Climate of Peru

Climate of Peru describes the diverse climates of this large South American country with an area of. Peru is located entirely in the tropics but features desert and mountain climates as well as tropical rainforests. Elevations above sea level in the country range from and precipitation ranges from less than annually to more than. There are three main climatic regions: the Pacific Ocean coast is one of the driest deserts in the world but with some unique features; the high Andes mountains have a variety of microclimates depending on elevation and exposure and with temperatures and precipitation from temperate to polar and wet to dry; and the Amazon basin has tropical climates, mostly with abundant precipitation, along with sub-tropical climates in elevations above.

Pacific coastal desert

The coastal desert of Peru extends unbroken from near the northern border with Ecuador to the southern border with Chile, a north to south distance of. Three names are sometimes applied to the desert in different parts of the coastline. The Sechura Desert is in northern Peru. Southward is the Peruvian coastal desert which becomes at an indefinite location the Atacama Desert which continues into Chile.
The Sechura is warmer and less impacted by the cloud cover that characterizes the more southern parts of the coastal desert, but there is a uniformity in precipitation along the entire coastline with less than annually. The desert strip along the Pacific is narrow, at its widest about before the land climbs into the Andes and precipitation increases with elevation.
The following table summarizes climatic statistics for cities in the north, central, and southern parts of the coastal desert

Location	Latitude	Average annual temp.	Hottest month	Coolest month	Annual precipitation	Wettest month	Climate
Talara	4.58° S					February –	BWh
Lima	12.05° S					July, August, September –	BWh
Tacna	18.01° S					August –	BWk

A characteristic of the Peruvian coastal desert is low average temperatures despite its tropical latitudes. In the tropics the average annual temperature is usually at least with little temperature variation among months. By contrast most of the Peruvian coastal desert has average annual temperatures of less than and with temperatures falling to or near during the Southern Hemisphere's winter. The relatively low temperatures of the Peruvian coastal desert are caused by the cold Humboldt Current. Ocean water temperatures in Lima in September, the coldest month, are as low as similar to water temperatures near Los Angeles during its winter months.
The cold waters of the Humboldt Current also create a moist fog called garúa in Peru. The cold water, especially in the Southern Hemisphere's winter from May to November, cause an inversion, the air near the ocean surface being cooler than the air above, contrary to most climatic situations. During the Southern Hemisphere's winter, the trade winds blow thick stratus clouds inland over coastal areas up to an elevation of and the dense fog coalesces into drizzle and mist. In the Southern Hemisphere's summer from December to April, the weather is mostly sunny.
The moisturizing impact of the fog is increased by the high average humidity of the coastal deserts. For example, Lima has an average humidity of 84 percent, more than double the average humidity of most deserts. As a result of the fog, Lima gets only 1,230 hours of sunshine annually, and less than 50 hours each in the months of July, August, and September. By contrast, Seattle, not noted for its sunny weather, receives 2,170 hours of sunshine annually and "foggy London town" receives 1,618 hours.
As elevation increases moving inland from Lima and other coastal locations, so also does precipitation. Chosica, inland from the Pacific at an elevation of gets annually of precipitation compared to Lima's precipitation of. Matucana, inland at an elevation of gets of precipitation.
Apart from the irrigated agriculture in 57 river valleys coming down from the Andes and passing through the desert en route to the ocean, the coastal desert is almost without vegetation. In a few favored locations, where mountains come close to the sea and the fog condenses on the mountain slopes, the garúa permits vegetation to thrive in "fog oases," called lomas in Peru. Lomas range in size from very small to more than and their flora includes many endemic species. Scholars have described individual lomas as "an island of vegetation in a virtual ocean of desert." Peru has more than 40 lomas totalling in area less than out of a total coastal desert area of.

Andean highlands

The chain of mountains called the Andes, comprising 28 percent of the national territory, runs the length of Peru, a narrow wide at the Ecuadorian border in the north and wide in the south along the border with Bolivia. The Andes, with elevations almost entirely above and mostly above, rise above the desert to the west and the tropical rainforest to the east. The mountain climates are cool, often cold, with varied precipitation depending upon exposure. In general the western slopes of the Andres, facing the Pacific Ocean, are drier than the eastern slopes. Beginning at latitude 8.64° S and continuing southward are many snow-capped and glaciated peaks more that in elevation. Thirty-seven mountain peaks in Peru rise to more than in elevation.
A general rule for mountainous areas is that temperature decreases by about for each increase in elevation provided that the change in altitude takes place at the same latitude and other factors such as precipitation and cloud cover are similar. The temperature decline with increasing elevation is less than the average on the Pacific coast side of the Andes because of the unusually low temperature of the fog-bound coast. The steep slopes and the sharp changes in elevation result in a large number of microclimates in which a change of location of a few kilometres can result in major climatic changes. The common precipitation regime of the Andes is a rainy summer season from October to April and a dry winter from May to September. Snow is common at elevations of more than. The city of Puno at that elevation has snow 14 days per year on average and it has snowed in every month of the year except November. Puno experiences freezing temperatures an average of 226 mornings annually, with freezes occurring in every month and the permanent snow line is at about.
The following table summarizes climatic statistics for cities in the Andes mountain region.

City	Latitude	Elevation	Average annual temp.	Warmest month	Coolest month	Annual precipitation	Wettest month	Climate
Arequipa	16.40° S							BWk
Cajamarca	7.16° S						Cwb
Cusco	13.52° S							Cwb
Huánuco	9.93° S							Bsh
Puno	15.84° S							ET

The indigenous peoples of Peru have been farming in the Andes for thousands of years despite the severe climatic limitations. Compensating for the lack of a freeze-free growing season at elevations above, indigenous farmers up until the 21st century have sought out microclimates and used techniques such as andenes and Waru Waru to capture and store heat and permit hardy crops such as potatoes to grow up to in elevation. Llamas and alpacas are grazed on the sparse vegetation of the puna zone up to elevations of.

Amazon rainforest

The Amazon rainforest region comprises about 60 percent of the total area of Peru and is characterized, as is the coast, by its climatic uniformity: hot average temperatures with little variation among the seasons and abundant precipitation. While there are locations that fit into all three of the Köppen tropical types of climate, Af, Am, and Aw, the differences among the three climates in Peru are small. The true tropical rainforest climate requires at least precipitation in all months of the year. Pucallpa has only one month that falls below that threshold; Puerto Esperanza has three months below the Af threshold. The driest months are in the Southern Hemisphere's winter of June through August.
The dividing line between the Amazon and Andean climates is uncertain, but depends mostly on elevation. Temperatures become cooler with elevation and around elevation the climate becomes sub-tropical rather than tropical, a climate often characterized as "eternal spring." In Oxapampa, Cfb under the Köppen classification, temperatures rarely fall below or rise above and rain is abundant year-round. A few locations at elevations similar to Oxapampa have a pronounced dry season and are classified as Cwb, rather than Cfb.
The following table summarizes climatic statistics for cities and towns in the Amazon rainforest region.

City	Latitude	Elevation	Average annual temp.	Warmest month	Coolest month	Annual precipitation	Wettest month	Climate
Iquitos	3.75° S							Af
Oxapampa	10.57° S						Cfb
Pucallpa	8.38° S							Am
Esperanza	9.77° S							Aw
Quince Mil	13.23° S							Af

While Quince Mil has the highest precipitation of places in Peru with a weather station, climatologists say that the slopes of low mountains northwest of Quince Mil in Manu National Park may receive more than of rain annually.