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Climate change will decrease problems with salination

Of course, too much salt in the soil is a problem. But it is not a problem which increases with climate change: If the soil is already too salty for agriculture, no climate change will make the situation worse - unused land remains unused, no loss. So I did not care about this at all.

But eventually I was provoked to care, by an argument along the line "you think more rain solves all problems, but if the soil is salty, it remains unusable". So, I cared a little bit, and it appeared that it is not at all obvious that salty soil remains unusable: The main ingredient one needs to get rid of the salt is simply more water, water which dissolves the salt and flows away, best to some ocean which is anyway full of salt.

So, ignoring the problems with salty soils, I have overseen a nice positive side effect of the predicted climate change: The predicted increase in precipitation helps to solve the problems with salty soil.

In part, this may even happen automatically, without any human intervention. Assume there is a salty lake - usually, this is a lake which has some inflow of water but no outflow because the region is too arid and the evaporation is so large that it is greater than the inflow. It follow that even if the inflow of water is not that salty at all, the salt remains in the lake. Now assume there will be much more rain, so that evaporation is no longer sufficient to get rid of that much larger inflow of new water. The water level increases, and after some time the water will flow out of the lake, creating a new (or reviving an old) river. The inflow of water will be much less salty, if it is not simply freshwater, but the outflow will be salty like the whole lake. The consequence is obvious: The amount of salt in the lake decreases. After some time, the lake will be a freshwater lake.

Similar things will happen on the ground, if the soil is salty. The rain is freshwater, it dissolves some salt, and if it flows away before evaporating, the salt content of that soil has decreased. This loss of salt will be a more serious effect than the loss of soil itself related with erosion, because the earth taken away because the speed of the water is too high will settle once the velocity decreases, so that what one region loses another one gaines. But dissolved salt will remain dissolved in the river up to the sea (with the nasty exception of water used for irrigation).

So by its very nature too much salt is also a strong indication of not enough water to wash it out. So the problem of salty soil is mainly a problem of arid regions. (And we will see below that irrigation often increases this problem.) And, on the other hand, if there is a lot of rain, enough that some of it flows away before evaporating, the problems with salt diminish, unavoidable: If rain falls onto salty soil, some of the salt will be dissolved, necessarily. If it flows away before evaporating, it takes also the dissolved salt away. There is essentially nothing one can do to prevent such a loss of salt even if one would like.

So, if the predicted increase of precipitation in the average leads to an increase of precipitation in a particular place, and if the new level of precipitation is large enough so that some part of the water flows away, the problems related with salty soil diminish almost automatically by themselves. As a consequence, in many regions where salty soil is a problem climate change will improve the situation and improve agriculture almost automatically.

But, of course, there is no reason to wait for what happens automatically. People can try to increase these positive effects. Not for free, of course, this needs some investment. But there are a lot well-known techniques for desalination of land. A good overview what one can do if the soil is too salty is given here (safety copy).

If one thinks about these methods, one can easily identify the central point:

Desalination needs water

The main ingredient one needs to get rid of the salt is water.

According to Wikipedia, "800 mm of water (or 8000 m\(^3\)/ha) is required to bring the soil salinity down to 60% of its original value in the soil layer at 40 to 60 cm depth", which is the soil layer which matters for most of agriculture.

This does not need much time. The time depends on the soil, for some soils most of the salt is already gone after two years, while for other soils may need longer time, six years or so, as can be seen in the table. The time on the properties of the soil itself, on the amount of water used for this, and how much water is contained in the soil if it is saturated.

Note also that even during such a desalination process the land does not have to remain completely unused. One can use during this period some more salt-tolerant crops.

Requirements for desalination

If desalination is done on the ground, a key point is that one needs drainage. There should be a way that the water which comes as rain water or as irrigation into the soil can, after having dissolved some salt, can flow away instead of evaporating and leaving the salt where it is.

Such drainage is useful anyway, even if the average rain is not much. Think about heavy rain events. This is something predicted to happen more often with warming. Drainage can prevent a lot of harm done to the crops by such heavy rain events, and also protect the soil from erosion. If the drainage is good enough to handle such events, then such heavy rain events will have even positive side effects for the soil - they wash out the remaining salt.

Example: Desalination of the IJsselmeer

Another quite different possibility for desalination by human influence has been realized on a large scale in the IJsselmeer in the Netherlands. This lake was initially salty, as part of the North Sea. In 1932 it was cut from the North Sea by a big dike, the Afsluitdijk, a 32 km dike connecting Friesland and Noord-Holland. After this, the inflow of water was restricted to the IJssel, a distributary of the Rhein, thus, to freshwater. On the seaside, there was only an outflow. The continued flow of riverwater flushed out the saltwater, so that it became a freshwater lake.

Later, a large part of the lake - which is now a whole province in the Netherlands named Flevoland - became a polder, that means, it was separated from the lake by dikes, and the water was pumped out, so that it became land which could be used for agriculture. If this would have been done when it was covered by saltwater, there would have remained some salt in the soil too. But once the lake was already freshwater, there was no such problem.

Preserving desalinated soil also needs water

Beyond the one-time desalination, some amount of water is also necessary to prevent a resalination. It is quite typical for irrigation in arid regions that one does not use much water, but only the amount of water necessary for the plants. In this case, salination will be a side effect. The reason is that some salt will reach the soil, simply by the wind. Moreover, there will be some salt in the water used for the irrigation too. That means, if the part of the water not used by the plants simply evaporates, the salt it contained remains, and even if that is not much salt, it becomes more with time. Roughly, to prevent such salination effect, the desalination has, in some small amount, to continue forever. So there is an amount of so-called "percolation water" (i.e. the extra amount of irrigation water on top of the crop consumptive use) required to conserve an acceptable salt balance of the soil. This amount depends on the soil as well as on the salt tolerance of the crops to be grown.

Note also that it is important that the percolation water flows away instead of evaporating on the soil itself and leaving the dissolved salt on the soil. Thus, the drainage is not only necessary during the desalination itself, but also later.

This resalination is a reason why not enough water is also a danger to those regions where agriculture with irrigation is yet possible, but where the water is nonetheless very scarce and expensive (as one has to expect in arid regions), so that people try to economize it as much as possible. The plausible result is that the water given to the soil is enough only for the plants to grow, but there is not given enough percolation water, or even none at all. Plausibly there will be also no investment in drainage, once too much water never happens. The quite predictable result is salination of the land irrigated in such a way.

What about the increase of volatility of the precipitation?

One prediction about the climate change is that the volatility of the precipitation increases. This is, of course, something negative. The point I want to make here is that for this particular problem - to get rid of the salt in the soil - an increase of volatility is not a problem at all.

The alarmists like to paint the horror picture of one extremely heavy rain leading to a flood catastrophe, and then a drought over the whole year. That this extreme horror has not much to do with reality is another question to be considered elsewhere. The only point I would like to make here is that even in this horror scenario the problem with salty soil will diminish. Why? If this heavy rain leads to a few days with everything under water, and then all this water will flow away (because stupid people have not build any infrastructure to save the water for the dry season), this will decrease the salt content of the soil quite a lot. Water needs not that much time to dissolve salt. So, a lot of it can dissolve during those few days. And, by construction, all this flows away, taking the dissolved salt away too into the direction of the ocean.

Even more funny is the point that what is an important part of the desalination technique - drainage - is what diminishes the harm of such heavy rain events too. So, investment into drainage gives higher profit - higher security against heavy rain events as well as better desalinization, which leads to more crops.

Last but not least, let's consider the situation where, on the one hand, precipitation increases, but, on the other hand, warming leads to a much higher precipitation, so that as a consequence the deficit of water even increases - in the average. But, given the much larger volatility, even in this case there may be a few heavy rains which wash out much salt, with the water flowing away, and then a large period of drought where nothing happens. So even this combination of two negative effects - increased evaporation and increased volatility - may not be sufficient to destroy the positive effects for the salt content of the soil.

Will the washing out of salt upstream increase the salinity of river water downstream?

One could imagine the other side of the effect that more rain is washing out the salt upstream. That means, the salt is flowing down the river. Maybe the water in the river becomes more salty if there is more rain, once more salt will be washed out? No. Simply the amount of additional water pouring down is greater than the additional amount of solved salt.

While this is also what common sense tells us, we can rely here also on explicit observations:

The amount of water flowing into the Sacramento and San Joaquin river delta is the single most important determinant of salinity at the export pumps, and the amount of inflow has been shown to be largely determined by hydrology. During rainy years, the average salinity at the pumps is low. The average electrical conductivity – a measure of salinity – at the banks pumping plant for the 1983 water year (one of the rainiest on record) was 276 lS/cm, corresponding to 431 mg/L. In the critically dry 1991 water year, electrical conductivity at the same location averaged 589 lS/cm, corresponding to 920 mg/L.
Vineis, P., Chan, Q., Khan, A. (2011). Climate change impacts on water salinity and health. J. Epidemiology and Global Health 1, 5-10

Are there some other salination problems caused in some way by climate change?

In principle, yes.

So, in principle, the expected rise of the sea level can lead to an increase of salination in the delta of rivers. This would matter only if people do nothing to defend their land against the rising sea level with dikes and dams. This is certainly possible, as discussed here.

Then, there will be some regions where, despite the increase of precipitation in the average, precipitation decreases. And, together with such a decrease in precipitation, there will be also all the related problems, inclusive salination problems. But, of course, these regions are exceptions once the average predicts more precipitation. Alarmists, of course, like to present the situation as if, despite more precipitation in the average, there are even larger regions where will be less precipitation than those where precipitation increases. In reality, these regions will be simply mentioned much more often in the mass media.

The alarmists also try to mingle salination problems caused by human behavior with problems caused by global warming. These are, essentially, only manipulations, but they often go unnoticed. If one writes, say, an article titled "Climate change impacts on water salinity and health", nothing prevents one from discussing a lot of salitation problems which are completely human-made and have no relation to climate change impact at all.

The fresh water stream dropped off significantly in the Padma since India commissioned the Farakka Barrage in 1975.
...
Another element that contributes to increasing salinity inland is shrimp farming – a rapidly developing business – whereby salt water is deliberately retained in ponds to cultivate shrimp.
Vineis, P., Chan, Q., Khan, A. (2011). Climate change impacts on water salinity and health. J. Epidemiology and Global Health 1, 5-10

In priniciple, one cannot object to this, last but not least a scientific paper has to discuss everything, and if one would like to distinguish the impact of climate change from that of other human influence on salination one would have to consider both.

Unfortunately, this simplifies the job of the alarmists, once they can cite parts of the paper out of that context, and present them as if they describe real harm caused by climate change.

Let's see how this works, starting with another quote from this paper:

In Australia with the removal of the natural vegetation, the amount of water entering the water table (called the recharge) has increased and the rising groundwater level has dissolved the accumulated salt within the soil. Eventually (after many decades), the groundwater level reaches the surface, bringing the salt with it. This results in the death of all but the most salt-tolerant plants with consequent changes to other parts of the ecosystem.
Vineis, P., Chan, Q., Khan, A. (2011). Climate change impacts on water salinity and health. J. Epidemiology and Global Health 1, 5-10

What caused this removal? Climate change or human activity? This is not obvious, but one can look into the article referenced there:

It has been highly modified by human activities over the 20th century in the form of large-scale clearing for agriculture leaving only small fragments of native vegetation (Hobbs, 1993). The replacement of deep-rooted native perennial vegetation with shallow-rooted annual crops and pastures has caused water tables to rise, resulting in water logging, dissolution of salts in the soil profile, and movement of these salts to the soil surface.
Jardine, A., Speldewinde, P.C., Carver, S., Weinstein, P. (2007). Dryland Salinity and Ecosystem Distress Syndrome: Human Health Implications. EcoHealth 4, 10-17

So, it was human behavior which caused the problem. In fact, the main mechanism of salination in such areas is irrigation, as described above: Given that water is deficit, one gives only as much water as necessary for the plants. That means, a large part of the water used for irrigation evaporates, leaving its salt content on the ground, and the remaining water is not sufficient to wash it away. Nonetheless, the mechanism mentioned in that article also explains some part of the problem: Plants with deep roots use deep water, removing them leaves that water unused, and the water table grows.

Now imagine some alarmist quoting the original paper in the following way:

... rising groundwater level has dissolved the accumulated salt within the soil. Eventually (after many decades), the groundwater level reaches the surface, bringing the salt with it. This results in the death of all but the most salt-tolerant plants with consequent changes to other parts of the ecosystem.
Vineis, P., Chan, Q., Khan, A. (2011). Climate change impacts on water salinity and health. J. Epidemiology and Global Health 1, 5-10

A nice horror scenario? Certainly.

And it even sounds plausible. Climate change predicts more precipitation, and more precipitation will cause an increase of the groundwater level. And what happens as a consequence - see the quote.

Except that the rise of the groundwater level will have such negative consequences only in quite exceptional circumstances. But what is more important, this mechanism does not increase the flow of water - the level rises because less of the water is taken away by plants with deep roots. The same holds for irrigation: Irrigation may increase the flow a little bit, but this part is intentionally quite small - it is, last but not least, an economic loss. The gain of salt from evaporating water will be greater. If the rise of the groundwater is, instead, caused by more rain, the reason for the rise is different, the increase comes from additional rain water coming down, so that the flow increases. This increase in the flow of water will take away also some salt.

Moreover, the removal of the deep-rooted plants is a one-time effect. It was in this case caused by humans. But even if global warming effects would cause them, by less precipitation in a given region (contrary to more precipitation in the average), it would remain a one-time effect. The positive effects of washing out salt are, instead, permanent effects: If there is enough water flowing away, there will be a permanent loss of salt, and if this loss is greater than the gain caused by evaporating irrigation water, the soil becomes less salty with time.

Last but not least, the regions where the loss of salt by precipitation flowing away is greater than the gain by evaporating irrigation water or salty dust are necessarily quite arid regions. Thus, this would be not a big loss for agriculture anyway.

Summary:
Climate change helps to solve problems with salty soils

To summarize, with salination we have found a problem which does not increase with climate change, but where climate change may help to solve them.

The prerequisite for solving problems with salination is that in an arid region with salty soil climate change leads to an increase of precipitation. Once climate change predicts that in the average the precipitation will be higher, it seems quite plausible that this will happen in a lot of such regions.

Of course, it does not follow from the average prediction that there will be more rain everywhere. It is quite plausible that some parts of the Earth will become even more arid than now. One should not forget that with temperature evaporation increases too, so that even with more rain the aridity can increase locally if the evaporation increases even more. Last but not least, how the patterns of the rainfall will change is hard to predict.

Nonetheless, the averages tell us what we can expect as a typical change, and what, instead, will happen seldom, as an exception. So, we have to expect that in a lot of arid regions with salty soil there will be more rain, thus, more water, the main ingredient for getting rid of the salt. So, existing problems with salt will not be able to prevent the agricultural use of former arid land where an increase of precipitation solves the problem with missing water for the plants. Instead, the greater amount of water will help to solve problems with salty soil.