Hawaii Drought - PowerPoint PPT Presentation

1 / 27
About This Presentation
Title:

Hawaii Drought

Description:

HRI time series (green bars) 27 stations from 3 islands ... The Hawaiian Islands are bordered approximately by two vertical lines. ... – PowerPoint PPT presentation

Number of Views:47
Avg rating:3.0/5.0
Slides: 28
Provided by: paosh
Category:

less

Transcript and Presenter's Notes

Title: Hawaii Drought


1
Hawaii Drought
  • Pao-Shin Chu
  • State Climatologist
  • Department of Meteorology
  • University of Hawaii

2
  • Drought is a chronic and troublesome problem in
    Hawaii, at one time or another affecting
    virtually every part of the state.  These events
    often reduce crop yields, diminish livestock
    herds, desiccate streams, irrigation ditches and
    reservoirs, deplete groundwater supplies, and
    lead to forest and brush fires.  
  • Source Hawaii Drought Monitor

3
  • Drought can be characterized from the
    perspectives of meteorology, agriculture,
    hydrology, and socio-economic impacts. 
  • The meteorological perspective would describe
    drought as a rainfall deficit compared with some
    normal or expected rainfall amount. 
  • The agricultural perspective could describe
    drought by its impacts on the agricultural
    industry due to reduced rainfall and water supply
    (e.g., crop loss, herd culling, etc.).
  •  
  • Hydrological descriptions of drought may compare
    stream flows, ground water, and reservoir levels
    to normal conditions.
  •  
  • Drought can also be described from the
    socio-economic perspective by the direct and
    indirect impacts droughts have on society and the
    economy (e.g., increased unemployment due to
    failure of an industry because of drought). 

4
Historical statewide drought events (Hawaii
Drought Monitor and R88)
5
(No Transcript)
6
HRI time series (green bars) 27 stations from 3
islands(Hawaii, Oahu, Kauai) Normalized winter
(NDJFM) rainfallNino 3.4 SST anomalies (solid
curve), Diamond for El Niño
7
Correlation coefficients between the seasonal SOI
and the seasonal Hawaiian rainfall
index.Quenouilles (1952) method was used to
account for the reduction of effective numbers of
degrees of freedom due to persistence. One and
two asterisks indicate significance at the 5 and
1 percent levels, respectively.
8
Drought forecasts from simple regression models
for winter 1983
  • Predicted rainfall Observed rainfall
  • Determined from
  • Spring 1982 -0.089 -1.10
  • Summer 1982 -0.982 -1.10
  • Autumn 1982 -0.894 -1.10

9
(No Transcript)
10
Chu and Chen (2005) Interannual and interdecadal
rainfall variations in the Hawaiian Islands. J.
Climate, 18, 4796-4813.
11
Winter rainfall difference (inches) of the (El
Niño/PDO) minus (La Niña/-PDO) composite. Dots
for rainfall stations (272).
12
The nonparametric Mann-Whitney test for winter
rainfall difference of the (El Niño/PDO) minus
(La Niña/-PDO).
13
Winter composite of SST (shading) and surface
wind (vectors). The unit for SST is C and for
wind vectors is m/s.
14
Winter 200-mb wind vectors. Isotach interval is
10 m/s. Area with wind speed greater than 40 m/s
is shaded.
15
Winter composite of east-west vertical
circulation. Longitude-height section of zonal
wind and negative pressure vertical velocity (U,
-?) is averaged over 15-25N. Shading is for
statistical significance. The Hawaiian Islands
are bordered approximately by two vertical lines.

16
  • To monitor meteorological droughts, the
    Standardized Precipitation Index (SPI) is used.
  • The SPI relies on monthly precipitation as the
    only input. SPI values can be generated for
    multiple time series (e.g., 3-mo, 12-mo). This
    is useful because drought affects various sectors
    over a wide range of time scales.

17
  • Computation of the SPI involves fitting a gamma
    probability density to a set of precipitation
    totals for a station using the maximum likelihood
    approximations.
  • The resulting gamma parameters are used to find
    the cumulative probability of a precipitation
    event for the given time scale.
  • The cumulative probability is then transformed to
    the standard Gaussian random variable with mean
    zero and unit variance, which is the SPI.

18
The SPI has been embraced by NDMC, WRCC, and the
NWS/Honolulu Forecast Office.
19
  • Drought classification based on SPI
  • (NDMC)
  • SPI values Designation
  • 0.00 to -0.99 Mild Drought
  • -1.00 to -1.49 Moderate Drought
  • -1.50 to -1.99 Severe Drought
  • -2.00 or less Extreme Drought

20
(No Transcript)
21
UH Hawaii State Climate Office and SSRIFunded
through DLNRs Water Commission Office
  • Drought Risk and Vulnerability Assessment and GIS
    Mapping Project

22
(No Transcript)
23
  • ? Another index, the Keetch/Byram Drought Index
    (KBDI), has been used for the southeast U.S. over
    30 years.

? The KBDI, which conceptually describes the soil
moisture deficit, is used to assess wildfire
potential as part of the revised 1988 U.S.
National Fire Danger Rating System.
? This index depends on daily rainfall amount,
daily maximum temperature, and the mean annual
rainfall.
24
  • The relationship between the KBDI and fire
    activity, as measured by total areas burned, in
    the Hawaiian Islands was explored (Dolling, Chu,
    Fujioka, 2005, Agricultural and Forest
    Meteorology).
  • Total acres burned (TAB) data from DLNR. Records
    are short, only 20 yrs (1976-96).
  • Because of the non-normally distributed nature of
    the TAB, a log transformation is applied to the
    TAB data. The correlation between KBDI and TAB
    is significant for Hawaii with a p-value well
    below the 5 level.

25
A strong relationship between the KBDI and fire
activity is found for the islands of Maui and
Hawaii.
26
Summary
  • Reviewed historical drought events in Hawaii.
  • Drought in Hawaii generally follows an El Niño
    event. Long-lead winter (spring) rainfall
    prediction is feasible.
  • Drought is also affected by the PDO cycle.
    Rainfall difference between (El Niño/PDO) and
    (La Niña/-PDO).

27
  • SPI time series for HVNP since 1950.
  • Drought risk and vulnerability assessment for
    Hawaii County.
  • Keetch/Byram drought index (KBDI) Relation
    between KBDI and fire activity for Hawaii is
    evident.
Write a Comment
User Comments (0)
About PowerShow.com