SPATIO-TEMPORAL CHARACTERISTICS OF FREQUENCY OF HEAVY RAINFALL EVENTS IN HUBEI PROVINCE AND ANALYSIS OF TOPOGRAPHIC RELATIONSHIP BASED ON GWR.

Based on the hourly heavy precipitation data from 74 national meteorological observation stations during the rainy seasons (May to September) from 1983 to 2017 in Hubei Province, the heavy precipitation events were classified into long and short duration heavy precipitation events according to their temporal and spatial characteristics. The methods of ordinary least squares (OLS) and geographically weighted regression (GWR) were used to quantitatively explore the relationship between heavy rainfall frequency and terrain factor. The results showed that the annual frequency of short duration heavy precipitation in extended rainy seasons in Hubei Province had obvious periodic variation, and there was one main oscillation mode in interdecadal variation (≥10 a), and two main oscillation modes in the variation of periods with a timescale shorter than interdecadal (<10 a). The ten-day frequency of long- duration heavy precipitation reached its peak in Meiyu periods, and decreased in midsummer periods, while the frequency of short duration heavy rainfall jumped in the middle of July after the end of Meiyu periods. The diurnal variation curves of long and short duration heavy rainfall were both single peak structures. The high-frequency stations of long and short-duration heavy precipitation in Hubei Province mostly appeared under specific terrain conditions where there were quasi-constant mesoscale convergence lines or vortices on the ground. Compared with the traditional OLS method, GWR significantly improved the fitting effect of heavy rainfall frequency, altitude and slope. Combined with the analysis of the significance of the fitting coefficients, GWR was not suitable for the mountainous areas with small samples and sparse sites in western Hubei Province, and more suitable for the central and eastern parts of Hubei Province which is home to medium and small-scale topography. In the geographically weighted regression model, the positive correlation between the altitude and the frequency of long-duration heavy precipitation was the largest on the west side of the eastern foot of Dabie Mountain, and the negative correlation was the largest on the south side of the western foothill of Dabie Mountain, while it was the opposite with slopes. Altitude and slope had a positive effect on the frequency of short-duration heavy precipitation. The greatest impact was on the west side of the eastern foot of the Dabie Mountains and the low-lying urban belt along the mainstream of the Yangtze River in the Wuhan-Huangshi region. They were -0.20 times/m and 6.43 times/degree respectively at the Wuhan station where the influence of terrain slope was much higher than altitude. [ABSTRACT FROM AUTHOR]