Process report Digitizing analog rainfall data from Pagasa Davao, rain gauge location Davao airport.
Vincent Oskam 04 november 2012
Description of digitization process of analag rainfall data from Pag-asa Davao, location international airport.
Process report Digitizing analog rainfall data from Pagasa Davao, rain gauge location Davao airport.
Project: Hydrologic model as science based decision tool for Davao City Document name: PA-02-b Organizations: HELP Davao Department of Science and Technology (DOST) Region XI Ateneo de Davao University
Vincent Oskam
Version 1.0 04 november 2012 Davao, Philippines
Description of digitization process of analag rainfall data from Pag-asa Davao, location international airport.
1. Introduction Davao City experiences regular water logging during high intensity rainfall events. There is no systematic registry of these events and high time resolution rainfall data is extremely rare and hard to obtain. There are monthly averages, but no detailed measurements of high intensity rainfall events. To make substantiated decisions in flood risk reduction interventions, the quantity and scope of the rainfall intensity and water logging has to be known to cost effectively design flood reduction interventions. Pag-asa Davao has manually registered rainfall daily for every six (6) hours since 1953. This is the only available long term and relatively high time resolution rainfall data for Davao City. By digitizing this analog data it becomes available for analysis of rainfall in Davao City. To ensure reliability this report describes the process of digitizing the analog data to ensure replicability. Chapter four describes the workflow of digitizing the analog data from Pag-asa. Chapter five describes the collected data and the check with overlapping data from the 911 AWS rain gauge in Davao city, 9.66 kilometers from the Pag-asa rain gauge. Chapter six covers the conclusion and advise following on the digitization process.
2. Summary Pag-asa Davao, location international airport, has manually recorded rainfall amounts for every six (6) hours since 1953. These measurements are done with a cylindrical rainfall gage and a ruler on one (1) decimal accurate. Pag-asa Davao was able to provide a total of 17 years of paper log sheets for the years 1985,1986,19891995-1997-2010. These logs have been digitized as accurate and reliable as possible, using a checksum to filter typing errors. The data is complete, not one missing registration or day has been encountered, the registration time is consistent on 2:00 am, 8:00 am, 2:00 pm and 8:00 pm. It is hard to comment on the representativeness of the data for Davao City as only 85 days of overlapping data are available from the Automated Weather Station at the 911 Emergency Central (911 AWS), approximately 9.66 kilometer from the Pag-asa station. Comparison over this period shows 1.33 times more rain in mm above the 911 AWS than above the Pagasa station.
Table of Contents 1.
Introduction .......................................................................................................................................... 2
2.
Summary ............................................................................................................................................... 3
3.
Data ....................................................................................................................................................... 5
4.
Digitization workflow ............................................................................................................................ 6 1.
Work method .................................................................................................................................... 8
5.
Results ................................................................................................................................................... 9
6.
Conclusions and advise ....................................................................................................................... 12
3. Data Since 1953, PAGASA Davao location international airport, has recorded, among other metereological data, rainfall amount for every six (6) hours. Method Rainfall measurements have been done manually with a ruler on 1 decimal accurate. Rainfall is collected in a vertical cylindrical rain gauge (figure 3.1) and is measured every 2:00 am, 8:00 am, 2:00 pm and 8:00 pm. Only when rain has fell in the last measurement window of six (6) hours. i.e. if no rain has been observed, water in the rain gauge will not be measured because it is assumed zero (0). Location The rain gauge is located outside of the PAGASA international airport office at 07˚ 07’N, 173˚ 39’E altitude 18 meters (Pag-asa, 1994), with sufficient surrounding clearing in horizontal and vertical direction. (Oskam, 2012) Timespan Pag-asa Davao has been able to make the handwritten log archives for the following years Figure 3.1 Pag-asa Davao rain gauge (Oskam, 2012) available for digitization:
1985-1986 1989-1995 1997-2010
A total of 23 years.
Figure 3.2 Time periods of digitized data - Generated with Microsoft Visio ©
Registration Rainfall has been recorded in millimeters on 1 decimal accurate on 1 paper graph sheet per day. If the rainfall amount was not enough to make an accurate measurement, but a trace of rain is visible the code 9999 is recorded. At the end of the day the day total sum has also been recorded at the bottom of the page.
4. Digitization workflow The handwritten logs have been manually typed into a digital spreadsheet file on a laptop computer. Logs Pag-asa uses a standardized printed graph sheet per day (illustration 4.1). Entering 4 columns of measured rainfall amount and a day total at the end of the paper sheet. Sheets are based on UTC time zone days, i.e. they contain 4 entries with data from 2:00 pm to 8:00 am the next day PHT.
Figure 4.1 - Pager log sheet with annotations (Pag-asa, 1994)
Spreadsheet Input field is used to type the data, mm in rain are entered as dot-less numbers,.i.e. 1.1 mm would be entered as 11 micrometer and traces are recorded as hyphon (-) and automatically corrected by the spreadsheet to 0. As check the day UTC) total is calculated to be checked with the day total of the paper log.
Figure 4.2 Used spreadsheet for digitization with annotations - created with Microsoft Excel Š
1. Work method To secure the reliability and verifiability of the digitized data, the work process and check strategy of digitizing the manual logs is clarified below. For every new sheet the date of the paper log sheet (Illustration 4.1) is checked with the date on the active spreadsheet line and the active column is checked with the red square indicating the beginning of a new paper sheet at 2:00 pm (Illustration 4.2). At the end of the four (4) day entries of the paper log sheet the day total of the paper log sheet is checked with the day total calculated by the spreadsheet. When total amount of daily rainfall on the paper sheet log and the spreadsheet are identical, no typing errors are assumed.
Figure 4.3 Digitization in process
When day totals are not identical, the origin of the error is checked manually. In most cases a typing error, in ten (10) cases a calculation error in the day total was made on the paper log sheet1. In these cases the spreadsheet was thoroughly checked for typing errors and the day total calculated by the spreadsheet is kept. The possibility of making a typing error that exactly corrects a calculation error on the paper log sheet is assumed negligible.
1
No notes has been taken on the date, time or amount of the calculation errors in the paper log sheets. Calculation errors are small, they occurred only in 0.12% of the digitized days and correction does not seem useful.
5. Results The digitization process resulted in 32128 entries. Four (4) Rainfall measurements a day in periods between January 1st 1984 and December 31st of 2010. Condition Archives of more than 27 years old meteorological data is kept by Pag-asa Davao. However, archives do show signs of insects and damage by age (figure 5.1). Some logs contain large amounts of ants or lice, some contain silverfish and overall they sporadically show holes either by insect or damage from the rusting bindings. Completeness/uniformity/consistency All archives show entries for every six (6) hours for every day within the year of that archive, not one case of missing entries or missing days has been encountered. Paper log sheets are uniform and the registration of data is consistent for every day. Errors Within the 8032 days of digitized rainfall, only 10 calculation errors in the day total have been observed, a fault margin of 0.12%. Accuracy of rainfall measurements is assumed, as it is not possible to verify.
Figure 5.1 Insects and damage of old age (Oskam, 2012)
Representativeness Rainfall data is extremely scarce for Davao City. Therefor it is hard to make an accurate comment on the representativeness of this data for Davao City. The only available data is that from the 911 emergency center Automated Weather Station (AWS) (Ateneo De Davao University) and the only overlapping period is July 27 2010 to December 31 2010. However, the registration of the AWS is sporadic, some dates are missing. Reliability of this data can be questioned. For the following comparison, only the 85 days of available total rainfall from the 911 AWS are used and compared with the same dates from Pagasa. Every comparison based on this data is arbitrary, caused by the sporadic availability of the 911 AWS data. The 85 days of available totals are not consecutive, therefor it could be so that rainfall over Pagasa, fell just before the total measurement, while it fell over the 911 AWS on a date without measurement. However, as this is the only available information at the time of writing, the comparison has been made. Over the 85 days, the 911 AWS measured 794.9 mm, average of 9.4 mm a day. The Pag-asa station measured only 598.4 mm, average of 7.04 mm, during the same days. A difference of 196.5 mm. The 911 AWS measured on total 1.33 times more rainfall than the Pag-asa station during the same period. The 911 AWS is approximately 9 2/3 kilometer straight line removed from the Pag-asa station. (Google, 2012)
Figure 5.2 Distance between Pag-asa Davao and 911 AWS - Generated in Google Maps Š (Google, 2012)
The following graph shows the daily total measurements of the 911 AWS and the Pag-asa station over the period of overlapping data. Dates where the 911 AWS has no data, the Pag-asa data is also left out. 120 100 80 pagasa
60
911 40 20 0 7/28/2010
8/28/2010
9/28/2010
10/28/2010
11/28/2010
12/28/2010
Figure 5.3 Rainfall during overlapping data from Pag-asa Davao and 911 AWS – Gen. Microsoft Excel©
The following graph shows the differences in daily total measurements between the 911 AWS and the Pag-asa station. Dates where the 911 AWS has no data, the Pag-asa data is also left out.
Pag-asa - (minus) 911 AWS 40 20 0 7/28/2010 -20
8/28/2010
9/28/2010
10/28/2010
11/28/2010
12/28/2010 difference
-40 -60 -80 -100 Figure 5.4 Difference between Pag-asa Davao and 911 AWS measurements in Pag-asa - 911 AWS – Gen. Microsoft Excel©
Every comparison based on this data is arbitrary, caused by the sporadic availability of the 911 AWS data. The 85 days of available totals are not consecutive, therefor it could be so that rainfall over Pagasa, fell just before the total measurement, while it fell over the 911 AWS on a date without measurement. However, as this is the only available information at the time the comparison has been made.
6. Conclusions and advise Pag-asa Davao has registered rainfall for every six (6) hours since 1953 up to the current date. Pag-asa was able to make the handwritten registrations available for digitization from the following years.
1985-1986 1989-1995 1997-2010
A total of 23 years.
Figure 6.1 Time periods of digitized data - Generated with Microsoft Visio ©
The data for all years is complete, not one (1) occurrence of missing registration or day has been encountered. Registration is consequent for every day on 2:00 am, 8:00 am, 2:00 pm and 8:00 pm. While checking for typing errors during the digitization the manually registered day total was compared to the automated calculated day total by the spreadsheet. This showed no more than ten (10) errors in 23 years, 0.12% of all registered days. Overall the data can be considered as professionally registered, complete, uniform, consistent and reliable. It is difficult to say how representative the data is for Davao City. Compared with sporadic data from an overlapping time period of 85 days of the 911 emergency central Automated Weather Station (911 AWS) it shows 1.33 times more rainfall than the Pag-asa station during the same days. Overall the 911 AWS rain patterns occasionally differ extreme from the Pag-asa registration.
Pag-asa - (minus) 911 AWS in mm/day 40 20 0 7/28/2010 -20
8/28/2010
9/28/2010
10/28/2010
11/28/2010
12/28/2010
-40
-60 -80 -100 Figure 6.2 Difference between Pag-asa Davao and 911 AWS measurements in Pag-asa - 911 AWS – Gen. Microsoft Excel©
The time period is too short to accurately assess the reprehensibility of either of the stations.
Advise Pag-asa owns valuable meteorological data over a long period of time. As meteorological data for Davao City is scarce and the handwritten paper logs are degrading on quality it is advised to digitize all of the Pag-asa Davao logs. Follow-up The actual analysis and comparisson of the digitized data will be reported in PA-02 – Standardized statistical precipitation events for Davao City.
7. Works Cited Ateneo De Davao University. (n.d.). Central_911. Retrieved 11 3, 2012, from WMDAS: http://202.91.163.247/wmdas/ws Google. (2012). Davao. Retrieved 11 4, 2012, from Google Maps: http://goo.gl/maps/yQIlS Oskam, V. (2012, 11 01-02). Observations. Davao, Philippines. Pag-asa. (1994). Surface observation 28-02-1994. PAGASA FORM 1001-AB, 1. Vierhout, M. M. (2012). PUM Expert's Final Report on Mission Drainage of Davao. Davao City.