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Spatial interpolation LocClim: Local Climate Estimator
LocClim: Local Climate Estimator

| Environment and Natural Resources, Working paper No. 9 (CD-ROM) | February 2002 |

New_LocClim CD cover Climatic conditions are recorded for very few locations on earth and most of the time, when an agricultural development project is planned, or when a climate-related risk assessment is to be carried out, the experts have to resort to using data from distant stations.

Dr Jürgen Grieser, now at the Global Precipitation Climatology Centre of the German Meteorological Service has spent several months with the Agrometeorology Group of the Environment and Natural Resources Service (SDRN) of FAO to develop a tool, LocClim, an abbreviation of Local Climate, to answer the very common question about climate in a location where there is no climate observing station.

LocClim was developed to provide an estimate of climatic conditions at locations for which no observations are available. To achieve this, the programme uses the 28800 stations of FAOCLIM 2.0, the global agroclimatic database maintained by the Agrometeorology Group of FAO.

LocClim Interface Next to a "no questions asked" automatic mode, the "benchmark" mode gives the user full control over the interpolation procedure (Inverse Distance Weighting). Inputs can be taken from the keyboard (location specified either by co-ordinates or by a click on a map) or from user-provided ASCII files. Output can be in the form of ASCII files or user-defined georeferenced grids in WinDisp format.

LocClim workbench 1 The programme also provides estimates of growing season characteristics based on a comparison of rainfall and potential evapotranspiration (Franquin's method).

LocClim workbench 2 Estimates of monthly, 10-daily and daily values of common climate variables are given together with error estimates, using a number of options to correct for regional variability, altitude dependency and horizontal gradients of the variables. For any given location LocClim searches for the nearest stations that fulfil given criteria (absolute number, maximum distance, altitude constraints).

If desired LocClim fits a linear altitude function through the observations to reduce all of them to the elevation of the desired location. This minimises the systematic error resulting from the different elevations of the neighbouring stations. The altitude of the desired location can either be given by the user or taken from a built-in digital elevation model (DEM) with a spatial resolution of 10 km and an altitudinal resolution of 20 m (DEM downgraded from the NOAA/NCDC Global Land One-kilometre Base Elevation). LocClim can perform climate gradient correction by fitting a plane surface to the observations over the latitude-longitude plane. Thus the smooth geographical climate variation is taken into consideration. If desired a shadowing routine can be applied that gives neighbours hidden by closer neighbours a low weight.

For details or for booking a copy of the LocClim CD-rom, kindly send an email to agromet@fao.org.

For more information, contact: Chief-SDRN@fao.org or Environment@fao.org

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