2020 Water Resilience Portfolio (draft)

California Natural Resources Agency | January 2nd, 2020

21st century California drought risk linked to model fidelity of the El Niño teleconnection

Nature Climate and Atmospheric Science | September 3rd, 2018

Greenhouse gas-induced climate change is expected to lead to negative hydrological impacts for southwestern North America, including California (CA). This includes a decr

Greenhouse gas-induced climate change is expected to lead to negative hydrological impacts for southwestern North America, including California (CA). This includes a decrease in the amount and frequency of precipitation, reductions in Sierra snow pack, and an increase in evapotranspiration, all of which imply a decline in surface water availability, and an increase in drought and stress on water resources. However, a recent study showed the importance of tropical Pacific sea surface temperature (SST) warming and an El Niño Southern Oscillation (ENSO)-like teleconnection in driving an increase in CA precipitation through the 21st century, particularly during winter (DJF). Here, we extend this prior work and show wetter (drier) CA conditions, based on several drought metrics, are associated with an El Niño (La Niña)-like SST pattern. Models that better simulate the observed ENSO-CA precipitation teleconnection also better simulate the ENSO-CA drought relationships, and yield negligible change in the risk of 21st century CA drought, primarily due to wetting during winter. Seasonally, however, CA drought risk is projected to increase during the non-winter months, particularly in the models that poorly simulate the observed teleconnection. Thus, future projections of CA drought are dependent on model fidelity of the El Niño teleconnection. As opposed to focusing on adapting to less water, models that better simulate the teleconnection imply adaptation measures focused on smoothing seasonal differences for affected agricultural, terrestrial, and aquatic systems, as well as effectively capturing enhanced winter runoff.

A 10 per cent increase in global land evapotranspiration from 2003 to 2019

Nature | May 26th, 2021

Accurate quantification of global land evapotranspiration is necessary for understanding variability in the global water cycle, which is expected to intensify und

Accurate quantification of global land evapotranspiration is necessary for understanding variability in the global water cycle, which is expected to intensify under climate change. Current global evapotranspiration products are derived from a variety of sources, including models, remote sensing and in situ observations. However, existing approaches contain extensive uncertainties; for example, relating to model structure or the upscaling of observations to a global level. As a result, variability and trends in global evapotranspiration remain unclear. Here we show that global land evapotranspiration increased by 10 ± 2 per cent between 2003 and 2019, and that land precipitation is increasingly partitioned into evapotranspiration rather than runoff. Our results are based on an independent water-balance ensemble time series of global land evapotranspiration and the corresponding uncertainty distribution, using data from the Gravity Recovery and Climate Experiment (GRACE) and GRACE-Follow On (GRACE-FO) satellites. Variability in global land evapotranspiration is positively correlated with El Niño–Southern Oscillation. The main driver of the trend, however, is increasing land temperature. Our findings provide an observational constraint on global land evapotranspiration, and are consistent with the hypothesis that global evapotranspiration should increase in a warming climate.

A 20,000-year record of ocean circulation and climate change from the Santa Barbara basin

Nature | October 12th, 1995

MUCH of the evidence for climate-driven fluctuations in ocean circulation during the past 20,000 years has come from studies of the North Atlantic region. The extent to w

MUCH of the evidence for climate-driven fluctuations in ocean circulation during the past 20,000 years has come from studies of the North Atlantic region. The extent to which such interactions have occurred in other ocean basins, and any associated teleconnec-tions between basins, is poorly understood. Here we present high-resolution palaeoclimate and palaeoceanographic records from a 20,000-year sedimentary sequence from the Santa Barbara basin, on the eastern margin of the North Pacific Ocean. The sequence shows oscillations of the benthic environment between low-oxygen conditions (laminated sediments) during periods of warm climate, and higher-oxygen conditions (non-laminated, bioturbated sediments) during cool intervals. Age differences between coexisting benthic and planktonic foraminifers indicate climate-related changes in the age and source-and, hence, oxygen content-of basin bottom waters. Relatively young bottom waters are associated with the cooler intervals and are considered to reflect high proportions of intermediate waters derived from proximal sources. Conversely, older bottom waters are associated with the warmer intervals and were derived from more distal sources. These climate-driven variations in ocean circulation appear to be synchronous with the main ocean-climate fluctuations in the North Atlantic region, suggesting that a tight coupling mechanism operates between the two basins.

A changing framework for urban water systems

American Chemical Society (ACS) | May 8th, 2013

Urban water infrastructure and the institutions responsible for its management have gradually evolved over the past two centuries. Today, they are under increas

Urban water infrastructure and the institutions responsible for its management have gradually evolved over the past two centuries. Today, they are under increasing stress as water scarcity and a growing recognition of the importance of factors other than the cost of service provision are forcing a reexamination of long-held ideas. Research and development that supports new technological approaches and more effective management strategies are needed to ensure that the emerging framework for urban water systems will meet future societal needs

A freshwater conservation blueprint for California: prioritizing watersheds for freshwater biodiversity

Freshwater Science, University of Chicago Press Journals | April 18th, 2018

Conservation scientists have adapted conservation planning principles designed for protection of habi- tats ranging from terrestrial to freshwater ecosystems. We

Conservation scientists have adapted conservation planning principles designed for protection of habi- tats ranging from terrestrial to freshwater ecosystems. We applied current approaches in conservation planning to prioritize California watersheds for management of biodiversity. For all watersheds, we compiled data on the pre- sence/absence of herpetofauna and fishes; observations of freshwater-dependent mammals, selected invertebrates, and plants; maps of freshwater habitat types; measures of habitat condition and vulnerability; and current manage- ment status. We analyzed species-distribution data to identify areas of high freshwater conservation value that op- timized representation of target taxa on the landscape and leveraged existing protected areas. The resulting priority network encompasses 34% of the area of California and includes ≥10% of the geographic range for all target taxa. High-value watersheds supported nontarget freshwater taxa and habitats, and focusing on target taxa may provide broad conservation value. Most of the priority conservation network occurs on public lands (69% by area), and 46% overlaps with protected areas already managed for biodiversity. A significant proportion of the network area is on private land and underscores the value of programs that incentivize landowners to manage freshwater species and habitats. The priority conservation areas encompass more freshwater habitats/ha than existing protected areas. Land use (agriculture and urbanization), altered fire regimes, nonnative fish communities, and flow impairment are the most important threats to freshwater habitat in the priority network, whereas factors associated with changing climate are the key drivers of habitat vulnerability. Our study is a guide to a comprehensive approach to freshwater conservation currently lacking in California. Conservation resources are often limited, so prioritiza- tion tools are valuable assets to land and water managers.

A spatially comprehensive, hydrometeorological data set for Mexico, the U.S., and Southern Canada 1950–2013

Nature | August 18th, 2015

A data set of observed daily precipitation, maximum and minimum temperature, gridded to a 1/16° (~6 km) resolution, is described that spans the entire country

A data set of observed daily precipitation, maximum and minimum temperature, gridded to a 1/16° (~6 km) resolution, is described that spans the entire country of Mexico, the conterminous U.S. (CONUS), and regions of Canada south of 53° N for the period 1950–2013. The dataset improves previous products in spatial extent, orographic precipitation adjustment over Mexico and parts of Canada, and reduction of transboundary discontinuities. The impacts of adjusting gridded precipitation for orographic effects are quantified by scaling precipitation to an elevation-aware 1981–2010 precipitation climatology in Mexico and Canada. Differences are evaluated in terms of total precipitation as well as by hydrologic quantities simulated with a land surface model. Overall, orographic correction impacts total precipitation by up to 50% in mountainous regions outside CONUS. Hydrologic fluxes show sensitivities of similar magnitude, with discharge more sensitive than evapotranspiration and soil moisture. Because of the consistent gridding methodology, the current product reduces transboundary discontinuities as compared with a commonly used reanalysis product, making it suitable for estimating large-scale hydrometeorologic phenomena.

A tale of two California droughts: Lessons amidst record warmth and dryness in a region of complex physical and human geography

American Geophysical Union (AGU) | November 19th, 2015

The state of California has experienced the worst drought in its historical record during 2012–2015. Adverse effects of this multi year event have been far from unifor

The state of California has experienced the worst drought in its historical record during 2012–2015. Adverse effects of this multi year event have been far from uniformly distributed across the region, ranging from remarkably mild in most of California’s densely populated coastal cities to very severe in more rural, agricultural, and wildfire-prone regions. This duality of impacts has created a tale of two very different California droughts—highlighting enhanced susceptibility to climate stresses at the environmental andsocioeconomic margins of California. From a geophysical perspective, the persistence of related atmospheric anomalies has raised a number of questions regarding the drought’s origins—including the role of anthropogenic climate change. Recent investigations underscore the importance of understanding the underlying physical causes of extremes in the climate system, and the present California drought represents an excellent case study for such endeavors. Meanwhile, a powerful El Niño event in the Pacific Ocean offers the simultaneous prospect of partial drought relief but also an increased risk of flooding during the 2015–2016 winter—a situation illustrative of the complex hydroclimatic risks California and other regions are likely to face in a warming world.

A typology of compound weather and climate events

Nature Reviews Earth & Environment | June 15th, 2020

Compound weather and climate events describe combinations of multiple climate drivers and/or hazards that contribute to societal or environmental risk. Although m

Compound weather and climate events describe combinations of multiple climate drivers and/or hazards that contribute to societal or environmental risk. Although many climate-related disasters are caused by compound events, the understanding, analysis, quantification and prediction of such events is still in its infancy. In this Review, we propose a typology of compound events and suggest analytical and modelling approaches to aid in their investigation. We organize the highly diverse compound event types according to four themes: preconditioned, where a weather-driven or climate-driven precondition aggravates the impacts of a hazard; multivariate, where multiple drivers and/or hazards lead to an impact; temporally compounding, where a succession of hazards leads to an impact; and spatially compounding, where hazards in multiple connected locations cause an aggregated impact. Through structuring compound events and their respective analysis tools, the typology offers an opportunity for deeper insight into their mechanisms and impacts, benefiting the development of effective adaptation strategies. However, the complex nature of compound events results in some cases inevitably fitting into more than one class, necessitating soft boundaries within the typology. Future work must homogenize the available analytical approaches into a robust toolset for compound-event analysis under present and future climate conditions.

Accounting for Climate Change

Department of Water Resources | April 29th, 2010

In recent years, evidence that global climate will have significant effects on water resources in California has continued to accumulate. Climate change can affect the am

In recent years, evidence that global climate will have significant effects on water resources in California has continued to accumulate. Climate change can affect the amount, timing, and form of precipitation, whether rain or snow, that California receives, as well as the sea level of the Pacific Ocean. Moreover, changes in weather, especially temperature, and atmospheric composition can affect water use and consumption. Changes in climate have occurred during the 20th century, with noticeable warming in the last two decades. Most scientists feel that changes during the last several decades are likely mostly due to human activities, but natural causes and variability cannot be ruled out as a significant component. Likewise, projections of amount of warming and other climate changes during the 21st century are wide ranging, depending on assumptions and models. A major cause of expected climate change is the increasing amounts of greenhouse gases, such as carbon dioxide, in the atmosphere as a result of man’s activities. These gases, as well as water vapor, allow solar radiation to pass inward through the atmosphere, but trap the longer wave infrared radiation reflected back from the earth’s surface. Greenhouse gases are accumulating in the atmosphere; the following chart shows the gradual build up in carbon dioxide at Mauna Loa in Hawaii, as measured by Scripps Institution of Oceanography scientists. The annual cycle is caused by northern hemisphere vegetation uptake during the growing season. Other significant greenhouse gases are methane, nitrous oxide, halocarbons (like freon and its replacements), and, of course, water vapor itself. Cloud cover is an important element in the global radiation balance. Whatever the causes, the prospects of significant changes warrant examination of how the State’s water infrastructure and natural systems can accommodate or adapt to climate changes and whether more needs to be done to detect, evaluate and respond to water resource system effects. Many uncertainties remain, primarily on the degree of change to be expected. Responsible planning requires that the California water planning community work with climate scientists and others to reduce these uncertainties and to begin to prepare for those impacts that are well understood, already appearing as trends, or likely to appear. In this section we review possible impacts and address some of the responses appropriate for water planners and managers.