Long term rainfall statistics are fundamental to the statistical analysis undertaken by hydrographers.

Recent drought events in Auckland, New Zealand during the summer period of 2013 (NIWA, 2013) were suspected of causing evaporation from rainfall storage gauges. This meant that storage gauge totals for that period would under represent total rainfall. The need to adjust intensity gauge totals to storage gauge totals is recommended by the New Zealand ‘National Environmental Monitoring Standards, (NEMS, 2013).

Experiments concluded that significant (35%) evaporation can occur from storage gauges during a single month. To address this problem we investigated the addition of environmentally safe and easy to use oil. This additive would attempt to prevent any evaporation and improve data quality. The addition of oil improved data validation with a minimal (2%) loss to evaporation for the same time period.

We concluded significant improvements in data validation are achieved by the addition of environmentally safe and easy to use oil in storage gauges.