The dynamics of ozone in the San Joaquin Valley of central California are studied by systematic diagnostic runs of the three-dimensional SARMAP Air Quality Model. Air quality in the San Joaquin Valley is the result of a complex combination of local and transported emissions. Simulations show that relatively brisk winds at points of inflow to the Valley produce a strong dependence of ozone in the Valley on upwind conditions. Furthermore, NOx influx from boundaries and local emissions has significantly greater impact on ozone production than ROG influx and emissions.
Climate change and the episodicity of sediment flux of small California rivers. Inman, Douglas L & Jenkins, Scott A.
The Journal of Geology:
http://dx.doi.org/10.1086/314346 DOI: 10.1086/314346
We studied the streamflow and sediment flux characteristics of the 20 largest streams entering the Pacific Ocean along the central and southern California coast, extending for 750 km from Monterey Bay to just south of the U.S./Mexico border. Drainage basins ranged in area from 120 to 10,800 km2, with headwater elevations ranging from 460 to 3770 m. Annual streamflow ranged from 0 to a maximum of m3/yr for the Santa Clara River in 1969, with 9 1#10 an associated suspended sediment flux of ton. Trend analyses confirm that El Nino/Southern Oscilla- 6 46#10 tion-induced climate changes recur on a multidecadal time scale in general agreement with the Pacific/North American climate pattern: a dry climate extending from 1944 to about 1968 and a wet climate extending from about 1969 to the present. The dry period is characterized by consistently low annual river sediment flux. The wet period has a mean annual suspended sediment flux about five times greater, caused by strong El Nino events that produce floodswith an average recurrence of ca. 5 yr. The sediment flux of the rivers during the three major flood years averages 27 times greater than the annual flux during the previous dry climate. The effects of climate change are superimposed on erodibility associated with basin geology. The sediment yield of the faulted, overturned Cenozoic sediments of the Transverse Ranges is many times greater than that of the Coast Ranges and Peninsular Ranges. Thus, the abrupt transition from dry climate to wet climate in 1969 brought a suspended sediment flux of 100 million tons to the ocean edge of the Santa Barbara Channel from the rivers of the Transverse Range, an amount greater than their total flux during the preceding 25-yr dry period. These alternating dry to wet decadal scale changes in climate are natural cycles that have profound effects on fluvial morphology, engineering structures, and the supply of sediment and associated agricultural chemicals to the ocean.
Climate-related change in an intertidal community over short and long time scales. Sagarin, R. D.; Barry, J. P.; Gilman, S. E. & Baxter, C. H..
Changes in the abundance of macroinvertebrate species documented in a rocky intertidal community between surveys in 1931-1933 and 1993-1996 are consistent with the predicted effects of recent climate warming. We resampled 57 0.84-m(2) plots of an intertidal transect first surveyed by W. G. Hewatt at Hopkins Marine Station (HMS), Pacific Grove, California, between 1931 and 1933. Replicating precisely the location of the plots and methodology used by Hewatt, we documented changes in the abundances of 46 invertebrate species, indicating that this intertidal community changed significantly during the 60 yr between surveys. Changes in abundance were related to geographic ranges of species. Most southern species (10 of 11) increased in abundance, whereas most northern species (5 of 7) decreased. Cosmopolitan species showed no clear trend, with 12 increasing and 16 decreasing. Although Hewatt did not record algal species as thoroughly as invertebrates, we were able to document a massive decline in cover of Pelvetia compressa, a cosmopolitan fucoid alga that is typically more common in the southern part of its range. Shoreline ocean temperature, taken daily at HMS, warmed by 0.79 degrees C during this 60-yr period, with average summer temperatures up to 1.94 degrees C warmer in the 13 yr preceding our study than in the 13 yr preceding Hewatt's. The hypothesis that climatic warming drove the observed range-related community shifts is supported further by historical records and data from other investigators. Several alternative hypotheses to explain changes in the invertebrate community at HMS, including habitat changes, anthropogenic effects, indirect biological interactions, El Nino-Southern Oscillation (ENSO) events, and upwelling are considered to be less important than climate change. Changes in species' abundances over a short period (3 yr) were relatively small compared to large species shifts over 60 yr and were unrelated to geographic range of the species, indicating that short-term population fluctuations play a relatively minor role in the long-term community changes that we observed.
Confronting Climate Change in California Ecological Impacts on the Golden State. Field, Christopher; Daily, Gretchen C; Davis, Frank W; Gaines, Steven; Matson, Pamela A; Melack, John & Miller, Norman.
The Union of Concerned Scientists and The Ecological Society of America :
Over the past century, human activities have dramatically altered the natural landscape
of California. Our historical legacy includes severe shrinkage and isolation of
natural habitats, altered flows in streams and rivers, extensive introductions of nonnative
plants and animals, and pollution of the air, land, and water. As we enter the
21st century, a powerful new agent—global climate change—will increasingly interact with the human
pressures that continue to stress California’s ecosystems. In the future, direct impacts generated by
the state’s rapidly growing human population will be intensified by the impacts of climate change.
Confronting Climate Change in California provides the California public and policy makers with insights
drawn from the best available science—insights that may help us safeguard both our ecological
heritage and our economic future. This summary highlights key findings.
Effects of Soil Moisture on Temperatures, Winds, and Pollutant Concentrations in Los Angeles. Jacobson, Mark Z.
Journal of Applied Meteorology:
This paper examines the effects of soil moisture initialization in a coupled air quality-meteorological model on temperature profiles, wind speeds, and pollutant concentrations. Three simulations, each with different initial soil moisture fields, were run. In the baseline simulation, predicted temperatures, wind speeds, and gas/aerosol pollutant concentrations accurately matched observations. In the other two simulations, soil moisture contents were initialized about 4% lower and higher, respectively, than in the baseline simulation. In the low-moisture case, predicted temperature profiles were hotter, near-surface wind speeds were faster, and near-surface pollutant concentrations were lower than observations and baseline predictions. In the high-moisture case, predicted temperatures were colder, wind speeds were slower, and pollutant concentrations were higher than observations and baseline predictions. Initial soil moisture contents affected vertical temperature profiles up to 600-mb altitude after two days. Elevated temperature changes were due in part to changes in sensible heat fluxes from the surface and in part to changes in elevated heat advection fluxes. Changes in temperature profiles affected wind speeds and boundary layer depths, which affected times and magnitudes, respectively, of peak concentrations. Slower wind speeds, associated with high soil moisture contents, delayed times of peak concentrations in the eastern Los Angeles basin. Faster wind speeds, associated with low soil moisture contents, advanced times of peak concentrations. High soil moisture contents resulted in thinner boundary layer depths, increasing average near-surface pollutant concentrations, including that of ozone. Low soil moisture contents resulted in thicker boundary layer depths, decreasing average concentrations, including that of ozone. At some locations, changes in the magnitude of peak ozone concentrations depended on how changes in soil moisture affected ozone precursors and destroyers.
Frequency distributions of daily precipitation in winter and daily stream flow from late winter to early summer, at several hundred sites in the western United States, exhibit strong and systematic responses to the two phases of ENSO. Most of the stream flows considered are driven by snowmelt. The Southern Oscillation index (SOI) is used as the ENSO phase indicator. Both modest (median) and larger (90th percentile) events were considered. In years with negative SOI values (El Nino), days with high daily precipitation and stream flow are more frequent than average over the Southwest and less frequent over the Northwest. During years with positive SOI values (La Nina), a nearly opposite pattern is seen. A more pronounced increase is seen in the number of days exceeding climatological 90th percentile values than in the number exceeding climatological 50th percentile values, for both precipitation and stream flow. Stream flow responses to ENSO extremes are accentuated over precipitation responses. Evidence suggests that the mechanism for this amplification involves ENSO-phase differences in the persistence and duration of wet episodes, affecting the efficiency of the process by which precipitation is converted to runoff. The SOI leads the precipitation events by several months, and hydrologic lags (mostly through snowmelt) delay the stream flow response by several more months. The combined 6-12-month predictive aspect of this relationship should be of significant benefit in responding to flood (or drought) risk and in improving overall water management in the western states.
Forest Pattern, Fire, and Climatic Change in the Sierra Nevada. Urban, Carol Miller; Dean L..
In the Sierra Nevada, distributions of forest tree species are largely controlled by the soil-moisture balance. Changes in temperature or precipitation as a result of increased greenhouse gas concentrations could lead to changes in species distributions. In addition, climatic change could increase the frequency and severity of wildfires. We used a forest gap model developed for Sierra Nevada forests to investigate the potential sensitivity of these forests to climatic change, including a changing fire regime. Fuel moisture influences the fire regime and couples fire to climate. Fires are also affected by fuel loads, which accumulate according to forest structure and composition. These model features were used to investigate the complex interactions between climate, fire, and forest dynamics. Eight hypothetical climate-change scenarios were simulated, including two general circulation model (GCM) predictions of a 2 x CO2 world. The response of forest structure,species composition, and the fire regime to these anges in the climate were examined at four sites across an elevation gradient. Impacts on woody biomass and species composition as a result of climatic change were site specific and depended on the environmental constraints of a site and the environmental tolerances of the tree species simulated. Climatic change altered the fire regime both directly and indirectly. Fire frequency responded directly to climate's influence on fuel moisture, whereas fire extent was affected by changes that occurred in either woody biomass or species composition. The influence of species composition on fuel-bed bulk density was particularly important. Future fires in the Sierra Nevada could be both more frequent and of greater spatial extent if GCM predictions prove true.
Isolating nitrated and aromatic aerosols and nitrated aromatic gases as sources of ultraviolet light absorption. Jacobson, M. Z..
Journal of Geophysical Research: Atmospheres:
Measurements in 1973 and 1987 showed that downward ultraviolet (UV) irradiances within the boundary layer in Los Angeles were up to 50% less than those above the boundary layer. Downward total solar irradiances were reduced by less than 14% in both studies. It is estimated that standard gas and particulate absorbers and scatterers accounted for only about 52-62% of the observed UV reductions at Claremont and Riverside. It is hypothesized that absorption by nitrated and aromatic aerosol components and nitrated aromatic gases caused at least 25-30% of the reductions (with aerosols accounting for about 4/5 of this percent). The remaining reductions are still unaccounted for. Absorbing aerosol components include nitrated aromatics, benzaldehydes, benzoic acids, aromatic polycarboxylic acids, phenols, polycyclic aromatic hydrocarbons, and nitrated inorganics.
Methane pool and flux dynamics in a rice field following straw incorporation. Bossio, D. A.; Horwath, W. R.; Mutters, R. G. & van Kessel, C..
Soil Biology & Biochemistry:
http://dx.doi.org/10.1016/S0038-0717(99)00050-4 DOI: 10.1016/S0038-0717(99)00050-4
Concerns for air quality have led to legislation restricting rice straw burning in some parts of the world. Consequently, growers must dispose of large amounts of residual rice straw by incorporation into the soil, which may have large effects on CH4 emissions from those fields. Our objective was to characterize how this recent change in management has affected overall CH4 emissions in a California rice field and establish relationships between organic matter availability, CH4 pool sizes and CH4 fluxes. Closed chamber measurements were used to monitor diurnal and post drain fluxes, to describe the seasonal pattern of CH4 emissions and estimate total CH4 fluxes on a large on-farm field trial during the 1997 growing season. Soil redox, temperature and plant growth and yield were also monitored. To establish relationships between CH4 pool sizes and fluxes, soil interstitial CH4 concentrations were monitored in the field and available organic matter in the spring was estimated with a laboratory incubation. Redox values in the soil were found to be 50 mV lower in plots in which straw had been incorporated (275 mV) than those in which it had been burned (225 mV). No significant treatment differences were seen in total soil organic matter contents in the spring. However, available organic matter was 1.5 times higher in straw incorporated than straw burned plots. Methane emissions peaked between 22.00 and 23.00 h on two different diurnal sampling dates. Methane emission after draining was about 10% of the flooded period total. A 5-fold increase in total CH4 emissions over the rice growing season was observed in plots in which rice straw had been incorporated each fall for 4 yr. Total cumulative CH4 flux, 1 May 1 October 1997, was 8.87 g C m2 in incorporated, winter flooded plots; 9.52 g C m2 in incorporated, non-winter flooded plots; 1.63 g C m2 in burned, winter flooded plots; and 2.25 g C m2 in burned, non-winter flooded plots. Soil CH4 concentrations at 10±15 cm depth was strongly associated with emissions to the atmosphere (r=0.89). A model developed by Nouchi et al. (1994) [Nouchi, I., Hosono, T., Aodi, K., Minami, K., 1994. Seasonal variation in methane flux from rice paddies associated with methane concentration in soil water, rice biomass and temperature and it's modeling. Plant and Soil 61, 195-208.] which could predict the CH4 flux based on soil CH4 concentrations and temperature was at to our data. The model was very successful at predicting flux rates and cumulative fluxes because conductance (CH4 flux divided by CH4 concentration in soil water) was highly correlated with soil temperature (r=0.88) throughout the period of high CH4 emissions. Organic matter availability and CH4 pool and flux dynamics were altered by straw incorporation practices as evidenced by increased conductance at the same interstitial CH4 concentration and increased emissions per unit available organic matter in rice straw incorporated plots.
Reexamining Fire Suppression Impacts on Brushland Fire Regimes. Keeley, Jon E.; Fotheringham, C. J. & Morais, Marco.
California shrubland wildfires are increasingly destructive, and it is widely held that the problem has been intensified by fire suppression, leading to larger, more intense wildfires. However, analysis of the California Statewide Fire History Database shows that, since 1910, fire frequency and area burned have not declined, and fire size has not increased. Fire rotation intervals have declined, and fire season has not changed, implying that fire intensity has not increased. Fire frequency and population density were correlated, and it is suggested that fire suppression plays a critical role in offsetting potential impacts of increased ignitions. Large fires were not dependent on old age classes of fuels, and it is thus unlikely that age class manipulation of fuels can prevent large fires. Expansion of the urban-wildland interface is a key factor in wildland fire destruction.