Roof Rainwater Harvesting

In the Virgin Islands more than 90% of the population utilize rainwater harvesting. This practice involves collecting rain from rooftops and storing it in cisterns, usually built into the house foundation. During times of heavy rainfall the cisterns may overflow and run-off. On the other hand, in times of low water levels residents may need to purchase water from private vendors, which can be costly and difficult for those living in hard to reach areas.

While the Virgin Islands building codes require households to have a cistern (if not connected to a public water supply), there is little research regarding the catchment efficiency based on roof type, the water harvesting potential of the VI and the proper sizing of cisterns. The CGTC plans to address some of these research questions.

Desalination

The VI has desalination plants on St. Thomas and St. Croix. The plants have been converted to use a technique called reverse osmosis (RO). Naturally in osmosis, liquid flows through a membrane from freshwater (less concentrated) to saltwater (more concentrated). Nevertheless, using pressurization, this process is reversed to produce freshwater. Reverse osmosis uses less energy than other forms of desalination and has less environmental impacts.

Desalination is quite energy intensive and even the most advance process, RO, uses 10-20 kWh per 100 gallons of water. In comparison, freshwater systems use 0.75 kWh.

The desalination process also generates a by-product, brine, which is highly concentrated with salt and chemicals. Disposing of brine often consists of releasing it back into the ocean which can harm marine wildlife.

Currently only 1% of global population depend on desalination for drinking water. It is mostly used in remote locations and arid regions by those whom can afford to build and operate the expensive plants.

Ocean impacts

As atmospheric temperatures rise, so will sea surface temperatures. In the Caribbean, ocean warming has already occurred over the past century (1.3 F) and currently that rate of warming is increasing. In fact, in the past 20 years surface temperatures have increased by 0.43 F per decade. This can have negative impacts on marine ecosystems which are highly dependent on temperature such as coral reefs.

Another ramification increasing concentrations of carbon dioxide to 415 ppm is ocean acidification. Fortunately, much of the carbon dioxide released into the atmosphere is absorbed by the oceans, lessening the effects of global warming. However this can have detrimental effects on marine life as carbonate, a key ingredient in shells and corals, is reduced.

Additionally as global temperature rises, melting land ice is leading to sea level rise. In the Caribbean, sea levels have been rising by 0.08 inches per year and the rate is accelerating. In the past decade levels have been rising at 3 times this amount (0.24 inches per year). By 2050, sea levels in the Virgin Islands will rise by 0.8 to 2.6 feet.

Water Scarcity

Freshwater resources are affected by precipitation levels, temperature, evaporation, watersheds and water use and management and climate change impacts in the USVI can amplify water scarcity. Climate change is expected to lengthen dry seasons, increase droughts and reduce annual precipitation. Additionally rising temperatures may increase evaporation causing issues for open reservoirs and for agricultural practices.

Fortunately the USVI already invests heavily in rainwater harvesting as local building codes ensure that all infrastructure includes cisterns. However, improved water use and management (through conservation and efficiency) may become more vital as increased droughts can limit the water available and flooding events can cause loss of water due to cistern overflow.

The USVI has recently been included in the U.S. Drought Monitor thanks to efforts to install weather stations across the territory as well as digitalize historical records. Drought is a natural hazard that creeps up on us, that’s why recognizing the drought early can help to lessen the negative impacts. Additionally the inclusion of the USVI in the U.S. Drought Monitor allows us to be eligible for increased drought relief funding. The current USVI drought monitor can be reviewed at this website.