• Hypothesis

Water standing on the surface evaporates faster than water held in the soil.

  • Methodology

Evaporation is an important facet of ecoroof performance. Because we could not measure it directly without damaging the roof, we devised the following experiment. We found three identical plastic tubs with tight sealing lids. In one tub we put a 2layer of dry soil that was similar in composition to that found on the ecoroof.
This tub was not covered. On the second tub we shaped aluminum foil to form a shallow funnel, sealing the edges with tape. The idea here was that rainwater would drain into the tub through the small hole in the center, but the foil cover would prevent any significant evaporation. The third tub was left empty and uncovered to represent the hard surface of the roof.
Each tub was weighed with its lid. We used the digital scale at the post office as it was the most accurate scale that we had 24 hour access to.

These three tubs were set in the open to collect rain over a 43 hour period.
The rain gauge tub (with aluminum foil) was then sealed with its lid, and the other two tubs were set in a protected area where they would not collect any more rain but would be subject to outdoor temperatures and humidity and would get daylight.

After 99.5 hours the tight sealing lids were put on the soil tub and open tub. Each of the three tubs was again weighed on the postal scale.
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