May 2025 science summary

Merry May,

This month I've got four articles on freshwater, plus one on whether climate mitigation can be harmful to wildlife if done wrong (spoiler: yup).

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FRESHWATER:
Petry et al. 2025 has predictions of changing streamflow and flooding across South America by 2100 under a moderate climate change scenario. Figure 4 has the key findings about how much more or less frequent floods may be. Note that “RP” means “return period” as in a “5 year flood” or “100 year flood” (the magnitude of flooding you’d expect on that frequency / rarity, so higher numbers mean more severe flooding). RPCF means how much more or less frequent those floods would be (with negative sign indicating less frequent flooding, e.g. the -2 on the Paraguay river in the Pantanal means half as often). But much more flooding is expected in Peru, Ecuador, Colombia, and Southern Brazil, and parts of the Amazon will see 1/10 as much flooding as they historically have. They find Pantanal floods (in the Paraguay River and some tributaries like Cuiaba and Negro) will be roughly half as frequent and half as severe, they don’t have a clear trend in the Chaco, and in Chile the area from roughly Santiago to Valdivia has some rivers where flooding will be ~2-3 times less frequent while the northern part of Chile will only see slightly less flooding.

Lehner et al. 2024 is a summary of a new "Global Dam Watch (GDW)" open dataset of 41,000 river barriers and 35,000 reservoirs (see Fig 1 for a map). While national and regional datasets are more complete (e.g., NID has 90k points in the US, AMBER has 630k in Europe), this is the most comprehensive free global dataset (see Table 2) and it includes estimated reservoir volumes mostly for reservoirs >10 km2.

Cho et al. 2023 did a ton of modeling (Fig 7) to estimate how conservation (mostly reforestation along streams) could have affected the water supply of São Paulo. They found the increased habitat could serve as an "invisible reservoir" for water in soil, and in a highly idealized scenario (lots of new forest in all the right places among others) streamflow could be boosted by 33% (and drought costs reduced by 28%). They don't report numeric results for their less ideal scenarios, and all scenarios exclude the water consumption of growing trees. In a conversation with one of the study's authors, they mentioned that it likely took about 30 years (I think) for the "water savings" of nature (fog capture plus slowing down runoff during high rain events) to outweigh the water consumption of growing trees. In other words, in this case in the short term adding trees could result in lower streamflow even though in the long run it would increase streamflow. Understanding the timeline and tradeoffs is key so people who live there know what to expect. From chatting w/ other hydrologists about this, it's clear that results like this vary a lot depending on things like soil type, weather and climate, type of forest, and much more. There's an article about this one at https://www.nature.org/en-us/about-us/where-we-work/latin-america/brazil/stories-in-brazil/invisible-reservoir/

Pompeu 2025 quantitatively models how different drivers have impacted total water surface area (as a decent proxy for total flow / water quantity) in the Pantanal. The paper found the biggest driver of water level was 1) the presence or absence of having natural vegetation at least 50m around springs, followed by 2) natural veg riparian buffers along rivers (buffer width increasing w/ river width as per the Forest Code), followed by 3) replacing conventional monoculture ag w/ something w/ deeper root systems (agroforestry, permaculture, full restoration if feasible, etc.), followed by 4) preventing more dams.


CLIMATE MITIGATION AND WILDLIFE:
Smith et al. 2025 asks what the net impact of climate mitigation on land (including bioenergy crops, reforestation, and afforestation) is on the total habitat area for 14,000 vertebrate species. Fig 1 summarizes the idea well - climate change can reduce suitable habitat, but climate mitigation can also either add or remove habitat directly. Fig 4 has their global recommendations - basically leave most ecosystems alone, reforest several areas (SE Asia, Eastern US, Mexico, and much of Europe) and in a few tiny places grow bioenergy crops. In other words, typically planting trees on grasslands or other habitat types destroys more habitat than it saves through climate mitigation. But planting trees in cleared forests is a win-win.


REFERENCES:
Cho, S. J., Klemz, C., Barreto, S., Raepple, J., Bracale, H., Acosta, E. A., Rogéliz-Prada, C. A., & Ciasca, B. S. (2023). Collaborative Watershed Modeling as Stakeholder Engagement Tool for Science-Based Water Policy Assessment in São Paulo, Brazil. Water, 15(3), 401. https://doi.org/10.3390/w15030401

Lehner, B., Beames, P., Mulligan, M., Zarfl, C., De Felice, L., van Soesbergen, A., Thieme, M., Garcia de Leaniz, C., Anand, M., Belletti, B., Brauman, K. A., Januchowski-Hartley, S. R., Lyon, K., Mandle, L., Mazany-Wright, N., Messager, M. L., Pavelsky, T., Pekel, J.-F., Wang, J., … Higgins, J. (2024). The Global Dam Watch database of river barrier and reservoir information for large-scale applications. Scientific Data, 11(1), 1069. https://doi.org/10.1038/s41597-024-03752-9

Petry, I., Miranda, P. T., Paiva, R. C. D., Collischonn, W., Fan, F. M., Fagundes, H. O., Araujo, A. A., & Souza, S. (2025). Changes in Flood Magnitude and Frequency Projected for Vulnerable Regions and Major Wetlands of South America. Geophysical Research Letters, 52(5). https://doi.org/10.1029/2024GL112436

Pompeu, J. (2025). Cross-Boundary Drivers of Water Cover Reduction in the Pantanal Wetland and Implications for its Conservation. Wetlands, 45(3), 32. https://doi.org/10.1007/s13157-025-01916-w

Smith, J. R., Beaury, E. M., Cook-Patton, S. C., & Levine, J. M. (2025). Variable impacts of land-based climate mitigation on habitat area for vertebrate diversity. Science, 387(6732), 420–425. https://doi.org/10.1126/science.adm9485


Sincerely,
 
Jon

p.s. This is a sea lion lazing about in Valdivia who happened to yawn as I was watching them.

June 2019 science journal article summary

I'm still not doing great with having a coherent theme; this month includes articles on biodiversity, remote sensing, dams, and coastal wetlands. The picture above is the first butterfly I've seen in my butterfly garden this year, eating from the first milkweed flower to open. After reading Sánchez-Bayo & Wyckhuys you may want to plant some too! If you know someone who wants to sign up to receive these summaries, they can do so at http://bit.ly/sciencejon


BIODIVERSITY:
The U.N.'s Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) released a summary of a major report in May describing global biodiversity loss and extinctions (Diaz et al. 2019). The short version is "nature is in trouble, and so are we as a result." The most reported estimate is that about 1 million species face extinction (many within decades) unless we act to prevent that. I'd recommend looking at the policy summary and at least reading the bold headlines to get a bit more of the key findings. A few others worth highlighting include: declines in crop and livestock diversity is undermining agricultural resilience, drivers of change in nature (e.g. land use, direct exploitation, climate change, pollution, and invasives) are accelerating, goals like the Aichi Biodiversity Target and the 2030 Agenda for Sustainable Development cannot be met without major transformative changes (changes which are possible, albeit challenging), the parts of the world where declining nature is expected to hit people the hardest tend to be poor and/or indigenous communities, international cooperation to build a more sustainable global economy will be key to solve this problem, addressing the sustainability of food will also be important, and land-based climate solutions (e.g. bioenergy plantations and afforestation) have some tradeoffs. Many of these are obvious; the summaries under each headline often include useful detail, but there's too much to summarize at this level. So skim through and dive into the topics that pique your interest.

Sanchez-Bayo & Wyckhuys 2019 looks across 73 studies of insect decline from cross the world, and look at the drivers and other commonalities. A key limit of the paper is that they excluded any study that did NOT show a chance in abundance or diversity, so it's utility is limited to explaining declines where they have happened (see section 4.1). The take-away is that habitat loss seems to be the primary driver (~50% of declines), followed by 'pollution' (~26%, mostly pesticides and fertilizer), then disease and invasive species (18%) and climate change (7%). That means a sole focus on pesticides will miss key drivers of the problem. Figure 3 has a breakdown by taxonomic order, highlighting that dung beetles are in real trouble.


REMOTE SENSING:
Raber and Schill 2019 is a methods paper describing their use of a cheap (<$5k) floating semi-autonomous drone to capture mm-scale 3D imagery of shallow coral reefs. The idea is to be able to track fine scale changes over time in coral more cheaply and accurately than using divers. They note that GPS accuracy was a problem but since the paper was written the authors have added a low cost RTK GPS at the nearest coast to solve that. The paper has lots of detail for anyone interested in trying it.

Pettorelli et al. 2018 is an overview of remote sensing of ecosystem functions (as opposed to the more commonly measured structure and composition). It's a good read, but for most people I'd recommend skipping to table 3 for an overview of existing sensors and data products that can map proxies of ecosystem function, and table 4 for some new and upcoming sensors and products.


DAMS:
Ezcurra et al. 2019 looks at how dams impact sediment transport in tropical estuaries, by comparing two undammed rivers to two dammed ones (see Fig 2 & 3 for a visual summary). They found that the coastal erosion due to dams leads to environmental impacts (fisheries decline, lost coastal protection, GHG emissions from eroded sediment, biodiversity loss) that may exceed the benefits of hydroelectric production on avoided GHG emissions. However, several assumptions in the paper are problematic (e.g. all eroded sediment is lost to the atmosphere as CO2 or methane), and likely pull towards overestimating the impacts. I'd focus more on the coastal changes than the potential implications.


COASTAL WETLANDS / BLUE CARBON:
Rogers et al. 2019 finds that coastal wetlands experiencing relative sea level rise (via either sea level rise or subsiding sea floor, or even sediment compaction and decomposition) sequester and store more soil carbon. They looked at relative levels over the last 6,000 years and how it related to soil carbon at different depths, as well as a site in Australia where there was rapid relative sea level rise in the last few decades. Their explanation is that as sediment accumulates, without relative sea level rise, the space available for vegetation shrinks, and thus organic sediment accumulates more slowly.


REFERENCES:
Ezcurra, E., Barrios, E., Ezcurra, P., Ezcurra, A., Vanderplank, S., Vidal, O., … Aburto-Oropeza, O. (2019). A natural experiment reveals the impact of hydroelectric dams on the estuaries of tropical rivers. Science Advances, 5(3), eaau9875. https://doi.org/10.1126/sciadv.aau9875

Díaz, S., Settele, J., Brondízio, E., Ngo, H. T., Guèze, M., Agard, J., … Zayes, C. (2019). Summary for policymakers of the global assessment report on biodiversity and ecosystem services-unedited advance version. Retrieved from https://www.ipbes.net/news/ipbes-global-assessment-summary-policymakers-pdf

Pettorelli, N., Schulte to Bühne, H., Tulloch, A., Dubois, G., Macinnis-Ng, C., Queirós, A. M., … Nicholson, E. (2018). Satellite remote sensing of ecosystem functions: opportunities, challenges and way forward. Remote Sensing in Ecology and Conservation, 4(2), 71–93. https://doi.org/10.1002/rse2.59

Raber, & Schill. (2019). Reef Rover: A Low-Cost Small Autonomous Unmanned Surface Vehicle (USV) for Mapping and Monitoring Coral Reefs. Drones, 3(2), 38. https://doi.org/10.3390/drones3020038

Rogers, K., Kelleway, J. J., Saintilan, N., Megonigal, J. P., Adams, J. B., Holmquist, J. R., … Woodroffe, C. D. (2019). Wetland carbon storage controlled by millennial-scale variation in relative sea-level rise. Nature, 567(7746), 91–95. https://doi.org/10.1038/s41586-019-0951-7

Sánchez-Bayo, F., & Wyckhuys, K. A. G. (2019). Worldwide decline of the entomofauna: A review of its drivers. Biological Conservation, 232(January), 8–27. https://doi.org/10.1016/j.biocon.2019.01.020