Study of Z-R relationship among different topographies in Northern Thailand

Abstract

Topography can affect climate. Different topographies have different climates. Rainfall in each area varies by topography. Northern Thailand has been chosen as a study area due to its various topographies such as ridge, flat, plain and valley. This research studies reflectivity data and rainfall rate. Z-R relationship is a relationship between a radar reflectivity (Z) and a rainfall rate (R). Z-R relationship can be used to determine characteristics of precipitation and rainfall and can be applied in hydro-meteorological model to forecast the weathers. Data are from Omkoi Radar Station, covering the area of 240 kilometre around the station. Further, daily rainfall data have been gathered from Thai Meteorological Department. In this study, topographies are classified by Topography Position Index, showing highland, flat and valley. The results show that the empirical relations of rainfall rate and reflectivity measured by radar vary among different topographies which are highland, flat and valley, i.e. Z = 94R 1.5 , Z = 137R 1.5 and Z = 143R 1.5 respectively. The data indicates that if A parameter is low, the cloud is cumulonimbus. If value of A parameter is high, the cloud is nimbostratus. The variety of rain-cloud type and Z-R relationship also varies by topography.