Step 7: Assess Climate Change Risk

The areas where the projected daily maximum temperature range sits in relation to the 34 °C threshold for three RCPs and two time periods are shown in Figure A3.

Figure A3. Mean daily maximum temperature in the warmest month of the sweet potato growing season of PNG today (top) compared with categorisation of regions in relation to the 34 °C threshold for growing sweet potato in 2050 (left column) and 2090 (right column) under different RCPs. Projected ranges of changes in temperature noted in brackets; green shows the range is below the threshold, orange shows range crosses threshold and red shows where the range is above the threshold. (Click to enlarge)

Looking at this plot in terms of vulnerability and risk, we can interpret the areas in green (temperature range below the threshold) as being fairly low risk of being limited by temperature, areas in orange as potentially at risk, and red areas as being very high risk of being unsuitable. The warmest month in the region of the southern lowlands is already close to 34 °C, so is projected to have increased risk of temperature impacts under all scenarios and time periods. Other than that region, the results suggest the effect of the emissions scenario is very important – under a very low scenario (RCP2.6), the increase in risk is seen southern lowlands, but is minimal even by 2090 over most of PNG. Under RCP4.5 some regions of the northern lowlands could be affected. Under RCP8.5, the temperature of the warmest month could be an important limiting factor to sweet potato growing in most of the lowlands by 2090.

Looking at daily minimum temperature of the coolest month of the growing season, we see that even under RCP8.5 by 2090 (Fig. A4), relatively small new areas are projected to become less limited by cool nights <10 °C. This is expected due to the steep climatic gradients on the slopes of the highlands.

Figure A4. Mean daily minimum temperature in the coolest month of the sweet potato growing season of PNG: categorisation of regions in relation to the 10 °C minimum threshold for growing sweet potato in 2090 under RCP8.5, green shows areas where the projected range is above the threshold (areas that are likely to become more suitable for sweet potato growing), orange shows where the range crosses the threshold (areas that may become more suitable for growing sweet potato), and red areas are where the temperature remains too cool. (Click to enlarge)

In a full risk assessment, this temperature analysis would then need to be combined with other analyses (e.g. rainfall, droughts, pests, disease, extreme events) to assess the overall risks and vulnerability of the industry.