Changing climate in the Bolivian Altiplano: CMIP3 projections for temperature and precipitation extremes

Rural agriculture in the Bolivian Altiplano is vulnerable to climate related shocks including drought, frost, and flooding. We examine multimodel, multiscenario projections of eight precipitation and temperature extreme indices for the Altiplano and compute temperature indices for La Paz/Alto, covering 1973-2007. Significant increasing trends in observed warm nights and warm spells are consistent with increasing temperatures in the tropical Andes. The increase in observed frost days is not simulated by the models in the 20th century, and projections of warm nights, frost days, and heat waves are consistent with projected annual cycle temperature increases; PDFs are outside their 20th century ranges by 2070-2099. Projected increases in precipitation extremes share the same sign as observed trends at Patacamaya and are consistent with annual cycle projections indicating a later rainy season characterized by less frequent, more intense precipitation. Patacamaya precipitation indices show shifts in observed distributions not seen in the models until 2020-2049, implying that precipitation changes may occur earlier than projected. The observed increase in frost days can be understood within the context of precipitation changes and an increase in radiative cooling. Model warm/wet biases suggest that a decrease in frost days may not occur as early or be as large as projected. Nevertheless, consistencies between simulated and observed extremes, other than frost days, suggest the directions of projected changes are reliable. These results are a first step toward providing the critical information necessary to reduce threats to food security and water resources in the Altiplano from changing climate.