TECH: Award-Winning Save-the-Rain App Reveals Potential for Rain Harvesting from Roofs

By Robert Thomason

Like all buildings, the White House has a roof.  According to a new computer application (or "app") by a Canadia researcher, the White House roof could be used to harvest as much as 724,900 liters (191,498 gallons) of water, based on the regional average of 1,110 mm of rain a year.  

Water Citizen calculates that this amount of harvested rain would water 1,271 rose bushes during the year, many more than are in the nearby Rose Garden.

Calculating the Potential for Rooftop Rain Harvesting By App

Mark Laudon, a GIS specialist from British Columbia, has developed a computer application that will help draw the rain harvesting footprint on any roof.  This "Save-the-Rain" app then estimates not only how many liters of rainwater could be gathered, but provides details on what can be done with that water.

In June, 2012, the World Bank honored Laudon for his app in the annual Apps for Climate competition. Scores of programmers submitted apps which visualize and analyze World Bank climate data in accessible and innovative ways.

Laudon's Save-the-Rain app was a result of another climate data related competition sponsored by his local government, Laudon said.

"They had a climate data catalog from which I was to choose data to build an app with," he recounted. "I was driving to work one day praying for an idea for an app and while passing through some corn fields, the idea popped into my head.

"I myself grew up in an area where our water was supplied by a creek. In the summer, the creek would dry up, and, consequently, we had to buy water via a water pump truck to make it through the summer. Kind of ironic actually given the fact we lived in British Columbia's rain forest."

The apps drew heavily on annual precipitation records and on accessibility to fresh water data, but Laudon's "Save-the-Rain" provided the most practical, hands-on app for either a policy maker or a practitioner who wants to convert rainwater runoff from a roof to a beneficial resource for the folks living under a given roof.

Laudon said that people from roofers to backyard gardners have contacted him about using the app. A farmer in Kenya e-mailed him telling of plans to build a 180,000-liter underground storage tank using the app to help determine placement of the system.

The app is simple to use. Type in an address or city, and an ariel photograph from Google maps of the area appears. Zoom into the an appropriately close level and click on the corners of the subject roof. The app draws a polygon over the roof area.

When you click on the "Finish" button, Save-the-Rain grabs the mean annual rainfall, as reported by the World Bank in millimeters, and calculates the liters of rain water expected to fall on that roof.
It then uses Pacific Institute tables to estimate how useful that rainwater would be.

For example, harvesting rain from the five distinct roof areas of the White House would yield almost 4.5 million liters of water in a year. That would grow 7,662 kilograms of corn, 2,327 kg of soy, 2,892 kg of rice and 6,140 kg of wheat or would provide almost a half million toilet flushes a year.

Sliding the map a few blocks east to examine the World Bank headquarters (which has a roof more in the shape of a rectangle) the app estimates that 2.9 million liters of water could be harvested, enough for 5,072 kg of corn, 1,541 kg of soy beans and 329,670 toilet flushes.

As shared in a YouTube video, comments on the Save-the-Rain App include Laudon has given a video explanation of his app on YouTube, and shares feedback from users aroudn the globe.

Other award-winning Apps for Climate included:

Globe Town, which gives a table of migration data to and from a country, and has a menu of data points such as withdrawals of freshwater, proportion of land that is very low lying, average annual precipitation and average proportion of people affected by droughts, floods and extreme temperatures.

Data-Story.org allows users to generate maps, bar charts, column charts or pie charts of World Bank indicators such as freshwater withdrawals (either in cubic meters or as a percentage of internal resources), investment in water and sanitation with private participation and other World Bank climate data.