Forecasting Evaporative Demand across the Conterminous US
Location
Eccles Conference Center
Event Website
http://water.usu.edu/
Start Date
3-29-2011 2:00 PM
End Date
3-29-2011 2:20 PM
Description
Agriculturalists and operational hydrologists often seek to predict actual evapotranspiration (ET) fluxes to provide guidance in decision-making. However, they are, in general, unable to estimate or forecast ET directly as they can seldom characterize actual moisture conditions in the soil and vegetation regimes at operationally useful time or space scales. Instead, they first estimate evaporative demand (EO) (sometimes known as "potential ET") as an upper limit to actual ET and then apply EO to drive hydrologic models or empirical relations that account for soil moisture conditions and vegetative constraints on moisture transfer, and thereby derive actual ET. A common, scientifically sound measure of EO is the reference crop ET (ETrc) measure provided by the Penman-Monteith equation.
Here we summarize the development of NWS's new near-term forecast system for ETrc. The forecast system has two components:
1. a daily to weekly ETrc forecast forced by temperature, dewpoint, wind speed, and cloud cover from the National Digital Forecast Database, all of which are already currently forecast and are available at an hourly time-step and a 2.5- to 5-km spatial resolution. '
2. an ETrc climatology forced by temperature, specific humidity, wind speed, and shortwave and longwave downwelling radiation from the North American Land Data Assimilation System (NLDAS). The NLDAS-derived ETrc time-series is 30 years long (1980-2009), daily, and CONUS-wide at a 1/8th-degree spatial resolution. This component provides a climatological context for the forecast ETrc to users who might otherwise be unfamiliar with the concept of ETrc.
The ETrc forecast system, which provides the first large-scale operational forecasts of evaporative demand and is operational at 12 Weather Forecast Offices across the conterminous US, is an early result of ongoing work within an EO-forecast/climatology framework at the Colorado Basin River Forecast Center (CBRFC). The primary goal of the work is to improve streamflow forecasts across the Colorado River basin and eastern half of the Great Basin by updating the Sacramento Soil Moisture Accounting ' (Sac-SMA) model underpinning the NWS River Forecast System. We are currently testing the streamflow simulation skill of replacing the Sac-SMA model'S current static EO driver with a new dynamic forecast EO in test-basins across the CBRFC domain. Other significant potential uses for forecast and near-term observed EO are in the monitoring and prediction of ongoing droughts (e.g., as an input to the US Drought Monitor) and in assisting local and regional agencies (e.g., Denver Water and the U.S. Bureau of Reclamation) in forecasting water demand.
Forecasting Evaporative Demand across the Conterminous US
Eccles Conference Center
Agriculturalists and operational hydrologists often seek to predict actual evapotranspiration (ET) fluxes to provide guidance in decision-making. However, they are, in general, unable to estimate or forecast ET directly as they can seldom characterize actual moisture conditions in the soil and vegetation regimes at operationally useful time or space scales. Instead, they first estimate evaporative demand (EO) (sometimes known as "potential ET") as an upper limit to actual ET and then apply EO to drive hydrologic models or empirical relations that account for soil moisture conditions and vegetative constraints on moisture transfer, and thereby derive actual ET. A common, scientifically sound measure of EO is the reference crop ET (ETrc) measure provided by the Penman-Monteith equation.
Here we summarize the development of NWS's new near-term forecast system for ETrc. The forecast system has two components:
1. a daily to weekly ETrc forecast forced by temperature, dewpoint, wind speed, and cloud cover from the National Digital Forecast Database, all of which are already currently forecast and are available at an hourly time-step and a 2.5- to 5-km spatial resolution. '
2. an ETrc climatology forced by temperature, specific humidity, wind speed, and shortwave and longwave downwelling radiation from the North American Land Data Assimilation System (NLDAS). The NLDAS-derived ETrc time-series is 30 years long (1980-2009), daily, and CONUS-wide at a 1/8th-degree spatial resolution. This component provides a climatological context for the forecast ETrc to users who might otherwise be unfamiliar with the concept of ETrc.
The ETrc forecast system, which provides the first large-scale operational forecasts of evaporative demand and is operational at 12 Weather Forecast Offices across the conterminous US, is an early result of ongoing work within an EO-forecast/climatology framework at the Colorado Basin River Forecast Center (CBRFC). The primary goal of the work is to improve streamflow forecasts across the Colorado River basin and eastern half of the Great Basin by updating the Sacramento Soil Moisture Accounting ' (Sac-SMA) model underpinning the NWS River Forecast System. We are currently testing the streamflow simulation skill of replacing the Sac-SMA model'S current static EO driver with a new dynamic forecast EO in test-basins across the CBRFC domain. Other significant potential uses for forecast and near-term observed EO are in the monitoring and prediction of ongoing droughts (e.g., as an input to the US Drought Monitor) and in assisting local and regional agencies (e.g., Denver Water and the U.S. Bureau of Reclamation) in forecasting water demand.
https://digitalcommons.usu.edu/runoff/2011/AllAbstracts/28