high of and a low of in Artigas confirm the milder winters in northwestern Uruguay, but even here temperatures have dropped to a subfreezing . Rainfall is fairly evenly distributed throughout the year, and annual amounts increase from southeast to northwest. Montevideo averages annually, and Artigas receives in an average year. As in most temperate climates, rainfall results from the passage of cold fronts in winter, falling in overcast drizzly spells, and summer thunderstorms are frequent. High winds are a disagreeable characteristic of the weather, particularly during the winter and spring, and wind shifts are sudden and pronounced. A winter warm spell can be abruptly broken by a strong pampero, a chilly and occasionally violent wind blowing north from the Argentine pampas. Summer winds off the ocean, however, have the salutary effect of tempering warm daytime temperatures. Land use and settlement patterns Uruguay may be divided into four regions, based on social, economic, and geographical factors. The regions include the interior, the littoral, Greater Montevideo, and the coast. The interior This largest region includes the departments of Artigas, Cerro Largo, Durazno, Flores, Florida, Lavalleja, Rivera, Salto, Tacuarembó, and Treinta y Tres and the eastern halves of Paysandú, Río Negro, and Soriano. The topsoil is thin and less suited to intensive agriculture, but it nourishes abundant natural pasture. Only 2 to 3% of Uruguay's land is forested. An estimated 30,000 to (17 to 23% of the total land) are arable, but only one-third of this (about 7% of the total productive land) was cultivated in 1990. Almost all of the interior consisted of cattle and sheep ranches; pasture accounted for 89% of the country's productive land. Sheep rearing was typically undertaken on medium-sized farms concentrated in the west and south. It began to boom as an export industry in the last quarter of the 19th century, particularly following the invention of barbed wire, which allowed the easy enclosure of properties. Uruguayan wool is of moderate quality, not quite up to Australian standards. Cattle ranches, or estancias, for beef and hides were typically quite large (over 10 km²) and were concentrated in the north and east. Dairying was concentrated in the department of Colonia. Because ranching required little labor, merely a few gauchos, the interior lacked a peasantry and large towns. Despite being sparsely populated, however, the interior was relatively urbanized in that the capital of each department usually contained about half