13. CWatM Glossary

General Model Terms

CWatM

Community Water Model - A hydrological model simulating the water cycle daily at global and local levels, historically and into the future, maintained by IIASA’s Water Security research group.

IIASA

International Institute for Applied Systems Analysis - The organization that developed and maintains CWatM, located in Laxenburg, Austria.

LHM

Large-scale Hydrologic Model - A category of models that CWatM belongs to, used for assessing climate-driven hydrologic changes from watershed to global scales.

WHM

Watershed Hydrologic Model - A model type configured with multiple subbasins for detailed watershed analysis.

Water-Energy-Food Nexus

The interconnected relationship between water resources, energy production, and food systems that CWatM is designed to analyze.

Hydrological Processes

Evapotranspiration (ET)

The sum of evaporation from the land surface plus transpiration from plants. CWatM can calculate this using Penman-Monteith or Hargreaves methods.

Baseflow

The portion of streamflow that comes from groundwater discharge rather than direct runoff.

Capillary Rise

The upward movement of water from groundwater to soil layers, occurring when groundwater level is close to the surface (0-5m depth in CWatM).

Interflow

Lateral subsurface flow that occurs above the groundwater table and contributes to streamflow.

Runoff Concentration

The process of collecting and routing surface runoff within a grid cell, calculated using a triangular weighting function in CWatM.

Preferential Bypass Flow

Fast flow paths through soil that bypass the soil matrix, controlled by an empirical shape parameter in CWatM.

Snowmelt

The process of snow turning into water, calculated using a degree-day factor approach in CWatM.

SWE (Snow Water Equivalent)

The amount of water contained within the snowpack.

SWEmax

Maximum Snow Water Equivalent - The peak amount of water stored as snow.

Calibration Parameters

Snowmelt Coefficient

Degree-day factor (m °C⁻¹d⁻¹) used to calculate snowmelt rate based on temperature.

Crop Factor (Kc)

Adjustment factor for crop evapotranspiration, ranging from 0.8 to 3.0 in calibration.

Soil Depth Factor

Factor for adjusting the overall soil depth of soil layers 1 and 2 (range: 0.8-1.8).

ARNO Beta

Empirical shape parameter of the ARNO model for infiltration capacity (range: 0.01-1.0).

Interflow Factor

Factor to adjust the amount of water that percolates from interflow to groundwater (range: 0.33-3.0).

Recession Coefficient Factor

Factor to adjust the base flow recession constant (range: 0.1-10.0).

Manning’s Coefficient (n)

Roughness coefficient for channel flow, ranging from 0.025 (lowland rivers) to 0.075 (mountainous rivers).

Normal Storage Limit

Threshold for reservoir storage levels (range: 0.15-0.85).

Lake A Factor

Calibration parameter for lake area calculations (range: 0.333-3.0).

Lake Eva Factor

Calibration parameter for lake evaporation (range: 0.5-3.0).

Technical and Computational Terms

NetCDF4

Network Common Data Form version 4 - File format used by CWatM for reading, storage, and production of data.

CF 1.6 Convention

Climate and Forecast metadata convention for NetCDF files, ensuring standardized variable names and units.

Kinematic Wave Approximation

Simplified form of the Saint-Venant equations used for routing water through channels.

Modified Puls Method

Approach used by CWatM for simulating lake dynamics.

Van Genuchten Model

Mathematical model describing soil water retention and hydraulic conductivity relationships.

Pedotransfer Function

Method to derive soil hydraulic parameters from standard soil properties using models like Rosetta.

D8 Flow Model

Eight-direction flow model defining dominant flow direction to neighboring grid cells.

PC-Raster Framework

Programming framework that influenced CWatM’s modular structure with initialization and dynamic classes.

Model Resolution and Scale

Spatial Resolution

CWatM can run at resolutions from 30 arcsec to 0.5 degrees (5 arcmin to 30 arcmin).

Temporal Resolution

Daily time steps for main calculations, with sub-daily time stepping (10 steps/day) for soil and river routing.

Grid Cell

Basic spatial unit of the model where calculations are performed.

Subbasin

Hydrological subdivision of a larger watershed for detailed analysis.

Upstream Area

The total drainage area contributing flow to a specific point.

Data and Input/Output

DDM30

0.5° drainage direction map used for ISIMIP compliance.

HydroSheds

High-resolution hydrological data source for river networks.

HydroLakes

Database providing information on 1.4 million global lakes and reservoirs with surface area ≥10ha.

HWSD

Harmonized World Soil Database version 1.2 - Source of soil property data.

ISIMIP

Inter-Sectoral Impact Model Intercomparison Project - Framework for comparing global model outputs.

Mask Map

Spatial definition of the model domain or catchment area.

Forcing Data

Meteorological input data driving the model (temperature, precipitation, etc.).

Climate Data Sources

EWEMBI

EartH2Observe, WFDEI and ERA-Interim data Merged and Bias-corrected for ISIMIP.

WFDEI

WATCH Forcing Data methodology applied to ERA-Interim.

MSWEP

Multi-Source Weighted-Ensemble Precipitation.

PGMFD

Princeton Global Meteorological Forcing Dataset.

GSWP3

Global Soil Wetness Project Phase 3.

GCM

General Circulation Model - Global climate models providing future projections.

RCP

Representative Concentration Pathway - Climate change scenarios (e.g., RCP4.5, RCP6.0, RCP8.5).

SSP

Shared Socioeconomic Pathway - Scenarios of socioeconomic global changes (SSP126, SSP370, SSP585).

CMIP6

Coupled Model Intercomparison Project Phase 6.

Model Integration

MODFLOW

Modular finite-difference groundwater flow model that can be coupled with CWatM for detailed groundwater simulation.

MESSAGE

IIASA’s energy system optimization model for energy planning.

GLOBIOM

Global Biosphere Management Model - IIASA’s land use and agriculture model.

EPIC

Environmental Policy Integrated Climate model for crop yield and management.

ECHO

Hydro-economic model for water infrastructure investment analysis.

MARINA

Model for water quality assessment.

Water Demand Sectors

Irrigation Water Demand

Water requirements for agricultural irrigation, accounting for soil moisture, irrigation methods, and climate.

Domestic Water Demand

Household water consumption requirements.

Industrial Water Demand

Water requirements for industrial processes.

Livestock Water Demand

Water consumption by livestock.

Environmental Flow Requirements

Minimum water flows needed to maintain ecosystem health.

Return Flow

Water that returns to the system after use (e.g., from irrigation or urban areas).

Calibration and Validation

NSE

Nash-Sutcliffe Efficiency - Performance metric for model calibration.

KGE

Kling-Gupta Efficiency - Alternative performance metric addressing NSE limitations.

DEAP

Distributed Evolutionary Algorithms in Python - Used for model calibration.

Spin-up Period

Initial model run period to establish equilibrium conditions before analysis.

Warm Start

Initializing model with saved state variables from a previous run.

Initial Conditions

Starting values for state variables at the beginning of a simulation.

File Formats and Standards

.ini File

Configuration file format used for CWatM settings.

.nc File

NetCDF file extension for model input/output data.

.csv File

Comma-separated values format for time series data.

FAIR Principles

Findable, Accessible, Interoperable, Reusable - Data management principles implemented in CWatM.

Git Hash

Version control identifier tracking specific model versions.

Hydrological Variables

Discharge

Volume of water flowing through a channel cross-section per unit time (m³/s).

TWS

Total Water Storage - Sum of all water stored in the system.

Channel Storage

Water temporarily stored in river channels.

Lake/Reservoir Storage

Water stored in lakes and reservoirs.

Groundwater Storage

Water stored in aquifers below the water table.

Soil Moisture

Water content in soil layers.

Interception Storage

Water temporarily stored on vegetation surfaces.

Depression Storage

Water accumulated in surface depressions.

Soil Parameters

Field Capacity (θfc)

Soil moisture content after excess water has drained.

Wilting Point (θwp)

Soil moisture content below which plants cannot extract water.

Saturated Water Content (θs)

Maximum water content when soil is fully saturated.

Residual Water Content (θr)

Minimum water content in dry soil.

Saturated Hydraulic Conductivity (Ks)

Rate of water movement through saturated soil.

Porosity

Fraction of soil volume occupied by pore spaces.

Bulk Density

Mass of dry soil per unit volume.

Channel Geometry

Channel Length

Length of the main channel within a grid cell.

Channel Slope

Gradient of the channel bed.

Channel Width

Bottom width of the channel cross-section.

Channel Depth

Depth of water in the channel.

Bankfull Discharge

Flow rate at which water begins to overflow the channel banks.

Model Outputs

Water Balance

Accounting of all water inputs, outputs, and storage changes.

Potential Discharge

Maximum possible flow under given conditions.

Potential Evaporation

Maximum evaporation rate under given atmospheric conditions.

Actual Evapotranspiration

Real water loss through evaporation and transpiration.

Water Availability

Amount of water available for human and environmental use.

Water Stress

Ratio of water demand to water availability.

Acronyms

BNR

Biodiversity and Natural Resources (IIASA program).

WAT

Water Security (IIASA research group).

IBF

Integrated Biosphere Futures (IIASA research group).

EAC

East African Community.

eLVB

Extended Lake Victoria Basin.

LRB

Liard River Basin.

GNU GPL

GNU General Public License - Open source license under which CWatM is released.

Note

This glossary is based on CWatM version 1.06 (October 2024). Terms and definitions may evolve with new model versions. For the most current information, refer to the official documentation at https://cwatm.iiasa.ac.at/

See also