Because Ecuador lies on the Equator, most of the country, except the Sierra, experiences a humid tropical climate. The Oriente is influenced throughout the year by an unstable maritime tropical air mass, while the Costa is subject to greater variations associated with seasonal movements of the intertropical convergence zone and the cold Peru Current. Local convectional processes dominate the weather in the higher parts of the Andes.

The Oriente experiences fairly continuous and abundant rainfall and high temperatures. The Costa generally has a wet season in the first half of the year and a relatively dry one in the second half. In some years, warm water collects off the coast, causing the weather phenomenon known as El Niño; this can result in torrential downpours that cause devastating ecological damage on the coast and occasionally even in the highlands. In the Sierra, rains reach a maximum during the equinoxes; there is a long dry season from June to September and a shorter one (the veranillo) from December through January.

Ecuador has a small area of truly dry climate at the Santa Elena Peninsula along the southern coast, with annual rainfall decreasing from about 40 inches (1,000 mm) near Guayaquil to only 4 inches (100 mm) at Salinas. In the highlands, annual rainfall decreases toward the centres of the canyons and valleys, sometimes dropping below 20 inches (500 mm) or even below 10 inches (250 mm). Most of the country, however, is humid, receiving more than 20 inches of rain a year. The southern coast and the highlands receive 30 to 80 inches (760 to 2,000 mm). The wettest areas, the northern coast and the Oriente, receive about 120 to 240 inches (3,000 to 6,000 mm) of rain.

Both the Costa and the Oriente are warm, with temperatures varying only slightly among the seasons; much wider differences occur between day and night. Average daytime high temperatures range from 84 to 91 °F (29 to 33 °C), while nighttime lows fall to between 68 and 75 °F (20 to 24 °C). As elevation increases, temperatures drop fairly predictably at a rate of about 9 to 11 °F (5 to 6 °C) for every 3,300 feet (1,000 metres). Pleasantly temperate climates occur between elevations of 2,600 and 6,600 feet (800 and 2,000 metres). At higher elevations, frost is a possibility, especially in areas of flat relief and during the cloud-free nights of the dry seasons. Above elevations of 11,800 to 12,500 feet (3,600 to 3,800 metres), agriculture becomes increasingly difficult because of the shrinking growing season and increasing frost hazard. Above 16,400 feet (5,000 metres) the peaks are snowcapped.

Plant and animal life

The wet lowlands of the Oriente and the northern and southeastern corners of the Costa are covered with tropical rainforest, containing various trees and lianas and many epiphytes. The forest thickens as it approaches the zone of maximum rainfall, which occurs between about 4,000 and 5,000 feet (1,200 and 1,500 metres) above sea level. In the Guayas River valley, the forest includes balsa, which is exploited for its light wood; in the eastern forest the cinchona trees were a valuable source of quinine before synthetic equivalents reduced demand for it. The trees of the Costa are rapidly being cut as land is converted for agriculture or for use as pastures, while the forest in the Oriente is threatened locally by small-scale ranching, African oil palm plantations, and subsistence farming.

In the Costa, between Esmeraldas and the Gulf of Guayaquil, where the climate is affected by the Peru Current, the northern rainforest gives way southward to deciduous and semideciduous woodland. There scattered palms produce the ivory-coloured tagua nuts previously used for making objects such as buttons, dominoes, mah-jongg tiles, umbrella handles, and religious figurines. Today they are used to make “vegetable ivory” crafts sold to tourists. The leaves of another palm, Carludovica palmata, also found in this woodland area, are collected, cut into narrow strips, bleached, and woven into Panama hats. Areas of swampy coast and the river floodplains were once covered by thick mangrove forest, but much of it has been removed to make way for shrimp aquaculture.

In the Sierra the valley interiors were originally covered with a thorny woodland, giving way toward the valley edges to a low evergreen forest and, at higher elevations, to the bunchgrasses of the high páramo, alpine vegetation characterized by tussock grasses, cushion plants, and the treelike frailejón (Espeletia). Much of the highland vegetation has been removed over the last 5,000 years for agriculture or has been altered by periodic burning.

In the rainforest live a wide variety of monkeys, as well as such carnivorous mammals as jaguars, ocelots, foxes, weasels, otters, skunks, raccoons, coatis (raccoon relatives), and kinkajous (tree-dwelling nocturnal animals in the raccoon family). Hoofed mammals include the tapir, deer, and peccary. Numerous species of rodents and bats inhabit the area.

Ecuadoran birdlife and fish life are notably rich. Some 1,500 species of birds have been identified, including condors, many hummingbirds, blue-footed boobies, and parrots. Bird-watching has become a significant source of tourist income. Among many types of North American birds that migrate to Ecuador for the winter are the Virginia rail, the kingbird, the barn swallow, and the scarlet tanager. The fish population is similar to that of the Amazon River, although in the west the electric eel and the piranha are not found. All major groups of reptiles are represented, with the Galapagos tortoises being particularly famous.