HYDROMETRIC TREND ANALYSIS

Executive Summary

Prepared for:

Environment & Sustainable Development Research Centre,

University of New Brunswick

Your Environmental Trust Fund at Work!

Project # 081688

November 25, 2008

“This report was prepared by R.V. Anderson Associates Limited for the account of the Environment & Sustainable Development Research Centre, University of New Brunswick. The material in it reflects our best judgment in light of the information available to R.V. Anderson Associates Limited at the time of preparation. Any use which a third party makes of this report, or any reliance on or decisions to be made based on it, are the responsibility of such third parties. R.V. Anderson Associates Limited accepts no responsibility for damages, if any, suffered by any third party as a result of decisions made or actions based on this report.”

EXECUTIVE SUMMARY

Hydro-Com Technologies, a division of R.V. Anderson Associates Limited, at the request of

the Environment & Sustainable Development Research Centre, University of New

Brunswick, completed a study to ascertain if significant trends in selected hydrologic

parameters attributable to climatic change could be detected using the records of 13

hydrometric stations in New Brunswick.

Analyses were performed on hydrometric data for the selected hydrometric sites to detect

trends in several hydrologic parameters. These parameters were: annual mean, maximum,

and minimum daily flows, mean seasonal daily flows (winter, spring, summer and autumn),

the number of days flow exceeded threshold values (90% of the mean maximum annual

daily flows, four, and five standard deviations above the mean of the daily flows), ice season

characteristics (earliest and latest dates of ice effects on hydrometric records, the number of

days with ice effect, and the estimated number of breakup events each year), and the Julian

dates of spring flooding. Seasonal values were determined based on dates defined by the

solstices. No adjustments for leap years were made.

Potential patterns in flood frequency over time were investigated by performing trend

analyses on the results of single-station-frequency analyses for 10-year intervals over the

period of record. The frequency analyses were done for different recurrence intervals

depending upon data adequacy.

Two statistics were used to assess the significance of any trends identified: r2 and the p-

value for the slope of the linear regression line. If the value of the slope was zero, no trend

exists. To determine if the slope value is significantly different from zero, its probability was

determined.

Time series data was extracted from Environment Canada’s Archived Hydrometric Data

HYDAT. For observed trend in hydrometric data, a linear regression was performed. For

trend analyses of annual hydrologic parameters (mean annual daily discharge, annual

maximum daily flows, annual peak instantaneous flows, and annual minimum daily flow), the

analyses were repeated for the years 1969 to 2006, the years for which data was available

from all stations used in this project, so that regional trends over a concurrent period of

record could be evaluated. For flow frequency, a similar approach using regression was

followed, but single-station-frequency analyses were done first to obtain the dataset for trend

analyses.

The results of the study are summarized in Table 1 and Figures 1(a-t). The study has lead to

the following conclusions:

1. Trends in hydrologic data are beginning to appear in the hydrometric records. As the

climate continues to change, trends in hydrologic data are expected to be more evident

and statistically significant.

2. The identification of observed trends that may persist into the future provides further

evidence that the hydrological regime is not stationary and will continue to change in the

future.

3. Linear trends are indicators of the direction of change in hydrologic parameters rather

than an accurate basis for climate change projections.

4. Trend detection is affected by the period of record used.

5. The dates of spring flooding have advanced earlier in the year. The magnitude of flood

peaks is significantly trending downward.

Arising from this study are the recommendations given below.

1. Hydrometric networks should be maintained and enhanced, as the detection of trends

depends upon the availability of good, multi-decadal hydrometric records.

2. Possible linkages between observed trends in climate and in hydrologic parameters

should be further investigated. Statistical analyses of trends in selected climate elements

should be correlated with statistical analyses of trends in hydrologic factors.

3. This study of the detection of trends in hydrometric records should be repeated in seven

to ten years, as additional data becomes available and the impacts of climate change the

hydrologic cycle intensifies.

4. An investigation of observed trends in groundwater levels should be undertaken as soon

as sufficient data becomes available. For this purpose, the existing groundwater

monitoring network should be maintained and enhanced.

5. The interaction of surface water and groundwater resources should be investigated

further, as climate-induced changes in the timing and amount of surface water may alter

groundwater recharge rates.

6. Sufficient information now exists from trend analyses and climate change projections for

the Province indicating that climate change is a real phenomenon, and the majority of

scientific opinion (IPCC1, 2001) is that climate change is likely to continue throughout the

21st century. As the impacts of the climate change may result in detrimental alterations

affecting the economy and environment, emphasis needs to be placed now on the

adaption of infrastructure to the changing hydro-climatic conditions.

Figure 1: Graphical Representation of Final Results

(a)

(b)

(c)

(d)

Figure 1: Graphical Representation of Final Results (continued)

(e) (g)

(f) (h)

Figure 1: Graphical Representation of Final Results (continued)

(l) (j)

(k) (i)

Figure 1: Graphical Representation of Final Results (continued)

(n) (p)

(o) (m)

Figure 1: Graphical Representation of Final Results (continued)

(s)

(t)

(q)

(r)