Potential EvaporationPotential Evaporationand Irrigation in and Irrigation in

Manoa ValleyManoa ValleyGeography 405Geography 405Liat Portner, George Bugarin, Alexa Grinpas,Henry Pascher, Liat Portner, George Bugarin, Alexa Grinpas,Henry Pascher, Nicole Miller, Maeghan Castillo, Joshua Silva, Elise Kama, Keiichiro Nicole Miller, Maeghan Castillo, Joshua Silva, Elise Kama, Keiichiro YoshidaYoshida

PurposePurpose

Main Objective: Main Objective:

Evaluate the water Evaluate the water balance of Manoa balance of Manoa

ValleyValley

Our Objective:Our Objective:

Estimate the Potential Estimate the Potential Evaporation and Evaporation and

Irrigation for Manoa Irrigation for Manoa ValleyValley

PE Modeling MethodsPE Modeling Methods

Net Radiation, (Air) Net Radiation, (Air) Temperature, Wind Temperature, Wind speed and Relative speed and Relative Humidity measured at Humidity measured at the 2 weather stations the 2 weather stations were used to calculate were used to calculate PEPE

Interpolated to Grid cells Interpolated to Grid cells using inverse distance using inverse distance weighting and the weighting and the Normal Ratio MethodNormal Ratio Method Distance from each Distance from each

grid to each weather grid to each weather stationstation

Mean PE at each grid Mean PE at each grid and both weather and both weather stationsstationsPE_i= [1/d_l*(PE_l*(N_i/N_l))]+[1/d_m

*(PE_m*(N_i/N_m))]1/d_l +1/d_m

Irrigation Sampling Irrigation Sampling MethodsMethods

Based on four Based on four main residential main residential streets, streets, spanning entire spanning entire length of Manoa length of Manoa ValleyValley

Rate, Rate, Frequency, Frequency, Area, Grid Area, Grid Location Location

Irrigation ModelingIrrigation Modeling

Interpolating to grid:Interpolating to grid:y = mean daily y = mean daily

irrigationirrigationx = mean daily (PE-x = mean daily (PE-

RF)RF)

Assumptions:Days with no rainfall- days with irrigation (and the reverse)All irrigation occurring at 6:00 PM

PE Results (1)PE Results (1)

•PE peaks during midday

•Low PE during night

•Driven by Radiation

•Cloud Cover

PE Results (2)PE Results (2)

Total (mm)

0-37.2

37.3 - 63.4

63.5 - 99.6

99.7 - 149.6

149.7 - 218.8

218.9 - 314.4

Seasonal variation of PESeasonal variation of PE

0.0

2.0

4.0

6.0

8/29 9/8 9/18 9/28 10/8 10/18 10/28 11/7

PE (

mm

)

2010

(a) PE Grid 1Grid 26Grid 59

1.0

3.0

5.0

8/29 9/8 9/18 9/28 10/8 10/18 10/28 11/7

(mm)

2010

(b) difference

Irrigation Results (1)Irrigation Results (1)

Peak mean PE correlates with IRR eventsPeak mean PE correlates with IRR events

Irrigation Results (2)Irrigation Results (2)

Total Irrigation (mm)

0-9

10-24

25-51

51-96

97-174

175-219

Total Irrigation (mm)

0-9

10-24

25-51

51-96

97-174

Discussion (1)Discussion (1)

•Inverse relationship between PE and RF

•Grids 6,12 and 19 can be accounted for by orientation of valley

Discussion (2)Discussion (2)

IRR aIRR

7.516309 0

0 0

0 0

0 0

9.166547 9.2

60.90217 61

92.21453 92.3

129.6004 129.6

198.5493 198.5

203.6276 203.6

•Direct relationship between PE and IRR

•Note: Irrigation not actually occurring in every grid cell

Basin TotalsBasin Totals

IRR mm IRR m^3 PE mm PE m^3

4084.676402

63369787.25

14110.47474

218910311.2

Potential Evaporation Potential Evaporation ErrorsErrors

Weather stationsWeather stations

Interpolating from only two sourcesInterpolating from only two sources

TopographyTopography

Crude assignment of mean values Crude assignment of mean values

Irrigation ErrorsIrrigation Errors

Measuring IrrigationMeasuring Irrigation Imprecise measuring toolsImprecise measuring tools Sample size and randomizationSample size and randomization

Interpolation AssumptionInterpolation Assumption Everyone irrigating when no rainEveryone irrigating when no rain Everyone irrigating at 6:00 PMEveryone irrigating at 6:00 PM Irrigation occurring in all gridsIrrigation occurring in all grids

ConclusionConclusion

PE and IRR lower at back of valley, higher at PE and IRR lower at back of valley, higher at frontfront

Rainfall decreases as PE increasesRainfall decreases as PE increases

Irrigation increases as PE increasesIrrigation increases as PE increases

Irrigation increases as rainfall decreasesIrrigation increases as rainfall decreasesMaking up for increasing demands of waterMaking up for increasing demands of waterLess water available because less water and Less water available because less water and land coverland cover

Questions?Questions?