Lake Titicaca, with nearly constant water temperature of 51F throughout the year, has a moderating influence on its surroindings; winter temperatures in its environs are slightly higher then those at similar altitudes elsewhere on the Altiplano. The southern areas that form the Bolivian part of the Gran Chaco have the highest temperatures in South America, with highs of over 104F and an average of 82.5F and 72F for the hottest and coolest months.
The rainy seasons lasts from approximately October to March and is longer in the north. The southwestern part of Bolivia is arid, and agriculture there is largely dependent of irrigation. The northeastern flanks of the lowlands have amount have abundant rainfall (an annual average of over 60 inches). The average annual precipitation at La Paz is 22.6 inches.
The extreme south is semiarid, with an average annual rainfall of 20 inches and frequent drought. The northern part of the eastern lowlands and the adjacent lower slopes of the Cordillera Oriental are covered by dense evergreen forests. The vegetation of the Bolivia Chaco is that of a dry savanna with scrublands, thorny bushes, and high grasses.