Application of a trigonometric approach to the regionalization of precipitation for a complex small‐scale terrain in a GIS environment

To regionalize precipitation on a small‐scale, complex, low mountain range terrain, trigonometric relationships were constructed in a geographical information system (GIS) environment using a digital elevation model (DEM). The large‐scale orographic effect and small‐scale windward and leeward effects on precipitation were recorded and quantified using a grid‐based combination of a terrain vector (slope angle, aspect) with a wind vector (wind direction, speed). This was based on the parameterization of a longer‐term wind‐precipitation distribution. Both effects were mapped for the meso‐scale Weißeritz River catchment in the Ore Mountains of Germany, using an estimate of spatially distributed slope precipitation. It was shown that the small‐scale windward and leeward effects modify the larger‐scale orographic effect spatially. It was determined that both the amount and the phase of the small‐scale windward and leeward effect correlates with the height above sea level. During the 1971–2003 growing seasons the amount of precipitation increased by 4% per 100 m, and for the 1971–2000 statistically heavy precipitation (SHP) (duration: 24 h, return period: 100 years) the increase was 1% per 100 m. The phase shift occurred because the main wind veered south‐west to west to north‐west with elevation increase, and it was more pronounced for mean than for heavy precipitation. Spatial slope precipitation was estimated to be within the 390–715 mm range for mean adjusted precipitation and 100–140 mm for SHP. The maximum of the windward and leeward effect on precipitation amounts to ± 25% of fallen precipitation. Copyright © 2008 Royal Meteorological Society