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1.
The impact of future climate change on the glaciers in the Karakoram and Himalaya (KH) is investigated using CMIP5 multi-model temperature and precipitation projections, and a relationship between glacial accumulation-area ratio and mass balance developed for the region based on the last 30 to 40 years of observational data. We estimate that the current glacial mass balance (year 2000) for the entire KH region is -6.6?±?1 Gta?1, which decreases about sixfold to -35?±?2 Gta?1 by the 2080s under the high emission scenario of RCP8.5. However, under the low emission scenario of RCP2.6 the glacial mass loss only doubles to -12?±?2 Gta?1 by the 2080s. We also find that 10.6 and 27 % of the glaciers could face ‘eventual disappearance’ by the end of the century under RCP2.6 and RCP8.5 respectively, underscoring the threat to water resources under high emission scenarios.  相似文献   

2.
Grain yields of wheat and maize were obtained from national statistics and simulated with an agricultural system model to investigate the effects of historical climate variability and irrigation on crop yield in the North China Plain (NCP). Both observed and simulated yields showed large temporal and spatial variability due to variations in climate and irrigation supply. Wheat yield under full irrigation (FI) was 8?t?ha?1 or higher in 80% of seasons in the north, it ranged from 7 to 10?t?ha?1 in 90% of seasons in central NCP, and less than 9?t?ha?1 in 85% of seasons in the south. Reduced irrigation resulted in increased crop yield variability. Wheat yield under supplemental irrigation, i.e., to meet only 50% of irrigation water requirement [supplemental irrigation (SI)] ranged from 2.7 to 8.8?t?ha?1 with the maximum frequency of seasons having the range of 4?C6?t?ha?1 in the north, 4?C7?t?ha?1 in central NCP, and 5?C8?t?ha?1 in the south. Wheat yield under no irrigation (NI) was lower than 1?t?ha?1 in about 50% of seasons. Considering the NCP as a whole, simulated maize yield under FI ranged from 3.9 to 11.8?t?ha?1 with similar frequency distribution in the range of 6?C11.8?t?ha?1 with the interval of 2?t?ha?1. It ranged from 0 to 11.8?t?ha?1, uniformly distributed into the range of 4?C10?t?ha?1 under SI, and NI. The results give an insight into the levels of regional crop production affected by climate and water management strategies.  相似文献   

3.
Simulating the impacts of climate change on cotton production in India   总被引：1，自引：0，他引：1  
General circulation models (GCMs) project increases in the earth’s surface air temperatures and other climate changes by the mid or late 21st century, and therefore crops such as cotton (Gossypium spp L.) will be grown in a much different environment than today. To understand the implications of climate change on cotton production in India, cotton production to the different scenarios (A2, B2 and A1B) of future climate was simulated using the simulation model Infocrop-cotton. The GCM projections showed a nearly 3.95, 3.20 and 1.85 °C rise in mean temperature of cotton growing regions of India for the A2, B2 and A1B scenarios, respectively. Simulation results using the Infocrop-cotton model indicated that seed cotton yield declined by 477 kg?ha?1 for the A2 scenario and by 268 kg?ha?1 for the B2 scenario; while it was non-significant for the A1B scenario. However, it became non-significant under elevated [CO2] levels across all the scenarios. The yield decline was higher in the northern zone over the southern zone. The impact of climate change on rainfed cotton which covers more than 60 % of the country’s total cotton production area (mostly in the central zone) and is dependent on the monsoons is likely to be minimum, possibly on account of marginal increase in rainfall levels. Results of this assessment suggest that productivity in northern India may marginally decline; while in central and southern India, productivity may either remain the same or increase. At the national level, therefore, cotton production is unlikely to change with climate change. Adaptive measures such as changes in planting time and more responsive cultivars may further boost cotton production in India.  相似文献   

4.
This paper explores changes in climatic variables, including solar radiation, rainfall, fraction of diffuse radiation (FDR) and temperature, during wheat season (October to May) and maize season (June to September) from 1961 to 2003 at four sites in the North China Plain (NCP), and then evaluates the effects of these changes on crop growth processes, productivity and water demand by using the Agricultural Production Systems Simulator. A significant decline in radiation and rainfall was detected during the 43 years, while both temperature and FDR exhibit an increasing trend in both wheat and maize seasons. The average trend of each climatic variable for each crop season from the four sites is that radiation decreased by 13.2 and 6.2 MJ m?2 a?1, precipitation decreased by 0.1 and 1.8 mm a?1, minimum temperature increased by 0.05 and 0.02°C a?1, maximum temperature increased by 0.03 and 0.01°C a?1, FDR increased by 0.21 and 0.38% a?1 during wheat and maize season, respectively. Simulated crop water demand and potential yield was significantly decreased because of the declining trend in solar radiation. On average, crop water demand was decreased by 2.3 mm a?1 for wheat and 1.8 mm a?1 for maize if changes in crop variety were not considered. Simulated potential crop yields under fully irrigated condition declined about 45.3 kg ha?1 a?1 for wheat and 51.4 kg ha?1 a?1 for maize at the northern sites, Beijing and Tianjin. They had no significant changes in the southern sites, Jinan and Zhengzhou. Irrigation, fertilization development and crop variety improvement are main factors to contribute to the increase in actual crop yield for the wheat–maize double cropping system, contrasted to the decline in the potential crop yield. Further research on how the improvement in crop varieties and management practices can counteract the impact of climatic change may provide insight into the future sustainability of wheat–maize double crop rotations in the NCP.  相似文献   

5.
A field experiment was conducted in a maize field in 2006 in an arid area of the Yellow River Basin in China. The daytime evapotranspiration (ETc) and soil evaporation beneath the maize canopy (E g) were measured by Bowen ratio energy balance method and micro-lysimeters, respectively. The results showed that the total ETc during maize growth season was 696 mm, and the maximum values occurred at about 90–140 days after sowing. The crop coefficient (K c), which was calculated from the ratio of ETc to reference evapotranspiration (ET0), was quite different from the values reported by other researchers in similar climate areas, with average values of 0.34, 0.47, 1.0 and 0.9 for initial, development, mid-season and late-season stages, respectively. High correlations between leaf area index (LAI) and average K c for every 4 days were obtained. The total E g was 201.4 mm with average values ranged from 0.92 to 2.05 for four growth stages of maize; and accounted for around 28.9 % of ETc. The ratio E g/ETc showed high negative relationship with LAI. These results were very important in precise management of irrigation for maize in Yellow River Basin areas.  相似文献   

6.
In this study, weighing lysimeters were used to investigate the daily crop coefficient and evapotranspiration of wheat and maize in the Fars province, Iran. The locally calibrated Food and Agriculture Organization (FAO) Penman–Monteith equation was used to calculate the reference crop evapotranspiration (ETo). Micro-lysimetry was used to measure soil evaporation (E). Transpiration (T) was estimated by the difference between crop evapotranspiration (ETc) and E. The single crop coefficient (K c) was calculated by the ratio of ETc to ETo. Furthermore, the dual crop coefficient is composed of the soil evaporation coefficient (K e) and the basal crop coefficients (K cb) calculated from the ratio of E and T to ETo, respectively. The maximum measured evapotranspiration rate for wheat was 9.9 mm?day?1 and for maize was 10 mm?day?1. The total evaporation from the soil surface was about 30 % of the total wheat ETc and 29.8 % of total maize ETc. The single crop coefficient (K c) values for the initial, mid-, and end-season growth stages of maize were 0.48, 1.40, and 0.31 and those of wheat were 0.77, 1.35, and 0.26, respectively. The measured K c values for the initial and mid-season stages were different from the FAO recommended values. Therefore, the FAO standard equation for K c-mid was calibrated locally for wheat and maize. The K cb values for the initial, mid-, and end-season growth stages were 0.23, 1.14, and 0.13 for wheat and 0.10, 1.07, and 0.06 for maize, respectively. Furthermore, the FAO procedure for single crop coefficient showed better predictions on a daily basis, although the dual crop coefficient method was more accurate on seasonal scale.  相似文献   

7.
The study compares two formulas for calculating the daily evapotranspiration ET0 for a reference crop. The first formula was proposed by Allen et al. (AL), while the second one was proposed by Katerji and Perrier with the addition of the carbon dioxide (CO2) effect on evapotranspiration (KP). The study analyses the impact of the calculation by the two formulas on the irrigation requirement (IR). Both formulas are based on the Penman-Monteith equation but adopt different approaches for parameterising the canopy resistance r c . In the AL formula, r c is assumed constant and not sensitive to climate change, whereas in the KP formula, r c is first parameterised as a function of climatic variables, then ET0 is corrected for the air CO2 concentration. The two formulas were compared in two periods. The first period involves data from two sites in the Mediterranean region within a measured climate change period (1981–2006) when all the input climatic variables were measured. The second period (2070–2100) involves data from a future climate change period at one site when the input climatic variables were forecasted for two future climate scenarios (A2 and B2). The annual cumulated values of ET0 calculated by the AL formula are systematically lower than those determined by the KP formula. The differences between the ET0 estimation with the AL and KP formulas have a strong impact on the determination of the IR for the reference crop. In fact, for the two periods, the annual values of IR when ET0 is calculated by the AL formula are systematically lower than those calculated by the KP formula. For the actual measured climate change period, this reduction varied from 26 to 28 %, while for the future climate change period, it varied based on the scenario from 16 % (A2) to 20 % (B2).  相似文献   

8.
Sensitivity of carbon uptake and water use estimates to changes in physiology was determined with a coupled photosynthesis and stomatal conductance (g s) model, linked to canopy microclimate with a spatially explicit scheme (MAESTRA). The sensitivity analyses were conducted over the range of intraspecific physiology parameter variation observed for Acer rubrum L. and temperate hardwood C3 (C3) vegetation across the following climate conditions: carbon dioxide concentration 200–700 ppm, photosynthetically active radiation 50–2,000 μmol m?2 s?1, air temperature 5–40 °C, relative humidity 5–95 %, and wind speed at the top of the canopy 1–10 m s?1. Five key physiological inputs [quantum yield of electron transport (α), minimum stomatal conductance (g 0), stomatal sensitivity to the marginal water cost of carbon gain (g 1), maximum rate of electron transport (J max), and maximum carboxylation rate of Rubisco (V cmax)] changed carbon and water flux estimates ≥15 % in response to climate gradients; variation in α, J max, and V cmax input resulted in up to ~50 and 82 % intraspecific and C3 photosynthesis estimate output differences respectively. Transpiration estimates were affected up to ~46 and 147 % by differences in intraspecific and C3 g 1 and g 0 values—two parameters previously overlooked in modeling land–atmosphere carbon and water exchange. We show that a variable environment, within a canopy or along a climate gradient, changes the spatial parameter effects of g 0, g 1, α, J max, and V cmax in photosynthesis-g s models. Since variation in physiology parameter input effects are dependent on climate, this approach can be used to assess the geographical importance of key physiology model inputs when estimating large scale carbon and water exchange.  相似文献   

9.
Fulu Tao  Zhao Zhang 《Climatic change》2011,105(3-4):409-432
Projections of future climate change are plagued with uncertainties from global climate models and emission scenarios, causing difficulties for impact assessments and for planners taking decisions on adaptation measure. Here, we developed an approach to deal with the uncertainties and to project the changes of maize productivity and water use in China using a process-based crop model, against a global mean temperature (GMT) increase scale relative to 1961?C1990 values. From 20 climate scenarios output from the Intergovernmental Panel on Climate Change Data Distribution Centre, we adopted the median values of projected changes in monthly mean climate variables for representative stations and driven the CERES-Maize model to simulate maize production under baseline and future climate scenarios. Adaptation options such as automatic planting, automatic application of irrigation and fertilization were considered, although cultivars were assumed constant over the baseline and future. After assessing representative stations across China, we projected changes in maize yield, growing period, evapotranspiration, and irrigation-water use for GMT changes of 1°C, 2°C, and 3°C, respectively. Results indicated that median values of projected decreases in the yields of irrigated maize without (with) consideration of CO2-fertilization effects ranged from 1.4% to 10.9% (1.6% to 7.8%), 9.8% to 21.7% (10.2% to 16.4%), and 4.3% to 32.1% (3.9% to 26.6%) for GMT changes of 1°C, 2°C, and 3°C, respectively. Median values of projected changes in irrigation-water use without (with) consideration of CO2-fertilization effects ranged from ?1.3% to 2.5% (?18.8% to 0.0%), ?43.6% to 2.4% (?56.1% to ?18.9%), and ?19.6% to 2.2% (?50.6% to ?34.3%), which were ascribed to rising CO2 concentration, increased precipitation, as well as reduced growing period with GMT increasing. For rainfed maize, median values of projected changes in yields without (with) consideration of CO2-fertilization effects ranged from ?22.2% to ?1.0% (?10.8% to 0.7%), ?27.6% to ?7.9% (?18.1% to ?5.6%), and ?33.7% to ?4.6% (?25.9% to ?1.6%). Approximate comparisons showed that projected maize yield losses were larger than previous estimates, particularly for rainfed maize. Our study presents an approach to project maize productivity and water use with GMT increases using process-based crop models and multiple climate scenarios. The resultant impact function is fundamental for identifying which climate change level is dangerous for food security.  相似文献   

10.
Temporal variations in atmospheric hydrogen sulphide concentrations and its biosphere-atmosphere exchanges were studied in the World’s largest mangrove ecosystem, Sundarbans, India. The results were used to understand the possible contribution of H2S fluxes in the formation of atmospheric aerosol of different size classes (e.g. accumulation, nucleation and coarse mode). The mixing ratio of hydrogen sulphide (H2S) over the Sundarban mangrove atmosphere was found maximum during the post-monsoon season (October to January) with a mean value of 0.59?±?0.02 ppb and the minimum during pre-monsoon (February to May) with a mean value of 0.26?±?0.01 ppb. This forest acted as a perennial source of H2S and the sediment-air emission flux ranged between 1213?±?276 μg S m?2 d?1(December) and 457?±?114 μg S m?2 d?1 (August) with an annual mean of 768?±?240 μg S m?2d?1. The total annual emissions of H2S from the Indian Sundarban were estimated to be 1.2?±?0.6 Tg S. The accumulation mode of aerosols was found to be more enriched with non-sea salt sulfate with an average loading of 5.74 μg m?3 followed by the coarse mode (5.18 μg m?3) and nucleation mode (1.18 μg m?3). However, the relative contribution of Non-sea salt sulfate aerosol to total sulfate aerosol was highest in the nucleation mode (83%) followed by the accumulation (73%) and coarse mode (58%). Significant positive relations between H2S flux and different modes of NSS indicated the likely link between H2S, a dominant precursor for the non-sea salt sulfate, and non-sea sulfate aerosol particles. An increase in H2S emissions from the mangrove could result in an increase in enhanced NSS in aerosol and associated cloud albedo, and a decrease in the amount of incoming solar radiation reaching the Sundarban mangrove forest.  相似文献   

11.
This paper examines the potential for the use of artificial neural networks (ANNs) to estimate the reference crop evapotranspiration (ET0) based on air temperature data under humid subtropical conditions on the southern coast of the Caspian Sea situated in the north of Iran. The input variables for the networks were the maximum and minimum air temperature and extraterrestrial radiation. The temperature data were obtained from eight meteorological stations with a range of latitude, longitude, and elevation throughout the study area. A comparison of the estimates provided by the ANNs and by Hargreaves equation was also conducted. The FAO-56 Penman–Monteith model was used as a reference model for assessing the performance of the two approaches. The results of this study showed that ANNs using air temperature data successfully estimated the daily ET0 and that the ANNs with an R 2 of 0.95 and a root mean square error (RMSE) of 0.41 mm day?1 simulated ET0 better than the Hargreaves equation, which had an R 2 of 0.91 and a RMSE of 0.51 mm day?1.  相似文献   

12.
This study is based on ground-based measurements of downward surface shortwave irradiance (SW), columnar water vapour (wv), and aerosol optical depth (τ) obtained at Thule Air Base (Greenland) in 2007–2010, together with MODIS observations of the surface shortwave albedo (A). Radiative transfer model calculations are used in combination with measurements to separate the radiative effect of A (ΔSWA), wv (ΔSWwv), and aerosols (ΔSWτ) in modulating SW in cloud-free conditions. The shortwave radiation at the surface is mainly affected by water vapour absorption, which produces a reduction of SW as low as ?100 Wm?2 (?18%). The seasonal change of A produces an increase of SW by up to +25 Wm?2 (+4.5%). The annual mean radiative effect is estimated to be ?(21–22) Wm?2 for wv, and +(2–3) Wm?2 for A. An increase by +0.065 cm in the annual mean wv, to which corresponds an absolute increase in ΔSWwv by 0.93 Wm?2 (4.3%), has been observed to occur between 2007 and 2010. In the same period, the annual mean A has decreased by ?0.027, with a corresponding decrease in ΔSWA by 0.41 Wm?2 (?14.9%). Atmospheric aerosols produce a reduction of SW as low as ?32 Wm?2 (?6.7%). The instantaneous aerosol radiative forcing (RFτ) reaches values of ?28 Wm?2 and shows a strong dependency on surface albedo. The derived radiative forcing efficiency (FEτ) for solar zenith angles between 55° and 70° is estimated to be (?120.6 ± 4.3) for 0.1 < A < 0.2, and (?41.2 ± 1.6) Wm?2 for 0.5 < A < 0.6.  相似文献   

13.
A regional sea-ice?Cocean model was used to investigate the response of sea ice and oceanic heat storage in the Hudson Bay system to a climate-warming scenario. Projections of air temperature (for the years 2041?C2070; effective CO2 concentration of 707?C950?ppmv) obtained from the Canadian Regional Climate Model (CRCM 4.2.3), driven by the third-generation coupled global climate model (CGCM 3) for lateral atmospheric and land and ocean surface boundaries, were used to drive a single sensitivity experiment with the delta-change approach. The projected change in air temperature varies from 0.8°C (summer) to 10°C (winter), with a mean warming of 3.9°C. The hydrologic forcing in the warmer climate scenario was identical to the one used for the present climate simulation. Under this warmer climate scenario, the sea-ice season is reduced by 7?C9?weeks. The highest change in summer sea-surface temperature, up to 5°C, is found in southeastern Hudson Bay, along the Nunavik coast and in James Bay. In central Hudson Bay, sea-surface temperature increases by over 3°C. Analysis of the heat content stored in the water column revealed an accumulation of additional heat, exceeding 3?MJ?m?3, trapped along the eastern shore of James and Hudson bays during winter. Despite the stratification due to meltwater and river runoff during summer, the shallow coastal regions demonstrate a higher capacity of heat storage. The maximum volume of dense water produced at the end of winter was halved under the climate-warming perturbation. The maximum volume of sea ice is reduced by 31% (592?km3) while the difference in the maximum cover is only 2.6% (32,350?km2). Overall, the depletion of sea-ice thickness in Hudson Bay follows a southeast?Cnorthwest gradient. Sea-ice thickness in Hudson Strait and Ungava Bay is 50% thinner than in present climate conditions during wintertime. The model indicates that the greatest changes in both sea-ice climate and heat content would occur in southeastern Hudson Bay, James Bay, and Hudson Strait.  相似文献   

14.
Global warming has caused unevenly distributed changes in precipitation and evapotranspiration, which has and will certainly impact on the wet-dry variations. Based on daily meteorological data collected at 91 weather stations in Northeast China (NEC), the spatiotemporal characteristics of dry and wet climatic variables (precipitation, crop reference evapotranspiration (ET0), and humid index (HI)) are analyzed, and the probable reasons causing the changes in these variables are discussed during the period of 1961–2014. Precipitation showed non-significant trend over the period of 1961–2014, while ET0 showed a significant decreasing trend, which led to climate wetting in NEC. The period of 2001–2012 exhibited smaller semiarid area and larger humid area compared to the period of 1961–1980, indicating NEC has experienced wetting process at decadal scale. ET0 was most sensitive to relative humidity, and wind speed was the second most sensitive variable. Sunshine hours and temperature were found to be less influential to ET0 in the study area. The changes in wind speed in the recent 54 years have caused the greatest influence on ET0, followed by temperature. For each month, wind speed was the most significant variable causing ET0 reduction in all months except July. Temperature, as a dominant factor, made a positive contribution to ET0 in February and March, as well as sunshine hours in June and July, and relative humidity in August and September. In summary, NEC has experienced noticeable climate wetting due to the significantly decreasing ET0, and the decrease in wind speed was the biggest contributor for the ET0 reduction. Although agricultural drought crisis is expected to be partly alleviated, regional water resources management and planning in Northeast China should consider the potential water shortage and water conflict in the future because of spatiotemporal dry-wet variations in NEC.  相似文献   

15.
Fisheries and aquaculture are important sources of food for hundreds of millions of people around the world. World fish production is projected to increase by 15% in the next 10 years, reaching around 200 million tonnes per year. The main driver of this increase will be based on fish farming management in developing countries. In Brazil, fish farming is increasing due to the climate conditions and large supply of water resources, with the production system based on Nile tilapia (Oreochromis niloticus) farming in reservoirs. Inland waters like reservoirs are a natural source of methane (CH4) to the atmosphere. However, knowledge of the impact from intensive fish production in net cages on CH4 fluxes is not well known. This paper presents in situ measurements of CH4 fluxes and dissolved CH4 (DM) in the Furnas Hydroelectric Reservoir in order to evaluate the impact of fish farming on methane emissions. Measurements were taken in a control area without fish production and three areas with fish farming. The overall mean of diffusive methane flux (DMF) (5.9?±?4.5 mg CH4 m?2 day?1) was significantly lower when compared to the overall mean of bubble methane flux (BMF) (552.9?±?1003.9 mg CH4 m?2 day?1). The DMF and DM were significantly higher in the two areas with fish farming, whereas the BMF was not significantly different. The DMF and DM were correlated to depth and chlorophyll-a. However, the low production of BMF did not allow the comparison with the limnological parameters measured. This case study shows that CH4 emissions are influenced more by reservoir characteristics than fish production. Further investigation is necessary to assess the impact of fish farming on the greenhouse gas emissions.  相似文献   

16.
Global aerosol and ozone distributions and their associated radiative forcings were simulated between 1850 and 2100 following a recent historical emission dataset and under the representative concentration pathways (RCP) for the future. These simulations were used in an Earth System Model to account for the changes in both radiatively and chemically active compounds, when simulating the climate evolution. The past negative stratospheric ozone trends result in a negative climate forcing culminating at ?0.15 W m?2 in the 1990s. In the meantime, the tropospheric ozone burden increase generates a positive climate forcing peaking at 0.41 W m?2. The future evolution of ozone strongly depends on the RCP scenario considered. In RCP4.5 and RCP6.0, the evolution of both stratospheric and tropospheric ozone generate relatively weak radiative forcing changes until 2060–2070 followed by a relative 30 % decrease in radiative forcing by 2100. In contrast, RCP8.5 and RCP2.6 model projections exhibit strongly different ozone radiative forcing trajectories. In the RCP2.6 scenario, both effects (stratospheric ozone, a negative forcing, and tropospheric ozone, a positive forcing) decline towards 1950s values while they both get stronger in the RCP8.5 scenario. Over the twentieth century, the evolution of the total aerosol burden is characterized by a strong increase after World War II until the middle of the 1980s followed by a stabilization during the last decade due to the strong decrease in sulfates in OECD countries since the 1970s. The cooling effects reach their maximal values in 1980, with ?0.34 and ?0.28 W m?2 respectively for direct and indirect total radiative forcings. According to the RCP scenarios, the aerosol content, after peaking around 2010, is projected to decline strongly and monotonically during the twenty-first century for the RCP8.5, 4.5 and 2.6 scenarios. While for RCP6.0 the decline occurs later, after peaking around 2050. As a consequence the relative importance of the total cooling effect of aerosols becomes weaker throughout the twenty-first century compared with the positive forcing of greenhouse gases. Nevertheless, both surface ozone and aerosol content show very different regional features depending on the future scenario considered. Hence, in 2050, surface ozone changes vary between ?12 and +12 ppbv over Asia depending on the RCP projection, whereas the regional direct aerosol radiative forcing can locally exceed ?3 W m?2.  相似文献   

17.
This study elucidates the characteristics of ambient PM2.5 (fine) and PM1 (submicron) samples collected between July 2009 and June 2010 in Raipur, India, in terms of water soluble ions, i.e. Na+, NH 4 + , K+, Mg2+, Ca2+, Cl?, NO 3 ? and SO 4 2? . The total number of PM2.5 and PM1 samples collected with eight stage cascade impactor was 120. Annual mean concentrations of PM2.5 and PM1 were 150.9?±?78.6 μg/m3 and 72.5?±?39.0 μg/m3, respectively. The higher particulate matter (PM) mass concentrations during the winter season are essentially due to the increase of biomass burning and temperature inversion. Out of above 8 ions, the most abundant ions were SO 4 2? , NO 3 ? and NH 4 + for both PM2.5 and PM1 aerosols; their average concentrations were 7.86?±?5.86 μg/m3, 3.12?±?2.63 μg/m3 and 1.94?±?1.28 μg/m3 for PM2.5, and 5.61?±?3.79 μg/m3, 1.81?±?1.21 μg/m3 and 1.26?±?0.88 μg/m3 for PM1, respectively. The major secondary species SO 4 2? , NO 3 ? and NH 4 + accounted for 5.81%, 1.88% and 1.40% of the total mass of PM2.5 and 11.10%, 2.68%, and 2.48% of the total mass of PM1, respectively. The source identification was conducted for the ionic species in PM2.5 and PM1 aerosols. The results are discussed by the way of correlations and principal component analysis. Spearman correlation indicated that Cl? and K+ in PM2.5 and PM1 can be originated from similar type of sources. Principal component analysis reveals that there are two major sources (anthropogenic and natural such as soil derived particles) for PM2.5 and PM1 fractions.  相似文献   

18.
The formation of gas-phase products from the reaction of OH radicals with isoprene for low-NOx conditions ([NOx] ≤ 1010 molecule cm?3) has been studied in an atmospheric pressure flow tube (Institute for Tropospheric Research-Laminar Flow Tube, IfT-LFT) operating in the temperature range of 293–343 K and a relative humidity of < 0.5 % up to 50 %. The photolysis of H2O2 or ozone photolysis in the presence of water vapour served as the NOx-free OH radical sources. For dry conditions at 293 K, the measured yields of methyl vinyl ketone (MVK), 0.07?±?0.02, and methacrolein (MACR), 0.12?±?0.04, were in reasonable agreement with literature data. Beside the C4-carbonyls, further product signals have been attributed tentatively to glycolaldehyde, methylglyoxal, hydroxyacetone, 3-methylfuran, C5-hydroperoxyenals (HPALDs) and C5-hydroxy-hydroperoxides. A simplified, “classical” reaction mechanism without efficient HPALD production describes well the observed yield for MVK and MACR. Unexpected high MVK and MACR yields of up to 0.65 in total were measured under conditions of a relative humidity of 50 % using both OH radical sources and two different measurement techniques for organics (proton transfer reaction mass spectrometry and gas chromatography with flame ionization detector). The reaction mechanism applied is not able to describe the strong increase of MVK and MACR yields with increasing water vapour content. The signal attributed to the HPALDs showed a distinct rise of about one order of magnitude increasing the temperature from 293 K to 343 K. A rough estimate leads to a HPALD yield of 0.32 at 343 K with an uncertainty of a factor of two. The results of this study do not support a predominant formation of HPALDs under atmospheric conditions in low-NOx areas. The surprisingly high MVK and MACR yields measured for a relative humidity of 50 % and the formation of glycolaldehyde, methylglyoxal and hydroxyacetone necessitate further research.  相似文献   

19.
Terrestrial carbon fluxes are an important factor in regulating concentrations of atmospheric carbon dioxide (CO2). In this study, we use a coupled climate model with interactive biogeochemistry to benchmark the simulation of net primary productivity (NPP) and its response to elevated atmospheric CO2. Short-term field experiments such as Free-Air Carbon Dioxide Enrichment (FACE) studies have examined this phenomenon but it is difficult to infer trends from only a few years of field data. Here, we employ the University of Victoria's Earth System Climate Model (UVic ESCM) version 2.8 to compare simulated changes in NPP due to an elevated atmospheric CO2 concentration of 550 ppm to observed increases in NPP of 23% ±2% from four temperate forest FACE studies between 1997 and 2002. We further compare two scenarios: elevated CO2 with climate change, and elevated CO2 without climate change, the latter being consistent with FACE methodology. In the climate change scenario global terrestrial and forest-only NPP increased by 24.5% and 27.9%, respectively, while these increases were 21.0% and 17.2%, respectively, in the latitude band most representative of the location of the FACE studies. In the scenario without climate change, terrestrial and forest-only NPP increased instead by 28.3% and 30.6%, respectively, while these increases were 24.3% and 14.4%, respectively, in the FACE latitudes. This suggests that the model may underestimate temperate forest NPP increases when compared to results from temperate forest FACE studies and highlights the need for both increased experimental study of other forest biomes and further model development.  相似文献   

20.
Reference crop evapotranspiration (ET0) is one of the most important climatic parameters which plays a key role in estimating crop water demand and scheduling irrigation. Under global warming and climate change conditions, it is needed to survey the trend of ET0 in Iran. In this study, ET0 values were determined based on FAO-56 Penman-Monteith equation over 32 synoptic meteorological stations during 1960–2005; and analyzed spatially and temporally in monthly, seasonal and annual time scales. After removing the significant lag-1 serial correlation effect by pre-whitening, non-parametric statistical Mann–Kendall (MK) test was used to detect the trends. The slope of the changes was determined by Sen’s slope estimator. In order to facilitate in trend analysis, the 10 moving average low pass filter were also applied on the normalized annual ET0 time series. Annual ET0 time series and filtered ones were then classified by hierarchical clustering in three clusters and then mapped in order to show the patterns of different clusters. Results showed that the significant decreasing trends were more considerable than increasing ones. Among surveyed stations, and on an annual time scale, the highest and lowest annual values of Sen’s slope estimator were observed in Tabas with (+) 72.14 mm per decade and Shahrud with (?) 62.22 mm per decade, respectively. Results also indicated that the clustered map based on normalized and filtered annual ET0 time series is in accordance with another map which showed spatial distribution of increasing, decreasing and non-significant trends of ET0 on annually time scale. Exploratory and visual analysis of smoothed time series showed increasing trend in recent years especially after 1980 and 1995. In brief, the upward trend of ET0 in recent years is a crucial issue with regard to the high cost of dam construction for agricultural aims in arid and semi-arid regions e.g. Iran.  相似文献   

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