Meterorology & Hydology

The meteorological module in ALCES® adopts a stock and flow bath-tub model that accounts for every cubic meter of water on and below the landscape. General conceptual representations of ALCES® hydrological module are depicted below. The level of complexity in terms of the number of components tracking water can be either increased or decreased to match the nature of the questions being asked or data available.

In the meteorological module of ALCES®, the mean and variance of annual temperature and precipitation (rain and snow) in each of the landscape and footprint types are specified. Additional inputs include the percentage of precipitation in each landscape type and footprint type is ultimately destined for evapotranspiration, surface runoff (either lotic or lentic), and infiltration into surficial aquifers. Surface and subsurface water entering and exiting the study area from outside the perimeter is tracked. The initial and maximum volume of reservoirs (surface water and ground water) located in the land base, the volume of water withdrawn by each land use sector from rivers and reservoirs, and the minimum percent of water required for in-stream needs and for exporting to downstream jurisdictions can also be specified.

Subsurface water (aquifers) can be stratified into, and tracked within, two types (saline, non-saline) and three depths (shallow, medium, deep).

All land uses requiring water require a consumption coefficient (for example, 270 m3 of water/human/yr for domestic purposes, 25 m3/Animal Unit of Cow/yr), the source of water extraction (lotic, lentic, reservoir, shallow aquifer, medium aquifer, deep aquifer) and the return destination (atmosphere, lentic, lotic, reservoir, aquifer) of the water following its use.

In the meteorological module, the average annual temperature and precipitation (rain and snow) in each of the landscape and footprint types are specified.  Future trends in these meteorological variables may be modelled as constant or random variables, with inter-annual variation specified by the user.   It is also possible to specify the percentage of precipitation in each landscape type and footprint type that ultimately enters mainstem rivers, plus the additional volume of water entering via rivers that flow into the land base.  The initial and maximum volume of reservoirs (surface water and ground water) located in the land base, the volume of water withdrawn by each land use sector from rivers and reservoirs, and the minimum percent of water required for in-stream needs and for exporting to downstream jurisdictions may also be specified.

Table Inputs

1. Mean and variance of precipitation in each landscape type
   - Enter the mean annual precipitation (cm) for each landscape type.  In many land bases, particularly small ones, it is appropriate to enter the same value for each landscape type.
   - Enter the standard deviation (cm) of annual precipitation among years for each landscape type.  In many land bases, particularly small ones, it is appropriate to enter the same value for each landscape type.
   - Enter the average percent of annual precipitation that falls as snow in each landscape type.  In many land bases, particularly small ones, it is appropriate to enter the same value for each landscape type.
   - Enter the percent of snow that is water
2. Mean and variance in temperature for each landscape type
   - Enter the mean annual temperature (degrees C) for each landscape type.  In many land bases, particularly small ones, it is appropriate to enter the same value for each landscape type
3. Percent of precipitation in each footprint and landscape type that enters mainstream rivers
   - Enter the percent for each footprint and landscape type
4. Reservoir metrics
   - Enter full reservoir capacity (m3)
   - Enter reservoir volume (m3) at the start of the simulation period
   - Enter the percent of water entering the reservoir that is lost to evaporation and leakage
5. Mainstem river and reservoir water demand metrics
   - Enter mainstem river water demand for each land use sector
   - Enter reservoir water demand for each land use sector
   - Enter average water return for each land use sector
6. Mainstem river water entering study area
   - Enter volume of water entering study area each year
7. Minimum instream needs and water export requirements
   - Enter minimum percent of gross water required for export
   - Enter minimum percent of gross water required for inflow needs

Switches

Meteorology random or constant

• Precipitation and temperature can be modeled in ALCES as either annually constant (deterministic) events or as stochastic events (incorporating estimates of inter-annual variance).  If the switch is down (0), then precipitation and temperature are constant, based on the average values entered in Tables 1 and 2.  If the switch is up (1) then the average precipitation and temperature in a given year of a simulation are drawn from a random distribution defined the averages and standard deviations entered in Tables 1 and 2.

New random values up vs replicated random down

• If precipitation and temperature are to be modelled in a stochastic fashion for multiple runs, then the starting random values for precipitation and temperature can be fixed among runs if this switch is down (0).  Alternatively, new random values for these variables are generated if the switch is up (1).

Climate change on or off

• Temporal trends in precipitation and temperature that reflect a "climate change" scenario may be specified in the climate change module.  To active this module, this switch must be up (1).

Lotic inputs from runoff or user-defined

• Users have the option of calculating water input to lotic and lentic systems using a mechanistic approach based on precipitation, evapotranspiration and surface runoff coefficients (switch down), or using empirical values from regional water flow models or monitoring programs (switch up).  In this latter approach (switch up), water movement is disconnected from precipitation and runoff coefficients.