Step 3: Find Climate Change Information

A literature and internet search reveals that there is some useful general information about cocoa farming in the Solomon Islands, including a chapter in the recently published book by the Secretariat of the Pacific Community (SPC) on climate change and agriculture (McGregor et al. 2016). A detailed analysis of the climate envelope for cocoa in Africa has been done previously (e.g. Läderach et al. 2013). However, there are no detailed previous studies of the optimal temperature envelope for cocoa growing specifically for Guadalcanal; so we need to do new analysis. The temperature and rainfall thresholds of the climate envelope for cocoa growing in general are fairly well known. According to McGregor et al. (2016) the relevant climate conditions are:

  • Annual average daily maximum temperature (Tmax) up to 30–32 °C
  • Annual average daily minimum temperature (Tmin) up to 18–21 °C
  • Annual average rainfall of 1250–3000 mm (1500–2000 mm is optimum)
  • No more than three months of rainfall of less than 100 mm/month per year
  • Fungal disease is most severe when annual rainfall is above 2500 mm.

To fully assess the risk with flooding we can’t just use the average climate, rather we need detailed daily rainfall datasets and hydrodynamic and geomorphological information about localised floods (e.g. the shape of catchments and flood plains, drainage capacity and rates of run-off, etc.). As this case study is based on a rapid assessment of change in flood risk we are only using existing and available data and information, with no new analysis.

To this end, previous work for the Solomon Islands (Australian Bureau of Meteorology and CSIRO 2014) has found:

  • Extreme wet days are projected to increase, where the 1-in-20-year event could become a 1-in-9-year event under moderate climate change (RCP2.6), or a 1-in-4-year event under a worst-case emissions scenario (RCP8.5) by 2090
  • Extreme wet seasons may increase (e.g. extreme swings of the El Niño Southern Oscillation)
  • Tropical cyclones vary a lot decade to decade, but over the long-term the average number of cyclones may decrease, but more of the ones that do occur might be intense.

All these results suggest that flooding will continue to vary a lot year to year and decade to decade, but over time the risk of floods and extreme rainfall events is likely to increase during this century, especially under a high emissions scenario.

References

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

McGregor, A., Bourke, R.M., Lebot, V. and Taylor, M. (2016). Chapter 5. Vulnerability of export commodities to climate change.In Vulnerability of Pacific Island Agriculture and Forestry to climate change. (Eds) M. Taylor, A. McGregor and B. Dawson. Secretariat of the Pacific Community (SPC) Noumea Cedex, New Caledonia: 239–294.

Läderach, P., Martinez-Valle, A., Schroth, G. and Castro, N. (2013). Predicting the future climatic suitability for cocoa farming of the world’s leading producer countries, Ghana and Côte d’Ivoire. Climatic Change 119: 841–854.