GLOBAL CHANGE THREATS TO HYDROLOGY GLOBAL CHANGE THREATS TO HYDROLOGY & TERRESTRIAL ECOSYSTEMS: & TERRESTRIAL ECOSYSTEMS:

IMPACTS OF GLOBAL WARMING & SPECIES INVASION IMPACTS OF GLOBAL WARMING & SPECIES INVASION IN HAWAI‘I IN HAWAI‘I

Thomas GiambellucaUniversity of Hawai‘i at Mānoa

EPSCoR Water Dynamics WorkshopBurlington, VT10 November 2008

Water, water, everywhere . . .Setting

• Extreme geographical isolation

• High water demand

• High inter-annual rainfall variability

• Prone to water shortage

Expectations and observations of warming shift attention to higher latitude land areas Figure 3.7Source: AR4, IPCC (2007)

1920-2005

1920-2005

High-latitudes: +2.3oC

Tropics: +0.8oC

Figure 3.5

Figure 3.5

Figure 3.5

Source: AR4, IPCC (2007)

However, while land areas have warmed fastest at high latitudes, warming of the Pacific Ocean shows cyclical patterns with respect to latitude

Pacific Decadal Oscillation (PDO)

Figure 3.28

Source: AR4, IPCC (2007); also see Mantua et al. (1997) and Power et al. (1999)

El Niño-Southern Oscillation (ENSO)

Source: AR4, IPCC (2007); also see Trenberth and Caron (2000)

Figure 3.27

Hawai‘i Temperature Index

GLOBAL TRENDS:

1906-2005: 0.074oC per decade

1976-2005: 0.177oC per decade

Source: AR4, IPCC (2007)

Source: Giambelluca et al. (2008)

HTI—PDO—SSTPDO

SST

Source: Giambelluca et al. (2008)

Hot Nights

Source: Giambelluca et al. (2008)

1975-2006 Trend

(oC per decade)

Minimum Temperature

Maximum Temperature

All Stations 0.275* 0.054

Low-Elevation 0.153* -0.007

High-Elevation 0.441* 0.085*Significant at p = 0.5

Decrease in Day-Night Temperature Difference

Source: Giambelluca et al. (2008)

Hawai‘i Rainfall: Long-Term Decrease

Source: Chu and Chen (2005)

Hawai‘i (winter) Rainfall Index (HRI)

• Mean altitude ~2200 m (7200 ft)• Frequency ~80%• Stable atmospheric layer • Forms a barrier to rising air• Because rising air is the

predominant means by which clouds form, cloud development is capped at the TWI level

• As a result, relatively thin clouds produce less precipitation when TWI is present

• Climate changes resulting in either more frequent or lower altitude TWI will cause a reduction in rainfall

Trade-Wind Inversion

Effect of Inversion on Rainfall

Source: Adapted from Tran (1995)

HaleNet: Haleakalā Maui

Effect of Inversion on Rainfall

Source: Adapted from Tran (1995)

HaleNet: Haleakalā Maui

TWI Trends

Source: Cao et al. (2007)

Warming and Ecosystem Services

Asner et al. (in review)

Warming & Carbon Dynamics

• Native forest site currently a net carbon sink (2.8-3.4 Mg C ha-1 yr-1)

• Gross primary production controlled mainly by PAR

• Ecosystem respiration controlled by temperature• Each 1ºC increase in temperature causes a 15%

increase in respiration loss• Warming may reduce competitiveness of native

trees versus invasive trees

Species Invasion & Hydrological Services

• Species invasion is a major environmental problem in Hawai‘i

• Success of invasive trees may be facilitated by warming

• What secondary impacts do these trees have on hydrological services?

• Psidium cattleianum is the most widespread invasive tree in Hawaii

Field Sites• Invaded Forest Site

– ‘ohia forest invaded by Psidium cattleianum (strawberry guava)

• Native Forest Site – Metrosideros polymorpha (‘ohia)– Cibotium spp. (hapu‘u; tree fern)

ETinvaded 27% more than ETnative

ET

Available Energy

SUMMARYSUMMARY• Hawai‘i is highly vulnerable to and prone to water Hawai‘i is highly vulnerable to and prone to water

shortageshortage

• Tropical areas like Hawai‘i are subject to significant Tropical areas like Hawai‘i are subject to significant impacts of global warmingimpacts of global warming

• Trends suggest Hawai‘i is getting warmer and drierTrends suggest Hawai‘i is getting warmer and drier

• Warming will have negative impacts on native Warming will have negative impacts on native forests and favor invasive treesforests and favor invasive trees

• Invasive trees can significantly reduce water Invasive trees can significantly reduce water availabilityavailability

• Findings suggest severe combined and synergistic Findings suggest severe combined and synergistic effects of climate change and species invasion on effects of climate change and species invasion on Hawai‘i’s terrestrial ecosystems and their servicesHawai‘i’s terrestrial ecosystems and their services

THANK YOUTHANK YOU

thomas@hawaii.edu