During the rainy season from June to December, the bajos are too muddy, and in the dry season they're parched.
Today's residents make little use of these low-lying swamps (which they call "bajos," the Spanish word for "lowlands"), and archeologists had long assumed that the Maya hadn't used them either. Sever and co-worker Dan Irwin have been looking at satellite photos and, in them, Sever spotted signs of ancient drainage and irrigation canals in swamp-like areas near the Mayan ruins. How did they thrive for so many centuries? An important clue comes from space: But Sever thinks disaster can be averted if researchers can figure out what the Mayans did right. It seems that modern people are repeating some of the Maya's mistakes. By 2020, only 2 percent to 16 percent of the original rain forest will remain if current rates of destruction continue. It's the ash that gives the soil its fertility, so within 3-5 years the soil becomes exhausted, forcing the farmer to move on and cut down a new section. About half of the original forest has been destroyed in the last 40 years, cut down by farmers practicing "slash and burn" agriculture: a section of forest is cut down and burned to expose soil for planting crops. Today, the rain forest is again falling under the axe. The root cause was a chronic food and water shortage, due to some combination of natural drought and deforestation by humans." "Now we think that all these things played a role, but that they were only symptoms. "Archeologists used to argue about whether the downfall of the Maya was due to drought or warfare or disease, or a number of other possibilities such as political instability," Sever says. Using classic archeology techniques, researchers find that human bones from the last decades before the civilization's collapse show signs of severe malnutrition. (Changes in cloud formation and rainfall are occurring over deforested parts of Central America today, studies show. The Maya must have relied on rainwater saved in reservoirs to survive, so a disruption in rainfall could have had terrible consequences. During the dry season in the Pet?n, water is scarce, and the groundwater is too deep (500+ feet) to tap with wells. Rising temperatures would have also disrupted rainfall patterns, says Oglesby. Those warmer temperatures would have dried out the land, making it even less suitable for raising crops.
The changing groundcover would have boosted the temperature of the region by as much as 6 degrees, according to computer simulations by NASA climate scientist Bob Oglesby, a colleague of Sever at the MSFC. Without trees, erosion would have worsened, carrying away fertile topsoil. In other words, the region became almost completely deforested. From pollen trapped in ancient layers of lake sediment, scientists have learned that around 1,200 years ago, just before the civilization's collapse, tree pollen disappeared almost completely and was replaced by the pollen of weeds.