Manoa Watershed Water Balance Study: Potential ET

Transcription

1 Manoa Watershed Water Balance Study: Potential ET Wyatt Blair, Josh Donovan, Max Irion, Jordan Muratsuchi, and David Heir Geography 405 Fall 2016

2 Overview Introduction Objectives Methodology Results Summary/Conclusion

3 Introduction Water is Life! Without the key process Evaporation/Evapotranspiration there would be no recharge of moisture back into the atmosphere. With our unique geographic location, it is very important to understand how each aspect of the watershed will contribute to the recharge of the islands basal aquifer.

4 Introduction Problem: The overall issue we are dealing with is understanding the hydrological cycle in the Manoa watershed. Our specific problem is calculating the Potential Evapotranspiration.

5 Introduction Evaporation: Flux of water vapor from open water surface, wet vegetation, or wet soil from the surface to the atmosphere. Transpiration: Water vapor transfer to the atmosphere occurring primarily through the stomata of living plants.

6 Introduction Evapotranspiration: Total flux of water vapor from the surface to the atmosphere. Potential Evapotranspiration: The evaporation rate if moisture does not limit it. Potential Evapotranspiration is influenced by: Humidity Gradient: Gradient near the moisture source. Turbulent Exchange: Transport humid air and replace it with dry air

7 Objectives To estimate the Potential Evapotranspiration (PET) in the Manoa watershed Use of Penman-Montieth Model or Penman to calculate PET Calculate PET for the two stations (Mauka and Lyon) with recorded data Convert the PET of both cells into mm/hr Interpolate PET data into each watershed grid Estimate/calculate the overall average PET of the watershed and individual cells hourly PET.

8 Methodology Our methodology for calculating PET is as follows: Decided on use of Penman-Monteith model Divided up Watershed into 191 raster cells Determined distances from each cell to both data stations Calculated normals for each hour of each cell as the October average (using Rainfall Atlas of Hawaii)

9 Methodology Calculated the PET for each hour at both stations using Penman-Monteith: We set r c = 0 to find PET Each variable can be found using the station data (Rnet, T, RH, Ws, SHF, Tsoil) and relevant equations This gave us PET in W/m 2. We then converted to mm/day and mm/hour

10 Methodology With PET values at the climate/data stations: PET at each grid cell was calculated using interpolation methods Inverse distance with normal ratio interpolation method was used Takes into account the distance from each climate station and the long-term average PET Result: PET values obtained for each hour of data for each grid cell

11 Results Total PET :558.95mm (average over watershed) Total Watershed PET: 6,253,278 m 3

12 PET Time Series Graph

13 Total PET of each Cell

14 Effects on PET Lyon Station Mauka Station

15 Effects on PET Lyon Station Mauka Station

16 Effects on PET Lyon Station Mauka Station

17 Effects on PET Lyon Station Mauka Station

18 Summary/Conclusion Mauka Station: noticeable patterns of elevated peaks with 2 distinctive troughs. This might suggest a persistent heavy rain event or multiple days without sunshine may have occurred with consecutive sunny/hot days preceding and ensuing the trough. Lyon Station: consistently noticeable lower peaks of PET with at least 4 successive troughs. This might suggest more frequent downpours and clouds, coupled with less energy able to hit the ground and canopy. The two stations only intersect consecutively twice. The trough at the beginning and the trough near the end of the study.

19 Summary/Conclusion PET for the watershed: mm (avg over watershed) Over 6 MILLION cubic meters of water potentially returned to atmosphere Lower valley has higher PET (less cloud cover, higher temp) Back of the valley has a lower PET (more rain, clouds and cooler temp)

20 Resources Web Pictures

21 Mahalo! Questions?