Environmental Reporting, Ministry for the Environment and Statistics New Zealand
Potential evapotranspiration deficit (PED) can be thought of as a drought index. It is the difference between how much water could potentially be lost from the soil through evapotranspiration and how much is actually available. When PED is high, plants do not have the full amount of water available they need for growth. As our climate changes, increasing temperatures and rainfall pattern changes are expected to increase PED, and the frequency and intensity of drought, particularly in currently drought-prone regions. More information on this dataset and how it relates to our environmental reporting indicators and topics can be found in the attached data quality pdf.
Method: NIWA interpolated daily Virtual Climate Station Network (VCSN) data for rainfall and potential evapotranspiration to create a regular 500m resolution grid of average annual PED for each growing year (NIWA, nd). PED anomaly is the difference between the most recent three-year average PED for 2013/14–2015/16 and the 30-year PED climate normal (1981/82–2010/11 average) VCSN interpolations. Using a three-year average accounts for inter-annual variability while providing information on recent conditions.