Effectiveness of Existing Drought Effectiveness of Existing Drought IndicatorsIndicators

Southeast-ACF Drought Early Warning Information Southeast-ACF Drought Early Warning Information System Development Workshop: Apalachicola River & System Development Workshop: Apalachicola River &

BayBay

April 27-28 2010April 27-28 2010

Apalachicola, FloridaApalachicola, Florida

Douglas Le ComteDouglas Le Comte

NOAA/NCEP Climate Prediction CenterNOAA/NCEP Climate Prediction Center

Douglas.lecomte@noaa.govDouglas.lecomte@noaa.gov

OutlineOutline

• A look at selected current drought indicatorsA look at selected current drought indicators

• An honest appraisal (probably politically incorrect) of An honest appraisal (probably politically incorrect) of how well they work… Doug’s Top 5!how well they work… Doug’s Top 5!

Atlanta Journal Cartoon

Lake Lanier drought index—the keep-it-simple approach

An effective drought index is one that does what you want it to do. You may want to merge several drought indicators to meet your needs, e.g., CPC delivery of historical river basin indices to the water commissions of GA, FL, AL in January 2001.

Desired Features of a Drought Index

• Understandable (what it means and how it’s calculated

• Available daily (short term index) or weekly (long-term index)

• Correlates with impacts

• Range of values easy to understand (e.g., percentiles, anomalies).

• Appropriate spatial resolution

• Can be imported into GIS (e.g. GeoTIFF)

• Has a long history and the archive is easy to find

Historical Perspective* The Drought Phenomenon

Definition – Sectors Impacted – Indices

Early 20th Century Drought Indices Incorporated some measure of precipitation over a given time Examples:

• 15 Consecutive Days with No Rain

• 21 Days or More with Precipitation less than One-Third (or 30%) of Normal

• Annual Precipitation less than 75% of Normal

• Monthly Precipitation less than 60% of Normal

• Any Amount of Rainfall less than 85% of Normal Other important climatic elements (soil

moisture, evapotranspiration, etc.) were not readily available at that time

* R. Heim (Inter-Regional Workshop on Indices andEarly Warning Systems for Drought WMO/NDMC/NOAA/UNCCD/USDALincoln, NE, USA – December 8-11, 2009)

These Basic Indicators Are Still Widely Used Today

Historical PerspectivePalmer’s Drought Index (1965)

and Crop Moisture Index (1968) CMI is computed on a weekly basis

for agricultural applications

Moisture Stress Index Developed in 2003 by NCDC Annual index for corn and soybeans

that relates moisture stress (drought and extreme wetness) to crop productivity Computed from Palmer Z Index and crop yield

Economic impacts

Post-Palmer Era

Indices Based On: Additional Observed Variables

Advanced Statistical Methodologies

More Sophisticated Models

Data from New Observational Platforms

Standardized Precipitation Index (SPI) Developed by Colorado’s McKee et al.

(1993)

Based on Probability Distribution of Precipitation, with Normalization

Can Compute for Different Time Scales for Differing Applications

http://www.ncdc.noaa.gov/oa/climate/research/prelim/drought/spi.htmlhttp://www.wrcc.dri.edu/spi/spi.html

http://www.agr.gc.ca/pfra/drought/mapscc_e.htm

Soil Moisture Soil Moisture Observation Networks Limited in U.S.

http://www.wcc.nrcs.usda.gov/scan/ http://www.cpc.ncep.noaa.gov/products/monitoring_and_data/topsoil.shtml

Soil Moisture Rely on Modeled Soil Moisture

http://www.cpc.noaa.gov/soilmst/leaky_glb.htmhttp://www.cpc.ncep.noaa.gov/products/Soilmst_Monitoring/US/Soilmst/Soilmst.shtmlhttp://mrcc.sws.uiuc.edu/cliwatch/drought/moisture.htmhttp://www.agr.gc.ca/pfra/drought/nlslmr_e.htm

Leaky Bucket Model

CPC “Leaky Bucket”

Using the NLDAS Ensemble Mean Soil Moisture as a Drought Indicator

NCEP Noah

NASA Mosaic

OHD SAC

Princeton VIC

Percentile soil moisture levels correspond to U.S. Drought Monitor levels D0 to D4

Shallow layers of soil moisture can be used as agricultural drought indicators. Model runoff as hydro indicators.

http://www.emc.ncep.noaa.gov/mmb/nldas/drought/

Ensemble Mean

Hybrid Product Integrates Radar Precipitation Estimates with In Situ Rain Gage Measurements

NOAA/NWS Advanced Hydrologic Prediction Service

http://water.weather.gov/index.php

Developed as support for U.S. Drought Monitor Operationally integrate multiple indicators in a weekly

update using a percentile ranking method Produced weekly using CPC’s real-time daily and weekly

climate division data and NCDC’s monthly archive of indices for 1932-2000

All parameters are first rendered as percentiles with respect to 1932-2000 data using a percent rank method

The parameters (drought indicators) are then combined using a weighting scheme

Short- and Long-Term Blends produced

U.S. Objective Blends

http://www.cpc.ncep.noaa.gov/products/predictions/tools/edb/droughtblend-access-page.html

Drought Assessments based on Aggregating Indicators

DWR NC

Based on Streamflow or Groundwater

Groundwater Observing Network Coarse

Hydrologic Indices

http://watermonitor.gov/

Based on Streamflow or Groundwater Streamflow – Need to Remove Peak

Flow from Hydrograph• Streamflow-based drought indicators

usually based on low-flow (base flow) or some averaged flow

Hydrologic Indices

http://watermonitor.gov/

Monthly Average Streamflow14-Day Average Streamflow

FloodMonitoring

DroughtMonitoring

Based on Streamflow or Groundwater Reservoir Data

• State data, no national access system

• Managed for different purposes (irrigation, urban water supply, flood control, etc.)

Hydrologic Indices

http://watermonitor.gov/

Arizona reservoir levels, September 2009, percent of capacity.

Provide Global Coverage Spatially Consistent Reflected Intensities at

Specific Wavelengths

Remotely-Sensed (Satellite-based) Indices

http://www.star.nesdis.noaa.gov/smcd/emb/vci/VH/index.php

http://www.agr.gc.ca/pfra/drought/mapscc_e.htm

Hybrid Drought Index that Integrates: Satellite-based observations of vegetation conditions Climate-based drought index data Biophysical characteristics of the environment

Vegetation Drought Response Index (VegDRI)

http://drought.unl.edu/vegdri/VegDRI_Main.htm

(Source: Wardlow, 2008)

My Top 5 Countdown

No. 5: KBDI

Timely: Daily

Good short term dryness indicator

April 23, 2010: Please Note: Due to technical difficultiesthe KBDI and Rainfall maps are inaccurate.We apologize for any inconvenience.

http://flame.fl-dof.com/fire_weather/KBDI/4km_main.html

No. 4: CPC Drought Indicator Blends

http://www.cpc.ncep.noaa.gov/products/predictions/tools/edb/droughtblend-access-page.html

Weekly, based on Climate Division data; weights somewhat subjective; not operational

No. 3: Soil Moisture Model (CPC)

http://www.cpc.ncep.noaa.gov/products/Soilmst_Monitoring/US/Soilmst/Soilmst.shtml

Daily, with 1-day lag, based on CD data; 1.6m depth; good mid-range indicator. Archive available. But, sometimes not realistic (e.g., see extreme drought in upstate NY).

No.2: NLDAS Soil Moisture

http://www.emc.ncep.noaa.gov/mmb/nldas/drought/

Promising! And yet… min 5-day lag, sometimes much longer; non-operational; very resource intensive, so computer crashes result in huge delays.

No. 1: USGS Streamflowhttp://waterwatch.usgs.gov/

So much to like! Current, real time, daily to 28-days, reliable, percentile format, zoomable,

A Variety of Format Options

Can show in Google Earth as well as Google Maps

Questions?Douglas.lecomte@noaa.govDouglas.lecomte@noaa.gov