Dials and knobs

This table highlights elements that can be varied between modeling scenarios. We have informally referred to these elements as the "dials and knobs" that can be adjusted within the model. This table presents these "Dials and Knobs" within the context of model settings for the scenarios run to date.


Related Dials and Knobs (things that can be changed between scenarios)

Sub-Models directly affected by these Dials and Knobs

Settings in Scenarios Run to Date
(refer also to the Scenarios Table )

Highlights of Lessons Learned from Model Results to Date (Subject to Change)

Exogenous Drivers


Choice of High, Middle, or Low Climate Change Scenario

Could also adopt uniform temperature changes, e.g., +/- Ref but leave other parameters (precip, etc. same as Ref)

Hydrology (including snow and reservoirs)

Agricultural water demand, crop and irrigation decisions

Forest sub-models

Urban water demand

Reference Case Scenario - MIROC (Ref) - middle range climate change; 5.5°C (10°F) increase in PNW annual mean temperatures over century

High Climate Change - Hadley (HighClim) - 7.6°C (14°F) increase in PNW annual mean temp. over century

Low Climate Change - GFDL (LowClim) - 1.5°C (3°F) increase in PNW annual mean temp. over century

Warmer atmospheric temperatures lead to reduced snow-pack (more precip. as rain, earlier snowmelt). However, snow makes up only about 7% of our water budget.

Warmer atmospheric temperatures lead to greater upland forest disturbance by wildfire, particularly under the High Climate Change scenario.

The basin's federal reservoirs appear to mitigate some of the downstream effects of these changes, and we observe fewer hydrologic changes in model results below reservoirs.

No strong trends over the century in annual precipitation in all scenarios. However, there is inter-annual and inter-seasonal variation within the three climate scenarios. For example the Ref (MIROC) scenario has wetter years in the middle part of the century; and summers become slightly drier in the HighClim (Hadley) scenario.

View related charts : Climate , Hydrology , Snow


Choice of projections in Reference or HighPop scenarios

Could also adopt incremental changes, e.g. +/- population projection in Ref

Urban water demand and land use sub-models

Reference Case - pop in 2010 = 2.41 M; 2100 = 5.37M

High Population Growth = population growth rates within UGBs doubled relative to Ref; pop. in
2100 = 8.25M

Development footprint , population density, and land values within UGBs are highest under the HighPop scenario -- the expanding development causes more loss of farm and forest lands than in the Ref scenario.

Relaxing the UGB expansion threshold lowers developed land values.

Urban reserves appear to constrain growth and increase population density and land values as the HighPop scenario approaches 2060. They decline after that date when expansion is no longer limited to urban reserves.

View related charts: Development


Could adopt incremental changes, e.g. +/- income projection in Ref

Urban water demand and land use sub-models

Reference Case - starting mean annual household income of $87,854 rising to $241,917 by 2100 (measured in 2005 dollars) from Woods and Poole (2011)

As income rises, urban water demand rises.

As income rises economic returns from developed land uses also rise which helps drive urban expansion.

Endogenous Drivers (Policies and Management)


Simple changes to rule curves possible - depending on time and resource constraints

Exploring re-authorization of stored water

Modeling of removal or addition of reservoirs is beyond project scope


Reference Case - rule curves implemented as of 2011; includes BiOp recommendations as of 2009 except selective withdrawal structure at Cougar

Early Reservoir Refill (EarlyRefill) (planned) - maintains Ref rule curves but shifts spring fill "ramp" to two weeks earlier

The reservoirs appear to perform well into the future (providing flood risk reduction and meeting spring and summer environmental flow targets).

The presence of the reservoirs modulates stream discharge dynamics in the lower watershed, suggesting that the reservoirs may offset some of the climate induced hydrologic changes in the valley. The change in winter precipitation from snow to rain (due to warmer atmospheric temperatures) may increase winter flood risks in the valley.

Early Reservoir Refill scenario not yet analyzed. Note that this rule change isn't in conflict with fisheries related rules AS LONG AS the reservoirs can still meet their spring and summer flow targets. The goal is to test whether this is still possible with earlier refill.

View related charts: Hydrology

Water Rights

Prioritize certain types of rights

Set or change thresholds for seasonal and permanent loss of use

Add rights (e.g., for tribes, stored water, Corp of Engineer water rights, etc.))

Set minimum flow requirements for specific reaches that supersedes other uses

Could convert rights from one use to another

Change limits on rate or duty


Reference Case - irrigation diversion rate cannot exceed 1/80 cfs/acre; duty cannot exceed 2.5 acre-feet/acre

Alternative scenario with changes in rate and/or duty for irrigation planned, details not yet specified

Water for diversion is most limited in smaller (lower order) streams. Caveat: lower order stream discharge is not as accurate in hydrology model.

Some “conflicts” observed in scenarios – “conflict” defined as “when available water is less than half the demand in an IDU”.

Irrigation water diversion rates do not approach legal maximum rate of 1/80th cfs/acre.

View related charts: Water Diversions

Forest Management

Select either variation on fire suppression (Ref or FireSuppress)

Change harvest rates; for example to aggressive harvest policy from before Northwest Forest Plan

Change minimum stand age for harvest

Forest sub-models

Reference Case - wildfire suppression at historical levels; forest area burned per year increases three-fold over historical rates; Harvest rate is set based on observed rate (1985-2010); stands must be 60 years or older to be harvested

Upland Wildfire Suppression (FireSupress) - fire suppression efforts increase to hold area burned per year to historical rates

Forests are the dominant “consumer” of water in the basin as measured by evapotranspiration – they use about seven times more water than irrigation in the Ref scenario.

Under the two higher change climate scenarios, the forest area burned per year increased 3 to 9 fold over historical rates. The corresponding reduction in forest cover and leaf area had the effect of reducing simulated basin-wide annual evapotranspiration.

Under the more intense climate change scenarios, forest transitioned to more subtropical (tan oak, Doug fir) forests; the rate of change increased with the incidence of fire, because fire opened up lands to transition to new forest types.

The burning of mature forests reduced the availability of forestland for harvest and affected the rate of harvest that could be sustained. More timber was available for harvest in the FireSupress scenario.

View related charts: Climate and Forest Management


Change UGB expansion threshold

Change use of urban reserves for Portland Metro UGB

Urban water demand and land use sub-models

Reference Case - UGBs expand when 80% developed; growth of Portland Metro UGB confined to urban reserves through 2060

Relaxed Urban Expansion (UrbExpand) - UGBs expand when 70% developed; no urban reserves

Development footprint and land values within UGBs are higher within HighPop and Ref scenarios.

In UrbExpand scenario, the lower housing density leads to lower land values.

Urban reserves appear to constrain growth and increase population density and land values as the HighPop scenario approaches 2060. They decline after that date when expansion is no longer limited to urban reserves.

View related charts: Development, Urban Expansion Impacts on Water Use

Crop and Irrigation Decisions

Could change relative energy price which affects irrigation decisions

Could change price of wheat or grass seed which affects crop choice

Crop and irrigation decision sub-models

Reference Case - Price of wheat ($64/ton) and grass seed ($5/bushel), and energy price does not rise (in real terms)

In the Ref scenario, total area covered by each agricultural land type remain about the same over the century with grass seed and pasture remaining the dominant crops by acreage.

Warmer temperatures lead to earlier crop planting dates, and as a result there is a shift in agricultural water demand to an earlier peak during the growing season.

There is a decline in agricultural lands and water demand for irrigation as cities expand and displace farmlands

View related charts:Agriculture

Urban Water Demand

Use a different function to determine future water price

Urban water demand

Reference Case - 15 year increase in price (1.5%/yr) to cover infrastructure backlog, then prices held near constant in real terms for pop. size

Full Cost Urban Water Pricing (FullCostUrb) - 15 year increase in price to reach estimated long-run average cost (LRAC), which depends on pop. size; prices then continue at LRAC

Increasing population leads to higher urban water demand.

In the Reference Case, during the first 15 years, there is a decrease in per capita consumption, reflecting the 15 year increase in water prices; later in the century there is slight increase in per capita water consumption as incomes continue to rise and prices decline slightly due to economies of scale as cities grow.

View related charts: Development, Urban Expansion Impacts on Water

Mainstem Water Temperature

Modify reservoir release rules to respond to downstream temperatures exceeding threshold (pending time and resource constraints; requires additional model development).


Stream temperature and fish sub-models

Reference Case - there are currently no feedbacks from stream temperature to water use/reservoirs/water rights in the model

Stream temperature results not analyzed pending implementation of improved stream temperature model.




Fisheries results not analyzed pending implementation of improved stream temperature model.

Off-line analysis suggests that the likelihood of capturing cold water native fish decreases with increasing stream temperature; if mean river temperature increases by 2 degrees by 2100, likelihood of occurrence of cold water salmonids projected to decrease by half.