Influence of the length of rainfall time series on rainwater harvesting systems: A case study in Berlin

- Using short-term instead of long-term time series to size rainwater tanks.
- For Berlin, 10-year time series could provide results equivalent to 30-year's.
- The influence of the time series length is greater for higher rainwater demands.
- A validation confirmed the similarity of results for short and long-term series.

This study evaluated the influence of using different rainfall time series lengths on the rainwater harvesting systems sizing. The main objective was to determine a short-term rainfall time series length can lead to results similar to those obtained with long-term rainfall time series. The study was conducted using daily rainfall data from Berlin, Germany. A 30-year time series was used as a reference and then shorter series were detached, i.e., 30 sets of 1-year, 29 sets of 2-year, and so on. A single-family house was used as a simulation model fixing the catchment area and a number of residents, and varying the time series length and the rainwater demand. Two simulation variables were evaluated: “optimal rainwater tank capacity” and “ideal potential for potable water savings”. The results obtained from the simulations for each short-term time series were compared to the results for the 30-year time series. The frequency of the optimal rainwater tank capacity results that were similar to those obtained for the 30-year time series and the relative and absolute differences between the ideal potential for potable water savings were evaluated. It was found that a series of 10 years of daily rainfall data is enough to generate results significantly similar to those of a 30-year time series. To validate the results obtained, the model was simulated again, using a series of 10-years of daily rainfall data not included in the 30-year time series used in the experiment. The validation has confirmed the experiment results.