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precipitation and evaporation are two vital components of water cycle, and Hydrogen and oxygen stable isotopes are important tracers in water, which are very sensitive to changes in the climate and the water cycle. Rayleigh Fractionation equation is usually applied to calculate isotope distributions in order to quantify the precipitation and evaporation processes. It is reasonable to explain the evaporation process using the Rayleigh fractionation equation. However, the composition of hydrogen and oxygen stable isotopes in the precipitation will change due to the effects of dynamic fractionation and dilution during raindrop fall. In this case, it is not feasible to rely entirely on the Rayleigh fractionation equation. In this paper, atmospheric precipitation isotopes data recorded during 1996–2016 in Hong Kong from the Global Network of Isotopes in Precipitation (GNIP) are analyzed, including local meteoric water line (LMWL), deuterium-excess (d), temperature effect and rainfall amount effect. The results indicate that precipitation is affected by secondary evaporation and dilution effects. In addition, the stable isotope composition in precipitation is the result of temperature and precipitation. Due to the effects of these two effects, changes of isotope composition in precipitation are not always consistent. When the rainfall density is very large, the temperature effect is covered up and the temperature is inversely related to the isotope composition of precipitation. In contrast, when the rainfall density is small, the temperature is positively related to the isotope composition of precipitation. Therefore, it is suggested to consider the rainfall density while studying the relationship between the isotope composition of precipitation and the local climate. These finds can provide some enlightenments and references on how to investigate the changing pattern of isotope composition in precipitation. [ABSTRACT FROM AUTHOR]

The recent intensification of extreme rainfall events has the potential to aggravate the frequency and intensity of floods in urban areas and signals the urgent need for accurate and high spatiotemporal resolution precipitation data for flood monitoring and warning to alleviate the associated damages. In this context, this paper aims to statistically assess the latest Integrated Multisatellite Retrievals from Global Precipitation Measurement (IMERG) multisatellite constellation and radar quantitative precipitation estimation (QPE) products against dense rain gauge network observations under multiple temporal scales (hourly and 3-hourly) and three spatial scales (grid cumulative, regional, and grid) over the Guangdong-Hong Kong-Macao Greater Bay Area (GBA) in China. The results indicate that (1) at the grid cumulative scale, QPE significantly outperforms IMERG products. The correlation coefficients of QPE (0.83 ≤ CORR ≤ 0.85) are much higher than those of IMERG products (0.35 ≤ CORR ≤ 0.56), the estimation of QPE is generally significantly underestimated (−0.23 ≤ BIAS ≤ -0.16), and the BIAS of IMERG products is larger than that of QPE (−0.24 ≤ BIAS ≤ 0.23). (2) At the regional scale, the accuracy of IMERG products has been significantly improved, with relatively high correlation coefficients (CORR≥0.8) and decreased root mean squared error (RMSE) values (1.18 mm ≤ RMSE ≤ 0.22 mm), and Taylor diagrams visually show that QPE is closer to the gauge observations than are IMERG products. (3) The evaluation results at the grid scale show that both IMERG products and QPE can accurately reflect the spatial distribution of precipitation. Among these results, the spatial distribution of QPE is the most consistent with the actual rainfall, although an obvious underestimation of rainfall occurs in areas with strong rainfall. (4) In terms of detection indicators, the three IMERG products are superior to QPE at capturing rainfall events and have more advantages over QPE in the estimation of instantaneous precipitation, especially for light rain events. However, QPE has better detection effects for rainfall events under rainstorm and heavy rainstorm events, indicating the hydrologic utility of this product. Among the three IMERG products, the IMERG Early Run (ER) product has the advantages of a short lag time and high accuracy, and it has the potential to be applied in flood forecasting. Future studies should improve IMERG algorithms and promote the application of QPE in urban rainstorm and flood research. • The quality of the IMERG products and radar quantitative precipitation estimation (QPE) is compared over the Guangdong-Hong Kong-Macao Greater Bay Area (GBA) in China. • The dense rain gauge network observations are used for evaluation in the GBA. • The evaluation of multisource precipitation products under different temporal and spatial scales has different results and effects. [ABSTRACT FROM AUTHOR]