Small islands are at risk of suffering from freshwater scarcity, paving the way for them to dry out in the future, a new study has found.

Scientists from the University of Colorado Boulder have developed a new model to predict the effects of climate change on small islands. In the process, they found that previous analyses of these places underestimated the number of islands that can go barren by mid-century.

From 50 percent, the number of islands possibly becoming arid in the future is actually 73 percent, putting approximately 18 million people "computationally disenfranchised," as described by study lead author Kris Karnauskas.

Karnauskas says these islands are already facing problems of sea level rise, but new data show that they are also at risk of having vulnerable rainwater.

"The atmosphere is getting thirstier, and would like more of that freshwater back," he says.

The Unfortunate State Of Small Islands

Small islands are among the most unfortunate places in the face of the changing climate. They are vulnerable to sea level rise, scarce resources and hazards of economy. To add to that, thousands of these islands are said to be too small to be considered in global climate models (GCMs) that scientists are not able to include them in studies investigating the impacts of climate change.

One particular area that scientists may have overlooked is the data on these islands' freshwater systems. As per GCMs, the percentage of islands getting wetter and drier are tied at 50 percent each. However, these models do not consider what occurs in unaccounted-for islands. In fact, Karnauskas and colleagues discovered that 73 percent of the islands will turn drier due to increased evaporation.

Underestimation of environmental situations appears not to be rare, as a recent study found that scientists have also undervalued the potential of sea level rise over the next century.

The Problem With Global Climate Models

The main dilemma of GCMs is that they are not completely sharp in terms of coming up with very detailed information of small objects, particularly tiny islands.

GCMs divide the Earth into grids, with each grid measuring about 240 x 210 kilometers (149 x 130 miles). Such dimensions are quite big for areas with small islands that it becomes impractical to include these tiny specks into the models.

Karnauskas compares the situation to pixels. If they are too big to consider the tiny freckles on a nose's image, then those freckles would go unnoticed. For these freckles to be resolved, extreme fine pixels are needed. Unfortunately, GCMs are not designed to have that feature.

The scenario of the unnoticed element in a grid box is applicable to many islands all across the globe. Part of this problem is that scientists are not able to determine the effects of climate change to these islands' freshwater situations.

Understanding The Water Situation In Small Islands

The primary method for determining how climate change affects freshwater supplies is to identify the evaporation and precipitation situations in the area.

Determining precipitation is easy and existing GCMs are able to detect this regardless if it is over land or over water. Even in tiny areas like Easter Island in Polynesia, experts are able to determine how much precipitation is most probably going to fall from the sky.

The biggest challenge then is identifying evaporation rates. This is because the models do not show the lands, it only depicts an all-water picture. Scientists cannot calculate evaporation of these lands based on the bodies of water surrounding the tiny islands because oceans follow different physical principles of evaporation.

Not being able to know the rate of evaporation leaves scientists baffled as to the true situation of freshwater supplies in tiny islands.

Karnauskas and colleagues then created a way to determine what is really going on in these small islands. He draws a cube diagram on a white board, which represents a three-dimensional image of an ocean grid cell. He prompts predicting where the tiny island ought to be in the cube and use the atmospheric information directly above it.

The method developed by the team is said to be feasible because the islands are so small that the climate directly above it is not much different from the climate over the ocean. This has been proven in an investigation of an island as big as Maui, where scientists were able to discover that weather centers at airports have little variations from the weather of stations hundreds of kilometers offshore.

Karnauskas calls this technique as "blind pig test," which is said to be successful if scientists are not able to distinguish whether what they are investigating is above land or above the water. This situation only means that experts do not need to have land information. As long as they know the situation in the atmosphere above it, then they can most likely predict the evaporation situation in that area.

Small islands may face drier situations far more than previously predicted, but with the new framework developed by the team, scientists may have more accurate information about the effects of climate change, which may help mitigate the severity of the situation.

The study was published in the journal Nature Climate Change on April 11.