Diurnal Variations of Summer Precipitation Linking to the Topographical Conditions over the Beijing-Tianjin-Hebei Region

The Beijing-Tianjin-Hebei (BTH) region of above 110 million people, located in North China, is confronted with high risks of precipitation-related disasters during the summer. Efforts to better understand diurnal variation characteristics of summer precipitation and associated physical driving processes are of vital importance to accurate forecast of short-time precipitation. Based on hourly gridded precipitation data at a fine resolution of 0.1 degrees newly developed by China Meteorological Administration (CMA), we investigate diurnal variations of summer precipitation and their linkages with the topographical conditions in the BTH region for the period of 2008-2018. Summer precipitation amounts are shown to nonlinearly change with the topographical height, the largest values occurring at the altitudes of around 350m in the BTH region. As a whole, diurnal variation of summer mean precipitation in the BTH region exhibits an S-shape structure with the peak appearing around 20:00LST. While the mountainous precipitation largely triggers the precipitation peak with contribution from coastal and plain areas, the large precipitation in early morning is dominated by the precipitation over coastal and plain areas. Heavy and very heavy precipitation frequencies generally decrease with topographical height while light precipitation frequency increases in a nonlinear manner. The physical processes explaining the tight precipitation-topography linkages are also discussed. Our findings are expected to provide useful information for the improvement of short-time precipitation forecast over the BTH region.