Hawaii Drought Update

1
Hawaii Drought Update Operational Drought
Monitoring

• Kevin Kodama
• Senior Service Hydrologist
• NOAA/NWS WFO Honolulu

2
Outline

• Current conditions
• Wet season rainfall (Oct-Apr)
• Drought Monitor
• Drought Outlook
• Hawaii Component of Drought Monitor Seasonal
  Drought Outlook
• New Product Drought Information Statement
• Monthly Rainfall Summary
• Standardized Precipitation Index (SPI)
• Questions?

3
Wet Season 2007-2008 Overview

• Near normal rainfall at many locations
• La Nina in place
• Distinct periods
• Oct Dry
• Nov Early Feb Very wet
• Mid Feb Apr Very dry
• 2007 2008 wet season 14th driest in 30 years
• Comparison 2006 2007, 8th driest
• Wettest 1981 1982
• Driest 1991 1992

4
Start of 2008 Dry Season

• Most gages recorded below normal rainfall in May
• Early May Good trade showers
• Mid Late May Stable conditions, little rain
• USGS reports very low streamflow at most
  locations statewide

5
Current Drought Monitor

• Severe drought
• West Molokai
• East Oahu (Waimanalo)
• Moderate drought
• Windward, Central Upcountry Maui
• Northwest Big Island
• Northeast Kauai
• Abnormal dryness rest of state

6
Drought Outlook

• Windward areas may see improvement if trade wind
  showers pick up as expected
• Leeward areas...no significant drought relief
  until October (start of wet season)
• Expansion of drought likely during next 4 months
• Worsening of existing drought in leeward areas
• Climate Prediction Center forecasts drier than
  normal dry season

7
Drought Monitor Hawaii Component

• How are the Drought Monitor (DM) depictions
  determined?
• Combine objective and subjective data
• Rainfall
• normal
• Standardized Precipitation Index (SPI)
• Streamflow from USGS
• Reservoir levels
• State Dept of Ag
• Upcountry Maui, Kohala/Hamakua
• Crop weather reports
• County water supply web sites
• Media

8
Drought Monitor Hawaii Component

• Suggested changes to HI depiction sent to
  national DM author of the week
• Challenge Condense complexity of drought into a
  single category
• Example Agriculture impacts
• Crops vs. livestock
• Irrigated vs. non-irrigated
• Timing
• Recent change Consult w/informal team
  consisting of county reps for water supply and
  agriculture. Provides vetted input for DM.

9
Seasonal Drought Outlook Hawaii Component

• Issued bi-weekly from NOAA Climate Prediction
  Center
• Covers next 3-month period
• Based on
• Statistical guidance Several types
• Computer model guidance Several types
• Existing climate and drought situation
• Seasonal considerations
• Local experience

10
Impact of El Nino La Nina on Wet Season Rainfall

• El Nino Abnormal warming of the equatorial
  waters in the central and east Pacific
• Strong likelihood of statewide drought during
  winter months (esp. Dec-Feb)
• La Nina Abnormal cooling of the equatorial
  waters in the central and east Pacific
• Tendency for wetter than normal winter months
• Relationship is poor

11
Impact of El Nino La Nina on Wet Season Rainfall

• Wet season rankings, past 30 years
• 1 wettest, 30 driest
• 1978-1979 through 2007-2008
• El Nino affected 7 wet seasons, dry overall
• Rankings 10, 19, 20, 21, 23, 28, 30
• La Nina affected 5 wet seasons, highly variable
  rainfall impacts
• Rankings 2, 11, 17, 24, 29

12
Drought Information Statement

• New product started June 10, 2008
• First time NOAA has a text product specific to
  drought
• Previously used Hydrologic Outlook or Public
  Information Statement to convey drought
  information
• Issued when severe drought (D2 category on
  Drought Monitor) present in Hawaii
• Includes
• Synopsis
• Summary of impacts
• Climate summary
• Precipitation/temperature outlook
• Hydrologic summary and outlook

13
Hawaii Monthly Precipitation Summary

• Issued by NOAA/NWS, generally w/in 1st week of
  new month
• Statewide weather summary
• Flooding and drought impacts
• County-based breakdown of rainfall details
• Data table with 110 gages
• Maps of gages with data tables
• Posted to NOAA/NWS Honolulu hydrology web page
  http//www.prh.noaa.gov/hnl/pages/hydrology.php

14
Sample Data Table

• Monthly
• Year-to-date totals
• Normals
• normal
• Grouped by island

15
Sample Precip Summary Map
16
Standardized Precipitation Index (SPI)

• Statistical adjustment of rainfall data
• SPI independent of both the location and the
  range of values so that different seasons and
  climate areas are represented on an equal basis.
• Simple Just need rainfall data
• Can vary number of months to accumulate
• Calculated monthly for over 52 sites in Hawaii
  since 2000
• Posted to NOAA/NWS Honolulu hydrology web page
  http//www.prh.noaa.gov/hnl/pages/hydrology.php

17
Kahua Ranch 12-mon SPI
18
Kahua Ranch 3-mon SPI
19
SPI Area Average Map

• Maps created for Kauai, Oahu, Maui, Big Island
• 12-, 6-, and 3-mon SPI
• Average of all available gages in zone

20
SPI Sample Output Table

• Data table posted to web
• SPI values for each site
• 1-, 2-, 3-, 6, 12-, 18-, 24-month
• Area averages also provided for all time
  intervals
• Early version posted about 2 weeks after end of
  month
• Full version with all available data posted about
  5 to 6 weeks after end of month

21
Questions?