CRHM: The Cold Regions Hydrological Model

• Technical Details
• Performance
• Download

CRHM has to date been installed by the following organizations;

Workshops and training courses have been held in

• Waterloo, ON (June 2008)
• Calgary, AB (June 2008)
• Winnipeg, MB (June 2009)
• Red Deer, AB (January 2010)
• Yellowknife, NWT (October 2010)
• National Hydrological Research Centre, Saskatoon, SK (September 2011)
• Coldwater Laboratory, Biogeoscience Institute, Kananaskis, AB (July 2012)

More information about the system is included in a recent publication -
C.R. Ellis, J.W. Pomeroy, T. Brown, and J. MacDonald 2010: Simulation of snow accumulation and melt in needleleaf forest environments Hydrology and Earth System Sciences 14: pp. 925–940 (2.02Mb PDF)

Further details are also available from the modelling page on the IP3 website.

Technical Details
Processes modelled by the software currently include;

• blowing snow redistribution
• snow and rain interception by forest canopies
• sublimation
• snowmelt in open and forested environments
• infiltration into frozen and unfrozen soils
• soil moisture storage and movement
• water movement along hillslopes (with and without permafrost)
• actual evaporation and evapotranspiration
• radiation exchange on complex surfaces and through vegetation
• wetland dynamics
• variable contributing area
• groundwater flow
• streamflow hydraulics

The model also supports the concept of distinct landscape elements (Hydrological Response Units or HRUs), which may be linked episodically in process-specific sequences such as blowing snow, overland flow, organic layer subsurface flow, mineral interflow, groundwater flow, and streamflow.

The software has been implemented as an object-orientated framework within which new representations of specific processes may be incorporated very easily, allowing direct comparison of competing algorithms within the same contexts and forcings. Users are able to select from a wide range of process models, with varying complexities of representation, to build a basin hydrology model suitable for their investigations: the software then links these together in the most logical order.

This also means that the system is not limited to use in the investigation of high-latitude / high-altitude cold regions: by assembling and selecting a suitably relevant set of models, it may be used to investigate the hydrology for a wide variety of landscape / climate combinations.

Note that the software does not provide a means of calibrating these models from streamflow observations; the aim is to encourage reliance on improvements in the numerical representation of the hydrological processes at work to improve predictive performance, rather than to support application of 'fudge factor' parameters in order to force convergence between predicted and observed datasets. This in turn allows the model to be used as a self-testing tool through which to diagnose the adequacy of the hydrological understanding encapsulated within the algorithms employed, thereby reducing uncertainty when the same models are used for predictive applications.

The complete set of CRHM modules has been classified into the following categories;

• Basin: sets HRU physical, soil and vegetation characteristics
  
  
• Observation: interpolates meteorological data to the HRU, using adiabatic and precipitation distribution relationships, and saturation vapour pressure calculations. Includes climate change (temperature, humidity, precipitation) feature to permit sensitivity analysis
  
  
• Snow Transport: blowing snow transport and sublimation
  
  
• Interception: forest canopy and vegetation interception of rainfall, and interception and sublimation of snowfall, including drip and unloading
  
  
• Radiation: selection of routines for shortwave direct and diffuse algorithms, slope corrections, snow albedo decay, longwave radiation, canopy transmissivity, and net radiation. Permits assimilation of sunshine hours or incoming shortwave observations, and estimation of radiation terms using meteorological relationships where observations are missing
  
  
• Evaporation: including the Granger-Gray, Penman-Monteith, Priestly-Taylor and Shuttleworth-Wallace algorithms and optional soil moisture withdrawal curve and rooting zone control
  
  
• Snowmelt: implements Gray’s Energy-Balance Snowmelt Model, Marks’ USDA SNOBAL, Essery’s simple land-surface scheme melt model as well as simple radiation and temperature index techniques
  
  
• Infiltration: variety of infiltration routines for frozen soils, including Gray’s prairie method, Zhao & Gray’s parametric method, a frost depth calculation, Ayer’s unfrozen soil infiltration, Green-Ampt infiltration and redistribution
  
  
• Soil Moisture Balance: multiple flowpath two-layer model with depressional storage, macropore and groundwater options
  
  
• Wetlands: permits open water evaporation and fill and spill or traditional routing from wetland or pond depressional storage
  
  
• Flow: mineral and organic layer flow over permafrost based on physically-based model, with timing and storage control of overland, interflow, sub-surface, groundwater and stream flow using options including the lag and route hydrograph method, a Richard’s Equation solution and/or Muskingum routing method

In most of these categories, a choice of process models is available, ranging from basic to strongly physically-based; this permits the most appropriate algorithms to be used for the available data, information reliability, basin characteristics, scale, intended output, and so on. For more information, download The Cold Regions Hydrological Model, a Platform for Basing Process Representation and Model Structure on Physical Evidence.

Performance
CRHM was included in the Snow Model Intercomparison Project for forest snow processes, SnowMIP2, a working group of the International Commission on Snow and Ice (now the Commission of Cryospheric Sciences), and a component of the Climate and Cryosphere project (CliC) and the Global Land Atmosphere System Study. The project tested the performance of thirty-three models from around the world at three representative sites, one at Alptal in Switzerland, the Boreal Ecosystem Research & Monitoring Site in Saskatchewan, and the Fraser Experimental Forest in Colorado, USA.

Details of the project are available on its website. The main paper published by the project is available from the AGU, with another from the Bulletin of the American Meteorological Society; both include detailed analyses of the predictive performance of CRHM in these settings.

Download
To download the CRHM software set-up kit, please complete and submit the request form.