The performance of the Weather Research and Forecasting (WRF) Model in quantitative precipitation forecasts (QPFs) across Taiwan during three mei-yu seasons between 2008 and 2010 is evaluated using observations from about 400 rain gauges. The QPFs, spanning a range of 12–36 h and run for two nested domains at grid sizes of 15 and 5 km, are verified. Both visual and statistical-based verification methods are used to provide complementary results. More emphasis is placed on intraseasonal variation and the diurnal cycle of mei-yu rainfall, as these aspects have been less well explored previously. While the categorical statistics indicate skill levels comparable to past studies, the model performs better for frontal rainfall in May than monsoon rainfall in June. The two WRF domains are found to capture the overall rainfall amount, its general spatial pattern, the increased rain from May to June, and the basic diurnal cycle to a reasonable extent. However, both domains exhibit a persistent eastward shift in rainfall areas throughout the season, from the upwind slope to near the ridge, mainly because of excessive daytime rainfall over the mountains that starts and ends too early (more so in June), combined with insufficient rainfall upstream (in plains and slopes) since the morning. Also, the 15-km domain has total rainfall amounts closer to the observations, but the 5-km domain suffers a larger underforecast with rainfall only at the resolvable scale. Despite this, the finer mesh is more capable of predicting the peak values and local variations in rainfall and, thus, has the same skill with higher hit percentages, especially toward the high thresholds.

[1] The objective of this paper is to describe a statistical downscaling model based on established links between large scale variables from a general circulation model (GCM) and regional rainfall to project climate change over East Asia in the 21st century. We develop a SVD (singular value decomposition)-based regression model to downscale the GCM data. In order to establish a link between monthly regional precipitation and large scale variable (mean sea level pressure, 10 m wind speed, or 2 m temperature), we used the IS92a scenario data of ECHAM4/OPCY3 and the data from the Climate Research Unit from 1901 to 1990. In the 20th century, their connections have remained unchanged over time for all seasons. The continuity of these relationships to the next century is tested by checking the similarity in the main SVD modes of predictors and the empirical orthogonal functions of predictors throughout the 20th and 21st century. Furthermore, comparing the SVD-downscaled and ECHAM4-projected changes of precipitation in the 2090s with respect to the 1990s reveals similar patterns over most areas with much more detailed regional characteristics, although the magnitude of change is not compatible. In all, the annual rainfall over East Asia is projected to increase over northern China and the Indochina peninsula and to decrease over the coast of southern China by the end of the 21st century.

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