Abstract:

The downscaling of precipitation based on the geographically weighted regression (GWR) model provides precipitation data with higher spatial resolution, making the spatial scale of precipitation estimation more refined, which is of great importance to regional hydrology and water resources management. Shaanxi Province is located in the central and western region of China, blocked by the Qinling Mountains and Loess Plateau, and exhibits significant regional climate differences. Therefore, the evaluation of the spatial and temporal patterns of precipitation in Shaanxi Province is essential. In this study, the Shaanxi Province was selected as the study area and the precipitation data from ground meteorological observation stations as the real values to verify the accuracy of Global precipitation measurement (GPM) precipitation data from the time scale of the year and spatial scale of the stations. The GWR model was used to downscale the GPM and compare and verify it with the measured precipitation data. Simultaneously, based on the downscaling method of annual precipitation data, the monthly scale was further extended to obtain higher resolution GPM monthly precipitation data and the influence degree of topography on the accuracy of satellite precipitation products was analyzed by combining the digital elevation model (DEM) data. Moreover, the correlation coefficient (CC), root mean square error (RMSE), and relative error (BIAS) were selected to verify the GPM precipitation data accuracy in the Shaanxi Province. Additionally, the GWR model was used to downscale the GPM precipitation data. DEM data were resampled to the same resolution as GPM data. At the same time, the GPM and DEM data under the resolution of 0.1°×0.1° were used as input elements to construct the GWR model and the constant term, DEM coefficient term, and residual of each grid center point were extracted from the regression model. The constant term and coefficient term were rasterized to obtain 1 km data, and the residual was interpolated to the spatial resolution of 1 km×1 km using the ordinary Kriging method. The GPM precipitation data with a spatial resolution of 1 km was calculated and the results show that: (1) The GPM satellite precipitation data demonstrated a good accuracy on the spatial and temporal scales of annual and station, and exhibited certain adaptability in the study region. The downscaling study of GPM precipitation data using the GWR model could greatly improve the spatial resolution of precipitation data, demonstrating a stronger ability to display spatial details. (2) The GWR downscaling results showed a good correlation between the observed precipitation data, CC=0.90 at year scale. The GPM precipitation data of spring and summer between downscaling results and the measured rainfall data of CC values were 0.92 and 0.80, respectively at seasonal scale. In the autumn of 0.93, the month scale correlation was also generally higher and showed better accuracy, meeting the needs of actual precipitation research data. On the whole, however, the GWR downscaling result was higher than the original precipitation data of GPM. (3) The results of downscaling precipitation showed a significant negative correlation with elevation. As the altitude increased, the precipitation decreased. Therefore, the GWR downscaling model was satisfactorily applied to the downscaling study of GPM precipitation data in the Shaanxi Province, which improved the spatial resolution of the data. This study can provide important data for hydrological research and improve the simulation accuracy.

Key words: Global precipitation measurement (GPM), precipitation, downscaling, geographically weighted regression model (GWR)