Making Sense of Twenty-First-Century Climate Change in the Altiplano: Observed Trends and CMIP3 Projections

Abstract

A synthesis is presented of the first phase in regionalizing climate projections for the Altiplano, an elevated central Andean plateau in Bolivia and Peru. A prerequisite to downscaling is analysis of the large-scale forcing provided by global, multimodel climate scenarios. Global climate models in the Coupled Model Intercomparison Project (CMIP3) archive are employed to qualitatively evaluate the direction of change in twenty-first-century projections of the annual cycle, indexes of extremes, and soil moisture. Analysis suggests the observed warming in the region is likely to accelerate in the coming decades under the high emissions scenario. Precipitation projections exhibit larger uncertainty but suggest an evolution toward a shorter, more intense wet season with weakened spring (September–November) precipitation and strengthened summer rainfall (January–March). These results are consistent with projections for the large-scale South American Monsoon, and station observations indicate trends similar to the projections. Extremes analysis suggests that precipitation may increasingly be experienced as intense storms, with more consecutive dry days. These results are consistent with soil moisture projections, which indicate drier conditions during the rainy season, despite the projected increase in precipitation. Our results suggest climatic changes in the Altiplano might have serious consequences for water management and indigenous agriculture. However, these climate model projections must be taken with caution, due to the relatively coarse grid scales employed and the model warm and wet biases. The results presented here will require further testing with improved, higher resolution climate models.