164 THE PLAIN OF THE PAMPAS 



Patagonia, has a medium rainfall. It decreases 

 gradually from north-east to south-west. There is a 

 rainfall of 1,200 to 1,000 millimetres on the lower 

 Parana, and only 400 to 600 millimetres on the 

 western edge of the Pampa. The zone which lies 

 between the 800 millimetres and 600 millimetres 

 average is more than 270 miles in breadth. But what 

 is most characteristic of the climate of the Pampa 

 is the equal distribution of the rain throughout the 

 year, and the absence of a real dry season. In this 

 the Pampa differs from the surrounding regions, both 

 in the south-west and the north. At Buenos Aires 

 the six months of the (relatively) dry season yield, 

 nevertheless, 44 per cent, of the total rainfall, and at 

 Bahia Blanca 40 per cent. This regularity diminishes 

 in proportion as one approaches the coast. At Rosario 

 the six months of the dry season only yield 30 per 

 cent, of the year's rain ; at Villa Mercedes (San Luis 

 province) 25 per cent. When one goes beyond the 

 limits of the prairies the ratio of rain in the dry season 

 decreases rapidly ; it is only 20 per cent, at C6rdoba 

 and 18 per cent, at San Luis. At C6rdoba, the curve 

 of the rainfall indicates a typical tropical regime, 

 with a summer maximum and a very low minimum in 

 winter. Passing south-eastward from Cordoba, at 

 Bellville, Villa Maria and especially Rosario, the 

 dryness of the winter diminishes, and at the same time 

 a secondary minimum appears in the middle of summer 

 (January-February). At Buenos Aires, the form of 

 the curve changes completely. The summer minimum 

 is almost as low as the winter minimum, and most 

 of the rainfall is in the spring (September) and the 

 beginning of the autumn (March). ^ 



' Argentine Mesopotamia, which is a continuation of the Pampean 

 region from the climatological point of view, is also, even in its northern 

 part, without the rigorous dry seasons of the Chaco. Ascending the 

 Parand, from Corrientes to Posadas, just as in passing from C6rdoba 

 to Buenos Aires, one notices that the winter minimum decreases. 



