Observation Date Notes: It has been standard climatological practice to allocate the 0900 local time daily reading to the PREVIOUS DAY since 16 hours of the 24 relate to it. The database stores this rainfall at the equivalent UTC time to the actual day and time of MEASUREMENT.
For CliFlo output the date/time is the date/time at the end of the measurement period (the same as stored in the database). This will differ from the "Form 301" (F301) format that NIWA often provides. A fuller explanation can be found in the description of maximum temperature Max Min Temperature: Details
WARNING: A major error during conversion of Synoptic rain up to 1991 for the Oracle database has been found. All values were treated as tenth mm, but synops reported WHOLE mm for values greater than 0.9mm. Thus values between 1 mm and 9 mm can no longer be distinguished from 0.1mm to 0.9mm, and all doubtful values now have a reliability of "?".
Rainfalls before 1972 are converted from inches to mm.
WATER BALANCE: estimates using a two-layered model (AWC (Available Water Capacity) of 75+75mm) are made where possible for Frequency="D" rain records from NZ stations. Mean daily ET is taken from the nearest source with Penman PE preferred over corrected Priestley-Taylor PE. Origin ranks (low to high) for combined PET and RAIN are "C", "T", "M", "S", "F", "E", "H", "Q", "P", "R", "D".
More details can be found in Water Balance