关键词: 降水, 三峡库区, MSWEP, GAM

Abstract:

Long time-series, spatially-contiguous and accurate precipitation products are one of the most important inputs for various studies, including climate change detection, hydrological modelling, drought monitoring, etc. However, due to its high spatio-temporal variability, precipitation is one of the meteorological elements that are most difficult to estimate. Recently, a new global gridded precipitation dataset that merges gauge measurements, satellite products, and reanalysis data, has been produced. Owing to its high spatial resolution, long time span, and comprehensive combination of different precipitation data sources, MSWEP data have received wide attention since its release. In this study, we first evaluated accuracy of MSWEP monthly precipitation using local gauge measurements in the Three Gorges Dam region, then produced more accurate precipitation data by combining MSWEP and gauge measurements with the GAM (Generalized Additive Model) method, and finally analysed precipitation changes before and after the dam water level rose to 135 m in June 2003. Main conclusions are drawn as follows. (1) No matter what methods are used, estimation accuracy of precipitation shows strong seasonality: more accurate in cold-dry season (spring and winter), while less accurate in hot-wet season (summer and autumn). Gauge measurement and MSWEP are complementary, with the former being more accurate in cold-dry season and the latter being more accurate in hot-wet season. (2) GAM can take advantages of both gauge measurements and MSWEP with flexibility and achieve more accurate precipitation estimation (rmse decreases by 17%-50%, and r increases by 10%-30%). There are still great seasonal variations in accuracy, with rmse being 8-20 mm in spring and winter and 20-50 mm in summer and autumn. (3) Based on the precipitation estimation results obtained in step 2, we found the following phenomena after the water level rose to 135 m in 2003: 1) dam regions south of the Yangtze River show a precipitation reduction over May-October; 2) dam regions in the western part show a precipitation increase over November-April; 3) The northwestern part outside core dam regions shows a precipitation increase over May-October, which is consistent with the results of other studies; 4) precipitation shows an increase in spatial heterogeneity, but a slight decrease in seasonality conveyed by an increase in proportion of precipitation in dry season.

Key words: precipitation, Three Gorges Dam region, MSWEP, GAM