Bolivia’s climate varies dramatically from one ecoregion to another, from the tropics in the eastern llanos to a polar climate in the western Andes. Summers are hot and humid in the east and dry in the west. Precipitation often changes temperatures, humidity, winds, air pressure and evaporation, resulting in very different climates in different regions. When the climate phenomenon known as El Niño occurs, it causes major changes in weather. Winters are very cold in the west, and it snows in the mountainous regions, while windy days are more frequent in the western regions. Autumn is dry in non-tropical regions.
- Llanos. A humid tropical climate with an average temperature of 30°C (86°F). Winds from the Amazon rainforest cause heavy rainfall. In May, there is little rainfall due to dry winds and most days have clear skies. However, southerly winds, called surazos, can bring cooler temperatures that last for several days.
- Altiplano. Polar desert climate, with strong and cold winds. The average temperature is between 15 and 20°C. At night, temperatures drop drastically to just above 0°C, while during the day it is dry and solar radiation is high. Ground frosts occur every month and snow is common.
- Valleys and yungas. Temperate climate. Moist northeasterly winds are driven into the mountains, making this region very humid and rainy. Temperatures are cooler at higher altitudes. Snow occurs at altitudes of 2,000 metres.
- Chaco. Subtropical, semi-arid climate. Rainy and humid in January and the rest of the year, with hot days and cool nights.