SUBANG RADAR CAPPI DATA PROCESSING AND Z-R OPTIMIZATION FOR QUANTITATIVE PRECIPITATION ESTIMATES (QPE) OVER LANGAT RIVER BASIN

Abstract

The main advantage of radar data over point gauge rainfall is its ability to provide continuous spatial and temporal resolution of rainfall details over a large area.  Weather radar transmits electromagnetic wave, interacts with raindrops and reflects some of the intercepted power (backscattering) that is subsequently converted into rainfall intensity. Despite its advantages, indirect rainfall estimation using radar reflectivity factor suffers from various sources of error such as ground clutter, partial beam occultation, beam blockage and attenuation effects.  Literatures on the use of radar quantitative precipitation estimates (QPE) in Malaysia have been increasing since the past 15 years ago. However, none of the previous work have detailed out the sources of radar data used and its processing for rainfall rate conversion. This paper will discuss the fundamentals in radar data acquisition and processing for rainfall input to a case study of Langat river basin, Malaysia. The methodology in raw radar data processing is decribed in details and the use of CAPPI data for rainfall estimation over Langat river basin is discussed. The findings indicate a good performance of the radar CAPPI data as an alternative source to the rainfall measurement for Langat river basin with correlation coefficient between radar rainfall and gauged rainfall ranging from 0.69 to 0.75. Improvement on radar rainfall estimates is also recommended by newly derived optimized Z-R equations based on monsoon season. The results presented in this study are encouraging, especially for the application of water resources management for the river basin.