Interpolation of forecasted weather

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The forecast data are initially stored as data on a regular latitude longitude grids. The OPE and HIS models are stored on a 0.25x0.25 degrees resolution; the EPS and MON models on a 0.5x0.5 degrees resolution and the SEA model on a 1.5x1.5 degrees resolution. The final targetgrid that is used in the crop simulation is the same for all models and defined in a projected coordinate system (ETRS-1989-LAEA).

Downscaling

In the first part (method B) of the downscalling method parameter values for a target gridcell are derived from the 4 closest source gridcells where closer source gridcells have a higher weight (inverse distance weighting).

In the second part (method D)of the downscalling a correction is made for systematic bias (systematic deviations between estimated downscalled source data and observed target data). For instance: temperature is correlated with elevation. The elevation values in the source grid are different from the elevation values in the target grid (they sample different locations). Therefor downscalled temperature will be biased depending upon the elevation differences, even if corrections are applied for elevation differences.

OPE & HIS

  • Conversion: WGS84 0.25x0.25 degrees => LAEA 25x25km
Black dots: regular 0.25 x 0.25 degrees latitude longitude gid to 25x25 km grid. Gray lines: 25x25 km climate grid.
  • Method B:
  • Method D:

EPS & MON

  • Conversion: WGS84 0.5x0.5 degrees => LAEA 25x25km
Black dots: regular 0.5 x 0.5 degrees latitude longitude gid to 25x25 km grid. Gray lines: 25x25 km climate grid.
  • Method B:
  • Method D:

SEA

  • Conversion: WGS84 1.5x1.5 degrees => LAEA 25x25km
Black dots: regular 1.5 x 1.5 degrees latitude longitude gid to 25x25 km grid. Gray lines: 25x25 km climate grid.
  • Method B:
  • Method D:

External links: Inverse Distance Weighting (IDW)

Storage of data

With the data available on regular 25x25km grid they can be stored in the MCYFS tables ECMWF_<MODEL>_DOWNSCALED_DATA where <MODEL> is to be replaced by the abbreviation of one of the six ECMWF products (ERA, HIS, OPE, EPS, MON or SEA).