Climate of Peru

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The climate of Peru is very diverse. The north-south extension of the country and the presence of the Andes mountains together produce a large variety of climates and microclimates. In general, the climate on the coast is subtropical and the region receives very little rainfall. The Andes mountains observe a cool climate with rainy summers and very dry winters. The eastern lowlands are warm and rainy with a short dry season from June through August.

[edit] The coast

The climate of the coast ranges from warm-semiarid north of 5°S to cool-arid south of 8°S. Despite the proximity to the equator (3°S-18°S), the entire coastal region has a marked annual temperature cycle in response to the direct effects of the sea surface temperature. The warmest period occurs from January through March and the coolest period from July through September. Day-night temperature differences increase away from the sea shore.

The northern coast's (3°S-6°S) temperature extremes range from 14°C to 38°C. Summers are characterized by hot, humid and sunny conditions,with occasional afternoon and nocturnal rainshowers. Summer rainfall totals rarely exceed 200 mm except during strong El Niño events, where they can exceed 4000 mm. Temperatures range from 20-23°C at night to 28-38°C during the day, the highest readings observed over the entire Peruvian coast. Winter is characterized by warm yet comfortable conditions and absence of rain. Temperatures range from 14-18°C at night and 22-29°C during the day.

The central and southern coasts (south of 6°S) enjoy a milder climate. Temperature ranges from 8 to 35°C and rainfall is scarce with annual totals below 150 mm. Summer is characterized by warm, moist and sunny conditions with lows between 18 and 22°C and highs between 24 and 30°C. Temperatures over 30°C are commonly observed less than 10 days per year except at the Ica deserts where summer highs can sometimes reach 35°C. Little or no rainfall occurs during the summer. Rare rainfall events are produced by the leftovers of Andean convection and occur during the night. Summer rainfall totals are generally less than 10 mm. Winter is characterized by overcast, cool and damp conditions. Frequent low cloud cover and persistent drizzle events help to keep daytime temperatures cool. Winter highs oscillate between 15 and 23°C and the lows between 8 and 15°C. Several weeks of persistent overcast skies and highs below 19°C are not uncommon between July and September. The so-called 'rainy season' develops by late May and comes to an end by mid October. Precipitation occurs in the form of nocturnal-morning drizzle and seasonal totals range between 10 and 150 mm. Winter precipitation favors the development of vegetation over particular coastal mountain ranges known as "Lomas". The desert green-up peaks between July and early November.

[edit] The Andes

The climate of the Andes exhibits the largest diversity among the country. Temperature is an inverse function of altitude varying from temperate (annual average of 18°C) in the low-lying valleys to frigid (annual average below 0°C) in the highest elevations. 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. There is a marked southwest-northeast rainfall gradient with the driest conditions (200-500 mm/year) along the southwestern Andes, and the wettest conditions along the eastern slopes (>1000 mm/year). Upon the interaction between the topography and the mean flow, some regions immediately east of the Andes can receive as much as 10000 mm/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 5000 during the rainy season, and occasional above 3800 m between May and Augusts.

[edit] The lowlands

The eastern lowlands are characterized by the Amazon Rainforest. The climate of this region is warm and rainy most of the year. Temperatures oscillate between 18-36°C most of the year and rainfall varies between 1000 and 4000 mm per year. South of 8°S, a short dry season occurs between June and August. Occasional cold surges that originate over Argentina may lower the temperature to 10-15°C. These events occur 1-5 times per year between May and September.