Trend detection

Topaloglu F (2006) Regional trend detection of Turkish river flow. Nord Hydrol 37 165-182... 

Trend Detection The Florida Everglades Case Study... 

The ozone behaviour on 550 K has been in August similar to July. On the 475 K surface ozone has declined both inside and on the edge region of the vortex, but only the linear ozone trend on the edge region is statistically significant -0,12 ppmV/year (se 0,04). On the 435 K surface there is no trend detectable in August. 

Differencing by one is similar to the first derivation of the time series. Because of the digital data structure, it is not a differentiation but a differencing. The differencing method is, therefore, a plot of the dependence of the slope of the series on time. This example (Fig. 6-8) does not indicate any trend with this method of trend-detecting. But maximum and minimum slope values can be observed every year. 

The remaining series from seasonal differencing is a good starting point for trend detection methods (Fig. 6-9). 

Loftis, J.C., Ward, R.D., Phillips, R.D. and Taylor, C.H. (1989) An Evaluation of Trend Detection Techniques for Use in Water Quality Monitoring Programs, EPA/600/3-89/037. US Environmental Protection Agency, Cincinnati, OH. 

While on-line implementation of the trend detection strategy is indeed feasible, the training of HMT models may be rather time consuming and inefficient. We note the following on the implementation issues ... 

Moreover, combining detail and approximation coefficients to build HMT models would be a natural next step in process trend detection, but this extension is hampered by computational difficulties as mentioned before. 

An Evaluation of Trend Detection Techniques for Use in Water Quality Monitoring Programs... 

The NS T Program has produced data uniquely applicable to trend detection but as O Connor (1996 and elsewhere) has elegantly pointed out, most chemicals at most locations show no statistically significant trend in concentration over time. For example, O Connor (1998) shows for a 10-year time period that out of 2744 combinations of 14 chemicals at 196 sites only 88 increases and 348 decreases are significant at the 95% confidence level. Chance alone predicts 69 increases and 69 decreases, so by this analysis it is quite possible that no real increases occurred in that time period and environmental quality may have improved. This is an important finding. 

No trend detected with the range of conditions tested. 

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