All ecosystems on earth will be impacted to some extent by climate change, and more frequent and severe droughts are forecast for many regions. Terrestrial ecosystems responses to drought vary dramatically, and understanding why there are such big differences is very important for predicting the impacts of drought at the global scale. To effectively forecast how terrestrial ecosystems such as deserts, grasslands, and forests will respond to drought, ecologists must first study how each system responds to drought of a given severity, and then improve existing models by incorporating the factors that account for large variation in response to drought.
The severity of the drought, expressed as the percentage decrease in precipitation relative to the mean, changes with mean annual precipitation. One of the first products of Drought Net has been characterizing differences in precipitation regimes of extreme wet and dry years (Knapp et al. 2015). The inter-annual variability of precipitation increases with decreasing mean annual precipitation so that a drought occurring 1 in 10 years in a location with 1000 mm per year equals a 40% deviation from the mean. On the contrary, a similar drought in a 250-mm site results in a 60% deviation.
Traditional site-based research by a single investigator working at a given site cannot provide this knowledge, as different methods are used in different studies. Coordinated experimental networks, with identical protocols and comparable measurements, are ideally suited for comparative studies at regional to global scales. This project will establish the Drought-Net Research Coordination Network to advance understanding of the determinants of terrestrial ecosystem responses to drought by bringing together an international group of scientists.
Drought-net used 1600-site database to assess the advantages and disadvantages of different experimental approaches to simulate drought (Knapp et al. 2017). The conclusion of this analysis was that passive rainfall interception as developed by Yahdjian et al (Yahdjian and Sala 2002) was the technique that simulated the best the different dimensions of drought.
Drought-Net used a fix design across its >100 sites, which are distributed around the world. All these sites simulate droughts that have an occurrence of 1 in 100 years. Drought-Net developed a tool to assess the percent reduction of precipitation that meets the 1/100 years criterion (Lemoine et al. 2016).
Drought-Net has developed a Distributed Graduate Seminars that trains the next generation of global change scientists in collaborative synthetic and network-level research, with emphasis on increasing the involvement of underrepresented groups and geographic regions. Open calls for participation in network events and network-related products (datasets, newsletters, papers, reports, etc.) are posted on the Drought-Net website, to encourage access by the broader scientific community and the general public.
References
Knapp, A. K., M. L. Avolio, C. Beier, C. J. Carroll, S. L. Collins, J. S. Dukes, L. H. Fraser, R. J. Griffin‐Nolan, D. L. Hoover, and A. Jentsch. 2017. Pushing precipitation to the extremes in distributed experiments: recommendations for simulating wet and dry years. Global Change Biology. in press doi: 10.1111/gcb.13504 PDF
Lemoine, N.P., J. Sheffield, J.S. Dukes, A.K. Knapp, M.D. Smith. 2016. Terrestrial precipitation analysis (TPA): A resource for characterizing long-term precipitation regimes and extremes. Methods in Ecology and Evolution 7: 1396-1401. PDF
Knapp, A. K., D. L. Hoover, K. Wilcox, M. Avolio, S. Koerner, K. La Pierre, M. Loik, Y. Luo, O. E. Sala, and M. D. Smith. 2015. Characterizing differences in precipitation regimes of extreme wet and dry years: Implications for climate change experiments. Global Change Biology (2015) 21, 2624–2633. doi: 10.1111/gcb.12888 PDF
Yahdjian, L., and O. E. Sala. 2002. A rainout shelter design for intercepting different amounts of rainfall. Oecologia 133:95-101. PDF