Abstract
Global positioning system (GPS) satellite delay is extensively used in deriving the precipitable water vapor (PWV) with high spatio–temporal resolution. One of the recent applications of GPS derived PWV values are to predict rainfall events. In the literature, there are rainfall prediction algorithms based on GPS-PWV values. Most of the algorithms are developed using data from temperate and sub-tropical regions. Mostly these algorithms use maximum PWV rate, maximum PWV variation and monthly PWV values as a criterion to predict the rain events. This paper examines these algorithms using data from the tropical stations and proposes the use of maximum PWV value for better prediction. When maximum PWV value and maximum rate of increment criteria are implemented on the data from the tropical stations, the false alarm ( F A ) rate is reduced by almost 17% as compared to the results from the literature. There is a significant reduction in F A rates while maintaining the true detection ( T D ) rates as high as that of the literature. A study done on the varying historical length of data and lead time values shows that almost 80% of the rainfall can be predicted with a false alarm of 26.4 % for a historical data length of 2 hours and a lead time of 45 min to 1 hour.
Highlights
Precipitable water vapor (PWV) is a measure of total moisture content in a vertical column of unit cross-section
As proposed by the three-factor algorithm [15], the maximum rate of increment of PWV is taken as the major factor and maximum PWV variation and monthly averaged PWV values are taken as the auxiliary factors
It can be seen that the use of the three-factor method improves the true detection rate for the tropical stations but the improvement is less compared to the sub-tropical stations
Summary
Precipitable water vapor (PWV) is a measure of total moisture content in a vertical column of unit cross-section. Radiosondes and microwave-radiometers are a few conventional technologies that can measure PWV. PWV measured by radiosondes have a poor temporal resolution with low spatial coverage. The microwave radiometers are expensive and not available everywhere Both the radiosonde and microwave radiometer readings are affected by severe weather events like heavy rain and thunderstorms. PWV observations from microwave radiometers are still of limited value in climate studies in predicting and tracking heavy rainfall cases [3]. Microwave radiometers can provide reliable PWV readings only under no rainfall conditions [4]. They are not able to give accurate readings for all-weather conditions [5]. GPS has an advantage over other instruments as it has higher spatio–temporal resolution and is an all-weather instrument
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