Hot & Dry in the Past and Present Here at UC Davis in the Central Valley of California, drought is a hot topic. In class, we discussed how the paleoclimate record can inform our understanding of patterns of drought and to place our recent droughts within the context of climate history. Furthermore, looking at droughts in the past allows us to better assess future drought risk and vulnerability. Drought is a regional phenomenon that is driven by, and linked to, global climate. Here we will explore the drought history and vulnerability of the Western United States. We focused on a paper by Cook et al. (2015) that compares historical observational records to models, in order to project future drought risk in the American Southwest and Central Plains. The Palmer Drought Severity Index (PDSI) uses temperature and precipitation data to reconstruct regional surface moisture balance. The net difference between input (precipitation) and output (evapotranspiration, i.e. the amount of water lost to the atmosphere from evaporation or transpiration by plants) provides a measure of drought. Although this model does not take into account short-term water storage like snowpack or reservoirs, it is an effective tool to model drought conditions. Cook and colleagues (2015) compare the PDSI outputs from three models to measured soil moisture at two depths (30 cm and 2 m) during the months of June, July, and August. To model future drought, the authors use projections from 17 general circulation models that use expected radiative forcing in 2100 (aka the “business as usual” level of emissions (RCP 8.5)). The PDSI, general circulation models, and expected emissions are then integrated with the North American Drought Atlas (NADA), which provides a historic record of drought during the past 1000 years based on tree ring analysis. Model outputs are then compared with model projections to forecast future drought conditions. Severe drought conditions are expected with an 80% chance of a multidecadal, or 35 year long, drought occurring before 2100. Drought has a long history of impacting civilizations, from the fall of the Old Kingdom in Ancient Egypt to the collapse of the Mayan Empire. A visual examination of the drought severity of the United States on this interactive map shows the severity of drought during the Dust Bowl, a large scale event that triggered migrations and economic depression across the US. Furthermore, new studies are pointing to drought severity as a precursor to political instability in Syria in recent years. Although drought has direct impacts on agriculture, economies, and human lives, there are many things that individuals can do to mitigate the impacts of drought. Understanding drought history and calibrating our models with historical data is important for developing water policy because it allows us to understand the natural variability within regional water systems and to better predict future extreme events. We can use paleoclimate evidence to motivate thoughtful policy on both the use and storage of water. Although our paleoclimate records rarely quantify water storage in the past, understanding the magnitude and duration of drought events can inform how much water must be stored during wet periods to plan for future drought events. By looking into the past, we are able to understand the major impacts of drought on humans and to constrain the range of variability within the hydrologic cycle. Policy and management decisions can be guided by the information from the past, yet challenges for adaptation remain. Regarding planning for drought in the Western US, Cook et al. 2015 comment “...perhaps most importantly for adaptation, recent years have witnessed the widespread depletion of nonrenewable groundwater reservoirs, resources that have allowed people to mitigate the impacts of naturally occurring droughts. In some cases, these losses have even exceeded the capacity of Lake Mead and Lake Powell, the two major surface reservoirs in the region. Combined with the likelihood of a much drier future and increased demand, the loss of groundwater and higher temperatures will likely exacerbate the impacts of future droughts, presenting a major adaptation challenge for managing ecological and anthropogenic water needs in the region.” Additional Resources: What is the PDSI? Wired Article on California Drought Journal article on links between drought and present conflict in Syria Interactive map of drought history in US Model projections of future drought New York Times article on CA drought Links between drought and human civilizations Tips for water saving |
ArchiveSea Levels: Past, Present and Future
How has El Niño changed in the past? Lessons from paleoclimate archives Paleoclimate into Policy: is there a bright future for learning from the past AuthorsWritten by the members of UC Davis GEL 232: K. Barclay, R. Banker, P. Edwards, C. Fish, K. Hewett, T. Hill, G. Hollyday, C. Livsey, H. Palmer, P. Shukla, D. Vasey. Categories
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