PRIMARY VALIDATION - RAINFALL DATA

1. PRIMARY VALIDATION - RAINFALL DATA • DATA VALIDATION • FINAL VALUE STORED IN “HIS” IS BEST REPRESENTATION • COMPREHENSIVE MANUAL VALIDATION • PROHIBITIVE IN THE PAST, IF NOT IMPOSSIBLE • PRIMARY VALIDATION • SUB-DIV. DPCs USING PRIMARY MODULE • DATA COMPARISON AT SINGLE STATION • DATA ENTRY CHECKS ALREADY DONE • TRANSCRIPTION ERRORS REMOVED • RAINFALL - HIGH VARIABILITY • MORE CHECKS SUBSEQUENTLY • SECONDARY VALIDATION, DIV. DPCs • NEIGHBOURING STATIONS OHS - 1

2. INSTRUMENTS & OBSERVATIONAL METHODS • WHY CERTAIN DATA IS SUSPECT ?? • OBSERVATIONAL PROCESS TO BE KNOWN • METHOD OF MEASUREMENT • TYPICAL ERRORS OF EQUIPMENT USED • DATA VALIDATION • NOT A MERE STATISTICAL EXERCISE • 3 BASIC EQUIPMENT • STANDARD RAINGAUGE (SRG) • SYPHON TYPE RECORDING RAINGAUGE (ARG) • TIPPING BUCKET RAINAGAUGE (TBR) OHS - 2

3. SRG • INSTRUMENT & PROCEDURE • CIRCULAR COLLECTOR FUNNEL (200 / 100 SQ.CMS) • COLLECTOR BOTTLE • BASE UNIT - PARTLY EMBEDDED • GAUGE READ ONCE OR TWICE IN A DAY • MEASURING GLASS • TYPICAL ERRORS • INCORRECT READING OF MEASURING GLASS • RECORDING INCORRECTLY IN THE FIELD SHEET • OBSERVATION AT NON STANDARD TIMES • WRONG MEASURING GLASS • GAUGE RIM DAMAGED, BLOCKAGE/LEAKAGE IN FUNNEL • COLLECTOR BOTTLE NOT PROPER • NON-STANDARD EXPOSURE CONDITIONS OHS - 3

4. ARG • INSTRUMENT & PROCEDURE • CIRCULAR COLLECTOR FUNNEL (324 SQ. CMS) • FLOAT CHAMBER & FLOAT SPINDLE • SYPHON CHAMBER • PEN, CHART, DRUM, CLOCK • CHART IS CHANGED ONCE IN A DAY • TABULATION OF ANALOGUE RECORD • TYPICAL ERRORS • BLOCKAGE/LEAKAGE IN FUNNEL • IMPERFECT SYPHONING OR FLOAT MOVEMENT • CLUTTERING IN PEN TRACE FOR HIGH INTENSITY • CLOCK IMPROPER • IMPROPER TABULATION • NON-STANDARD EXPOSURE CONDITIONS OHS - 4

5. TBR • INSTRUMENT & PROCEDURE • CIRCULAR COLLECTOR FUNNEL • TIPPING BUCKET ARRANGEMENT - KNIFE EDGE • REED SWITCH REGISTER EACH TIP • DATA LOGGER • CONTINUOUS RECORDING • PRE-SET TIME INTERVAL OR REGISTER TIPS • TYPICAL ERRORS • BLOCKAGE/LEAKAGE IN FUNNEL • BUCKET DAMAGED OR IMBALANCED • REED SWITCH NOT EFFICIENT • NON-STANDARD EXPOSURE CONDITIONS OHS - 5

6. DATA VALIDATION - INDEPENDENT SOURCES • COMPARING DAILY RAINFALL • OBSERVED AT SAME STATION BY SRG AND ARG • MUTUAL DIFFERENCES • CHANGE IN EXPOSURE • INSTRUMENT ACCURACY • PRECISION IN TABULATING ARG CHART • MUST BE LESS THAN 5% • SIGNIFICANT DIFFERENCES BE PROBED FURTHER • SRG RECORD - GENERAL MORE RELIABLE • ERRORS IN ARG - NORMALLY SYSTEMATIC OHS - 6

7. OHS - 7

8. OHS - 8

9. SRG ARG SRG ARG SRG ARG OHS - 9

10. BEWARE OHS - 10

11. SRG - ARG : POSSIBLE SCENARIOS • ARG - CONSISTENTLY HIGHER OR LOWER • ARG OUT OF CALIBRATION • ACCEPT SRG AND ADJUST ARG • INCREASED DIFFERENCES AT HIGH INTENSITY • ARG WORKING IMPERFECTLY AT HIGH INTENSITY • ACCEPT SRG AND ADJUST ARG • ALTERNATE + & - DIFFERENCES • SRG READ AT NON-STANDARD TIMES • ACCEPT ARG AND ADJUST SRG • INCORRECT TABULATION • ACCEPT SRG AND ADJUST ARG • HIGH DIFFERENCES ONLY ON ISOLATED DAYS • DATE, TABULATION OR DATA ENTRY ERRORS OHS - 11

12. CHECKING AGAINST DATA LIMITS • MAXIMUM LIMIT • ABSOLUTE MAXIMUM LIMIT • HIGHEST EVER RECORDED • PMP MAPS - 1DAY • 50 YEAR - 1HR ISOLINES • GENERAL PERCEPTION / EXPERIENCE • VERY BROAD LIMIT • DEFINES THE BOUNDARY - ALMOST ABSOLUTELY • RARE OCASSIONS!! - NEW MAXIMA EXPERIENCED OHS - 12

13. OHS - 13

14. CHECKING AGAINST DATA LIMITS • UPPER WARNING LEVEL • OPERATIONAL LIMIT • TO FLAG A FEW HIGH DATA VALUES • DERIVABLE USING SUITABLE STATISTICS • 99 %ILE OF NON-ZERO RAINFALL VALUES • 1 IN 100 VALUES WILL BE FLAGGED • 1 OR 2 VALUES A YEAR (DAILY DATA) • PROVIDES A CROSS CHECK ON DATA ENTRY CHECKS OHS - 14

15. OHS - 13