Seasonal streamflow forecasts: Difference between revisions
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==Overview== | ==Overview== | ||
Seasonal streamflow forecasts, also called seasonal water supply forecasts, are widely | Seasonal streamflow forecasts, also called seasonal water supply forecasts, are widely consulted by water managers and water users throughout the Colorado River Basin to inform general expectations for the coming runoff season and specific operational decisions such as reservoir release schedules and water allocations. Forecasts are issued from mid-winter (Dec/Jan) through July for a several month forecast period: April-July (most common), March-June, or May-August, depending on the usual runoff peak. | ||
There are two primary federal providers of operational seasonal streamflow forecasts: ( | There are two primary federal providers of operational seasonal streamflow forecasts for the basin: | ||
*Colorado Basin River Forecast Center (CBRFC), one of the 11 NOAA National Weather Service River Forecast Centers | |||
*Natural Resource Conservation Service (NRCS) National Water and Climate Center | |||
CBRFC and NRCS use different modeling approaches and their respective forecasted streamflow volumes for the same forecast point may differ. Before 2012, they coordinated their forecasts so that their forecasted streamflow volumes were the same. | |||
CBRFC seasonal streamflow forecasts are critical inputs into Reclamation's operational models, 24-Month Study and MTOM. | |||
==Methods== | |||
In the snowmelt-dominated headwaters of the Colorado River Basin, predictability of streamflow on seasonal timescales in the basin arises from ''initial moisture conditions'': the observed snowpack and soil moisture conditions. The skill of the forecasts increases through the winter and spring months as the accumulating snowpack provides more information about the upcoming runoff. Soil moisture deficits or surpluses in the fall, before snow begins to accumulate, indicate whether an an unusually low or high proportion of the snowpack will become runoff in the stream. | |||
Lower-elevation watersheds which have little or no snowmelt contributing to the annual hydrology cannot be forecast as skillfully as higher-elevation watersheds that are snowmelt-dominated. In all cases, the primary source of forecast uncertainty and error is due to lack of knowledge of how the weather and climate will evolve between the date the forecast is issued (e.g., April 1st) and the end of the forecast period (e.g., July 31st). Other uncertainty and error comes from inaccurate representation of the snowpack and/or soil moisture observations used as inputs into the forecast model, and biases in the model itself. | |||
The CBRFC uses a relatively simple dynamical or process-oriented model framework for its seasonal forecasts, coupling a snow model (SNOW-17) with a rainfall-runoff model (Sacramento Soil-Moisture Accounting; SAC-SMA). | |||
Revision as of 18:01, 5 April 2021
Overview
Seasonal streamflow forecasts, also called seasonal water supply forecasts, are widely consulted by water managers and water users throughout the Colorado River Basin to inform general expectations for the coming runoff season and specific operational decisions such as reservoir release schedules and water allocations. Forecasts are issued from mid-winter (Dec/Jan) through July for a several month forecast period: April-July (most common), March-June, or May-August, depending on the usual runoff peak.
There are two primary federal providers of operational seasonal streamflow forecasts for the basin:
- Colorado Basin River Forecast Center (CBRFC), one of the 11 NOAA National Weather Service River Forecast Centers
- Natural Resource Conservation Service (NRCS) National Water and Climate Center
CBRFC and NRCS use different modeling approaches and their respective forecasted streamflow volumes for the same forecast point may differ. Before 2012, they coordinated their forecasts so that their forecasted streamflow volumes were the same.
CBRFC seasonal streamflow forecasts are critical inputs into Reclamation's operational models, 24-Month Study and MTOM.
Methods
In the snowmelt-dominated headwaters of the Colorado River Basin, predictability of streamflow on seasonal timescales in the basin arises from initial moisture conditions: the observed snowpack and soil moisture conditions. The skill of the forecasts increases through the winter and spring months as the accumulating snowpack provides more information about the upcoming runoff. Soil moisture deficits or surpluses in the fall, before snow begins to accumulate, indicate whether an an unusually low or high proportion of the snowpack will become runoff in the stream.
Lower-elevation watersheds which have little or no snowmelt contributing to the annual hydrology cannot be forecast as skillfully as higher-elevation watersheds that are snowmelt-dominated. In all cases, the primary source of forecast uncertainty and error is due to lack of knowledge of how the weather and climate will evolve between the date the forecast is issued (e.g., April 1st) and the end of the forecast period (e.g., July 31st). Other uncertainty and error comes from inaccurate representation of the snowpack and/or soil moisture observations used as inputs into the forecast model, and biases in the model itself.
The CBRFC uses a relatively simple dynamical or process-oriented model framework for its seasonal forecasts, coupling a snow model (SNOW-17) with a rainfall-runoff model (Sacramento Soil-Moisture Accounting; SAC-SMA).
[[File:<FILENAME>|frame|Figure 1. (Image source: [ ])]]
Relevance and Application
Data and Tools
Additional Resources
State of the Science Report
Chapter XX of the State of the Science report (XXXXX
New and Notable Research (2020-present)
[<URL FOR PAPER>]
Summary