Publication Date:
2012-12-21
Description:
Topography exerts influence on the spatial precipitation distribution over different scales, known typically at the large scale as the orographic effect, and at the small scale as the wind-drift rainfall (WDR) effect. At the intermediate scale (~ 1–10 km), which is characterized by secondary mountain valleys, topography also demonstrates some effect on the precipitation pattern. This paper investigates such intermediate-scale topographic effect on precipitation patterns, focusing on narrow-steep valleys in the complex terrain in southern Germany, based on the daily observations over a 48-yr period (~ 1960–2007) from a high-density rain-gauge network covering two sub-areas, Baden-Wuerttemberg (BW) and Bayern (BY). Precipitation data at the valley and non-valley stations are compared under consideration of the daily general circulation patterns (CPs) classified by a fuzzy-rule based algorithm. Scatter plots of precipitation against elevation demonstrate a different behavior of valley stations comparing to non-valley stations. A detailed study of the precipitation time series for selected station triplets, each consisting of a valley station, a mountain station and an open station have been investigated by statistical analysis with the Kolmogrov–Smirnov (KS) test supplemented by the one-way analysis of variance (one-way ANOVA) and a graphical comparison of the means. The results show an interaction of valley orientation and the moisture flow direction of the CPs at the intermediate-scale, i.e. when the valley is shielded from the moisture flow, the precipitation amount within the valley is comparable to that on the mountain crest; when the valley is open to the moisture flow, the precipitation within the valley is much less than that on the mountain. Such a phenomenon, whereby the precipitation is "blind" to the valleys at the intermediate scale conditioned on CPs, is defined as the "narrow-valley effect" in this work, and it cannot be captured by the widely used elevation–precipitation relationship. This implies that the traditional geostatistical interpolation schemes, e.g. ordinary kriging (OK) or external drift kriging (EDK) applying digital elevation model (DEM) as external information are not sufficient. An interpolation experiment applying EDK with orographic surrogate elevation defined in this paper as auxiliary information to account for the valley effects shows improvement for the cross-validation.
Print ISSN:
1812-2108
Electronic ISSN:
1812-2116
Topics:
Geography
,
Geosciences
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