Environmental Degradation: Southern Brazil

A human-made drought in the Parana basin

The Río de la Plata receives its waters from two main basins, the Paraná basin made up of three sub-basins and the Uruguay river basin, which is not as extensive and has less influence on the overall hydrological balance of the Río de la Plata. which will be the subject of a separate presentation.

The macro basin of the Paraná river in turn is made up of three different sub-basins, of which there are two, which are larger in size and are determinants of the great hydrological phenomena that affect the middle and lower courses of the Paraná river and its delta.

The first is the sub-basin of the Paraguay river which is located to the northwest and which is very extensive and heterogeneous and the second is the great sub-basin of the upper Paraná that is located northeast of the macro basin and which is also very extensive and presents a relative homogeneity both ecosystem as climatic.

As we said the sub-basin of the Paraguay river occupies a wide surface and is extremely asymmetric. It is made up of two types of contributions, from two very different regions and that hydraulically behave in a radically opposite way.

On the one hand, a part of its waters come from the arid and mountainous Andes mountain range contributed by the Bermejo and Pilcomayo rivers. It is an area of ​​flows that present a great irregularity in time with increasing destructiveness as a result of a general runoff in a relatively short period of time, and fairly long periods of scarce or very few flows that give rise to severe droughts that have been their main characteristic throughout history. Another feature of the western sub-basin is its muddy waters, waters that come loaded with sediment as a result of intense erosion in its Andean headwaters. Most of the sediments contributed to the Paraná delta and the Río de la Plata come from this source.

1. 

The other half of the Paraguay basin comes from the huge, swampy and floodable ecosystem called the Gran Pantanal. This ecosystem is characterized by retaining water during the rainy season and releasing it with much more regular filtered sediment flows in the less rainy season. It is a gradual runoff and with relatively minor flow variations. Both completely different provenances compensate each other, on the one hand the fast and muddy waters of the Bermejo and Pilcomayo rivers and on the other the relatively limpid slow waters filtered by the large swamp give rise to a flow with moderate oscillations.

However, the Paraguay river basin is not the main cause of the current drought situation in the southern cone of South America.

In reality, the cause of current drought processes are concentrated in a single sub-basin. It is a very extensive hydraulic region, which is not only very important for its size, but also for the fallen rains, for the large population that inhabits it and which exceed 50 million people, or 70% of the entire population. from the Paraná river basin.

For this reason, we are going to refer above all to said sub-basin, which is the main cause of these abnormal drought episodes that are being experienced in early 2020.

The Alto Paraná basin.

There are by far the main causes of the river droughts that have been taking place in recent weeks.

As we indicated before, the alarming droughts that have occurred in recent months in the rivers of the Plata basin, the Paraná river, the Iguazú river, the Uruguay river and others have several causes and many of them are the result of the human occupation of the high basins. This phenomenon is especially widespread in the Alto Paraná basin and we should not refer to it.

Obviously, the drought worsens when the rains decrease or it simply stops raining for a long period. The rains in the upper Paraná basin are summer rains, that is, they occur between the months of December and April. If during this period it has rained little or it has not rained, potential conditions are created for the flow rates to decrease, the floodplains to dry up, navigation or the use of pumps at the intakes for urban supply or for irrigation.

But that is not the only cause of the drought, because in normal situations, what happened was that when in the dry season it rained little or it did not rain (which generally happens June to October) the flow of the rivers was anyway fed by the innumerable springs that sprouted near its banks or at the bottom of the same channels. These were and are those that maintain a base flow and prevent rivers from drying out even in major droughts.

But something happened that radically changed this dynamic.

In the last 50-60 years, hundreds of thousands of km2 of natural forests in the Alto Paraná basins were felled or burned in order to expand livestock grazing or to plant industrial crops, especially soybeans.

In order to expand the grazing and develop crops, the trees are eliminated, leaving the soil bare for a good part of the year (before planting and even a few weeks later), for this reason the surface runoff multiplies. There is much less infiltration and the layers lose a large part of their volumes stored in the rains to discharge them in the dry months. That is what happened in the upper basin of the Paraná, which has been and is the source of most of the rainwater in the Paraná and La Plata region.

Furthermore, dozens of dams were built in the same basin, some very large, 35 dams in Brazilian territory, which increased evaporation in its numerous reservoirs and were used to retain flows for the production of electrical energy and sometimes to maintain irrigation levels in irrigated crops.

All this made that when the rainy season ended, we note that this year there was little rain, and the little water that rained drained quickly giving rise to a decrease in flows in the autumn months, the effect was felt .

Especially since there were no new rains (because it was a dry season) to compensate for it.

When there is little water, the managers of the reservoirs retain the water and do not let it flow to maintain the levels and continue to produce electricity and also for other purposes, for example, for irrigation, aggravating the downstream situation.

It should not be forgotten that the rivers of the Alto Paraná are the main source of water for the entire basin,

In them there are 37 reservoirs, most of them large or very large, among which is the gigantic Itaipu dam, which is largely where it is decided how much water continues to run down the Paraná river and how much water is retained. This situation becomes even more acute when the managers of Yacyretá, the other large dam that was built downstream, also retain water for these same purposes. There are 37 large dams, if we add Yacyretá, 38, that affect the water balance of the entire upper basin and therefore indirectly the middle and lower courses of the Paraná river.

The result is a drop in levels in the middle and lower courses of the great rivers.

If we look closely at the high basin of the Paraná we observe that the Alto Paraná is formed by five great rivers: the Paranaiba river, the Grande river, the Tieté river, the Parapanema river and the Iguazú river.

All of them are large rivers, have a length of more than 800 kilometers and an average flow of more than 1000 m3 per second. They are also intensely intervened rivers. They have 37 large dams. The Tieté river has 11 dams The parapanema river 11…. The big river has 6, the paranaiba river 2, the Iguazú river 5, and in the axis of the Paraná, 2

To these are added the gigantic Itaipu reservoir on the Brazilian Paraguayan border and the huge Yacyretá dam on the border between Argentina and Paraguay.

In the Alto Paraná basin, the original vegetation prior to the Portuguese colonization was completely modified, including widespread removal of forests, hundreds of thousands of km2 burned or felled replaced by pastures or crops. This change in vegetation cover leads to a decrease in infiltration and therefore of the base flow in the channels when the rains stop). On the other hand, the reservoirs of the 37 dams generate evaporation in the reservoirs, there are 37 reservoirs with a total area of ​​several hundreds of thousands of hectares. This evaporation has a great impact. Furthermore, as these dams were built to generate electricity, when a drought occurs, the managers of the dams try to retain the little water that arrives, further reducing the lower channels.

It follows from all this that the main cause of the great drought has been and is the systematic and unnatural occupation and intervention of the rivers in the Alto Paraná basin, which incidentally is almost exclusively in Brazilian territory.

50 million inhabitants live there. Almost half of the production in all of Brazil, 37 large dams, cut rivers, dammed flows, the effect it is having is not surprising. It was expected. and finally, something that we have not talked about and will also be the subject of a future video, which is the influence of the elimination of jungles and forests on the local climate. Which surely is not minor.

In conclusion, wherever you look at it, it is an excessive occupation of the local ecosystem space, the consequences of which are beginning to be felt and which, if radical measures are not taken, will continue to worsen in the near future.