Rainfall and drought: our changing climate

This section provides statistics on rainfall and drought in New Zealand over time, and possible impacts on health.

Rainfall and drought patterns in New Zealand are projected to change in the future.  The West Coast is likely to receive more rainfall.  The north and eastern parts of the North Island, and north-eastern South Island, are projected to receive less rainfall.   

Droughts have not been occurring more frequently to date. But projections are that New Zealand will spend 10 percent more time in drought conditions by the middle of the 21st century [1].

On this page

Data shows dry areas of New Zealand in the past 14 years
Droughts and heavy rainfall can affect health
Long term monitoring of New Zealand’s drought-sensitive health effects

Data shows dry areas of New Zealand in the past 14 years

Eastern areas of New Zealand have been most affected by a lack of rainfall over recent years.

Soil moisture deficit is one way to measure drought.  It measures how much moisture (in millimetres) is available to pasture plant roots. 

We used NIWA weather data to determine how many days of soil moisture deficit are experienced by different regions within New Zealand, and show how these are changing over the past 14 years.

Our results show that eastern regions of New Zealand experience dry conditions more frequently.  We cannot say whether there has been an increase in drought due to climate change, because we need longer-term data.  

Movie 1: Days of soil moisture deficit, 2000-2013, by territorial authority, New Zealand

Droughts and heavy rainfall can affect health

Drought and heavy rainfall can affect health in different ways.  

  • In periods of heavy rainfall, flooding and swollen rivers can cause injury.
  • Food production decreases in dry conditions, because plant growth decreases when it is very dry.  Drinking-water availability and quality can also be affected. 
  • There is some evidence that cryptosporidiosis and giardiasis are affected by rainfall patterns [2]. Exactly how these diseases are affected is not clear. Some studies suggest that surface run-off following heavy rainfall contaminates drinking water sources. Other studies show increases with drought conditions. It has been suggested that the parasite cysts concentrate in remaining ground water, before being washed out when the drought breaks.
  • Droughts and heavy rainfall can have effects on mental health [3].

Download factsheet on pdficon small drought, climate change and health

Long term monitoring of New Zealand’s drought-sensitive health effects

Health experts believe that we will see rates of cryptosporidiosis and giardiasis change as a result of more time spent in drought conditions.  We need longer-term health data before we can conclusively say whether New Zealand is seeing such effects as a result of climate change.

We reviewed notified cases of cryptosporidiosis and giardiasis in New Zealand from 1996 to 2015 (Figure 1).  We found no observable increase or decrease in notifications. The initial increase in 1996–1999 is thought to be primarily due to improved reporting rates after a new surveillance database began operation.  

Figure 1

Many of the indicators we would like to measure, like drinking-water availability and instances of intense rainfall, do not have available data.  

Information about the data

For more information about the data and indicators, download the metadata datasheets below:

References

1. Clark A, Mullan A, Porteous A. 2011. Scenarios of regional drought under climate change. NIWA Client Report WLG2012-32. Wellington: National Institute of Water and Atmospheric Research.

2. Lal A, Baker MG, Hales S, French NP. 2013. Potential effects of global environmental changes on cryptosporidiosis and giardiasis transmission. Trends in Parasitology 29(2): 83-90. doi: 10.1016/j.pt.2012.10.005

3. Berry H, Bowen K, Kjellstom T. 2010. Climate change and mental health: A causal pathways framework. International Journal of Public Health 55: 123-132. doi: 10.1007/s00038-009-0112-0