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• California has shown a wide range of ombroxeric levels (OXI). • Upper strong dry level was found in the north of the State. • Lower weak arid level was found in both the Sonora and Mojave deserts. • Annual trend results have shown an increase in bioclimatic drought throughout California. • June, July and August are the months that show the highest levels of bioclimatic drought. Drought occurs naturally all over the world. Global warming has led an increase in the areas affected by this phenomenon. The study of drought involves the analysis of indicators and indices used to assess changes in the hydrological cycle of a region. A large number of indices developed for drought monitoring are based on meteorological and hydrological variables. This research has applied the Ombroxeric Index for the first time in California. It is based on the concept of ombroxericity: a condition of the territory characterised from an ombrothermic point of view, which can develop in relatively humid areas/zones, depending on the time scale of the study (i.e. monthly, seasonal or annual basis). Temperatures and precipitation from 180 meteorological stations have been considered for a period of observation from 1980 to 2016. In order to know the evolution of this index, a modified trend analysis based on the Mann-Kendall test and a modified Sen slope analysis were used. Empirical Bayesian Kriging was applied as an interpolation technique. Results are presented in both surface and contour maps. California showed a wide range of ombroxeric levels that went from upper strong dry in northern zones, to lower weak arid. Trend results showed an increase in bioclimatic drought throughout the whole State. In addition, summer showed the highest levels on the Ombroxeric Index. An increase in drought trends was observed at the seasonal level, being more pronounced in summer and spring. In both cases are increases in the central (+5 and +3.6 units year−1 respectively) and the southern (+4 and +4.5 units year−1 respectively) areas of the State. Increasing frequency and severity of droughts could have implications for the management of water resources and the survival of Californian vegetation types, such as conifers. [ABSTRACT FROM AUTHOR]

The San Francisco Bay Area is no stranger to the emerging water challenges of climate change and population growth. As California bounces back from one of the most severe droughts in the state's history, utilities are forced to look for more resilient ways to manage their water resources. In the search for enhanced water reliability and resiliency, water providers must identify viable and innovative ways to increase water supplies and decrease demands. These decisions will be highly dependent on local characteristics, and the population dynamics that greatly affect supply, demand, and adaptation capacity in each region. This article explores the evolving supply and demand dynamics in 26 interconnected water utilities in the Bay Area. These utilities reflect not only the challenges that much of the state is facing due to the ongoing drought, but also the stresses of a growing population and shifting socioeconomic characteristics. The region has made significant investments in water efficiency and conservation that have helped increase resilience during the current drought, but conservation can only go so far and many uncertainties remain about future directions for supply and demand management. We explore: (1) how the supply and demand landscapes have evolved in these utilities over the past few decades, (2) what the main drivers have been, and (3) identify opportunities for the region to move forward in response to changing dynamics. The result is a holistic perspective that can help inform water managers and policy makers in preparation for the future. [ABSTRACT FROM AUTHOR]

Summary: This article aims to assess the value of adaptive reservoir management versus traditional operation practices in the context of climatic change for Northern California. The assessment uses adaptive decision model being developed for planning and operational management of the Northern California (central valley) water resources system (), coupled with a dynamic downscaling and hydrologic modeling system described in . The assessment process compares the water system response in four simulated scenarios, pertaining to two management policies (traditional and adaptive) and two hydrologic data sets (one for the historical and a second for a future scenario). The assessments show that the current policy, which is tuned to the historical hydrologic regime, is unable to cope effectively with the more variable future climate. As a result, the water supply, energy, and environmental water uses cannot be effectively satisfied during future droughts, exposing the system to higher vulnerabilities and risks. By contrast, the adaptive policy maintains similar performance under both hydrologic scenarios, suggesting that adaptive management constitutes an effective mitigation measure to climate change. [ABSTRACT FROM AUTHOR]

A series of drought simulations were performed for the California Central Valley using computer applications developed by the California Department of Water Resources and historical datasets representing a range of droughts from mild to severe for time periods lasting up to 60 years. Land use, agricultural cropping patterns, and water demand were held fixed at the 2003 level and water supply was decreased by amounts ranging between 25 and 50%, representing light to severe drought types. Impacts were examined for four hydrologic subbasins, the Sacramento Basin, the San Joaquin Basin, the Tulare Basin, and the Eastside Drainage. Results suggest the greatest impacts are in the San Joaquin and Tulare Basins, regions that are heavily irrigated and are presently overdrafted in most years. Regional surface water diversions decrease by as much as 70%. Stream-to-aquifer flows and aquifer storage declines were proportional to drought severity. Most significant was the decline in ground water head for the severe drought cases, where results suggest that under these scenarios the water table is unlikely to recover within the 30-year model-simulated future. However, the overall response to such droughts is not as severe as anticipated and the Sacramento Basin may act as ground-water insurance to sustain California during extended dry periods. [ABSTRACT FROM AUTHOR]

The article offers information on the drought crisis in California as of August 2014, which has resulted in the degradation of aquatic habitats and reflects on the effect of climatic change. According to Peter Moyle, biologist at the University of California in Davis, California, the Navarro River has dried completely, which normally happens in the end of October. Topics discussed include effects on the ecosystem, climatic shift, and hydrological cycle.

Since the winter of 2013-2014, California has experienced its most severe drought in recorded history, causing statewide water stress, severe economic loss and an extraordinary increase in wildfires. Identifying the effects of global warming on regional water cycle extremes, such as the ongoing drought in California, remains a challenge. Here we analyse large-ensemble and multi-model simulations that project the future of water cycle extremes in California as well as to understand those associations that pertain to changing climate oscillations under global warming. Both intense drought and excessive flooding are projected to increase by at least 50% towards the end of the twenty-first century; this projected increase in water cycle extremes is associated with a strengthened relation to El Niño and the Southern Oscillation (ENSO)-in particular, extreme El Niño and La Niña events that modulate California's climate not only through its warm and cold phases but also its precursor patterns. [ABSTRACT FROM AUTHOR]