LISFLOOD model requires gridded meteorological maps of precipitation, average temperature, potential evaporation rate from free water surface, bare soil surface and evapo-transpiration for reference crop surface.
For EFAS v4.0, precipitation and temperature 6-hourly 5 km grids were produced by interpolating point data using SPHEREMAP algorithm. SPHEREMAP (Willmott et al., 1985) is the adaptation to spherical coordinates of Shepard's inverse distance weighting (Shepard, 1968). It is based on a combined distance and angular weighting plus a correction using the gradient of the observations. Several radius are defined within SPHEREMAP for the calculation of the weights. First of all, an initial search radius for stations around the grid point is defined based on the number of available stations in the data set and the size of the gridding area. Based on the initial radius, a radius for switching the calculation rule of the distance weights is defined. Finally, a small radius "epsilon" around the grid point is defined. Between four and up to ten stations are utilised to interpolate the value at the grid point. If less than four station were found within the initial search radius, then this radius is increased step wise until at least 4 stations are detected. The angular weights are used to take the possible clustering of stations into account. Clustered station are less weighted than solitary stations. Distance and angular weights are combined and adjusted by the gradient to get the final applied interpolation weights. (Creation of EFAS grids#DescriptionofSPHEREMAP).
Evaporation daily grids were derived using Penman-Monteith equation and LISVAP model (Burek et al. 2013), based on gridded minimum and maximum daily temperature, wind speed, solar radiation and vapour pressure. Daily grids were then dis-aggregated to created 6-hourly grids. For each day, evaporation rates stay the same for each 6-hourly grid and they correspond to the rates in the daily grids.
The data record spans from January 1990 to December 2017.
Figure 3.1 - EFAS v4.0 - Spatial distribution of available 6-hourly precipitation observations for the period 2010-2017
Figure 3.2 - EFAS v4.0 - Spatial distribution of available 6-hourly average temperature observations for the period 2010-2017
REFERENCE
Yamamoto, J.; An Alternative Measure of the Reliability of Ordinary Kriging Estimates; Mathematical Geology, 2000, 32, 489-509
Krige, D.;Two-dimensional weighted moving average trend surfaces for ore valuation; Proceedings of the Symposium on Mathematical Statistics and Computer Applications in Ore Valuation, 1966, 13-38
Willmott, C.; Rowe, C. & Philpot, W.; Small-scale climate maps: A sensitivity analysis of some common assumptions associated with grid-point interpolation and contouring; The American Carthographer, 1985, 12, 5-16