The extreme, prolonged rainy seasons in 2010 and 2011 offer a preview of the damage such shifts may bring to urban areas in the future. In Medellín, heavy rains created rivers in the city center and led to devastating landslides. In one case, more than 100 people were killed or missing after an avalanche of mud buried dozens of homes on a hillside above the city.
The Bogotá River, choked with sediment and trash, overflowed its banks and flooded low-lying neighborhoods in and around the nation's capital. All told, more than three million Colombians – about seven percent of the total population – were displaced or suffered significant damage to their homes in 2011 alone as a result of flooding, according the World Bank.
Models predict that warming in the Andes is likely to contribute both to more flooding and more drought in the region as mountain environments change. According to the Inter-American Institute report, the average temperature of the Andes has increased by 0.7 degrees Celsius over the past 60 years. That's similar to the global average, but high altitude ecosystems like páramos and cloud forests in the tropical Andes are particularly sensitive to warming – much like coral reefs, glaciers and polar regions.
Ruiz, who contributed to the report, noted that an analysis of weather records at one páramo research station showed increases in minimum temperatures were almost twice that of lower elevations, while increases in maximum temperatures jumped to nearly three times the average at lower elevations.
Climate change research here is in its early stages, and scientists are still teasing out which changes in the high mountains are the result of climate change and which are more likely the result of other human-caused changes, namely, agriculture, ranching and mining. Research suggests a combination of both is to blame for increasing temperatures and declines in key species, including some frailejónes.
Conrado Tobón, a hydrologist at the National University of Colombia in Medellín, studies how climate change is altering the water cycle of high Andean ecosystems. In 2005, his team began studying the eco-hydrology of páramos and high Andean forests that are crucial to the water supply of Bogotá, Medellín and Quito, Ecuador.
The team took minute-by-minute measurements of conditions like precipitation, temperature, wind, evaporation rate and water content of the soil. The goal is to do a complete accounting of the movement of water from the time it hit the surface of a plant and passed through moss and soil, until it flowed out of the basin and into the network of high forest streams on its way to the lowlands.
They also used data on precipitation in Colombia from the Intergovernmental Panel on Climate Change (IPCC) to model changes under different temperature and precipitation scenarios. The researchers modeled for páramos degraded by agriculture and mining as well as protected ones like Chingaza. Tobón's results confirm what other models are showing: Precipitation will likely decrease in the páramos and high Andean forests, perhaps even leading to a sustained drought.
But overall drier conditions don't necessarily mean less risk of flooding – quite the opposite, in fact. At his own research stations in the northern Andes, Ruiz noticed increasing incidences of extreme rains, which are likely to cause more runoff and soil erosion. It's a perfect recipe for flooding.
"Dry periods are getting longer and wet seasons are getting more intense," he said. "Páramos are thus getting washed by intense, short-lived thunderstorms and downpours that cannot be handled by vegetation adapted to drizzles."
Local climate changes are partly to blame. The conversion of mountain forest to pasture and croplands has raised temperatures in the region, prompting a lifting of the cloud level – enough to leave some cloud forests and páramos below the fog, and increasing solar radiation. This decrease in cloud cover is one of the biggest contributors to climatic stress in the páramos, according to Ruiz.