Human alteration of global surface water storage variability.

Knowing the extent of human influence on the global hydrological cycle is essential for the sustainability of freshwater resources on Earth1,2. However, a lack of water level observations for the world's ponds, lakes and reservoirs has limited the quantification of human-managed (reservoir) changes in surface water storage compared to its natural variability3. The global storage variability in surface water bodies and the extent to which it is altered by humans therefore remain unknown. Here we show that 57 per cent of the Earth's seasonal surface water storage variability occurs in human-managed reservoirs. Using measurements from NASA's ICESat-2 satellite laser altimeter, which was launched in late 2018, we assemble an extensive global water level dataset that quantifies water level variability for 227,386 water bodies from October 2018 to July 2020. We find that seasonal variability in human-managed reservoirs averages 0.86 metres, whereas natural water bodies vary by only 0.22 metres. Natural variability in surface water storage is greatest in tropical basins, whereas human-managed variability is greatest in the Middle East, southern Africa and the western USA. Strong regional patterns are also found, with human influence driving 67 per cent of surface water storage variability south of 45 degrees north and nearly 100 per cent in certain arid and semi-arid regions. As economic development, population growth and climate change continue to pressure global water resources4, our approach provides a useful baseline from which ICESat-2 and future satellite missions will be able to track human modifications to the global hydrologic cycle.

Global loss of lake water storage.

Drying trends are prevalent worldwide.

Recent trends in continuing medical education among obstetrician-gynecologists.

OBJECTIVE: To estimate current trends in continuing medical education among obstetrician-gynecologists in relation to the Maintenance of Certification program. METHODS: A validated questionnaire was mailed to 1,030 randomly selected physicians of the American College of Obstetricians and Gynecologists in the United States, Puerto Rico, and Canada. Participants were asked about current practices and opinions regarding continuing medical education activities. Responses were compared between members mandated for Maintenance of Certification (board certification 1986 or later; time-limited certificate) or not (board certification before 1986; nontime-limited certificate). RESULTS: Five hundred twenty (50.4%) surveys were completed. Respondents were more often male (57.1%), generalists (87.3%), in community-based (73.8%) group practices (77.2%) with mean (±standard deviation) age 52.4±9.9 years. College physicians mandated to participate in the Maintenance of Certification program were more likely to rely on Annual Board Certification articles as a major source of continuing medical education credits compared with those not requiring Maintenance of Certification (79.9% compared with 44.6%, P<.001). This finding remained significant after multivariable adjustment for age, gender, years in practice, and practice type (odds ratio [OR] 9.09, 95% confidence interval [CI] 4.03-20.5). Conversely, Maintenance of Certification requirement led to decreased use of the national or international meetings (OR 0.31, 95% CI 0.14-0.67) and self-selected continuing medical education materials (OR 0.29, 95% CI 0.14-0.60) as sources of continuing medical education credits. Despite these differences, physicians in both groups equally valued the relevance of Annual Board Certification articles (92.6% compared with 96.4%, P=.23), the importance of content at academic meetings (98.3% compared with 99.3%, P=.33), the usefulness of simulation drills (97.8% compared with 94.3%, P=.35), and the general ability of continuing medical education activities to improve skills as a physician (90.9% compared with 86.4%, P=.20). CONCLUSION: Requirement of the Maintenance of Certification program has led to significant changes in continuing medical education choices by obstetrician-gynecologists. The changes in continuing medical education appear related to mandated obligations rather than personal preference.