The climate in this national park is so diverse that areas with a severe dry season lasting 4 or 5 months are immediately followed by others, near the summit or on the Caribbean side, where there is constant rainfall, which gives rise to a forest mass rich in epiphytes.

At the western foot of the cone average annual rainfall is between 2,500-3,000 mm., from May to November and at the eastern foot it varies between 3,000-4,000 mm.  The climate of the highlands and intermediate zones is chilly, with a tendency to become cold, and it is strongly affected by the Caribbean winds, which bring most of the rainstorms and showers in the region.  The temperatures fluctuate between 24º C in the lowlands to 14.9º C on the rim of the volcanoes.

The differences in altitude and climate play an important role in the distribution of the flora and fauna. Identification has been made in the park of 257 species of birds, including the resplendent quetzal, the black-faced solitaire, the great curassow, the Montezuma oropendula, the emerald toucanet, the elegant trogon, the blue-throated goldentail, the spectacled owl, the white-fronted amazon, the three wattled bellbird, the green amazon and the laughing falcon.  Other mammals that find refuge in this remote mountainous region are cougars, jaguars, tiger cats, and howler falcon.  Other mammals that find refuge in this remote mountainous region are cougars, jaguars, tiger cats, howler, spider and white faced capuchin monkeys, ocelots, tayras, kinkajous, two-toed sloths, white-nosed coaties, and Northern tamanduas.  Felines, tapirs, Bonaparte tinamous and black guans abound in the cupey groves.

Rincón  de la Vieja Volcano stands at 1,895 metres above sea level.  It has an active crater, which emits steam and gases of magmatic origin. Between it and Rincón de la Vieja and Santa María Volcanoes lies a depression, presumably from another very erode crater, with a lake of cold water. It is known as Lake Los Jilgueros and measures 6.5 hectares, and is also surrounded by lush evergreen vegetation. In the western sector a colonizing process has begun on the rocky terrain where the acid clouds emitted by the volcano burned the plant life away.  On the southern slope, between 700 and 900 metres above sea level, there is a faultline with a number of fumaroles at the sites known as Las Hornillas and Las Pailas. Mention must also be made of the hot springs near the Park Headquarters.  San Roque and Cañas Dulces, neighbors of the volcano, are dacitic domes in which the magma was unable to reach the surface as it solidified too soon.

Las hornillas are kitchen stoves where columns of steam, sulfur dioxide, hydrogen sulfide and other gases shoot out of cracks and fissures in the earth’s crust.  Las Pailas are sites with geysers and bubbling mud pots that are associated with hot-water underground reservoirs buried beneath layers of mud.  They extend over approximately 50 hectares.