Attributes of Lake Okanagan evaporation and development of a mass transfer model for water management purposes

Figures & data

Figure 1. Lake Okanagan, study instrumentation and notable locations of long-term monitoring nearby. Satellite imagery is copyright the Microsoft Corporation. Inset regional location map adapted from Ferguson et al. (1974).

Figure 2. Mean monthly Kelowna A temperatures, 1981–2010 and those observed during the study period. The bars represent one standard deviation from the mean.

Figure 3. Seven-day running means of air temperature, wind speed, vapour pressure and latent heat flux measured at Manhattan Point (dashed line) and Gartrell Point (solid line) during the study period.

Table 1. Monthly, seasonal, annual observations from Manhattan and Gartrell Points and the north and south arm buoys.

	Gartrell	Manhattan	North Tws	North de	North Ri	South Tws	South de	South Ri
	λE (W/m^2)	λE (W/m^2)	(°C)	(kPa)		(°C)	(kPa)
January	74.3	70.4	4.5	0.31	–3.25	4.30	0.39	–2.5
February	35.7	52.9	3.9	0.29	1.14	3.41	0.25	0.09
March	21.3	29.6	4.2	0.25	0.29	3.80	0.21	0.62
April	16.0	26.9	6.1	0.25	0.94	5.55	0.21	1.3
May	26.7	44.4	11.8	0.50	0.43	10.46	0.41	0.86
June	38.7	47.9	15.9	0.59	0.03	14.75	0.49	0.32
July	73.1	104.3	21.6	1.14	0.07	20.51	0.99	0.29
August	92.9	108.1	22.6	1.32	–0.13	21.7	1.17	0.08
September	77.3	89.3	20.0	1.08	–0.44	19.01	0.97	–0.09
October	59.5	76.9	14.6	0.77	–1.37	13.14	0.63	–0.57
November	59.4	67.2	9.2	0.57	–2.27	7.94	0.43	–1.58
December	83.7	71.0	5.8	0.46	–2.27	5.21	0.37	–2.4
DJF	65.4	65.1	4.6	0.34	–1.34	4.42	0.34	–1.54
MAM	20.9	32.9	7.0	0.32	0.57	6.62	0.27	–0.93
JJA	72.1	89.4	20.5	1.06	–0.02	19.4	0.93	–0.21
SON	65.3	77.8	15.4	0.85	–1.21	13.4	0.67	–0.74
2012	49.1	63.8	13.1	0.63	0.02	11.06	0.52	–0.01
2013	56.1	67.1	14.1	0.76	–0.36	11.19	0.57	–0.35
Period of study	55.7	65.4	12.6	0.67	–0.33	11.41	0.58	–0.27

Figure 4. Wind roses for each of the three buoys deployed for period of study. The thick white line illustrates the relative frequency with which wind blows from each 10° of compass direction. Satellite imagery copyright the Microsoft Corporation.

Figure 5. Seven-day running means of T_ws, surface–atmosphere vapour pressure differences, and the Richardson number measured at the north (dotted line), center (thick line), south (thin line) buoys during the study period.

Figure 6. Daily evaporation rates from each beacon vs. the product of wind speed and the vapour pressure gradient from each buoy. Left to right are the relationships between evaporation measurements from Gartrell Point and the product of wind speed and the surface–atmospheric vapour pressure differences at (a) the south, (b) the center and (c) the north buoys. Similarly, the relationships between evaporation at Manhattan Point and the product of wind speed and the surface–atmospheric vapour pressure differences at (d) the south, (e) the center and (f) the north buoys.

Figure 7. Seasonal cycles are apparent in monthly values of K derived from Gartrell Point evaporation rates and wind and surface–atmosphere vapour pressure differences from the south buoy. The inset shows the dynamic between monthly K and the Richardson number measured at the south buoy from July 2012 to July 2013.

Figure 8. Half-hourly observations of the product of wind speed and surface–atmospheric vapour pressure differences and the Richardson number measured at the south buoy, and evaporation measured at Gartrell Point and the derived K for 11 and 12 July 2013.

Table 2. Monthly mass transfer coefficients derived from data at Manhattan Point and the north buoy. Results of the error analysis are also included. K is the mass transfer coefficient from Equation (3) and r² is the regression coefficient of the line of best fit from the monthly split sample. E_d is the average daily error and E_v is the monthly error.

Month	K	r^2	Ed (%)	Ev (%)
January	1.78	0.45	26.3	3.9
February	1.63	0.82	2.5	–12.5
March	1.25	0.66	13.3	5.0
April	1.30	0.67	1.1	–12.9
May	1.22	0.78	4.2	–1.5
June	0.86	0.56	–2.9	–20.1
July	1.00	0.58	1.4	–6.4
August	1.00	0.31	–6.3	–9.8
September	0.96	0.69	–7.1	–8.8
October	0.97	0.63	5.7	–1.3
November	1.09	0.69	8.6	–3.1
December	1.18	0.72	9.7	–1.2
Average	1.19	0.63	4.71	–5.73

Ferguson, H. L., J. C. Foweraker, P. L. Hall, E. C. Halstead, H. I. Hunter, T. A. J. Leach, E. G. Le Breton, et al. 1974. Technical supplement I to the final report on water quantity in the Okanagan Basin. Office of the Study Director, Penticton: Canada British Columbia Okanagan Basin Agreement. 553 pp.

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