cox PM, Taylor CM, 2003.Explicit representation of subgrid heterogeneity in a GCM land surface scheme. Journal of Hydrology , 4(3), 530-543
  • Oki, T. and U. C. Sud (1998). "Design of Total Runoff Integrating Pathways (TRIP) - A Global River Channel Network." Earth Interactions 2(1): 1-36. 


LPJmL model for simulating changes in water resources in the Ganges basin
LPJmL is global dynamic vegetation and hydrology model operating at a 0.5 degree resolution. It has been developed mainly at the Potsdam Institute for Climate Impact Research. The model simulates the coupled global carbon and hydrological cycles. Recently, LPJmL is extended with a crop growth module and a reservoir operation module. It explicitly accounts for the demand, withdrawal and redistribution of water for agriculture and other sectors. Therefore, LPJmL can be regarded as a water resources model rather than a hydrological model only. The strenght of  LPJmL is the ability of simulating the interactions between water availability and crop production, as well as the combined impact of changes in water efficiency, changes in cropping patterns, climate change and infrastructural changes on water resources and crop production. Within HighNoon, it is therefore a very useful tool to address the future water resources situation in the Ganges basin.


Regional Model (REMO) 
REMO from Max-Planck Institute for Meteorology is a three dimensional hydrostatic atmospheric circulation model, which solves the primitive equations of the atmospheric motion. REMO (Jacob, 2001, 2009) is a combination of two models, dynamical core and discretisation in space and time have been taken from the Europa Model from DWD and Physics has been taken from ECHAM4 (GCM of MPI-M).

The atmospheric prognostic variables of REMO are horizontal wind components, temperature, pressure, specific humidity, and cloud liquid water content. The model uses the Arakawa-C grid for horizontal represen-tation in which all variables except the wind component are defined in the centre of the respective grid box, and a hybrid of p and η using 27 levels in vertical. The prognostic variables of REMO are adjusted towards the large scale forcing in a lateral sponge zone of 8 grid boxes in which the lateral boundary conditions (LBC) influence decreases exponentially towards the inner model domain.

 

 

The soil temperature over land is calculated using a diffusion equation solved in five different layers covering up to 10m in the lower most soil. The  sub grid scale precipitation processes follow the Tiedtke (1989) convective scheme. The seasonal cycle of vegetation is represented by monthly varying fields of LAI, fractional green vegetation cover and snow-free land surface albedo. 

For HighNoon simulation over India, REMO was used in climate mode with a horizontal resolution of 0.22 x 0.22 (~25 x ~25 Km). In the climate mode, the model has to be initialized once and uses surface parameters over land, SST over ocean and varying lateral boundary values during the whole simulation. The update of lateral boundary has temporal resolution of 6 hr. and is interpolated into a 2 minute time step. Model domain is 60.125E - 100.125E and 4.125N – 40.125N, with 27 vertical levels (i.e. 181 x161 grid points).

References

  • Jacob D, A note to the simulation of the Annual and Interannual Variability of the Water Budget over the Baltic Sea Drainage Basin, Meteorology and Atmospheric Physics, Vol. 77, No. 1-4, pp 61-74, 2001
  • Jacob, D. (2009). Regional Climate Models: Linking Global Climate Change to Local Im-pacts. The Springer Encyclopedia of Complexity and Systems Science, pp 7591-7602