Soil moisture in December 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), Tarawa (Western Kiribati), and Vila (Vanuatu) project moist soil moisture at this time. It is important to note that the situation in Vanuatu and Fiji could change with continuation of El Niño.
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 December. Well below normal rainfall occurred over most of Tuvalu, New Caledonia, and especially French Polynesia last month. Particularly dry conditions were observed in the Society Islands, Marquesas and Gambier with up to 25% of normal rainfall recorded in that area.
Warm conditions also affected all of French Polynesia during December, with anomalies of more than 2°C in Tahiti (the warmest December since 1957). Mean maximum monthly temperature (29°C) and a maximum daily temperature (33.2°C) records were also established.
Estimated soil moisture conditions at the end of December 2009, using monthly rainfall data. Soil moisture projections for individual Pacific Island countries are dependent on data availability at the time of publication.