Climate of Peru - Andean Highlands

Andean Highlands

The Peruvian Andes (clima de Sierra in Spanish) exhibits the largest diversity among the country. Temperature is inversely proportional to altitude, varying from temperate (annual average of 18 °C/64 °F) in the low-lying valleys to frigid (annual average below 0 °C/32 °F) in the highest elevations. The maximum temperature is often steady throughout the year, the low varying due to the presence of clouds in the rainy season, which help keeping to some extent the daytime heat during the night. In the absence of clouds, nights are much colder.

Precipitation varies in different scales and has a marked seasonality. The rainy season starts in September but peaks between January and March, whereas the May–August period is characterized by strong insolation, very dry conditions and cold nights and mornings, which is almost the exact reverse, in terms of insolation, to the coast climate. There is a marked southwest-northeast rainfall gradient with the driest conditions (200–500 mm/7.9–19.7 in/year) along the southwestern Andes, and the wettest conditions along the eastern slopes (>1,000 mm/39.4 in/year). Upon the interaction between the topography and the mean flow, some regions immediately east of the Andes can receive as much as 10,000 mm (393.7 in)/year. Rainfall is also larger over mountain ranges than over valley floors, since most of the rainfall occurs in the form of afternoon convective storms. Lakes also modulate the distribution and rainfall amounts. Lake Titicaca, for example, induces nocturnal convective storms that produce twice as much rainfall over the lake than over the surrounding terrain. Occasionally thunderstorms can be accompanied by frequent cloud to ground lightning, strong winds and damaging hail, especially during the onset of the rainy season and over higher elevations. Snowfall is frequent above 5,000 m (16,404 ft) during the rainy season, and occasional above 3,800 m (12,467 ft) between May and August.

Some representative averages

• Chachapoyas, Peru; 2,435 m (7,989 ft); annual mean temperature 15.3 °C (59.5 °F); annual mean precipitation 796 mm (31.3 in), Climate type Cwb.
• Cuzco, Peru; 3,249 m (10,659 ft); annual mean temperature 12.5 °C (54.5 °F); annual mean precipitation 736 mm (29 in), Climate type Cwb.