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Philippe Crochet Icelandic Meteorological Office

SWSA 2003 - 2nd SRNWP Workshop on statistical and dynamical adaptation QPF mapping in Iceland using topographic information. Philippe Crochet Icelandic Meteorological Office. Position of the problem.

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Philippe Crochet Icelandic Meteorological Office

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  1. SWSA 2003 - 2nd SRNWP Workshop on statistical and dynamical adaptationQPF mapping in Iceland using topographic information Philippe Crochet Icelandic Meteorological Office

  2. Position of the problem The direct interpolation of precipitation from sparse data over complex terrain is not always relevant because of the presence of strong variability induced by topography. Methodology The QPF map is derived by combining information from the DMO (ECMWF 0.5°), the observed precipitation accumulated over a period of a few weeks ending at the forecast issuing time and the topographic features derived from a digital elevation model (DEM). Limits of the method The proposed method is not aimed at filtering out the forecast errors but only to deal with the interpolation errors over complex terrain.

  3. Base map (2km) Combined map QPF map

  4. Sampling procedure

  5. Basic Comparison

  6. Ongoing work Apply directly the statistical model to the DMO (no base map) Statistical model: modify some predictors and the sampling procedure Identify better the wet/dry areas (when the spatial intermittency is high) Interpolate the residuals (spatial variability not explained by the statistical model) and add it to the MLR maps

  7. Summary Within the limits of the information provided by a NWP model, the proposed method attempts to map the QPF by exploring the statistical relationship between precipitation and topographic as well as geographic features. It is able to highlight information over rugged terrain especially when large precipitation amounts are forecasted. It requires a DEM and a representative sampling of the domain under consideration (ground network and NWP model) • Basic comparison (SPLINE / MLR): • Similar results at most verified sites ( most of them < 200m height) • Some improvements in areas with complex topography (W and SE) • The estimates over the southern sides of Reykjanes and Snæfellsnes • peninsulas can sometimes be worse

  8. References • [1]: Benichou, P., O. Le Breton, 1987: Prise en compte de la topographie pour la cartographie des champs pluviométriques statistiques. La Météorologie, 7(19), 23-34. • [2]: Wotling, G., Ch. Bouvier, J. Danloux, J.M. Fritsh, 2000: Regionalization of extreme precipitation distribution using the principal components of the topographical environment. J. Hydrol. 233, 86-101. • [3]: Alpert P. 1986 : Mesoscale indexing of the distribution of orographic precipitation over high mountains. JCAM, 25, 532-545. • [4]: Daly, C., Neilson, R.P., Phillips, D.L. 1994: A statistical-topographic model for mapping climatological precipitation over mountainous terrain. JAM, 33, 140-158. • [5]: Kyriakidis, P.C., K. Jinwon , N.L. Miller, 2001 : Geostatistical mapping of precipitation from gauge data using atmospheric and terrain characteristics. JAM, 40, 1855-1877. • [6]: Barros A.P. and D.P. Lettenmaier 1993: Dynamic modeling of the spatial distribution of precipitation in remote mountainous areas. MWR, 121, 1195-1214. • [7]: Pandey, G.R., D.R. Cayan, M.D. dettinger, K.P. Georgakakos, 2000: A hybrid orographic plus statistical model for downscaling daily precipitation in nothern California. Journal of Hydrometeorology, 1, 491-506. • [8]: Smith, W.H.F., and P. Wessel 1990:Gridding with a continuous curvature splines in tension. Geophysics, 55, No3, 293-305. • [9]: Crochet, P., 2002: A linear model for mapping precipitation in Iceland. Veðurstofa Íslands, Report 02028. • [10]: Tustison, B., D. Harris, E. Foufoula-Georgiou, 2001: Scale issues in verification of precipitation forecasts . JGR, Vol. 106, D11, 11775-11784

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