The Extraordinary California Drought of 2013-2014: Character, Context, and the Role of Climate Change

American Meteorological Society (AMS) | September 1st, 2014

The event: 2013/14 drought in California. Nearly the entire state of California experienced extremely dry conditions during 2013 (Fig. 2.1a). Statewide, 12-month

The event: 2013/14 drought in California. Nearly the entire state of California experienced extremely dry conditions during 2013 (Fig. 2.1a). Statewide, 12-month accumulated precipitation was less than 34% of average (Fig. 2.1b), leading to a wide range of impacts. In early 2014, state and federal water agencies announced that agricultural water users in the Central Valley would receive no irrigation water during 2014 (DWR 2014; USBR 2014), and that a number of smaller communities throughout California could run out of water entirely within a 90-day window (USDA 2014a). Low rainfall, unusually warm temperatures, and stable atmospheric conditions affected the health of fisheries and other ecosystems (CDFW 2014), created highly unusual mid-winter wildfire risk (CAL FIRE 2014), and caused exceptionally poor air quality (BAAQMD 2014). Such impacts ultimately resulted in the declaration of a state-level “drought emergency” and the federal designation of all 58 California counties as “natural disaster areas” (USDA 2014b).

The Future Hydrology of the Colorado River Basin

Utah State University | August 31st, 2020

Long-range planning of the water supply provided by the Colorado River requires realistic assessments of the impact of a continuation of the current drought that began in

Long-range planning of the water supply provided by the Colorado River requires realistic assessments of the impact of a continuation of the current drought that began in 2000, the impact of potentially extreme future droughts, and the long-term and progressive decline in watershed runoff that is caused by a warming climate. Water-supply managers want to know the maximum plausible stresses to water users so that plans for conservation, reservoir operations, and/or construction of new infrastructure can be properly developed. River managers want to know the implications of various water-supply plans on the flow-regime and water-quality characteristics of the Colorado River and its headwater branches in order to develop natural resource management plans that maintain desired attributes of river ecosystems. Although it is relatively easy to qualitatively describe scenarios of drought or water abundance, it is much harder to quantitatively estimate likely future conditions. In the white paper, we developed methods to make such quantitative estimates, thereby providing an approximate answer to the question, “How dry might future conditions in the Colorado River watershed become?” It is difficult to assign a probability to this assessment, and our analysis is guided by the principle that what has happened in the past might happen again in the future.

The growing importance of oceanic moisture sources for continental precipitation

Nature Portfolio (Springer Nature) | July 24th, 2020

The precipitation that falls on the continents defines the extent and nature of terrestrial ecosystems and human activity in them, all of which are adapted to a

The precipitation that falls on the continents defines the extent and nature of terrestrial ecosystems and human activity in them, all of which are adapted to and maintained by present-day precipitation. In essence, precipitation is supplied by moisture that either comes directly from the ocean, or is subsequently recycled from the continents themselves. Both the processes that control evaporation and the main mechanisms of moisture transport clearly differ between the ocean and the continent, thus within the context of a changing climate, it may be expected that the relationship between precipitation of oceanic and terrestrial origin varies globally and regionally, as will the influence of these two basic components of total precipitation on global and regional precipitation trends, especially in tropical regions. We describe an approach based on a Lagrangian technique for estimating the precipitation in a target region given the proportions of moisture transported from the two sources (ocean and continent) to reveal that the percentage of precipitation of oceanic origin has increased globally in the current climate (1980–2016). The greatest observed rate of increase is in the tropical regions; furthermore, the trends of precipitation in these regions are controlled by trends in precipitation for which the source of moisture is the ocean.

The importance of system configuration for distributed direct potable water reuse

Nature Portfolio (Springer Nature) | April 27th, 2020

Water and wastewater infrastructure worldwide faces unprecedented demand and supply conflicts that require unconventional solutions. In this study, we develop a novel mod

Water and wastewater infrastructure worldwide faces unprecedented demand and supply conflicts that require unconventional solutions. In this study, we develop a novel modelling framework to assess the environmental and economic implications of a hybrid water supply system that supplements a centralized surface water supply with distributed direct potable reuse (DPR) of municipal wastewater, as a strategy to address such challenges. The model is tested with real water and wastewater systems data from the City of Houston, Texas. Results show that supplementing the conventional centralized water supply with distributed DPR would reduce water age in the drinking-water distribution network and hence improve water quality; properly designed system configurations attain system-wide net energy savings even with the high energy consumption of existing technologies used for advanced treatment of the wastewater. A target energy efficiency for future advanced treatment technologies is identified to achieve net energy saving with all hybrid system configurations. Furthermore, distributed DPR remains financially competitive compared with other unconventional water supply solutions. The modelling framework and associated databases developed in this study serve an important research need for quantitatively characterizing distributed and hybrid water systems, laying the necessary foundation for rational design of integrated urban water systems.

The Innovation Deficit in Urban Water: The Need for an Integrated Perspective on Institutions, Organizations, and Technology

Environmental Engineering Science (Mary Ann Liebert, Inc.) | August 1st, 2013

Interaction between institutional change and technological change poses important constraints on transitions of urban water systems to a state that can meet fut

Interaction between institutional change and technological change poses important constraints on transitions of urban water systems to a state that can meet future needs. Research on urban water and other technology- dependent systems provides insights that are valuable to technology researchers interested in assuring that their efforts will have an impact. In the context of research on institutional change, innovation is the development, application, diffusion, and utilization of new knowledge and technology. This definition is intentionally inclusive: technological innovation will play a key role in reinvention of urban water systems, but is only part of what is necessary. Innovation usually depends on context, such that major changes to infrastructure include not only the technological inventions that drive greater efficiencies and physical transformations of water treatment and delivery systems, but also the political, cultural, social, and economic factors that hinder and enable such changes. On the basis of past and present changes in urban water systems, institutional innovation will be of similar importance to technological innovation in urban water reinvention. To solve current urban water infrastructure challenges, technology-focused researchers need to recognize the intertwined nature of technologies and institutions and the social systems that control change.

The key role of dry days in changing regional climate and precipitation regimes

Nature Portfolio (Springer Nature) | March 13th, 2014

Future changes in the number of dry days per year can either reinforce or counteract projected increases in daily precipitation intensity as the climate warms. We

Future changes in the number of dry days per year can either reinforce or counteract projected increases in daily precipitation intensity as the climate warms. We analyze climate model projected changes in the number of dry days using 28 coupled global climate models from the Coupled Model Intercomparison Project, version 5 (CMIP5). We find that the Mediterranean Sea region, parts of Central and South America, and western Indonesia could experience up to 30 more dry days per year by the end of this century. We illustrate how changes in the number of dry days and the precipitation intensity on precipitating days combine to produce changes in annual precipitation, and show that over much of the subtropics the change in number of dry days dominates the annual changes in precipitation and accounts for a large part of the change in interannual precipitation variability.

The key role of dry days in changing regional climate and precipitation regimes

Nature Portfolio (Springer Nature) | March 13th, 2014

Future changes in the number of dry days per year can either reinforce or counteract projected increases in daily precipitation intensity as the climate warms. We

Future changes in the number of dry days per year can either reinforce or counteract projected increases in daily precipitation intensity as the climate warms. We analyze climate model projected changes in the number of dry days using 28 coupled global climate models from the Coupled Model Intercomparison Project, version 5 (CMIP5). We find that the Mediterranean Sea region, parts of Central and South America, and western Indonesia could experience up to 30 more dry days per year by the end of this century. We illustrate how changes in the number of dry days and the precipitation intensity on precipitating days combine to produce changes in annual precipitation, and show that over much of the subtropics the change in number of dry days dominates the annual changes in precipitation and accounts for a large part of the change in interannual precipitation variability.

The Key Role of Heavy Precipitation Events in Climate Model Disagreements of Future Annual Precipitation Changes in California

American Meteorological Society (AMS) | August 6th, 2013

Climate model simulations disagree on whether future precipitation will increase or decrease over Cal- ifornia, which has impeded efforts to anticipate and adapt

Climate model simulations disagree on whether future precipitation will increase or decrease over Cal- ifornia, which has impeded efforts to anticipate and adapt to human-induced climate change. This dis- agreement is explored in terms of daily precipitation frequency and intensity. It is found that divergent model projections of changes in the incidence of rare heavy (.60 mm day21) daily precipitation events explain much of the model disagreement on annual time scales, yet represent only 0.3% of precipitating days and 9% of annual precipitation volume. Of the 25 downscaled model projections examined here, 21 agree that pre- cipitation frequency will decrease by the 2060s, with a mean reduction of 6–14 days yr21. This reduces Cal- ifornia’s mean annual precipitation by about 5.7%. Partly offsetting this, 16 of the 25 projections agree that daily precipitation intensity will increase, which accounts for a model average 5.3% increase in annual pre- cipitation. Between these conflicting tendencies, 12 projections show drier annual conditions by the 2060s and 13 show wetter. These results are obtained from 16 global general circulation models downscaled with dif- ferent combinations of dynamical methods [Weather Research and Forecasting (WRF), Regional Spectral Model (RSM), and version 3 of the Regional Climate Model (RegCM3)] and statistical methods [bias cor- rection with spatial disaggregation (BCSD) and bias correction with constructed analogs (BCCA)], although not all downscaling methods were applied to each global model. Model disagreements in the projected change in occurrence of the heaviest precipitation days (.60 mm day21) account for the majority of disagreement in the projected change in annual precipitation, and occur preferentially over the Sierra Nevada and Northern California. When such events are excluded, nearly twice as many projections show drier future conditions.

The Lower Colorado Basin Fiscal Years 2019 & 2020

U.S. Bureau of Reclamation (USBR) | January 4th, 2021

The magnitude and spatial patterns of historical and future hydrologic change in California’s watersheds

Ecological Society of America (ESA) | February 12th, 2015

Process-based models that link climate and hydrology permit improved assessments of climate change impacts among watersheds. We used the Basin Characterization Model (BCM

Process-based models that link climate and hydrology permit improved assessments of climate change impacts among watersheds. We used the Basin Characterization Model (BCM), a regional water balance model to (1) ask what is the magnitude of historical and projected future change in the hydrology of California’s watersheds; (2) test the spatial congruence of watersheds with the most historical and future hydrologic change; and (3) identify watersheds with high levels of hydrologic change under drier and wetter future climates. We assessed change for 5135 watersheds over a 60-year historical period and compared it to 90-year future projections. Watershed change was analyzed for climatic water deficit, April 1st snowpack, recharge, and runoff. Watersheds were ranked by change for the historical and twofuture scenarios. We developed a normalized index of hydrologic change that combined the four variables, and identified which watersheds show the most spatial congruence of large historical change and continued change under the two futures. Of the top 20%of all watersheds (1028), 591 in the Sierra Nevada Mountains and Northwestern eco-regions have high spatial congruence across all time periods. Among watersheds where change accelerates in the future, but not historically, a majority are congruent between both climate models, predominantly in the Sierra Nevada, Cascade Ranges and the Northwestern eco-regions. This congruence of impacts in watersheds under drier or wetter scenarios is driven by snowpack, but in areas with low snowpack, hydrologic change varied spatially depending on projected precipitation and temperature, with 151 watersheds in Northwestern California showing high levels of drying under the drier scenario, while 103 watersheds in Central western and Southwestern California show increasing hydrologic activity under the wetter scenario. In some regions, the loss of snowpack allows the cycle of runoff and recharge to function without delay represented by springtime snow melt, causing these watersheds to become more immediately hydrologically responsive to changing climate. The study also found watersheds with low rainfall that have already passed through their highest response to changing climate, and show less future change. The methods used here can also be used to identify watersheds resilient to changing climate.