Abstract
The availability of accurate and reliable rainfall data that are applicable to various phenomenological, climatological, and modeling studies is important, especially in the Philippines, which is considered to be highly vulnerable to natural hazards and a changing climate. The presented strategy involved constructing a dataset consisting of synoptic data, automatic rain gauge (ARG) measurements, and satellite data that are co-registered, consistent, and formatted in the same manner. Although sparse in number, the synoptic stations provide the most accurate rainfall information and were used as the baseline for creating the dataset. The ARGs that are within a distance of 1 km to the synoptic stations were used to determine the correction factors needed to make the synoptic and ARG data consistent. Subsequently, the corrected ARGs were used to make the satellite IMERG data consistent with both ARG and synoptic data. In case of the latter, only IMERG pixels with at least 10 ARGs within the relatively large footprint of the satellite sensor were used in estimating the required correction parameters derived from a combination of a power transform and linear regression correction techniques. The final results show good agreement of synoptic and corrected ARG data with correlation coefficients of 0.94 and 0.97 for the 10 day and monthly data, respectively, and improvement in the linear regression slope from 0.67 to 0.90 for 10 day data, and 0.70 to 0.94 for monthly data. In addition, the corrected ARG data agree well with the corrected IMERG data, with correlation coefficients of 0.88 and 0.93 for the 10 day and monthly data, respectively, and an improvement in slope from 0.66 to 0.87 for 10 day data, and 0.74 to 0.99 for monthly data. The merit of using a combined dataset is illustrated through comparative analyses of the IMERG data and spatially interpolated synoptic and ARG data. The results show general agreements in spatial patterns of rainfall across the datasets, especially in areas where in situ measurements are recorded. The observed discrepancy when ground data is limited emphasizes the need for satellite IMERG data to obtain the true spatial patterns of rainfall distribution.
Highlights
Synoptic stations provide the most accurate rainfall measurements in the Philippines because they are manned, regularly calibrated, and the measurement procedures follow the standards set by World Meteorological Organization (WMO)
Reliable and accurate rainfall information is needed because rainfall is the key source of clean fresh water that is critically needed for domestic use and to sustain agriculture, forests, lakes, and rivers in the country
This study explored the creation of a rainfall dataset that would be effective in meeting most of these needs
Summary
Rainfall is essential to life and is the primary source of fresh water needed by humans, plants, and animals. It is responsible for the movement of enormous amounts of water and heat through the Earth’s atmosphere, and is a major part of the Earth’s energy budget and climate. In the Philippines, rain is driven mainly by the monsoons: the Summer Monsoon, called Habagat, and the Winter Monsoon, called Amihan. The Summer Monsoon is usually carried by southwest winds and is the predominant weather pattern from June until
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