Characteristics of rainfall-radar reflectivity relationship over Lower Northern Thailand

摘要

According to the regularly flash flood and landslide occurrences over the lower Northern area in past decade, the appropriate warning system development has been considered more serious in Thailand. Unfortunately, these disaster events mostly occur in the mountainous area, where not only the rain gauges are scarcity and absence, but also the power supply is unavailable. Radar stations had been installed in Thailand for a couple decades, of which the active radius covers the whole area of the country. Therefore, the rainfall detection from radar information becomes one of the interesting approaches to develop effective warning system. Since, the rainfall (R)-radar reflectivity (Z) could be expressed in linear or empirical power function, the investigation of characteristics of Z-R relationship for this risky flash flood area was undertaken under the collaboration between Thai Meteorological Department (TMD) and Naresuan University(NU). Phitsanulok radar station, located in the middle of lower Northern Thailand, was selected to study. The installed radar in this station is DWSR-74C Doppler radar of which active radius is 240 km. The rainfall events during August-September 2007 were analyzed for Z-R relationship. In the study, two techniques of spatial Probability Technique (SPT) and Buffer Probability Technique (BPT) were proposed. These techniques were developed based on GIS basic function and probability matching method. Using these two techniques, the Z-R pairs can be analyzed for both linear and empirical power relationship. It is found that empirical power function is more appropriate to describe Z-R relationship than linear function for the studied area. However, this research is just the early state of Z-R relationship investigation; the warning system development needs further study on the other parameters that relevant to rainfall and flash flood occurrence.