SOME PRECIPITATION  INFORMATION NEEDS FOR 

GEWEX AND WCRP

Rick LawfordTokyo, Japan

December 5, 2007

WCRP Strategic Objectives:

Seamless Prediction of the Total Physical Climate System from Weeks Through DecadesSynthesizes Ongoing Observational and Modeling Activities of the all Relevant WCRP ComponentsThree Central Themes:

Describe Structure and Variability of the Total Climate System Through Modeling and Observational StudiesAssess the Predictability of the Total Climate System by Making PredictionsUnderstand Mechanisms and Uncertainty of Regional Climate Change Prediction

THE GEWEX MISSION CAN BE DESCRIBED AS“THE DEVELOPMENT AND APPLICATION OF PLANETARYEARTH SCIENCE, OBSERVATIONS AND MODELS TO THEPROBLEMS OF CLIMATE AND WATER RESOURCES”

THE PROGRAM ENTAILS:‐

GLOBAL DATA SETS DERIVED FROM SATELLITE DATA, IN SITUDATA AND DATA ASSIMILATION CAPABILITIES,

‐

PARAMETERIZATION DEVELOPMENT AND PREDICTABILITY STUDIES‐ FIELD AND PROCESS STUDIES‐ APPLICATIONS

EMERGING ISSUES IN WCRP AND GEWEX

- ATMOSPHERIC CHEMISTRY AND CLIMATE CHANGE

-GLOBAL CHANGE AND THE CRYOSPHERE

- TROPICAL COVECTION AND ITS FEEDBACK TO THE GLOBALCIRCULATION AND REGIONAL MONSOONS

- AEROSOLS, CLOUDS AND PRECIPTATION

- EXTREME EVENTS

Global Precipitation Climatology Project (GPCP)Global Precipitation Climatology Project (GPCP)Bob Adler NASA/GSFC Laboratory for Atmospheres

VARIABLEVARIABLE HOR. RESHOR. RES VERT RESVERT RES ACCURACYACCURACYPRECIPITATIONPRECIPITATION 1010--50 km50 km 0.1 mm/ h0.1 mm/ h

SOIL MOISTURESOIL MOISTURE 1010--100 km100 km 10 cm (30 cm)10 cm (30 cm) 5%5%

STREAMFLOWSTREAMFLOW B: 1B: 1--10 KM10 KM 1 cm (*)1 cm (*) 5% (m5% (m33/s)/s)

LAKE LEVELSLAKE LEVELS 11--10 km10 km 1 cm1 cm 5% (cms)5% (cms)

SNOW COVERSNOW COVER 11--10 km10 km 10%10%

CLOUDSCLOUDS 100 m 100 m –– 10 km10 km .1 km.1 km 5% cover5% cover

WATER VAPORWATER VAPOR 10 10 –– 100 km100 km .1 km.1 km 5%5%

SURFACE FLUXSURFACE FLUX 10 10 –– 100 km100 km 5%5%

SW RADIATIONSW RADIATION 4 4 –– 100 km100 km 5 W/m5 W/m22

PARTIAL LISTING OF WATER CYCLE DATA REQUIREMENTS

A COMPLETE TABLE IS PROVIDED IN THE IGWCO THEME REPORT.

The role of scale is important for representing precipitation in

models.

Scale influences measurements and model outputs. 

** *

LOCAL

Gauge

CLOUD

AircraftRadar

Turbulence

CONVECTIVESTORMS

Convection

RadarTRMMCRMs

SYNOPTICSCALES

GLOBALSCALE

AtmosphericCirculation

ClimateVariability/ Change

SatelliteNWP models

SatellitesGCMsV

ISSUE:

The role of scale is important for representing precipitation in

models.

Scale influences measurements and model outputs. 

** *

LOCAL

Gauge

CLOUD

AircraftRadar

Turbulence

CONVECTIVESTORMS

Convection

RadarTRMMCRMs

SYNOPTICSCALES

GLOBALSCALE

AtmosphericCirculation

ClimateVariability/ Change

PARAMETERIZATIONS SEAMLESS PREDICTION

SatelliteNWP models

SatellitesGCMsV

The challenge: To effectively address precipitation issues at the  climate scale we must understand and reproduce precipitation  processes  in models by dealing with processes on all these scales 

as well as their interactions. 

WHY PRECIPITATION DATA IS NEEDED FOR CLIMATE  RESEARCH

CLIMATE APPLICATIONS:

1. Precipitation plays an importantrole in removing moisture fromthe atmosphere. This affects theprofile of atmospheric moistureand its horizontal distribution.

Data needed:- Data on moisture source

and in the amount removedduring a particular timeinterval.

2. Precipitation recharges water systems on the surface that in turn lead to increases soil moisture, decreases ocean salinity and benefits vegetation, ecosystems and societies.

Data requirements:Measures of the quantity of precipitation and their error characteristics during specific time intervals (6h to a day) reaching the surface on an area (<10 km2) are needed.

GEWEX PARTICIPATES WITH OTHER GROUPSTO ASSESS SATELLITE DATA PRODUCTS

THE PLANS FOR AN INTEGRATEDPRECIPITATION PROJECT AREBEING DEVELOPED IN CONJUNCTIONWITH IWGP AND IGWCO.  

GPCP DOES NOT PRODUCETHE HIGH RESOLUTION MAPS THATHYDROLOGISTS REQUIRE.

HIGH RESOLUTION MAP PRODUCEDBY THE PERSIANN SYSTEM

GEWEX SUPPORTS THE GPM MISSION TO PROVIDE AS A COMPREHENSIVE APPROACH TOPROVIDING HIGH RESOLUTION PRECIPITATION DATA TO USERS.

GEWEX IS COLLABORATING WITH IWGP TO PLAN FOR ANINTERCOMPARISONOF HIGH RESOLUTION SATELLITEPRECIPITATION PRODUCTS. 

3. Precipitation or the lackthereof plays a major rolethe hazardous and extremeweather and climate events.

Too much water (or snow)!!

FloodsErosion Landslides

Avalanche

High resolution data (1 km) at highfrequency (1 hr) are needed to givereliable hazard warnings and toproperly characterize the conditionsleading to these events.

3. Precipitation or the lackthereof plays a major rolethe hazardous and extremeweather and climate events.

Too little water!!

Droughts

Precipitation measurements areimportant to characterize the severityof drought and to monitor the rain eventsthat may bring droughts to a conclusion.

4. Precipitation plays a major role in the energy budget of the tropics  and in global climate system

THE FORMATION OF PRECIPITATION IN THE ATMOSPHERE RELEASES LATENT

HEAT WHICH 

DIABATICALLY WARMS THE ATMOSPHERE.  THE IMPACT OF THIS HEAT RELEASE VARIES 

ACCORDING TO LATITUDE AND THE ALTITIDUE WHERE THE HEAT RELEASE IS OCCURING.

STRATIFORM

CONVECTIVE

TRMM PROVIDESTHIS INFORMATIONOVER THE TROPICS– GPM WILLPROVIDE DATA FORTHE EXTRA‐TROPICSAS WELL

For the Amazon

Component GHCN CMAP GPCP NCEP LW Marengo 

(2003)

P 8.6 5.6 5.2 6.4 5.9 5.8

E 4.3 4.3 4.3 4.3 4.3 4.3

R 2.9 2.9 2.9 2.9 2.9 2.9

∇Q 1.4 1.4 1.4 1.4 1.4 1.4

P‐E 4.3 1.3 0.9 2.1 1.6 1.5

Imbal. 48% 51% 68% 27% 44% 48%

5. Precipitation accuracy is a limiting factor in our ability to close the global water budget

GEWEX HAS PARTIALLY ADDRESSED THIS 

PROBLEM THROUGH ITS GLOBAL 

PRECIPITATION CLIMATOLOGY PROJECT 

(GPCP) WHICH NOW HAS PRODUCED 25+ 

YEARS OF MONTHLY PRECIPITATION MAPS 

BY MERGING SATELLITE AND GAUGE DATA.

PRECIPITATION IS NOT ADEQUATELY 

MEASURED TO DO AUTHORITATIVE GLOBAL 

WATER BUDGET STUDIES.  GAUGE DATA ARE 

VERY EXTENSIVE OVER SOME COUNTRIES BUT 

VERY LIMITED OVER OTHERS AND OVER THE 

OCEANS. 

6. Observed changes in streamflow may be the result of  changes in precipitation regimes?

(After Stewart et al,2003)

TO WHAT EXTENT ARE THESE CHANGES THE RESULT OF:1) WARMER SPRING TEMPERATURES?2) CHANGES IN THE RATIO OF RAIN TO SNOWFALL? 3) CHANGES IN PRECIPITATION AMOUNTS, 4) CHANGES IN VEGETATION COVER?

Significant changes inrunoff regimes are occurringin western North America.

Models are unable to reproduce theDiurnal Cycle of Convective 

Precipitation  for JJA

Observed Frequency 1976‐97Time of maximum

CCSM  Frequency 1983‐88Time of maximum

Modeled frequency occurs about 2 hoursearlier than observed

(A. Dai 2001)

7. Precipitation is a critical benchmark variable for assessing the ability  of climate models to address the “wet”

part of the climate system

GLOBAL CLIMATE MODELS DO NOT HANDLE PRECIPITATION ADEQUATELY.  

COMPREHENSIVE UNIFORM DATA SETS ARE NEEDED TO MONITOR AND PROVIDE A 

SCIENTIFIC BASIS FOR MODEL IMPROVEMENT.

Uncertainty of Uncertainty of Climate PredictionsClimate Predictions

Annual PrecipitationAnnual Precipitation (Hadley and Max Planck Climate Models,(Hadley and Max Planck Climate Models,

2070s, A2 Scenario)2070s, A2 Scenario)

SO, IF WE ARE MAKING THESE GAINS IN OUR ABILITY TO OBSERVEPRECIPITATION WHY DO WE HAVE DIFFICULTY PREDICTING IT?

Updrafts/ VerticalVelocity

Moisture flux

When the Humidity exceeds acertain threshold the excessrains out.

This approach does notneed precipitationobservations to makethe prediction itself.Measurements do helpus to specify the errors inthe predictions.

Challenge: How can we makemore effective use ofprecipitation measurementsin predictions?

The standard model

SO, IF WE ARE MAKING THESE GAINS IN OUR ABILITY TO OBSERVEPRECIPITATION WHY DO WE HAVE DIFFICULTY PREDICTING IT?

Priorities for futuredevelopments:- New approaches to

precipitation dataassimilation

- Parameterizations basedon precipitationmicrophyscis

Challenge: How can we makemore use of precipitationmeasurements in predictions?

WCRP, PARTICULARLY GEWEX, ENDORSES GPM AS AN ESSENTIAL NEXT STEP IN PREDICTING

PRECIPITATION

THE GEWEX VISION:

WE WOULD LIKE TO SEE A STRONGER LINK BETWEEN THE WEATHER AND CLIMATEMODELLING COMMUNITY AND THE GPM DEVELOPMENT COMMUNITY TO ENSUREA COORDINATED APPROACH TO PRECIPITATION PREDICTION IS DEVELOPED.

GPM OFFERS GOOD PROSPECTS FOR MORE EFFECTIVELY  PREDICITNG PRECIPITATION. SOME ISSUES THAT MAY STILL 

NEED TO BE ADDRESSED:CAN WE IMPROVE THE ABILITY OF SPACE‐BASED SENSORS TO MEASURE SOLID 

PRECIPITATION?

HOW CAN WE EFFECTIVELY CHARACTERIZE THE ERROR CHARACTERISTICS OF

GPM 

MEASUREMENTS IN TERMS OF REGION, INTENSITY AND CLIMATE?

CAN MORE SATELLITE DATA BE MADE AVAILABLE TO USERS  CLOSER TO REAL‐

TIME? (WE SHOULD WORK TOWARDS THIS GOAL TO EXPLOIT ITS FULL 

BENEFITS)

WHAT MICROPHYSICAL FIELDS WILL BE AVAILABLE FOR RESEARCH AND MODEL 

DEVELOPMENT?

HOW CAN WE ENGAGE THE MODELLING COMMUNITY MORE EFFECTIVELY IN THE 

EXPLOITATION OF GPM DATA?

IS THE FRAMEWORK FOR MOVING GPM DATA INTO OPERATIONS ADEQUATE?