B21C-0366
Homogenization of Daily Temperature Series for Detecting Heat Waves in the Mediterranean Environment
Extreme temperature events such as the 2003 European summer heat wave have a strong impact on the environment, society and economy (Kovats, R.S. and C. Koppe, 2005; Poumadere, M. et al., 2005). In order to perform reliable and detailed analysis of extreme temperature events it is important to use long daily and high quality and temperature series. However, many long instrumental climate records are characterised by artificial shifts due to changed measuring conditions such as site displacement, technical development or land-use changes among others. The detection and correction of these aberrations is necessary to get homogeneous time-series which are indispensable for reliable climate and climate impact studies. The Mediterranean region has a long and rich history in monitoring the atmosphere, going back to the 19th century. This area is considered as a "Hot Spot" of climate change (Giorgi, F., 2006) which will suffer from even more severe and frequent heat waves in the future (Diffenbaugh, N.A. et al., 2007). Unfortunately most climate studies are based on non-homogenized and not necessarily valid for climate analysis. To address this problem we developed and applied a new homogenization procedure based on well-established homogenization-methods to adjust more than 170 Mediterranean daily maximum temperature series. An adapted penalized log-likelihood procedure based on (Caussinus H. and O. Mestre, 2004), to detect an unknown number of breaks and outliers is used in combination with a nonlinear model based on (Della-Marta, P.M. and H. Wanner, 2006), for the correction of the time series. The strengths of this approach are: (i) that no metadata is needed for break detection, and (ii) an adjustment of mean daily values, variance, skewness and higher order moments becomes possible. Beside the innovative daily data homogenization approach, a new percentile based heat-wave definition considering Tmax and an adapted bootstrap resample procedure (Zhang, X. et al., 2005) to remove percentile-induced inhomogeneities is applied to analyse past and recent trends of heat waves in the Greater Mediterranean area. The new corrected temperature series illustrate significant changes in heat wave length, frequency and severity. The homogenized time series are needed for all kind of temperature related climate and impact studies, extreme value analysis, and can be compared with model projections. This work is supported by the EU IP CIRCE (Climate Change and Impact Research: the Mediterranean Environment).
B21C-0367
Variability of terrestrial carbon budget in response to ENSO, IODM, and AO/NAO
Terrestrial ecosystem carbon dioxide budget shows evident spatial and temporal variability, making quantification and understanding difficult. Several studies have indicated that the variability is relevant with meteorological teleconnection events such as El Niño and Southern Oscillation (ENSO). This study analyzed the variability with respect to several major teleconnection patterns: ENSO, Indian Ocean Dipole Mode (IODM), and Arctic Oscillation (AO) / North Atlantic Oscillation (NAO). Terrestrial carbon budget was simulated with a process-based terrestrial ecosystem model, Vegetation Integrative SImulator for Trace gases (VISIT), during the period 1901-2002 (analyzed only for 1970-2002), using CRU/TS2.1 data. Anomalies in photosynthetic uptake, respiratory release, and net budget were correlated with indices of the teleconnection patterns. The result shows that ENSO was the most influential pattern on the temporal variability in global terrestrial carbon budget, mainly over tropics. IODM exerted second important effects on the carbon budget in many tropical and temperate regions. AO/NAO affected both photosynthesis and respiration in the same direction, offsetting each other, and then the impact on net budget was small. This study carries implications for the present variability and future change in terrestrial carbon budget, at least partly, on the basis of the relationship with the multiple teleconnection patterns.
B21C-0368
Biogeophysical Climate Feedbacks From Hurricanes
Hurricanes can devastate thousands of hectares of forested area producing changes beyond simply vegetation damage and biomass loss. This study reports changes in regional climate associated with Hurricane Rita which made landfall on the Gulf Coastal Plain on September 24th, 2005. Our analyses suggest that over severely disturbed forested areas, the biogeophysical effects produced by Rita may have affected the precipitation pattern producing a decrease in precipitation the following winter and an increase the next summer season. The dominant biogeophysical effect was a change in albedo as ~14,000 km2 of forested area were disturbed (downed and dead, snapped and structurally damaged trees) by Rita, equivalent to a carbon release of 32 to 43% of the net annual U.S. sink in forest trees. As recent studies project a likely increase in hurricane intensity during the 21st century, understanding the relationship between natural events such as hurricanes and climate is critical.
B21C-0369
The Temporal Dynamics of the Impacts of U.S. Tropical cyclones on Forest Tree Mortality and Carbon Flux
Tropical cyclones cause extensive damage to forested ecosystems. A number of studies were carried out on the impacts of tropical cyclones on forest at regional scale (i.e. U.S. states). There exist, however, few studies on the dynamic impacts of historical tropical cyclones at a continental scale. Here we synthesized field measurements, satellite image analyses, and empirical models to evaluate forest and carbon cycle impacts from historical tropical cyclones from 1851 to 2000 over the continental U.S. Results demonstrated an average of 97 million trees affected each year over the entire United States, with a 53 Tg annual biomass loss, and average carbon release of 25 Tg yr-1. In addition, U.S. forests experienced twice the impact before 1900 than after 1900 due to more active tropical cyclones and a larger extent of forested areas. The forest impacts and biomass loss had significant inter-annual and inter-decade variation, which had significant correlation with the frequency of tropical cyclones, especially hurricane frequency. Results serve as an important baseline for evaluating how potential future changes in hurricane frequency and intensity will impact forest tree mortality and carbon balance.
B21C-0370
El Nino Southern Oscillation Influences Forest Growth Response to Increasing Carbon Dioxide and Troposheric Ozone in Northern Wisconsin, USA
Coupled climate-carbon cycle models treat the feedbacks between terrestrial ecosystem CO2 uptake, atmospheric CO2 concentration, and climate, as constants or fixed ratios. Here we show large annual variability in these feedbacks with dependence upon global climatic phenomena. In a large-scale, open-air exposure (FACE) experiment in northern Wisconsin, USA, we examined the direct effects of elevated CO2 concentration (+CO2; 560ppm), elevated O3 concentration (+O3; 1.5X background), and their combination (+CO2+O3), on the growth (C storage) of model aspen (Populus tremuloides Michaux.) forest ecosystems. After 11 years' fumigation, +CO2 increased height, diameter, main stem volume, and biomass of trees and tree stands, whereas +O3 decreased them. The combination of +CO2+O3 resulted in no net growth effect compared to the control treatments. Annual growth responses ranged from 0 to +40% in +CO2 and 0 to –13% in +O3. These responses interacted strongly with present-day interannual variability in local climatic conditions, in particular the mean daily influx of photosynthetically active radiation (PAR) during mid summer, and the mean daytime temperature during autumn of the previous year. Biological mechanisms relating PAR and temperature with growth responses to +CO2 and +O3 are clear and unequivocal. Furthermore, we found the growth responses closely related to the cold phases of the El Niño Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). In years that both ENSO and PDO were in their cold phases, our experimental forests exhibited their greatest relative growth responses to +CO2 and +O3. Our experiment demonstrates that combined, greenhouse gasses and global climate variability induce changes in the annual rates of C fixation and storage by forest ecosystems, which would then feed back on the climate system.
B21C-0371
Linkages among vegetation, topography and climate variations over the Pearl River basin in southern China
This study explores the relationships among vegetation, topography and climate variations over the Pearl River basin in southern China by analyzing a 25-year (1982-2006) monthly Normalized Difference Vegetation Index (NDVI) dataset. A data mining approach is used to group the NDVI and the topographic information of the Pearl River basin into different ecological zones according to twelve months of a year. It is found that elevation is the predominant factor in every month for grouping ecological zones. The elevation of the first split node of the ecological zones is high for the months from May to September and low in the months of March, April, October and November. In the vegetation leave growing month (April) and falling month (November), the numbers of the ecological zones recognized by the data mining approach are large compared with those detected in other months. This would reveal a respond of seasonal variations of vegetation life cycle. The relationships between the time series of the NDVI and weather variables, including precipitation, temperature and solar radiation from 1982 to 2002, are also analyzed. The correlation coefficients of the NDVI with solar radiation and temperature are positive in most months. However, the correlation coefficient of NDVI and precipitation is always negative. From these correlation coefficients, we found that the solar radiation is a dominate factor for vegetation growth in most area of the Pearl River basin, which matches the study of Nemani et al. (2003). Further, this study reveals that compared with those with low elevations, the ecological zones with high elevations are more sensitive to climate change. Nemani, R. R, C. D. Keeling, H. Hashimoto, and et al. (2003), Climate-driven increases in global terrestrial net primary production from 1982 to 1999, Science, 300, 1560-1563.
B21C-0372
Age-Related Response of Carbon Fluxes to Environmental Constraints in an Age- Sequence of Temperate Pine Forests
The age-related response of carbon (C) fluxes to environmental constraints was evaluated using five years (2003-2007) of flux data in an age-sequence (5-, 18-, 33-, and 68-years-old) of four eastern white pine (Pinus strobus L.) plantation forests growing on dry, sandy soils in southern Ontario, Canada. Daily fluxes of gross ecosystem production (GEP), ecosystem respiration (RE), and net ecosystem productivity (NEP) fluxes were normalized by differences in site index, grouped into constraint days with dry (VWC <0.07), wet (VWC > 0.15) , hot (Tair > 20° C), cold(5 < Tair <15° C), cloudy (PAR < 800 µmol m-2 s-1), high VPD (VPD > 1kPa) conditions and compared to days with unconstraint conditions. Results suggested that daily GEP was increasingly negatively affected by cloudy < high VPD < dry < cold conditions and stimulated only during hot conditions. Daily RE was reduced by 40 to 60% on cold days and stimulated on hot and dry days. NEP was most negatively affected during dry conditions, however, sensitivity to drought stress decreased with stand age. NEP benefited only from cold conditions due to a larger reduction in RE than GEP. Combined environmental variable analysis suggested that NEP mostly benefited from cold-wet- cloudless conditions and decreased severely during dry-hot-high VPD conditions. Monthly GEP and RE increased across the age-sequence and NEP peaked at the 33-year-old site during months with unconstraint climatic conditions. In contrast, during periods constraint by drought and high temperatures (late summer 2004, spring 2005, summer 2007), monthly GEP, RE and NEP were highest at the 18-year-old site where trees benefited from constant deep soil water access (at ~1m soil depth) and reduced at the other sites. These results suggest that weather and climate anomalies may have primarily negative effects on net forest ecosystem C sequestration. A better understanding of the age-related response to changing climatic and environmental conditions including extreme events such as droughts and heat waves is imperative to improve large-scale estimates in forest C exchange.
B21C-0373
Diagnosing Variability of Forest Productivity Using Eddy Covariance Data and a Light-use Efficiency Model
Nine years of eddy covariance measurements in a mature coastal Douglas-fir (Pseudotsuga menziesii) forest were used to calibrate a light-use efficiency (LUE) model. Daily total gross primary production (PG) was simulated as a function of absorbed photosynthetically active radiation (Qa), temperature (T), vapour pressure deficit (D) and relative extractable water (REW). Light absorption was modelled using Beer's law, assuming constant leaf area index (LAI). The objectives were to calibrate the model, assess the individual importance of environmental stresses in controlling PG, and quantify the overall fraction of inter-annual variability of PG attributed to climate variability. Using constrained nonlinear regression, the model calibration was able to explain 84 % of the variation in daily PG, however, model errors were not randomly distributed and the model failed to match observed inter-annual variability. Model residuals indicated strong seasonality, corresponding closely with indirect estimates of stand architecture. This suggests that use of Beer's law and the assumption of static LAI in the simulation of Qa may limit the ability of simple LUE models to simulate productivity of temperate evergreen forest ecosystems. After accounting for light saturation, the model indicated that T, D, and REW all exerted significant influence over daily PG. Residual analysis suggested that REW substantially reduced annual PG in 6 of 9 years. The individual effects of T and D on PG were more difficult to assert, owing to interdependence between driving variables, acclimation of photosynthesis to winter and summer temperature regimes, and seasonal variation in anisohydric behaviour.
B21C-0374
The 2008 South China Freeze and its Impact on the Forests
An unprecedented calamity caused by snow and freezing rain occurred in South China in 2008. This freeze was closely related to the La Nina phenomenon according to a report from the World Meteorological Organization. The freeze stroke 19 provinces in China, and damaged forests of 19.33 million ha with a standing volume loss of 371 million m3. It is estimated that the direct economic loss in the form of destroyed forests is over $8 billion. The indirect loss in the form of impaired ecological functions, such as water and soil conservation, water resources conservancy, biodiversity and forest carbon pool etc is enormous. The calamity of snow and freezing rain affected the structure and function of forest ecosystems. The snow load and freezing rain caused mechanical damage to the trees, with the species of Pinus massoniana, Cunninghamia lanceolata, Pinus elliottii and Phyllostachys pubescens etc. being the most seriously affected. The cold weather could also cause the physiological hurt to the trees. The change of the biotic components leads to the change of abiotic components in the ecosystems. The sunlight under the canopy was intensified due to the opening up of the canopy. The air temperature in the forest, the nutrient and microorganism in soil, the litterfall dynamic were also affected. The alteration of the forest ecosystem structure brought in the alteration of its functions. The damage of the ecosystem structure weakened the capacity of the water and soil conservation, water resources conservancy and reduced the biodiversity in forest ecosystems. Forest gaps allow more sunlight into the freeze-damaged ecosystem, inducing the invasion of more masculine species. The direction and progress of the community succession was therefore altered. At the same time, the freeze made a great impact on the stability and health of the forest ecosystem, increasing the potential risk of outbreak of forest fire and plant diseases/insect pests. Some suggestions on the rebuilding and recovery of damaged forest were given in this paper.
B21C-0375
Insects Extend the Consequences of a Warm, Dry Summer for Tree Growth in the Subsequent Summer near the Arctic Treeline in Alaska
Treeline positions have important implications for surface energy budgets and carbon cycling in high latitude environments. Warming temperatures during the 20th century have been associated with both positive and negative growth trends in treeline white spruce. It has been suggested that negative growth trends may reflect the increasing importance of drought stress as a constraint on tree growth, although direct observations of water stress near the treeline are lacking. We set out to develop a more mechanistic understanding of environmental controls on gas exchange physiology and growth of white spruce near the Arctic treeline in Alaska. Our three-year study was carried out on a riverside terrace along the Agashashok River in Noatak National Preserve. The terrace is capped with a layer of sand/silt that grades from 10 cm depth at the upstream end to 45 cm depth at the downstream end. White spruce of similar size occur along the gradient at similar density, providing an opportunity to examine the role of parent material depth as a control on tree physiology and growth. Air temperatures during the 2006 growing season were near normal, there was no evidence of water stress and white spruce branch extension growth was near the long-term average. The 2007 growing season was exceptionally warm and dry. Stomatal closure was observed during mid-July throughout most of the diurnal cycle in trees growing on less than 30 cm of parent material. The warm, dry conditions and water-stress in the trees may have precipitated a major insect outbreak, which affected nearly all mature trees in the landscape. Branch extension growth in 2007 was reduced to 70 percent of that observed during the 2005 and 2006 growing seasons. Air temperatures during the 2008 growing season returned to near normal. There was no evidence of water stress, but the insect outbreak persisted and branch extension growth did not recover, remaining similar to that observed in 2007. Results of our study highlight the importance of extreme events in shaping the complexity of tree-insect-environment relations at the Arctic treeline and offer an important caution to studies that correlate tree growth with climate. Unfavorable climate conditions in one year may have consequences that persist beyond the return to favorable conditions.
B21C-0376
Climate Change Scenarios Produce Novel Plant Communities in Simulated Arctic Tundra Ecosystems
Arctic tundra plant communities are strongly limited by the availability of nitrogen, as well as the cold climate conditions that are common in these regions. Perturbations to the environment, such as a change in climate, will likely lead to changes in these plant communities. With rising concentrations of greenhouse gases, global temperatures are expected to rise by several degrees by the end of this century, and arctic ecosystems are expected to experience greater warming than temperate regions. Short-term experimentation has resulted in shifts in plant community composition due to changing environmental conditions, but the short length of these experiments does not allow us to determine how the plant community may equilibrate to these new conditions. In this study, we use a transient vegetation dynamics model to simulate long-term shifts in arctic plant communities that are caused by climate change. The model uses climate conditions, nitrogen dynamics, and plant characteristics to examine how plant communities respond to different environmental conditions. For our analyses, we exposed Low Arctic plant communities to a warming climate, and then compared the resultant community to unperturbed communities originally grown in the warmer conditions. We found dramatic differences in the functional type composition of these communities, with greater graminoid abundance and lower deciduous shrub abundance in the climate change scenario, compared to system with the historically warm climate. These results remained stable within the community despite the similarity in climate and the convergence of soil organic matter quantities between the two systems. A proposed hypothesis is that climate change does not merely shift the location of arctic tundra plant communities, but produces new, stable compositions, which can then affect how the vegetation interacts with its environment.
B21C-0377
Altered Rainfall due to Climate Change: Modeling the Ecological Effects on Grasslands
The acceleration of the hydrological cycle due to global climate change is predicted to cause more extreme precipitation, characterized by fewer but more intense storms. Such altered rainfall patterns will have significant impacts on water limited ecosystems such as grasslands. This project used a land surface model, the Community Land Model 3.0 coupled with a dynamic vegetation model, to examine how changing the size and frequency of rain events impacts plants, surface hydrology and surface energy budgets in the tallgrass prairie ecosystem. We applied a similar rainfall scheme as the Rainfall Manipulation Plots at Konza Prairie Biological Station in Kansas, which consisted of an altered rainfall treatment, with fewer but more intense events, and an ambient treatment, which replicated the natural pattern of rain. Both the model and field experiments show a reduction in grass productivity from the ambient to the altered treatment and a negative correlation between soil moisture variability and productivity. In addition, based on the modeling results, the altered rainfall treatment increases runoff, decreases evapotranspiration, and increases sensible heat flux at the expense of latent heat flux.
B21C-0378
Quantification of Microbial Osmolytes in a Drought Impacted California Grassland
With drought frequency and severity likely increasing in the future, understanding its effect on terrestrial carbon (C) and nitrogen (N) cycling has become essential for accurately modeling ecosystem responses to climate change. Microbes respond to drought stress by accumulating internal solutes, or osmolytes, such as amino acids, betaines and polyols, to balance cell membrane water potential as the soil dries. However, when seasonal rains arrive, internal solutes are released and rapidly mineralized. We have been studying these processes in a California grassland. Beginning in summer 2007, we made monthly measurements of soil moisture, individual amino acid concentration in total soil and in microbial biomass, total dissolved organic carbon and nitrogen (DOC and DON), and microbial biomass carbon and nitrogen (MBC and MBN). We expected microbial concentrations of the known amino acid osmolytes glutamate (glu) and proline (pro) to fluctuate inversely with soil moisture. However, pro was only recovered in Mar 2008 (0.30 μg C g-1 dry soil) and the glu concentration varied proportionally with soil moisture: lowest during summer (0.06 g H2O g-1 dry soil, 2.22 μg glutamate-C g-1 dry soil) and highest in winter (0.27 g H2O g-1 dry soil, 4.43 μg glutamate-C g-1 dry soil). The trend from DOC, MBC, and DON measurements was opposite, however, with all concentrations decreasing as soil moisture shifted from dry to wet, (DOC: 64.61 to 32.49 μg C g-1 dry soil respectively). MBN was the exception to this trend, with concentrations staying nearly constant across seasons. These patterns suggest that the expected amino acids glu and pro are not being used for microbial osmoregulation in the CA grassland, and given the summer to winter decrease in MBC, the primary osmolyte source is likely to be either polyol-type compounds such as mannitol or betaines. The implications for terrestrial carbon cycle are considerable because as the frequency of drought increases, the accumulation and release of osmolytes in response to drought has potential to pump carbon out of the grassland ecosystem.
B21C-0379
Measuring and Modeling Ecosystem Photosynthetic Productivity and Respiration in Responses to Climatic Fluctuations in the Past 60 Years at an Oak-Grass Savanna in California
To predict ecosystem sustainability in future climate scenarios, one of essential questions are how and why current plant species are adaptable to the climate that they have experienced. Based on multi-year measurements of ecosystem CO2 exchange with the eddy-covariance technique at an oak-grass savanna, we were interested in comparing seasonal and inter-annual patterns between oak tree canopy and annual grassland and understanding biogeophysical reasons underlying differences in patterns. With these understanding, we further inferred to the two dominant vegetation layers in response to historical climate fluctuations and teleconnection events. We also examine the Century Model to understand uncertainty in predicting ecosystem photosynthetic productivity and respiration in response to climate fluctuations with considerations of soil carbon and nitrogen dynamics. Modeling results were also compared with empirical analyses. This study provided a practicable approach to examine the potential effects of climate fluctuations and extreme events on ecosystem CO2 exchange, implying assessment of longer-term ecological and biometeorological measurements.
B21C-0380
A probabilistic model framework for evaluating year-to-year variation in crop productivity
Most models describing the relation between crop productivity and weather condition have so far been focused on mean changes of crop yield. For keeping stable food supply against abnormal weather as well as climate change, evaluating the year-to-year variations in crop productivity rather than the mean changes is more essential. We here propose a new framework of probabilistic model based on Bayesian inference and Monte Carlo simulation. As an example, we firstly introduce a model on paddy rice production in Japan. It is called PRYSBI (Process- based Regional rice Yield Simulator with Bayesian Inference; Iizumi et al., 2008). The model structure is the same as that of SIMRIW, which was developed and used widely in Japan. The model includes three sub- models describing phenological development, biomass accumulation and maturing of rice crop. These processes are formulated to include response nature of rice plant to weather condition. This model inherently was developed to predict rice growth and yield at plot paddy scale. We applied it to evaluate the large scale rice production with keeping the same model structure. Alternatively, we assumed the parameters as stochastic variables. In order to let the model catch up actual yield at larger scale, model parameters were determined based on agricultural statistical data of each prefecture of Japan together with weather data averaged over the region. The posterior probability distribution functions (PDFs) of parameters included in the model were obtained using Bayesian inference. The MCMC (Markov Chain Monte Carlo) algorithm was conducted to numerically solve the Bayesian theorem. For evaluating the year-to-year changes in rice growth/yield under this framework, we firstly iterate simulations with set of parameter values sampled from the estimated posterior PDF of each parameter and then take the ensemble mean weighted with the posterior PDFs. We will also present another example for maize productivity in China. The framework proposed here provides us information on uncertainties, possibilities and limitations on future improvements in crop model as well.
B21C-0381
The effect of irrigation in mitigating drought impact on maize yield during the 2003 heat wave in France
We quantify the influence of irrigation on minimizing negative maize yield anomalies during the 2003 heat wave and associated drought in France. Spatially distributed irrigation shares of maize were calculated earlier and correlate negatively to the negative yield anomaly between 44.5 and 48 degrees latitude. The shares are used to weigh irrigated and non-irrigated simulations with the EPIC crop-growth model that runs on a 10 by 10 km grid with relevant land use, terrain, soil and management information. The model reasonably reproduces regionally reported yields from 1999-2003. We aim to quantify the relative impact of water deficiency vs. increased temperatures on plant stress. Modeling suggests that drought mitigation increased with increasing irrigation shares for irrigation shares <40%.The extra mitigation effect was less obvious for regions normally dependent on irrigation (shares>40%). Modeled median irrigation rate increased with 84 mm year-1 (18%) or about 575 million m3 compared to 2002 (assuming 0.68 million ha of irrigated maize). Thus, even partial drought mitigation required a substantial amount of water.
B21C-0382
Forecasting Food Production for Zimbabwe
Land reform plans instituted by the government and inconsistent rainfall have combined to impact the reliability of food production in Zimbabwe, and threaten the livelihoods of millions of people in this southern African country. Studies have shown the ability of harvest time (March/April) normalized difference vegetation index (NDVI) to estimate food production in Zimbabwe. This study will investigate two approaches to forecasting NDVI values for crop-growing regions of Zimbabwe. The first will look at a one-step forecast, where environmental variables are used to directly estimate growing season NDVI with a three-month or greater lead time. This timing is viewed as a necessary prediction window to provide early warning and institute mitigation measures. The second method is a two-step approach where environmental variables are used to forecast rainfall, which is then used to forecast NDVI. This two- step approach provides additional lead time to allow for greater anticipation of food shortages. This study will use relatively coarse resolution global climate model (GCM) variables such as surface temperature, pressure and humidity fields. In both methods, the lagged variables will be explored to establish a relationship between these global fields and the dependent variable. Areas with strong and similar relationships will be spatially aggregated and used as predictors to the target variable. This spatial aggregation will reduce the impact of high-frequency spatial information on the resulting forecast. In the case of the on-step approach, the target variable will be the harvest-time NDVI, while in the two-step approach the target variable is rainfall, which will then be used to predict the harvest time NDVI. The resulting model will be a simple multiple regression using the spatially aggregated GCM variables as input to predict future NDVI or precipitation. Validation of this technique will be done using a cross-validation approach for the available NDVI years. The errors from this cross-validation will determine the feasibility of using the technique to reliably forecast food production in Zimbabwe. The data will then be used to forecast the coming year in Zimbabwe with a statement on the estimated production for the 2008-09 growing season.
B21C-0383
Seasonal changes in assimilation for Saguaro cacti (Carnegiea gigantean) corresponding to height and aspect in the Sonoran Desert
The saguaro cactus is a long lived desert columnar cactus that is considered a foundation species of the Sonoran Desert due to its highly depended upon fruits, seeds and flowers. Surprisingly, little is known about the physiology of this ecologically important species. Recent global climate models have predicted changes both in the spatial and temporal distribution of precipitation in America's deserts over the next 50 to 100 years, however do to the lack of physiological data for the saguaro cacti it is uncertain how saguaros will respond to the predicted climate changes. The goal of this study was to measure CO2 flux from the saguaro cacti to explain changes in seasonal variation, vertical height, and aspect. The study site is located at the Desert Laboratory in Tucson, Arizona. Ten cacti were used for diurnal gas exchange measurements at four time periods during 2008 to capture pre-monsoon, monsoon and post-monsoon events. The results of this study will help further the understanding of how climate changes will affect the health of the saguaro cacti.
B21C-0384
Solar Activity, Ultraviolet Radiation and Consequences in Birds in Mexico City, 2001- 2002
Anomalous behavior in commercial and pet birds in Mexico City was reported during 2002 by veterinarians at the Universidad Nacional Autonoma de Mexico. This was attributed to variations in the surrounding luminosity. The solar components, direct, diffuse, global, ultraviolet band A and B, as well as some meteorological parameters, temperature, relative humidity, and precipitation, were then analyzed at the Solar Radiation Laboratory. Although the total annual radiance of the previously mentioned radiation components did not show important changes, ultraviolet Band-B solar radiation did vary significantly. During 2001 the total annual irradiance , 61.05 Hjcm² to 58.32 Hjcm², was 1.6 standard deviations lower than one year later, in 2002 and increased above the mean total annual irradiance, to 65.75 Hjcm², 2.04 standard deviations, giving a total of 3.73 standard deviations for 2001-2002. Since these differences did not show up clearly in the other solar radiation components, daily extra-atmosphere irradiance was analyzed and used to calculate the total annual extra-atmosphere irradiance, which showed a descent for 2001. Our conclusions imply that Ultraviolet Band-B solar radiation is representative of solar activity and has an important impact on commercial activity related with birds.
B21C-0385
MODIS Land and Sea Surface Temperature Observations as Thermal Indicators - Implications for Coastal Climate Variability
The climate conditions in the intertidal zone have been traditionally either modeled or observed using in situ data and thermal engineering models. But these methods are constrained either by their sparse distribution or their data intensive requirements, thus limiting our ability to predict the effect coastal climate patterns on species distributions. Satellite remote sensing provides an alternate approach, given the regular global coverage at moderate spatial resolutions. Since the intertidal zone habitat is exposed to both marine conditions (high tide) and terrestrial conditions (low tide), both the sea surface temperature and the land surface temperature play an important role in organism survivability. We compare five years (2003 to 2007) of land surface temperature (LST) and sea surface temperature (SST) data from MODIS Terra and Aqua instruments along US West Coast to the surface temperature predictions from a biophysical model. The daytime observations from Terra (morning) and Aqua (afternoon) platforms provide us with an indicator of the heating gradient (difference in LST between Aqua and Terra) during the day. The results indicate that a high fraction of MODIS heating gradient values (81% during warmer months and 89% during cooler months) falls within one standard deviation of the corresponding model gradient and is indicative of a high agreement between MODIS and model heating gradients during the satellite overpass times. During cooler months, the root mean squared difference between the gradients ranges from 0.2 ° C/hr at the southern locations to 0.45 ° C/hr at the northern locations, while during warmer months, the difference ranges from 0.12 ° C/hr at the southern locations to 0.86 ° C/hr at the northern locations. This indicates that the MODIS gradient adequately represents the thermal gradients experienced by the species between the satellite overpass times and can be used as a proxy to predict intertidal thermal conditions.
B21C-0386
Long-term ecological impacts of springtime extreme temperature fluctuations
Extreme climate and weather events such as droughts, heat waves, cold waves, large spring temperature fluctuations and floods are among the most devastating natural disasters for mankind, wildlife and vegetation. Their sudden occurrences have frequently led to downfall of prosperous dynasties as well as fundamental shifts in structures and functions of ecosystems that persist long after their often short but lethal initial strike. Springtime extreme weather events are particularly interesting because they occur during the crucial time when biological activities and environmental conditions are most sensitively coupled. In this paper, we will give an overview on the ecological significance of springtime extreme temperature fluctuations. We will use the 2007 Easter Freeze as a case study to show how such a short but extreme temperature disturbance could have sustained impacts on the structures and functions on every level of forest ecosystem hierarchies.
B21C-0387
Imapct of midlatitude and tropical drought on terrestrial ecosystems and the global carbon cycle
A rare drought occurred from 1998 to 2002 across much of the Northern Hemisphere midlatitude regions. Using observational data and numerical models, we analyze the impact of this event on terrestrial ecosystem and the global carbon cycle. The biological productivity in these regions were found to decrease by 0.9 PgC/y compared to the average of the previous two decades, in conjunction with significantly reduced vegetation greenness. The drought led to a land carbon release that is large enough to significantly modify the canonical tropically dominated ENSO response. An atmospheric inversion reveals that during the 1998- 2002 drought period, Northern Hemisphere midlatitude changed from a 1980-1998 average of 0.7 PgC/y carbon sink to nearly neutral to the atmosphere, while a forward model suggests a change of 1.3 PgC/y in the same direction. This large CO2 source explains the consecutive large increase in atmospheric CO2 growth rate of about 2 ppmv/y in recent years, as well as the anomalous timing of events. This Northern Hemisphere CO2 anomaly was largely caused by reduced vegetation growth due to less precipitation, but also with significant contribution from higher temperature that directly increases respiration loss and indirectly further reduces soil moisture. Since the Northern Hemisphere midlatitude landscape has been significantly modified by agriculture, grazing, irrigation and fire suppression, the strong signature in the global carbon cycle of a drought initiated by changes in tropical oceanic temperatures is a remarkable manifestation of climate variability, with implications for carbon cycle response and feedback to future climate change.
B21C-0388
Effects of Solar Dimming and Brightening on the Terrestrial Carbon Sink
A decrease in total solar radiation (Liepert, 2002, Stanhill and Cohen, 2001, Wild et al., 2005) has been observed at the earth surface over the 1950-1990 period, called solar dimming. Such dimming gradually started to transform into brightening in some regions of the world since the late 1980s (Wild et al. 2005). Both dimming and brightening are likely to be linked to an increase and decrease in cloud cover and scattering and absorption of light by tropospheric and stratospheric aerosols respectively (Kvalevag and Myhre, 2007). Theoretical and observational studies have shown that plant photosynthesis of forest and crop ecosystems is more efficient under diffuse light conditions (Gu et al., 2003, Niyogi et al., 2004, Oliveira et al., 2007, Roderick et al., 2001). However, this effect has not yet been accounted for in global carbon cycle simulations because such models lack the mechanism that includes the diffuse irradiance effects on photosynthesis. The aim of this study is to estimate the impact of changes in radiation during the 1900-2100 period on land productivity and carbon storage. We use an offline version of the land surface scheme of the Hadley centre model (Mercado et al., 2007) which has been modified to account for variations of direct and diffuse radiation on sunlit and shaded canopy photosynthesis. Additionally, we use short wave and photosynthetic active radiation fields reconstructed from the Hadley centre climate model which takes into account the scattering and absorption of light by tropospheric and stratospheric aerosols. We describe the simulation of the land carbon cycle through the dimming-brightening periods, and diagnose the impact that changes in diffuse radiation had on the land carbon sink. We also discuss the implications of these results for the future land carbon-sink, under likely changes in the atmospheric aerosol loading.
B21C-0389
Contingenet Productivity Responses to More Extreme Rainfall Regimes Across a Grassland Biome
Climate models predict, and empirical evidence confirms, that more extreme precipitation regimes are occurring in tandem with warmer atmospheric temperatures. These more extreme rainfall patterns are characterized by increased event size separated by longer within season drought periods, and represent novel climatic conditions whose consequences for different ecosystem types are largely unknown. The focus of this talk will be the impacts of extreme rainfall events on soil water content and ecosystem function, and we will present results from experimental manipulations of rainfall in four native grassland sites within the Great Plains Region of North America (USA). Along this precipitation-productivity gradient, our results suggest strong sensitivity to more extreme growing season rainfall regimes, with responses of aboveground net primary productivity (ANPP) contingent on mean soil water levels for different grassland types. At the mesic end of the gradient (tallgrass prairie), longer dry intervals between events led to extended periods of below-average soil water content, increased plant water stress and a reduction in ANPP. The opposite response occurred at the dry end (semi-arid grasslands), where a shift to fewer, but larger, events increased periods of above-average soil water content, reduced seasonal plant water stress and resulted in an increase in ANPP. These results highlight the inherent complexity in predicting how terrestrial ecosystem will respond to forecast novel climate conditions as well as the difficulties in extending inferences from single site experiments across biomes. Even with no change in annual precipitation amount, ANPP responses in a relatively uniform physiographic region differed in both magnitude and direction in response to within season changes in rainfall event size/frequency. From a mechanistic perspective, we believe that these contingent responses reflect strikingly different consequences for soil water content as a result of the interplay between increased rain event size and lengthened interval between events.
B21C-0390
A Pacific Northwest old-growth forest's response to climate variability and extreme climate events over 10 years.
This study analyses eddy-covariance (EC) measurements carried out over a 10 year period in a Pacific Northwest old-growth Douglas-fir (Pseudotsuga menzesii) and Western Hemlock (Tsuga heterophyllia) forest (500-years old) in southern Washington State, USA and characterizes the seasonal and interannual variability in net ecosystem productivity (NEP), gross primary productivity (GPP) and ecosystem respiration (Reco) and primary climatic controls on these fluxes. This forest acted on average as a carbon (C) sink during the study period. However the forest transitioned from an annual net carbon sink (NEP = + 217 g C m-2 year-1) in 1999 to a source (NEP = - 100 g C m-2 year-1) in 2003. The measurement period included three moderate to strong ENSO events, a major shift in the PDO as well as seasonal drought and cold extremes. The carbon sink year (1999) occurred during a strong La Niña while the source year (2003) occurred during El Niño. When ocean-atmospheric ciculations were in- phase, i.e. all were negative (cool) or positive (warm), the greatest anomalies in carbon flux and mechanistic variables (light use-, water use-efficiency) were observed. Annual averages were + 0.63 g C m-2 day-1 (- 0.27 g C m-2 day-1) for NEP, 3.1 mg C / g H2O (4.1 mg C / g H2O) for WUE, and 1.7 g C MJ-1 (2.1 g C MJ-1) for diffuse LUE during in-phase cool (warm) years. Over the 10 years, we observed high variability in seasonal temperature and precipitation including severe summer drought (2002) and record annual rainfall (1998-1999, 2000-2001). Seasonal to interannual variability in precipitation and the consequent water balance appears to influence the timing of the switch from photosynthesis-dominance to respiration-dominance, ultimately determining whether the forest will be an annual net carbon sink (switches in late summer) or source (switches in early summer). Years with average climate were observed to be average both in NEE and Reco, but enhanced (1999) or suppressed (2003) ecosystem respiration had a significant influence on the carbon balance of the old- growth forest.