I am not so sure that La Nina anomalies will increase over time. I also don't know if you mean the SST anomalies of La Nina, or the weather patterns associated with La Nina. As far as what we can expect regarding predictable La Nina weather patterns, nothing will change quickly, on average, even as the climate may slowly change (mainly global warming). It is inconclusive whether ENSO behavior, in terms of SST patterns, will change as the overall climate slowly changes. There are projected changes in the average temperature and precipitation for the next 50 years, according to the climate change models, and one might suppose that those might be additional to the "normal" patterns associated with today's La Nina events. Or, the climate change patterns might interact with the ENSO patterns in a more complicated way, where we could not just add one to the other. All of these possible long-term outcomes are not clear currently, because different models handle it in different ways. But I think it's fairly safe to assume, for now, that in the near future (the next, say, 15-20 years) the temperature and rainfall patterns associated with La Nina will remain approximately the same as they are currently, based on historical data and our current climate models (not the climate change models). Even without cllimate change, the average climate effects of La Nina (or El Nino) are not expected to appear the same way in every La Nina, and in some regions the expected effects sometimes may not occur at all.