The crux with variability: too much or too little

In hydrology we measure and follow the water. What if there is too much or too little? It happens a lot. As a field hydrologist, I frequently have to determine the location of a measurement, the time to take the measurement, the location to set up a field experiment, or the amount of a tracer to inject to study a hydrological system. However, this is a very bumpy road, as variability is often not in favor of my decisions because the distribution is wider than expected, bimodal instead of unimodal, or the probability of an event is theoretically small, but still an extreme event occurs during our experiment. I will showcase some examples to demonstrate what I mean and what I experienced, as well as how frequently the PhD students or Postdocs have suffered as a result of my decisions or of the unexpected variability: Climatic variability resulted in a winter without snow, just as new sensors were already deployed. Or the winter snowpack was extremely high, preventing any work at high altitudes in the Alps until mid of July, thereby reducing our field season by half. An ecohydological study to observe the effects of drought in a forest with a rainout shelter was ineffective because it occurred during an extremely dry year, making the control just as dry as our drought treatment. The automatic water sampler was set-up to collect stream water samples, but it was washed away four weeks later by the 50-year flood. The calculated amount of artificial tracer was either way too low, because the transit times of the system were much longer than expected, or it was far too high, resulting in colored streams or samples that had to be diluted by a factor of 100 due to much faster transit times Finally, and most expensively, we installed many trenches along forest roads to measure subsurface stormflow but after three years, we abandoned the measurements because we never measured a drop of water coming out of the trenches, as the bedrock permeability was much higher due to many high permeable fissures that prevented the formation of subsurface stormflow.  These experiments or observations failed because of unexpected variability in input, system properties or a lack of technical variability in the equipment. I will reflect on residual risk of failure in fieldwork related to that crux and discus approaches to reduce this risk.