Soil moisture in November 2009

Estimates of soil moisture shown in the map (right) are based on monthly rainfall for one station in each country. Currently there are not many sites in the water balance model, but more stations will be included in the future.

The information displayed is based on a simple water balance technique to determine soil moisture levels. Addition of moisture to the available water already in the soil comes from rainfall, with losses via evapotranspiration. Monthly rainfall and evapotranspiration are used to determine the soil moisture level and its changes. These soil moisture calculations were made at the end of the month, and for practical purposes, generalisations were made about the available water capacity of the soils at each site.

Aitutaki (Southern Cook Islands), Nadi (Fiji), and Fua’amotu (Tonga) project important soil moisture deficits at this time. Tarawa (Western Kiribati) projects moist soil moisture, while Vila (Vanuatu) is moderate at this time.

As a whole, the regional rainfall developments were largely characterised by drier than normal conditions for many island groups as a result of the continuation and strengthening of El Niño during November. Well below normal rainfall occurred over most of Vanuatu and New Caledonia last month, with many stations recording 30% to 60% of normal levels. Southeast Australia was also very dry, with Sydney reporting only 13mm of rain for the month. Dry conditions were also reported for Samoa, and extended to neighboring Tonga, which had three stations that received less than 60% of normal rainfall during November.

Estimated soil moisture conditions at the end of November 2009, using monthly rainfall data. Soil moisture projections for individual Pacific Island countries are dependent on data availability at the time of publication.