llennia. Panama is also home to Balboa Hill, which offers a view of both the Pacific Ocean and the Atlantic Ocean.
Nearly 500 rivers lace Panama's rugged landscape. Mostly unnavigable, many originate as swift highland streams, meander in valleys, and form coastal deltas. The Kampia Lake and Madden Lake (filled with water from the Río Chagres) provide hydroelectricity for the area of the former Canal Zone. The Río Chepo, a major source of hydroelectric power, is one of the more than 300 rivers emptying into the Pacific. These Pacific-oriented rivers are longer and slower running than those of the Caribbean side. Their basins are also more extensive. One of the longest is the Río Tuira which flows into the Golfo de San Miguel and is the nation's only river navigable by larger vessels.
Panama has a tropical climate. Temperatures are uniformly high—as is the relative humidity—and there is little seasonal variation. Diurnal ranges are low; on a typical dry-season day in the capital city, the early morning minimum may be 24°C and the afternoon maximum 29°C. The temperature seldom exceeds 32°C for more than a short time. The humidity however, is around 80 percent for most of the year. Temperatures on the Pacific side of the isthmus are somewhat lower than on the Caribbean, and breezes tend to rise after dusk in most parts of the country. Temperatures are markedly cooler in the higher parts of the mountain ranges, and frosts occur in the Cordillera de Talamanca in western Panama.
Climatic regions are determined less on the basis of temperature than on rainfall, which varies regionally from less than 1.3 to more than 3 meters per year. Almost all of the rain falls during the rainy season, which is usually from April to December, but varies in length from seven to nine months. The cycle of rainfall is determined primarily by two factors: Moisture from the Caribbean, which is transported by north and northeast winds prevailing during most of the year, and the continental divide, which acts as a rainshield for the Pacific lowlands. A third influence that is present during the late autumn is the southwest wind off the Pacific. This wind brings some precipitation to the Pacific lowlands, modified by the highlands of the Península de Azuero, which form a partial rainshield for much of central Panama. In general, rainfall is much heavier on the Caribbean than on the Pacific side of the continental divide. The annual average in Panama City is little more than half of that in Colón. Although rainy season thunderstorms are common, the country is for the most part outside the normal path for Atlantic hurricanes.
Panama's tropical environment supports an abundance of plants. Forests dominate, interrupted in places by grasslands, scrub, and crops. Although nearly 40 percent of Panama is still wooded, deforestation is a continuing threat to the rain-drenched woodlands. Tree cover has been reduced by more than 50 percent since the 1940s. A nearly impenetrable jungle forms the Darien Gap between Panama and Colombia. It creates a break in the Pan-American Highway, which otherwise forms a complete road from Alaska to Patagonia. Subsistence farming, widely practiced from the northeastern jungles to the southwestern grasslands, consists largely of corn, bean, and tuber plots. Mangrove swamps occur along parts of both coasts, with banana plantations occupying deltas near Costa Rica. In many places, a multi-canopied rain forest abuts the swamp on one side of the country and extends to the lower reaches of slopes in the other.
The country is divided into nine provinces, as well as several indigenous comarcas (administrative region for an area with a substantial Indian population). The provincial borders have not changed since they were determined at independence in 1903. The provinces are divided into districts, which in turn are subdivided into sections called "corregimientos." Configurations of the corregimientos are changed periodically to accommodate population changes as revealed in the census reports.
Panama had a rich Pre-Colombian heritage of n