Comparison of Point Measurements within SFWMD

and NARR-A values

Alicia FoggApril 26th, 2005

µ0 20 40 60 8010

Miles

South Florida Water Management District

• 6 million people live in the SFWMD

•Encompasses 17,000mi2

•1800 mi of canals and levees

•200 major water control structures

•70 critical•130 manually operated

•27 pump stations•6 under remote control

Simple Water Balance

Purpose: develop simple water balance approach to quantify change in storage

QHinQHout

qRAIN

qET

Control Volume

Continuity Equation over Control Volume:

( (

Area

Data Sources for Simple Water Balance

Horizontal Data

Structure Flow– Monitored at each Structure

Vertical Data

Rainfall – Point data at Structures and NEXRAD data over entire region

ETp – no Points in region

???

Weather Measurements within the SFWMD

• SFWMD has database containing over 22,000 time series variables

• 16 potential evapotranspiration (ETp) and only one evapotranspiration rate site

• 69 Operations and Maintenance rainfall sites operating on a real-time basis

Potential Evapotranspiration Stations within SFWMD

• Highly monitored system with over 22,000 variables contained within parameter database

•16 potential evapotranspiration measurement sites recorded daily

• Potential Evapotranspiration dependent on

•Wind Speed

•Water Availability

•Net radiation

•Vegetation Type

ETp – Historic and Recorded

0

1

2

3

4

5

6

Janu

ary

Februa

ryMarc

hApri

lMay

June Ju

ly

Augus

t

Septem

ber

Octobe

r

Novem

ber

Decem

ber

Pote

ntia

l Eva

pora

tion[

mm

/day

]

Historic ETp

Measured ETP

• SFWMD recommends using ETp daily values for vertical components.

• ETp is a measure of the vegetation and the atmospheric conditions – not dependent on the amount of moisture!!!

• Florida is WET, but not all of the ground is inundated all the time.

NARR-A Monthly Data

Queried 56 points in Southern Florida for a one-year period November 2002 to October 2003.

NARR-A Monthly Data

Calculating Monthly ET

• The results obtained from NARR-A in W/m2 mm/day

• Interpolate the Point data to Raster

• Use Zonal Statistics to determine Attribute Series for area of interest

Interpolated Evaporation SurfaceFor this time period [October 2003]

Lowest ET values over Everglades

Highest ET values over the Oceans.

Fairly Consistent ET value over Land ~ 3 – 3.5 mm/day

Comparing Results of Point Method and Areal Estimation

Historic Values Closest Etp Station IDW SFWMD stations NARR IDW

January 79.67 98.20 98.25 64.22

February 88.48 93.92 94.39 62.89

March 121.83 109.19 110.01 96.08

April 132.60 135.14 135.60 100.46

May 143.53 150.09 150.42 111.61

June 126.00 121.81 121.85 117.53

July 128.34 140.59 139.59 132.08

August 124.62 118.31 119.00 121.93

September 104.10 110.28 110.94 106.27

October 98.58 109.46 108.29 98.14

November 80.10 90.59 90.27 74.66

December 73.16 73.02 73.04 62.17

1301.01 1350.57 1351.65 1148.02

NARR-A Monthly data is ~ 15% lower than recorded ETp stations

Looking at the Area of Interest

0

1

2

3

4

5

6

Janua

ry

February

March

April

MayJu

ne July

Augus

t

Septembe

r

October

Novem

ber

Decem

ber

Pot

entia

l Eva

pora

tion

and

Late

nt H

eat E

vapo

ratio

n [m

m/d

ay] Historic ETp

NARR LatentHeatMeasured ETP

Monthly Latent Heat Values for Southern Florida are lower than ETp values recorded – as should be expected.

Conclusions

• Latent Heat evaporation values and observed ETp values show same temporal trend

• NARR-A results correlate well to observed data

• NARR-A 3-hr time steps have potential to be useful for estimates of evaporation

Thank You To..

• Dr. Maidment• SFWMD – M Mierhoffer, R Mireau, K Stewart• CRWR team members

– Jon Goodall– Nate Johnson– Becky Teasley– Jessica Watts

Questions?