Potential historical temporal trends in monthly, seasonal, and annual mean, minimum, and maximum streamflows and date of the spring freshet runoff peak were investigated for the Okanagan and Similkameen Rivers in south-central British Columbia, Canada. There appears to be no compelling evidence that streamflow patterns in the Okanagan and Similkameen Rivers have changed over the available hydrometric record, nor does there appear to be evidence that future changes in streamflow patterns are imminent or likely

Kaya Forest

Sierra Rayne

English

AbstractPotential historical temporal trends in monthly, seasonal, and annual mean, minimum, and maximum streamflows and date of the spring freshet runoff peak were investigated for the Okanagan and Similkameen Rivers in south-central British Columbia, Canada. There appears to be no compelling evidence that streamflow patterns in the Okanagan and Similkameen Rivers have changed over the available hydrometric record, nor does there appear to be evidence that future changes in streamflow patterns are imminent or likely.</jats:p

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Absence of historical temporal trends in monthly, seasonal, and annual streamflows for the Okanagan and Similkameen Rivers in south-central British Columbia, Canada

1 
Preprint submitted to Nature Precedings 
Absence of historical temporal trends in monthly, seasonal, and annual streamflows for the Okanagan 
and Similkameen Rivers in south-central British Columbia, Canada 
 
Sierra Rayne a,* and Kaya Forest b 
 
a
 Chemologica Research, PO Box 74, 318 Rose Street, Mortlach, Saskatchewan, Canada, S0H 3E0 
b
 Department of Environmental Engineering, Saskatchewan Institute of Applied Science and Technology, Palliser Campus, PO Box 1420, 600 6th 
Avenue NW, Moose Jaw, Saskatchewan, Canada, S6H 4R4 
 
*
 Corresponding author. Tel.: +1 306 690 0573. E-mail address: rayne.sierra@gmail.com (S. Rayne). 
 
 
The rapidly growing population in the semi-arid climate of south-
central British Columbia, as well as the legal implications of trans-
boundary water agreements such as the International Joint 
Commission (IJC), have led to substantial interest in the hydrology of 
this region and debate over the resulting environmental management 
policies [1-12]. In a previous work [13], we showed that - despite 
substantial increases in population and agricultural activities over the 
past century - the net water yield from the Canadian portion of the 
Okanagan Valley has not changed significantly during this time. In 
the current study, we examine potential historical temporal trends in 
monthly, seasonal, and annual mean, minimum, and maximum 
streamflows for the Okanagan and Similkameen Rivers (Figures 1 
and 2), as well as any time trends for the date to peak of the spring 
freshet on both river systems. 
 
 
Figure 1. Schematic map of the Okanagan Valley watershed showing 
locations of major municipalities, lakes, rivers, and the hydrometric 
monitoring station under consideration (08NM085). 
 
Historical streamflow data was obtained [14] for the following two 
Environment Canada hydrometric monitoring stations in the 
Okanagan and Similkameen Valleys which are located farthest 
downstream near the United States-Canada border (Table 1): 
Okanagan River near Oliver (08NM085; in Canada) and the 
Similkameen River near Nighthawk (08NL022; USGS stn. 
12442500; in the United States). 
 
Figure 2. Schematic map of the Similkamen Valley watershed 
showing locations of major municipalities, lakes, rivers, and the 
hydrometric monitoring station under consideration (08NL022). 
 
Statistical analyses of streamflow data were conducted using the 
nonparametric Mann-Kendall test for the trend and the nonparametric 
Sen’s method for the magnitude of the trend [15-20]. 
 
Table 1. Hydrometric station information for the sites under study. 
 Okanagan River 
near Oliver 
Similkameen River 
near Nighthawk 
Station ID 08NM085 08NL022 
Latitude (N) 49°6'53" 48°59'5" 
Longitude (W) 119°33'50" 119°37'2" 
Gross drainage area (km2) 7540 9190 
Period of recorda 1958-2010 1929-2010 
Gauge type continuously 
recorded 
continuously 
recorded 
 
With the sole exceptions of isolated statistically significant declines 
in mean monthly flow during November (-0.8%/year, p<0.05), and in 
the monthly maximum daily flows during November (-0.9%/year, 
p<0.01) and December (-0.7%/year, p<0.05), both on the Okanagan 
River near Oliver (08NM085), there are no other statistically 
significant trends in monthly, seasonal, and annual streamflows, or in 
maximum and minimum daily streamflows during each month, at 
either of the downstream stations on the Okanagan and Similkameen 
Rivers (Tables 2-4). 
 
In addition, there are no significant temporal trends in the calendar 
day upon which the spring freshet peak occurs: Okanagan River near 
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Oliver (08NM085), test Z=1.098, Q=0.230 days/year, Qmin,95=-0.136 
days/year, and Qmax,95=-0.618 days/year; Similkameen River near 
Nighthawk (08NL022), test Z=0.065, Q=0.000 days/year, Qmin,95=-
0.105 days/year, and Qmax,95=-0.123 days/year. These findings 
contrast with previous studies and their interpretations as summarized 
in a recent trans-boundary water agreement study (see ref. [21] and 
references therein). Based on our examinations, there appears to be 
no compelling evidence that streamflow patterns in the Okanagan and 
Similkameen Rivers have changed over the available hydrometric 
record, nor does there appear to be evidence that future changes in 
streamflow patterns are imminent or likely. 
 
References 
 
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Phase 1. Summit Environmental Consultants Ltd.: Vernon, BC, 
Canada, 2005. 
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Basin Agreement. Consultative Board: Ottawa, ON, Canada, 1974. 
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Table 2. Summary of non-parametric Mann-Kendall test statistics for temporal trends in mean monthly, seasonal, and annual streamflows at the 
hydrometric monitoring stations on the Okanagan River near Oliver (08NM085) and the Similkameen River near Nighthawk (08NL022). Values are 
in m3/s. 
 Okanagan River near Oliver (08NM085) Similkameen River near Nighthawk (08NL022) 
 Mann-Kendall trend Sen's slope estimate Mann-Kendall trend Sen's slope estimate 
Time period Test Za Significanceb Qc Qmin,95d Qmax,95e Test Z Significance Q Qmin,95 Qmax,95 
January -0.990 n/s -0.040 -0.142 0.024 1.868 n/s 0.057 0.000 0.113 
February -0.176 n/s -0.009 -0.127 0.090 1.158 n/s 0.028 -0.023 0.095 
March -0.238 n/s -0.020 -0.185 0.155 1.836 n/s 0.058 -0.004 0.138 
April -0.399 n/s -0.031 -0.190 0.154 0.983 n/s 0.140 -0.144 0.425 
May 0.230 n/s 0.027 -0.246 0.393 -0.424 n/s -0.167 -0.876 0.580 
June 0.268 n/s 0.026 -0.309 0.348 -0.465 n/s -0.272 -1.255 0.698 
July 1.051 n/s 0.081 -0.088 0.313 -0.094 n/s -0.012 -0.376 0.313 
August 0.913 n/s 0.058 -0.059 0.187 -0.184 n/s -0.008 -0.122 0.084 
September 1.105 n/s 0.056 -0.049 0.148 -0.216 n/s -0.005 -0.067 0.057 
October -1.351 n/s -0.033 -0.095 0.018 -0.139 n/s -0.006 -0.070 0.062 
November -2.516 * -0.080 -0.154 -0.019 0.759 n/s 0.031 -0.088 0.132 
December -1.818 n/s -0.054 -0.120 0.003 0.228 n/s 0.007 -0.073 0.087 
April-July 0.560 n/s 0.269 -0.734 1.420 -1.085 n/s -0.967 -2.878 0.906 
January-March -0.591 n/s -0.121 -0.497 0.258 1.831 n/s 0.159 -0.011 0.352 
April-June 0.276 n/s 0.095 -0.643 1.076 -1.024 n/s -0.657 -2.336 0.773 
July-September 1.266 n/s 0.219 -0.169 0.676 -0.073 n/s -0.017 -0.546 0.425 
October-December -1.956 n/s -0.200 -0.402 -0.001 0.453 n/s 0.064 -0.213 0.308 
Annual 0.184 n/s 0.010 -0.142 0.155 -0.489 n/s -0.048 -0.243 0.146 
a
 The absolute value of the test statistic (Z) is compared to the standard normal cumulative distribution to define if there is a trend or not at the 
selected level α of significance. A positive (negative) value of Z indicates an upward (downward) trend. b The smallest significance level α with 
which the test shows that the null hypothesis of no trend should be rejected. n/s=not significant. *=significant at α=0.05. **=significant at α=0.01. 
***=significant at α=0.001. c The Sen's estimate for the true slope of the linear trend. d The lower limit of the 95% confidence interval of Q (α= 0.05). 
e
 The upper limit of the 95 % confidence interval of Q (α= 0.05). 
 
Table 3. Summary of non-parametric Mann-Kendall test statistics for temporal trends in maximum daily streamflows during each month at the 
hydrometric monitoring stations on the Okanagan River near Oliver (08NM085) and the Similkameen River near Nighthawk (08NL022). Values are 
in m3/s. 
 Okanagan River near Oliver (08NM085) Similkameen River near Nighthawk (08NL022) 
 Mann-Kendall trend Sen's slope estimate Mann-Kendall trend Sen's slope estimate 
Time period Test Za Significanceb Qc Qmin,95d Qmax,95e Test Z Significance Q Qmin,95 Qmax,95 
January -1.350 n/s -0.058 -0.163 0.028 1.672 n/s 0.074 -0.020 0.173 
February -0.583 n/s -0.050 -0.206 0.117 0.877 n/s 0.036 -0.042 0.124 
March -0.552 n/s -0.049 -0.247 0.176 1.391 n/s 0.076 -0.033 0.190 
April -0.376 n/s -0.053 -0.259 0.196 0.400 n/s 0.146 -0.573 0.778 
May 0.215 n/s 0.041 -0.371 0.517 -0.351 n/s -0.200 -1.566 1.000 
June 0.338 n/s 0.062 -0.312 0.572 -0.196 n/s -0.183 -1.834 1.344 
July 1.496 n/s 0.186 -0.043 0.622 -0.139 n/s -0.033 -0.691 0.559 
August 1.036 n/s 0.083 -0.080 0.333 -0.008 n/s 0.000 -0.149 0.165 
September 1.342 n/s 0.114 -0.066 0.307 0.253 n/s 0.018 -0.084 0.120 
October -1.849 n/s -0.071 -0.146 0.008 -0.485 n/s -0.037 -0.200 0.108 
November -2.685 ** -0.105 -0.182 -0.032 1.627 n/s 0.162 -0.045 0.374 
December -2.025 * -0.082 -0.160 -0.004 0.547 n/s 0.040 -0.117 0.182 
a
 The absolute value of the test statistic (Z) is compared to the standard normal cumulative distribution to define if there is a trend or not at the 
selected level α of significance. A positive (negative) value of Z indicates an upward (downward) trend. b The smallest significance level α with 
which the test shows that the null hypothesis of no trend should be rejected. n/s=not significant. *=significant at α=0.05. **=significant at α=0.01. 
***=significant at α=0.001. c The Sen's estimate for the true slope of the linear trend. d The lower limit of the 95% confidence interval of Q (α= 0.05). 
e
 The upper limit of the 95 % confidence interval of Q (α= 0.05). 
 
  
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Table 4. Summary of non-parametric Mann-Kendall test statistics for temporal trends in minimum daily streamflows during each month at the 
hydrometric monitoring stations on the Okanagan River near Oliver (08NM085) and the Similkameen River near Nighthawk (08NL022). Values are 
in m3/s. 
 Okanagan River near Oliver (08NM085) Similkameen River near Nighthawk (08NL022) 
 Mann-Kendall trend Sen's slope estimate Mann-Kendall trend Sen's slope estimate 
Time period Test Za Significanceb Qc Qmin,95d Qmax,95e Test Z Significance Q Qmin,95 Qmax,95 
January -0.798 n/s -0.022 -0.076 0.034 0.412 n/s 0.010 -0.033 0.054 
February -0.744 n/s -0.019 -0.077 0.042 0.999 n/s 0.027 -0.025 0.079 
March -0.123 n/s -0.006 -0.122 0.102 1.028 n/s 0.024 -0.017 0.071 
April -0.361 n/s -0.025 -0.157 0.088 1.424 n/s 0.078 -0.025 0.199 
May -1.043 n/s -0.078 -0.206 0.078 -0.069 n/s -0.014 -0.531 0.451 
June 0.130 n/s 0.006 -0.131 0.171 -0.498 n/s -0.130 -0.726 0.438 
July 0.606 n/s 0.028 -0.075 0.141 -0.347 n/s -0.019 -0.172 0.123 
August 0.568 n/s 0.028 -0.064 0.120 -0.473 n/s -0.015 -0.080 0.046 
September 0.284 n/s 0.008 -0.054 0.072 -0.979 n/s -0.022 -0.065 0.025 
October -1.826 n/s -0.036 -0.094 0.003 -1.073 n/s -0.020 -0.065 0.019 
November -1.573 n/s -0.053 -0.127 0.007 -1.611 n/s -0.052 -0.123 0.013 
December -1.734 n/s -0.036 -0.089 0.004 -1.362 n/s -0.036 -0.088 0.016 
a
 The absolute value of the test statistic (Z) is compared to the standard normal cumulative distribution to define if there is a trend or not at the 
selected level α of significance. A positive (negative) value of Z indicates an upward (downward) trend. b The smallest significance level α with 
which the test shows that the null hypothesis of no trend should be rejected. n/s=not significant. *=significant at α=0.05. **=significant at α=0.01. 
***=significant at α=0.001. c The Sen's estimate for the true slope of the linear trend. d The lower limit of the 95% confidence interval of Q (α= 0.05). 
e
 The upper limit of the 95 % confidence interval of Q (α= 0.05). 
 
 
 
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Evidence of climate change effects on the hydrology of streams in south-central

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Historical trends in annual water yields for the Okanagan Basin, British Columbia, Canada. Nature Precedings,

Hydrologic response to scenarios of climate change in the Okanagan Basin, British Columbia.

Identiﬁcation of hydrological trends in the presence of serial and cross correlations: A review of selected methods and their application to annual ﬂow regimes of Canadian

Identiﬁcation of temporal trends in annual and seasonal low ﬂows occurring in Canadian rivers: The eﬀect of short- and long-term

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Non-parametric tests against trend.

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http://precedings.nature.com/documents/6584/version/1

Absence of historical temporal trends in monthly, seasonal, and annual streamflows for the Okanagan and Similkameen Rivers in south-central British Columbia, Canada

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