Step 6: Construct Climate Change Projections

For the analysis of future temperature and rainfall conditions in Solomon Islands we can apply the projected change to the observed dataset using a simple scaling approach – adjusting the observed climate surface up or down using the change factor from projections.

The absolute change in temperatures (°C) is applied using an addition:

current + change = future

The proportional change in rainfall (%) is applied using a multiplication:

current × %change = future

Two change factors are applied for each time period and each RCP: the lower end of the projected range, and the upper end.

For example, if the average daily maximum temperature in a spatial grid cell is 29.5 °C and the range of projected change is 1.5–2.8 °C, then the future value of that cell is 31–32.3 °C.

Following this, the values that are over a threshold are found. The cell is categorised into one of three categories:

  1. The range of future conditions is below the threshold.
  2. The range of future temperature crosses the threshold (the high value is over, the low is under).
  3. The range of future temperature is all above the threshold.

For the example in this case study, the temperature range of 31–32.3 °C for a threshold of 32 °C would be in category 2 (the low end of the range of 31 °C is below the threshold of 32 °C, and the high end of 32.3 °C is above it).

Note that the baselines are slightly different between the observations and the projections: 1970–2000 for Worldclim observations, and 1986–2005 for the Australian Bureau of Meteorology and CSIRO (2014) projections. The observed data or the projections can’t be adjusted so the results are used as they are and this point is communicated in the results.

Reference

Australian Bureau of Meteorology and CSIRO (2014). Climate Variability, Extremes and Change in the Western Tropical Pacific: New Science and Updated Country Reports. Pacific-Australia Climate Change Science and Adaptation Planning Program Technical Report. Australian Bureau of Meteorology and Commonwealth Scientific and Industrial Research Organisation (CSIRO), Melbourne, Australia