Accumulated winter chill is decreasing in the fruit growing regions of California. Baldocchi, Dennis & Wong, Simon.
http://dx.doi.org/10.1007/s10584-007-9367-8 DOI: 10.1007/s10584-007-9367-8
We examined trends in accumulated winter chill across the fruit growing region of central California and its internal coastal valleys. We tested the hypothesis that global warming is in motion in California and is causing accumulated winter chill to decrease across the fruit and nut growing regions of California. The detection of potential trends in accumulated winter chill (between 0 and 7.2°C) was determined using two complementary climate datasets. The California Irrigation Management Information System (CIMIS) contains hourly climate data and is suitable for computing accumulated chill hours and chill degree-hours. But, its longest data records extend back only to the 1980s. The National Weather Service Coop climate record is longer, extending beyond the 1950s at many sites. But its datasets only contain information on daily maximum and minimum temperatures. To assess long term trends in winter chill accumulation, we developed an algorithm that converted information from daily maximum and minimum temperature into accumulated hours of winter chill and summations of chill-degree hours. These inferred calculations of chill hour accumulation were tested with and validated by direct measurements from hourly-based data from the CIMIS network. With the combined climate datasets, we found that the annual accumulation of winter chill hours and chill degree hours is diminishing across the fruit and nut growing regions of California. Observed trends in winter chill range between -50 and -260 chill hours per decade. We also applied our analytical algorithm to project changes in winter chill using regional climate projections of temperature for three regions in the Central Valley. Predicted rates of reduced winter chill, for the period between 1950 and 2100, are on the order of -40 per decade. By the end of the 21st century, orchards in California are expected to experience less than 500 chill hours per winter. This chronic and steady reduction in winter chill is expected to have deleterious economic and culinary impact on fruit and nut production in California by the end of the 21st Century.
Adaptability and adaptations of California's water supply system to dry climate warming. Josué Medellín-Azuara, Julien J. Harou, Marcelo A. Olivares, Kaveh Madani, Jay R. Lund, Richard E. Howitt, Stacy K. Tanaka, Marion W. Jenkins, Tingju Zhu.
http://dx.doi.org/10.1007/s10584-007-9355-z DOI: 10.1007/s10584-007-9355-z
Economically optimal operational changes and adaptations for California's water supply system are examined for a dry form of climate warming (GFDL CM2.1 A2) with year 2050 water demands and land use. Economically adaptive water management for this climate scenario is compared to a similar scenario with the historical climate. The effects of population growth and land use alone are developed for comparison. Compared with the historic hydrology, optimized operations for the dry climate warming scenario raise water scarcity and total operation costs by $490 million/year with year 2050 demands. Actual costs might be somewhat higher where non-economic objectives prevail in water management. The paper examines the economical mix of adaptation, technologies, policies, and operational changes available to keep water supply impacts to such modest levels. Results from this screening model suggest promising alternatives and likely responses and impacts. Optimized operations of ground and surface water storage change significantly with climate. Dry-warm climate change increases the seasonal storage range of surface reservoirs and aquifers. Surface reservoir peak storage usually occurs about a month earlier under dry-warm climate change.
Recent publications suggest that anthropogenic aerosols suppress orographic precipitation in California and elsewhere. A field campaign (SUPRECIP: Suppression of Precipitation) was conducted to investigate this hypothesized aerosol effect. The campaign consisted of aircraft measurements of the polluting aerosols, the composition of the clouds ingesting them, and the way the precipitation-forming processes are affected. SUPRECIP was conducted during February and March of 2005 and February and March of 2006. The flights documented aerosols and orographic clouds flowing into the central Sierra Nevada from upwind densely populated industrialized/urbanized areas and contrasted them with the aerosols and clouds downwind of the sparsely populated areas in the northern Sierra Nevada.
SUPRECIP found that the aerosols transported from the coastal regions are augmented by local sources in the Central Valley, resulting in high concentrations of aerosols in the eastern parts of the Central Valley and the Sierra foothills. This pattern is consistent with the detected patterns of suppressed orographic precipitation that occur primarily in the southern and central Sierra Nevada but not in the north. The precipitation suppression occurs mainly in the orographic clouds that are triggered from the boundary layer over the foothills and propagate over the mountains, although the elevated orographic clouds that form at the crest are minimally affected. The clouds are affected mainly during the second half of the day and the subsequent evening, when solar heating mixes the boundary layer up to cloud bases. Local, yet unidentified non-urban sources are suspected to play a major role.
California is home to some of the worst air quality in the nation, notably in the San Joaquin Valley and South Coast air basins. Ninety percent of the state’s population lives in areas that are out of attainment with at least one of the federal air quality standards, which are designed to be protective of human health.
Climate change will likely make it more difficult to meet air quality standards in the future. Emission reduction measures that appear sufficient to bring a region into attainment under current conditions could be insufficient in the future, necessitating additional emission reductions. These additional reductions and the associated cost are known as the “climate penalty.” Through a process known as air quality planning, state and regional agencies are responsible for demonstrating to the US Environmental Protection Agency how California will come into compliance with federal air quality standards. Air quality planning involves the quantification of the emission reductions necessary to bring a region into compliance, the identification and design of programs to achieve those reductions, and the demonstration of compliance through modeling.
An ensemble approach for attribution of hydrologic prediction uncertainty. Wood, Andrew W. & Lettenmaier, Dennis P..
Geophysical Research Letters:
Hydrologic prediction errors arise from uncertainty in initial moisture states (mainly snowpack and soil moisture), in boundary forcings (primarily future precipitation and temperature), and from model structure and parameter uncertainty. We evaluate the relative importance of initial condition and boundary forcing uncertainties using a hindcastbased framework that contrasts Ensemble Streamflow Prediction (ESP) with an approach that we term ''reverse- ESP''. In ESP, a hydrologicmodel with assumed perfect initial conditions (ICs) is forced by a forecast ensemble resampled from observed meteorological sequences; whereas reverse- ESP combines an ensemble of resampled ICs with a perfect meteorological forecast. The framework shows that in northern California, US, ICs yield streamflow prediction skill for up to 5 months during the transition between the wet and dry seasons, whereas during the reverse transition, climate forecast information is critical. In southern Colorado, IC knowledge outweighs climate predicti skill for shorter periods due to a more uniform precipitation regime.
A two-page hand out that charts average minimum and maximum temperature anomalies and increases for the 16 climate zones in California from 1920 to 2003. The annual minimum area-weighted temperature averaged over all of California has increased 0.33 degrees F per decade during the period 1920 to 2003. The annual maximum area-weighted temperature averaged over all of California has increased 0.1 degrees F per decade during the period 1920 to 2003. Data Source for Hand Out: National Climatic Data Center (NCDC) http://cdiac.ornl.gov/epubs/ndp/ushcn/state_CA_mon.html
A regional air quality model was used to quantify the effect of temperature, humidity, mixing depth, and background concentrations on ozone (O3) and airborne particulate matter during three air quality episodes in California. Increasing temperature with no change in absolute humidity promoted the formation of O3 by +2 to +9 ppb K−1 through increased reaction rates. Increasing temperature with no change in relative humidity increased predicted O3 concentrations by +2 to +15 ppb K−1 through enhanced production of hydroxyl radical combined with increased reaction rates. Increasing mixing depth promoted the formation of O3 in regions with an over-abundance of fresh NO emissions (such as central Los Angeles) by providing extra dilution. Increasing temperature with no change in absolute humidity reduced particle water content and promoted the evaporation of ammonium nitrate at a rate of −3 to −7 μg m−3 K−1. Increasing temperature with no change in relative humidity maintained particle water content and moderated ammonium nitrate evaporation rates to a maximum value of −3 μg m−3 K−1 during warmer episodes and increased ammonium nitrate condensation by +1.5 μg m−3 K −1 during colder episodes. Increasing mixing depth reduced the concentration of primary particulate matter but increased the formation of secondary particulate matter in regions with an over-abundance of fresh NO emissions. O3 transported into California from upwind areas enhanced the formation of particulate nitrate by promoting the formation of N2O5 and HNO3 at night. A 30 ppb increase in background O3 concentrations (roughly doubling current levels) increased maximum PM2.5 concentrations by +7 to +16 μg m−3 even when temperature was simultaneously increased by +5 K with no change in absolute humidity (most unfavorable conditions for nitrate formation).
Are We in the Midst of the Sixth Mass Extinction? A View from the World of Amphibians. Wake, David B. & Vredenburg, Vance T..
Many scientists argue that we are either entering or in the midst of the sixth great mass extinction. Intense human pressure, both direct and indirect, is having profound effects on natural environments. The amphibians'frogs, salamanders, and caecilians'may be the only major group currently at risk globally. A detailed worldwide assessment and subsequent updates show that one-third or more of the 6,300 species are threatened with extinction. This trend is likely to accelerate because most amphibians occur in the tropics and have small geographic ranges that make them susceptible to extinction. The increasing pressure from habitat destruction and climate change is likely to have major impacts on narrowly adapted and distributed species. We show that salamanders on tropical mountains are particularly at risk. A new and significant threat to amphibians is a virulent, emerging infectious disease, chytridiomycosis, which appears to be globally distributed, and its effects may be exacerbated by global warming. This isease, which is caused by a fungal pathogen and implicated in serious declines and extinctions of >200 species of amphibians, poses the greatest threat to biodiversity of any known disease. Our data for frogs in the Sierra Nevada of California show that the fungus is having a devastating impact on native species, already weakened by the effects of pollution and introduced predators. A general message from amphibians is that we may have little time.