Comparison of Point Measurements within SFWMD and NARR-A values Alicia Fogg April 26th, 2005

South Florida Water Management District 200 major water control structures 70 critical 130 manually operated 27 pump stations 6 under remote control 6 million people live in the SFWMD Encompasses 17,000mi2 1800 mi of canals and levees

Simple Water Balance ( ( Purpose: develop simple water balance approach to quantify change in storage Continuity Equation over Control Volume: qRAIN ( ( qET Area Control Volume QHout QHin

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 Potential Evapotranspiration dependent on Wind Speed Water Availability Net radiation Vegetation Type Highly monitored system with over 22,000 variables contained within parameter database 16 potential evapotranspiration measurement sites recorded daily

ETp – Historic and Recorded

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 Surface For 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 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?