People who live in the tropics can expect to see more rainfall in the future as the climate changes, NASA research shows. The research lead by Jet Propulsion Laboratory scientist Hui Su revealed current climate models are underestimating the decreases in high clouds in these regions. The decreases already are observable but they have not been integrated into most climate models.

The research, published in Nature Communications last week, compared data from the past several decades with climate simulations from the same times and found most models were underpredicting increases in precipitation. Su and the team at JPL found the models that were best at predicting precipitation had come close to mapping clouds correctly, NASA said.

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The tropical regions, or areas with a tropical climate, sit around the center of the Earth's equator. The region is classified as the area between the Tropic of Cancer, the northern tropic barrier, and the Tropic of Capricorn, the southern tropic barrier. Their points mark the farthest latitudes north and south at which the sun is still directly overhead. The area between these points is warm year round, with no defined seasons, but the conditions like precipitation and humidity can vary greatly from one area to another. 

Clouds in all regions of the world, including the tropics, are one of the most difficult factors for climate models to predict accurately. The way the clouds react to a changing climate and the way that influences the climate further is difficult for researchers to predict without a margin of error that is too large for the results to be reliable. The reason is, in part, due to the fact that clouds not only help reflect rays that heat the planet back into space, but they also hold water vapor and have a warming effect on the Earth as well. This is why many of the models the JPL team looked at underestimated increases in precipitation.

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The main issues with the models were traced back to the modeling of high clouds and circulation, Su and his team found. The hope is that with this research the models will be able to adjust and better predict these factors in future modeling.

Observations conducted over the last 30 to 40 years show there has been a decrease in high clouds that the models failed to predict. And as the high clouds decrease the tropical atmosphere will cool due to a lack of clouds trapping the heat in. The rainfall would counter the cooling from the lack of trapped heat because the water that’s traveling from the surface up to the atmosphere brings heat with it as it travels, once in the upper atmosphere that heat is released.

The reason Su and his team of researchers say they believe there will be more rainfall in the future than previously predicted is that the models that best predicted clouds also predicted an increase in precipitation that already has been observed. So if the models more accurately predict the cloud models, they should also predict more rain in the future as the climate warms and the high clouds shrink.