GIS User Group

May 14th , 2008

Daymet

Peter Thornton (CGD) and Michele Thornton (ISSE) will discuss recent and ongoing updates to Daymet. Daymet is a method for interpolating daily surface weather observations of maximum and minimum temperature and daily total precipitation to provide estimates in regions without observations.  The Daymet algorithm uses latitude, longitude, and elevation associated with the observation sites to diagnose horizontal and vertical gradients, and makes predictions at unmeasured sites based on these gradients and the observed values from the surrounding region. Daymet also includes algorithms to estimate daily vapor pressure (humidity) and incident shortwave radiation using only the commonly available temperature and precipitation observations.  The method has been applied to generate 1 km gridded fields of daily surface weather variables over the conterminous United States for the period 1980-2004.  A project is underway now to update that database to cover all of North America, and to bring the time period up through 2007, with a scheduled completion date of July 2009. Inputs for the Daymet algorithm are being derived from the most current elevation and weather station data.  These include the Shuttle Radar Topography Mission (SRTM) elevation data at a 1km x 1km pixel  resolution and daily weather observations from across North America including the United States, Canada, and Mexico.  A North American land/water mask is also being derived from the MODIS Land/Water Mask Product.  GIS processing techniques on these inputs will be discussed.

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