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Paraguay - Climate

Paraguay experiences a subtropical climate in the Paranena region and a tropical climate in the Chaco. Paraguay is open to dry, cold polar winds from the south and to hot, humid north winds from southwestern Brazil; sudden sharp drops in temperatures are not uncommon. During the winter months (roughly May through August), temperatures generally range from 16° to 21°C (60° to 70°F). During the summer (October through March), temperatures range from about 25° to 38°C (77° to 100°F), with extremes of 43°C (109°F) and above in the west.

Rainfall in the Paraneña region is fairly evenly distributed. Rain usually falls when tropical air masses are dominant. The least amount of precipitation is in August, when averages in various parts of the region range from two to ten centimeters. The most amount of precipitation falls during the months of March through May and October to November.

The Chaco region experiences seasons that alternately flood and parch the land. Rainfall is light, varying from 50 to 100 centimeters (20 to 40 inches) annually, except in the higher land to the northwest where it is somewhat greater. Rainfall is concentrated in the summer months, and extensive winter deserts become summer swamps.

Deforestation is a concern in Paraguay, about a third of the nation’s forests and woodlands has been lost. The absence of trees contributes to the loss of soil through erosion. Another environmental issue is water pollution. Many of the country’s rivers suffer from toxic dumping. Tanneries are particularly harmful, releasing mercury and chromium into rivers and streams. Runoff from toxic chemicals used by farmers also seeps into Paraguay’s waters. Out of the nations 94 cu km of renewable water resources 78 percent is to support farming, and 7 percent is used for ind strial purposes. About 93 percent of the city dwellers and 59 percent of the rural people have access to pure drinking water.

The Paranena region is humid, with abundant precipitation throughout the year and only moderate seasonal changes in temperature. During the Southern Hemisphere's summer, which corresponds to the northern winter, the dominant influence on the climate is the warm sirocco winds blowing out of the northeast. During the winter, the dominant wind is the cold pampero from the South Atlantic, which blows across Argentina and is deflected northeastward by the Andes in the southern part of that country. Because of the lack of topographic barriers within Paraguay, these opposite prevailing winds bring about abrupt and irregular changes in the usually moderate weather. Winds are generally brisk. Velocities of 160 kilometers per hour have been reported in southern locations, and the town of Encarnacion was once leveled by a tornado.

The Paranena region has only two distinct seasons: summer from October to March and winter from May to August. April and September are transitional months in which temperatures are below the midsummer averages and minimums may dip below freezing. Climatically, autumn and spring do not really exist. During the mild winters, July is the coldest month, with a mean temperature of about 18°C in Asuncion and 17°C on the Parana Plateau. There is no significant north-south variation. The number of days with temperatures falling below freezing ranges from as few as three to as many as sixteen yearly, and with even wider variations deep in the interior. Some winters are very mild, with winds blowing constantly from the north, and little frost. During a cold winter, however, tongues of Antarctic air bring subfreezing temperatures to all areas. No part of the Paranena region is entirely free from the possibility of frost and consequent damage to crops, and snow flurries have been reported in various locations.

Moist tropical air keeps the weather warm in the Paranena region from October through March. In Asuncion the seasonal average is about 24°C, with January—the warmest month—averaging 29°C. Villarrica has a seasonal mean temperature of 21°C and a January mean of 27°C. During the summer, daytime temperatures reaching 38°C are fairly common. Frequent waves of cool air from the south, however, cause weather that alternates between clear, humid conditions and storms. Skies will be almost cloudless for a week to ten days as temperature and humidity rise continually.

As the soggy heat nears intolerable limits, thunderstorms preceding a cold front will blow in from the south, and temperatures will drop as much as 15°C in a few minutes. Rainfall in the Paranena region is fairly evenly distributed. Although local meteorological conditions play a contributing role, rain usually falls when tropical air masses are dominant. The least rain falls in August, when averages in various parts of the region range from two to ten centimeters. The two periods of maximum precipitation are March through May and October to November.

For the region as a whole, the difference between the driest and the wettest months ranges from ten to eighteen centimeters. The annual average rainfall is 127 centimeters, although the average on the Parana Plateau is 25 to 38 centimeters greater. All subregions may experience considerable variations from year to year. Asuncion has recorded as much as 208 centimeters and as little as 56 centimeters of annual rainfall; Puerto Bertoni on the Parana Plateau has recorded as much as 330 centimeters and as little as 79 centimeters.

In contrast to the Paranena region, the Chaco has a tropical wet and- dry climate bordering on semi-arid. The Chaco experiences seasons that alternately flood and parch the land, yet seasonal variations in temperature are modest. Chaco temperatures are usually high, the averages dropping only slightly in winter. Even at night the air is stifling despite the usually present breezes. Rainfall is light, varying from 50 to 100 centimeters per year, except in the higher land to the northwest where it is somewhat greater. Rainfall is concentrated in the summer months, and extensive areas that are deserts in winter become summer swamps. Rainwater evaporates very rapidly.