Bolivia - Climate

Although Bolivia is located entirely within the tropics, the large altitude variations within the country imply that it has almost every conceivable type of climate ranging from Andean glaciers, via salt deserts, to steaming rainforest. Bolivia is a very heterogeneous country both with respect to climate and with respect to development. Some regions have extremely harsh climates with sub-zero temperatures most of the year and very little rain. Other regions are hot and constantly humid. Some people live in remote areas without road access in simple one-room dwellings without electricity, piped water, bathroom, or any other basic conveniences. Other people live in mansions with home cinema, swimming pool, fitness room, and servants.

The “normal” climate in Bolivia includes tremendous climate variability with either El Niño or La Niña conditions almost every year. If each of these events causes losses of 3- 4% of GDP, they make all the difference between a country growing steadily towards prosperity and a country permanently stuck in poverty. Vulnerability has clearly been reduced since the devastating El Niño episode of 1982-83, but further steps to reduce vulnerability are still necessary.

Contrary to expectations, and contrary to the predictions of most General Circulation models, this evidence shows a consistent cooling trend of about 0.2ºC per decade over all highland areas, and only slight, scattered evidence of warming in the lowland areas. No systematic trends in precipitation were detected, only decade-long cycles. The colder winters in the already cold highlands could potentially have an adverse effect on the predominantly poor and indigenous population who inhabit the Bolivian highlands, since one of their main worries and limitations on agricultural productivity is frost.

Since the predominantly poor and indigenous population in the highlands experienced a negative effect due to recent cooling and the much richer population in the lowlands experienced slightly positive effects of modest warming, the overall effect of recent climate change would be an increase in inequality between Bolivian municipalities and an increase in poverty. Places where temperatures oscillate close to the freezing point inherently have more unpredictable weather than places which are consistently hot and humid, and temperature variations close to zero have more severe consequences. The modest impacts of climate change (the slow, systematic changes in average temperature and precipitation) do not preclude large impacts from climate variability

Bolivia's glaciers, situated between lat 14°37' and 18°23' S. on the southern edge of the tropical zone of the Southern Hemisphere, are affected by the change between intertropical circulation in the summer and southeast trade winds in the winter. During the southern summer, this generally means precipitation that decreases in amount and duration from north to south. Some believe that the term "summer" is appropriate for the rainy season in Bolivia, in contrast to the central tropics of Venezuela, Colombia, and Ecuador, even though others give a different view. Inhabitants of these countries, however, seldom refer to summer or winter; they speak of dry and rainy seasons. The dual climatic situation and the orientation and elevation of its mountain ranges are the determining factors in the occurrence and distribution of Bolivia's glaciers.

Because of the year-round high position of the Sun in the tropics, north-south exposure differences are less apparent than they are outside the tropics. In the Southern Hemisphere, the effect of the Sun increases in importance toward the south, however, and the cycle of cloud formation during the day must then be taken into consideration with respect to the exposure differences that affect the mass balance of a glacier. Because cloud cover descends very regularly at night to a level of 3,500 to 4,000 m, the glaciers are fully exposed to the morning Sun even during the rainy season. The cloudiness that develops during the forenoon protects the glaciers from radiation during the rest of the day. Because the Sun shines on the eastern slopes in the early morning and because the northern slopes have greater solar radiation in the Southern Hemisphere, the east-to-north slope exposures have comparably smaller glacierization. The snowline is lower on the western and southern slopes and rises substantially (100 to 300 m) on the eastern and northern slopes. The solar-radiation effect increases toward the arid regions to the south. Combined with the extreme dryness of the air, solar radiation produces a peculiar phenomenon on firn and glacier surfaces, the intensified development of snow and ice penitents.

The patterns of warming/cooling show a distinct geographical distribution, with the highland stations in the southwestern part of Bolivia showing consistent cooling, and the lowland areas to the north and east showing slight warming. This is consistent with NCDC data from neighboring countries, which show cooling in many parts of Peru and Chile but warming in Brazil.

The general cooling of the highlands appears to be inconsistent with the rapid melting of several Bolivian glaciers (especially the Chacaltaya and the Zongo glaciers close to El Alto), but it is not. First of all, the glaciers have been melting continuously since the Little Ice Age (about 1550 to 1850), with only a brief slowdown during the relatively cool period of 1950-1980, and it is normal for melting to accelerate towards the end (just like a small ice cube melts faster than a big ice cube). In addition, glaciers depend on other factors than temperature, notably precipitation, but also cloud cover, relative humidity and the intensity of solar irradiation. A study of oxygen isotope series generated from ice cores from two Bolivian glaciers suggests that precipitation has decreased steadily since about 1974.

The reduction in precipitation is likely associated with the general reduction in cloud cover over the tropics since measurements began in the early 1980s, and less clouds means more intense solar irradiation, which accelerates glacial melt. Decreased cloud cover at this altitude also works to amplify the diurnal temperature range, increasing daytime temperatures (which would cause increased melting), but reducing night-time temperatures even more (because of the missing cloud-blanket), which explains the reduction in average temperatures.

These glaciers are sensitive to changes in summer temperatures and precipitation. This explains why the ENSO (El Niño-Southern Oscillation) has such a strong effect on Bolivian glaciers. During ENSO’s warm and dry phase (El Niño), the mass balances are always negative, implying shrinking glaciers. In the cooler and more humid La Niña phase, the glaciers return to equilibrium and sometimes show a small increase. The increase in the glacier regression rate since the end of the 1970s appears to coincide with the Pacific shift of 1976, the date after which the El Niño event became more frequent and more intense. It was the unusually strong El Niño event of 1997/98, which caused the permanent closing of the World’s highest ski-resort on the Chacaltaya glacier.

Bolivia's government declared a state of emergency 21 November 2016 due to water shortages in large swaths of the country amid the worst drought in 25 years, making funds available to alleviate a crisis that has affected families and the agricultural sector. Bolivia's Vice Ministry of Civil Defense estimated that the drought has affected 125,000 families and threatened 290,000 hectares of agricultural land and 360,000 heads of cattle. President Evo Morales called on local governments to devote funds and workers to drill wells and transport water to cities in vehicles, with the support of the armed forces, from nearby bodies of water. The drought prompted protests in major cities and conflicts between miners and farmers over the use of aquifers.