April 2026 science summary

Hello there,

This month I've got two articles about moisture cycling and water security, and one on predicted climate change and wildfire intensity in the Pantanal.

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GLOBAL WATER SECURITY:
Posada-Marín et al. 2024 is an interesting take on water security, arguing that since 40% of originates on land (upwind, potentially out of the hydrologic basin), accounting for that reveals more vulnerabilities (Fig 3) and risks to water security (Fig 5). Some of the results in Fig 5 don't look right to me, like the Paraná seems to have the same hazard for upstream vs. upwind approach, the vulnerability goes down from an upwind perspective (to middle), but Fig 5 says its risk is very high and unchanged. But despite that, the core idea is important: without accounting for where precipitation comes from, water security cannot be assured.


PANTANAL:
In a local example of what the paper above found, Bergier et al. 2018 shows that because much of the rain that falls in the Pantanal originates via trees transpiring moisture in the Amazon, continued Amazonian deforestation could lead to a 30% decrease in rain by 2100 (relative to 1961-1990, Table 2). Their estimate of reduced "precipitable water" of 25% was a hand-wave though: they arbitrarily picked a number that was more conservative than Boers et al. 2017 (which found losing 30-50% of the forest would decrease rain in the remaining forest by 40%). In better news, they found a 3C temperature increase would only drop rainfall by 1%.

Under the most likely SSP2-4.5 climate change scenario, Neto et al. 2026 predict that extreme heat days (where daily max temp >the 90th percentile) in the Pantanal will increase from an average of 36.5 days over the last 30 years to 85.8 from 2030-2060 (a 135% increase ). And days experiencing heatwaves (six or more consecutive days of extreme heat) will increase from the recent average of 8.8 to 50.7 under SSP2-4.5 (a rise from ~1 heatwave per year to ~5-6). This in turn is likely to drive increased wildfire intensity. Fig. 9 shows the spatial pattern of warming by season (a=summer, b=fall, c=winter, and d= spring when the biggest increase is seen).


REFERENCES:
Bergier, I., Assine, M. L., McGlue, M. M., Alho, C. J. R., Silva, A., Guerreiro, R. L., & Carvalho, J. C. (2018). Amazon rainforest modulation of water security in the Pantanal wetland. Science of The Total Environment, 619–620, 1116–1125. https://doi.org/10.1016/j.scitotenv.2017.11.163

Neto, J. B. F., Shen, S., de Cássia Ramos, R., & Pereira, G. (2026). Towards a new climate regime: heatwaves proliferate and reshape seasonality in the world’s largest tropical wetland. Bulletin of Atmospheric Science and Technology, 7(1), 5. https://doi.org/10.1007/s42865-026-00122-8

Posada-Marín, J., Salazar, J., Rulli, M. C., Wang-Erlandsson, L., & Jaramillo, F. (2024). Upwind moisture supply increases risk to water security. Nature Water. https://doi.org/10.1038/s44221-024-00291-w


Sincerely,

Jon

P.s. If you look closely at the image above, you can see a big alligator chilling on the riverbank behind me. She was unconcerned by our kayaks though.