Abstract
Abstract. This study evaluated the performance of the WRF-ARW (Weather Research and Forecasting with Advanced Research) weather prediction model in simulating the spatial and temporal patterns of an extreme rainfall period over a complex orographic region in north-central Portugal. The analysis was performed during the rainy season and, more specifically, the month of December 2009. In this period, the region of interest was under the influence of a sequential passage of low-pressure systems associated with frontal surfaces. These synoptic weather patterns were responsible for long periods of rainfall, resulting in a high monthly precipitation. The WRF model results during the study period were furthermore evaluated with the specific objective to complement gaps in the precipitation recordings of a reference meteorological station (located in Pousadas), the data of which are fundamental for hydrological studies in nearby experimental catchments. Three distinct WRF model runs were forced with initial fields and boundary conditions obtained from a global domain model: (1) a reference experiment with no nudging (RunRef); (2) observational nudging for a specific location, i.e. the above-mentioned Pousadas reference station (RunObsN); and (3) nudging to the analysed field (RunGridN). Model performance was evaluated, using several statistical parameters, against a dataset of 27 rainfall stations that were grouped by elevation. The three model runs had similar performances, even though RunGridN resulted in a slight improvement. Regarding the other two experiments, this improvement justifies its use for complementing the surface measurements at the Pousadas reference station. Overall model accuracy, expressed in root mean square error (RMSE), of the three runs was comparable for the stations of the different elevations classes. Even so, it was slightly better for stations in the lowlands than the highlands. Furthermore, model predictions tended to be less accurate for stations located in rough terrain and deep valleys.
Highlights
Deterministic modelling of the complex interactions in nature is a valuable instrument for scientists as well as policy makers
The climate is classified as wet Mediterranean, according to Köppen–Geiger climate classification, with a mean annual rainfall ranging from 800 mm at the littoral zone to 2300 mm in the inland mountains due to the marked influence of topography on spatial rainfall patterns
The present analysis focused on the month of December 2009, combining an exceptional amount of rainfall with the occurrence of various gaps in the records at the Pousadas meteorological station
Summary
Deterministic modelling of the complex interactions in nature is a valuable instrument for scientists as well as policy makers. Hydrological modelling is widely used for addressing present and future problems such as water availability for agricultural purposes and human consumption, surface water contamination, and flooding risk. Both short and high-intensity as well as prolonged and low-intensity rainfall events can play a key role in catchmentscale runoff generation and associated phenomena such as flooding. Saturation-excess runoff generation, when large amounts of rainfall cause soils to become saturated and prevent further infiltration, can be associated with prolonged floods at larger spatial scales.
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