The great droughts of 1924-25 and 1968-69 in the argentinean central andes. Impacts and responses

PRIETO M. R.; ARANEO D. C.; VILLALBA R.

Mendoza

Congreso; CONGREMET XI; 2012

Centro Argentino de Meteorólogos

Although the drought frequency has not increased in the Andes Cordillera in the last 100 years, the hazard has increased for the population of the province of Mendoza, Argentina, if having to deal with such an event. This because of the biggest water demand for domestic consumes, watering and energy production. Another important factor to consider is the extraordinary glaciers recession in the same time lapse. The goal of the present work has been the study of two events of extreme drought through historic documentation, meteorological records and tree rings. We also point at the most relevant historic droughts through newspaper data and tree rings, analyzing the overflow of the Atuel, Tunuyan, Mendoza and San Juan rivers between 1906 and 2004 and their standardized flow volume. We compared both situations. The first one, 1924-25 with a population scenario relatively scarce, a reduced fresh water net, a limited use of energy only for public lights, transport (the tramway), wineries functioning and domestic use, even though with an intensive use for watering. The second one, 1968-69, with a noticeable population growth, wide fresh water net, generalized use of the hydroelectric energy and similar use of artificial watering. Through them we have been able to appreciate the significant impact the lack of water produced in the spring-summer period of those years and what it meant for a province such as Mendoza, which agricultural, economic and daily life depends on the flow volume of those rivers originating in the oriental slope of the Andes Cordillera. We analyze the critical situation posed by the newspapers in both periods. The first one characterized by the poor snowfall and the second one because of the scarce snow in the cordillera, in addition to the low temperatures that did not allow for the glacier fusion during the spring of those years. In both cases this resulted in a decrease in the flow volume of the province rivers and of the phreatic layer, with the resulting watering problems for agriculture and, domestic and industrial consume. In 1968-69 the problem became more acute with the scarce energy given the lack of water in the Atuel river, so much so that a lake formed by the fusion of the glaciers contributing to this river was dynamited. We examined the consequences of the lack of water through the local newspapers (Los Andes journal) plus economic and energetic data from the Dirección de Estadísticas of the Province of Mendoza. We have taken into account the following variables: surface and subterranean water resources, impact over the wetlands environment, the agricultural production and the population. The analysis of the winter atmospheric circulation for the 1924-25 event shows an anomalous intensification of the westerlies flow south of 40°S and of the Pacific anticyclone between 30°and 35°S, which would be associated to a decrease in the frequency and intensity of the storms coming from the Pacific towards the region, thus the storms would be forced to transit through major latitudes. In addition, the seas adjacent to the south American coasts presented strong negative temperatures anomalies that would contribute to the local stabilization of the atmosphere inferior layers, with increase and inhibition of the humidity contribution. In the case of 1968-69, the circulation presents similar characteristics but with the systems run around 10° latitude to the south and a marked intensification of the Atlantic anticyclone. This leaves the study region affected by a strong anomalous flow of the east that would aggravate even more the drought conditions. We concluded that both droughts were strong intensity and complexity events, even though derived from different atmospheric circulation patterns, which influenced in the agricultural demand for watering and the daily water use in Mendoza. Similar dry cycles occurred in previous decades did not have the journalistic repercussion that this phenomenon reached during those years (38 and 35 mentions respectively). For the 1924-25 drought the press limited itself to point at the lack of water for agriculture and domestic consume and the failure to deliver water in the departments of Mendoza. On the contrary, the impact in 1968-69 was larger given that the population was three times more in relation to 1924. Besides, because in 1958 when the first hydroelectric plant over the Atuel River begun working, the energy in Mendoza was only obtained through thermal generation and through small hydroelectric plants. The local press talked about the decrease in the rivers flow volume in both years. In the months of November and December of 1968 because of the problems related with hydroelectric energy generation. In January, February and March of 1969 the press comments were on the effects of the scarce water over the agricultural production, undergoing a decrease between 30% and 40% globally that year. This leads to wonder what would the consequences presently be when facing a scenario like the above described, considering that although the cultivated surface has remained more or less constant, the Mendoza population has more than duplicated in respect to 1968. Plus, the demand for electric energy for domestic and industrial consume is considerably bigger, all of which drive us to pose that the vulnerability of the Mendoza inhabitants has also increased exponentially. This study will be useful in face of the possible repetition of the phenomenon, as consequence of the global climatic change, for developing preventive work and political actions allowing for the prevention and alleviation of its effects.