Big Impacts: Hurricanes and El Niño
Although some historical evidence suggests that rainfall increases during cooler times, and thus decreases during warmer times, alteration of the El Niño Southern Oscillation and storm variability by climate change could offset the reduction in trade wind, orographic driven precipitation. The general future increase in sea surface temperatures along the equatorial Central and Eastern Pacific projected by the Hadley HADCM2 and other models - A2 and B2 - we have looked at (Figure 17 in Chapter 4A and Figure 29 in Chapter 5C) suggests a greater tendency for El Niño-like conditions. It is uncertain whether future increases in ocean temperatures might change the character of the El Niño Southern Oscillation so that El Niños appear more or less frequently.
Increased tropical and equatorial sea surface temperatures however could lead to increased hurricane activity and the possibility of large-scale damage to property and resources. Hurricane Iniki made landfall on the island of Kauai, Hawaii, in September 1992 causing 7 deaths, 1.8 billion dollars in damage, and $260 million in Federal Emergency Management Act disaster relief costs. This is in spite that Iniki landed on the 4th most populous island in the state (Island populations from largest to smallest: Oahu > Big Island of Hawaii > Maui > Kauai). Had Iniki landed on Oahu, and specifically Honolulu and Waikiki, the cost and level of destruction would have been significantly greater not only to the island itself, but the entire state’s economy.
The sea level pressure projections (Figure 24) for December, January, and February suggest that the level of storminess will increase around Hawaii during the winter months. This increased storminess and associated precipitation during the winter months (also when evaporation is lowest due to cooler temperatures) could offset the loss of water from increased evaporation due to higher average yearly temperatures predicted by the regional climate models. The issues brought up (see previous section C. Temperature and Rainfall) with the inability of the relatively course regional scale precipitation models to resolve the smaller scale processes (e.g. orographic) that impact the hydrology of islands are also relevant to the impact of increased storminess and resultant rainfall to the islands of Oahu.
Figure 24. The ratio of sea level pressure variance for December-January-February for the period 2006-2036 compared to 1990-2020 and the period 2070-2100 compared to 1990-2020. Higher ratios (>1 in yellow and orange) indicate more storminess in the future periods.
