2. Model Design ¶

Contents

Model Design

Background ¶

Water Futures and Solutions Initiatives (WFAS)¶

Water Futures and Solutions Initiatives is using a multi-model approach for global climatic, hydro-socioeconomic modeling in order to assess possible futures. We use three leading global hydrological models H08, WaterGAP and PCR-GLOBWB for estimating water demand and supply. This approach is used for a better understanding of the uncertainty and limitations of modeling. It provides a degree of confidence in the results an is in-line with the ISI-MIPS approach of multi-modeling

Figure 1: Potential population under severe water scarcity in 2050 - Middle of the Road Scenario - WFAS fast-track analysis

Nexus Integration - Water Energy Food Environment ¶

In the framework of the Integrated Solution project
the Community Water Model (CWatM) will be coupled with the existing IIASA models MESSAGE and GLOBIOM
in order to do enhanced water assessments and an improved analysis feedback on water, energy, food and environmental aspects

Figure 2: IIASA model interactions

CWAT and the IIASA global hydro-economic model ¶

The Community Water Model will help to develop a next-generation hydro-economic modeling tool that represents the economic trade-offs among water supply technologies and demands. The tool will track water use from all sectors and will identify the least-cost solutions for meeting future water demands under policy constraints. In addition, the tool will track the energy requirements associated with the water supply system (e.g., desalination and water conveyance) to facilitate the linkage with the energy-economic tool. The tool will also incorporate environmental flow requirements to ensure sufficient water for environmental needs. The new hydro-economic model will be linked to CWatM by GAMS output and input files (gdx-files).

Model design and processes ¶

Design ¶

The Community Water Model (CWatM) will be designed for the purpose to assess water availability, water demand and environmental needs. It includes an accounting of how future water demands will evolve in response to socioeconomic change and how water availability will change in response to climate.

Figure 3: CWatM - Water related processes included in the model design

Processes ¶

Calculation of potential Evaporation¶

Using Penman-Montheith equations based on FAO 56

Calculation of rain, snow, snowmelt¶

Using day-degree approach with up to 10 vertical layers Including snow- and glacier melt.

Land cover¶

using fraction of 6 different land cover types

Forest
Grassland
Irrigated land
Paddy irrigated land
Sealed areas (urban)
Water

Water demand¶

including water demand from industry and domestic land use via precalculated monhly spatial maps
including agricultural water use from calculation of plant water demand and livestock water demand
Return flows ((water withdrawn but not consumed and returned to the water circle)

Vegetation¶

Vegetation taken into account for calculating

Albedo
Transpiration (including rooting depth, crop phenology, and potential evapotranspiration)
Interception

Soil¶

Three soil layers for each land cover type including processes:

Frost interupting soil processes
Infiltration
Preferential flow
Capillary rise
Surface runoff
Interflow
Percolation into groundwater

Groundwater¶

Groundwater storage is simulated as linear groundwater reservoir

Lakes & Reservoirs¶

Lakes are simulated with weir function from Poleni for rectangular weir.
Reservoirs are simulated as outflow function between three storage limits (conservative, normal,flood) and three outflow functions (minimum, normal, non-damaging)

Routing¶

Routing is calculated using the kinematic wave approach

Features of the Model ¶

Community Model ¶

Feature	Description
Programming Language	Python 3.x with some C++ for computational demanding processes e.g. river routing
Community driven	Open-source but lead by IIASA GitHub repository
Well documented	Documentation, automatic source code documentation GitHub Docu
Easy handling	Use of a setting file with all necessary information for the user Complete settings file and Output Meta NetCDF information
Multi-platform	Python 3.x on Windows, Mac, Linux, Unix - to be used on different platforms (PC, clusters, super-computers)
Modular	Processes in subprograms, easy to adapt to the requirements of options/ solutions Modular structure

Water Model ¶

Feature	Description
Flexible	different resolution, different processes for different needs, links to other models, across sectors and across scales
Adjustable	to be tailored to the needs at IIASA i.e. collaboration with other programs/models, including solutions and option as part of the model
Multi-disciplinary	including economics, environmental needs, social science perspectives
Sensitive	Sensitive to option / solution
Fast	Global to regional modeling – a mixture between conceptional and physical modeling – as complex as necessary but not more
Comparable	Part of the ISI-MIP community

Demo of first results ¶

Here are some first demonstration of the model run:

Demo of the model