Hajar Mountains Oman III, 2015

Year Estimated enhancement Probability of a
positive enhancement
2013 18 per cent 99 per cent
2014 33 per cent 90 per cent
2015 20 per cent 99.9 per cent
2013-14 18.5 per cent 99 per cent
2013-2015 18 per cent 99.9 per cent

*The 2014 result shows a particular high enhancement with lower statistical probability.
We believe it is more useful to disregard this particularly high figure and to look to the 2013-2014 and 2013-2015 combined data results

In 2015 six Atlant units were deployed (compared with two in 2013 and four in 2014), along with an expanded network of 179 rain gauges and an additional two SODAR units. The experimental design deployed a balanced randomized operating schedule with dynamically (wind) defined target and control areas with strict operational controls, as opposed to opportunistic cloud-determined operation and data gathering.

The challenges of statistical modelling and analysis of rainfall data – due to the huge variability associated with where and when rainfall occurs – can be addressed with a ground-based system with a well-defined downwind target area. The further prerequisites are sufficient rainfall gauges spread over this area and adequate care taken when analysing the data obtained from these gauges to account for the spatial and temporal correlation in rainfall. The steps taken in this area are detailed in the full trial report (see link of this page).

From a statistical perspective the 2015 trial represents possibly the most well instrumented rainfall enhancement trial that has been conducted to date. Headline results from the 2015 trial are set out in the table above (along with corresponding 2013 and 2014 results).