SWSA 2003 - 2nd SRNWP Workshop on statistical and dynamical adaptation

QPF mapping in Iceland using topographic information

Philippe Crochet

Icelandic Meteorological Office

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.

Position of the problemPosition of the problem

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).

MethodologyMethodology

The proposed method is not aimed at filtering out the forecasterrors but only to deal with the interpolation errors over complex terrain.

Limits of the methodLimits of the method

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Base map (2km)Base map (2km)

Combined mapCombined map

QPF mapQPF map

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Sampling procedure

Basic Comparison

Ongoing work

Statistical model: modify some predictors and the sampling procedure

Interpolate the residuals (spatial variability not explained by thestatistical model) and add it to the MLR maps

Identify better the wet/dry areas (when the spatial intermittency is high)

Apply directly the statistical model to the DMO (no base map)

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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 Snæfellsnespeninsulas can sometimes be worse

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