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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?
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