Characteristics of regional climate change and pattern analysis on Ordos Plateau

The characteristics of precipitation, temperature and their combination determine the special ecological environment pattern of Ordos Plateau. Analyzing its evolutionary trend attributes to understanding the succession process of the ecological environment of Ordos Plateau and has crucial instructional significance on the ecological restoration research being conducted in this region. Four time scales, arranging from ten days, one month, one season (growing season contrasting to non-growing season)to one year were adopted to analyze the climate data which included nearly 30 years and were collected by eight weather stations on Ordos Plateau. The results indicated that the mean annual temperature and the mean monthly temperature of February, September and December, had increased significantly during the late 30 years. The annual precipitation did not show significant changes but its distribution pattern had changed obviously. The ratio of precipitation of major growing season (May-October)to annual precipitation had increased distinctively, and five counties‘ precipitation reached statistically significant level.And the ratio of precipitation of latter growing season (September)to one year decreased significantly while the ratio of non-growing season (November-next April)to one year changed insignificantly. The results showed that maybe the interaction of increased mean temperature and insignificant change of precipitation in non-growing season was one of the reasons why the desertifieation of the region was deteriorating in recent years. Using some factors closely relating to vegetation succession such as mean annual temperature, mean annual precipitation, distributive pattern of precipitation, mean temperature of the coldest month, mean temperature of the warmest month, precipitation of the warmest month,mean temperature of growing season, precipitation of growing season, potential evapotranspiration(PET) and radiative dryness index( RD1), to synthetically analyze the climate characteristics of Ordos Plateau. The regionalized Ordos Plateau to three synthetical climate types were recognized as follows: Type 1, semi-humid and low evaporation(including Jungar Banner, Dongsheng City and Ejin Horo Banner), Type 11,semi-arid, semi-humid and moderate evaporation(including Uxin Banner and Dalad Banner), Type 111, arid and high evaporation(including Hanggin Banner,Otag Banner and Otog Qian Banner).     

Radiative dryness index and potential productivity of vegetation in China

The Chikugo Model is used to estimate radiative dryness indexes (RDI) and net primary productivity (NPP) of vegetation zones in China by calculating cli-matic parameters. That provides the water-heat equilibrium condition, potential primary production for natural vegetation in various vegetation zones, and their geographical distribution pattern. That could be used as the basis for study the effect of global climate change on ecosystems.     

Modeling the impacts of temperature and precipitation changes on soil CO2 fluxes from a Switchgrass stand recently converted from cropland

Switchgrass(Panicum virgatum L.) is a perennial C_4 grass native to North America and successfully adapted to diverse environmental conditions. It offers the potential to reduce soil surface carbon dioxide(CO_2) fluxes and mitigate climate change. However, information on how these CO_2 fluxes respond to changing climate is still lacking. In this study, CO_2 fluxes were monitored continuously from 2011 through 2014 using high frequency measurements from Switchgrass land seeded in 2008 on an experimental site that has been previously used for soybean(Glycine max L.) in South Dakota, USA. DAYCENT, a process-based model, was used to simulate CO_2 fluxes. An improved methodology CPTE[Combining Parameter estimation(PEST) with "Trial and Error" method] was used to calibrate DAYCENT. The calibrated DAYCENT model was used for simulating future CO_2 emissions based on different climate change scenarios. This study showed that:(i) the measured soil CO_2 fluxes from Switchgrass land were higher for 2012 which was a drought year, and these fluxes when simulated using DAYCENT for long-term(2015–2070) provided a pattern of polynomial curve;(ii) the simulated CO_2 fluxes provided different patterns with temperature and precipitation changes in a long-term,(iii) the future CO_2 fluxes from Switchgrass land under different changing climate scenarios were not significantly different, therefore, it can be concluded that Switchgrass grown for longer durations could reduce changes in CO_2 fluxes from soil as a result of temperature and precipitation changes to some extent.     

Effects of climate change on water resources in Tarim River Basin, Northwest China

Based on hydrology, temperature, and precipitation data from the past 50 years, the effects of climate change on water resources in Tarim River Basin in Northwest China were investigated. The long-term trends of the hydrological time series were detected using both parametric and nonparametric techniques. The results showed that the increasing tendency of the temperature has a 5% level of significance, and the temperature increased by nearly 1℃ over the past 50 years. The precipitation showed a significant increase in the 1980s and 1990s, and the average annual precipitation exhibited an increasing trend with a magnitude of 6.8 mm per decade. A step change occurred in both the temperature and precipitation time series around 1986. The streamflow from the headwater of the Tarim River exhibited a significant increase during the last 20 years. The increase in temperature, precipitation, and streamflow may be attributed to global climate change.     

Climate effects of nuclear war in China

By utilizing simulations of climatic respponse to nuclear smoke, which were made by the Lawrence Livermore National Laboratory, USA, climate change in China induced by a large-scale nuclear war is analysed. Remarkable climate change in China following nuclear smoke injections is found. The surface air temperature decreases dramatically around all China, surface cooling is 13 ℃ averaging over whole China in July and maximum cooling is 23. 4 ℃ , 3 ℃ cooling in January and maximum 8℃ for the 150 Tg smoke injection (equivalent to the base-line nuclear war). However, the change in temperature is unhomogeneous, implying that the rise in temperature happens over some parts of China. An averaging precipitation decrease in many of months of the experimental year. The precipitation defect is dependent on a scale of nuclear war, the deduction is 1.8mm/day averaging over China in July in the 150 Tg smoke injection, and 0.1 mm/d in January. Nevertheless, the precipitation enhancement in a few months over some re     

Modeling effects of temperature and precipitation on carbon characteristics and GHGs emissions in Abies fabric forest of subalpine

Abies fabric forest in the eastern slope of Gongga mountain is one type of subalpine dark coniferous forests of southwestern China. It is located on the southeastern edge of the Qinghai-Tibet plateau and is sensitive to climatic changes. A process-oriented biogeochemical model, Forest-DNDC, was applied to simulate the e ects of climatic factors, temperature and precipitation changes on carbon characteristics, and greenhouse gases (GHGs) emissions in A. fabric forest. Validation indicated that the Forest-DNDC could be used to predict carbon characteristics and GHGs emissions with reasonable accuracy. The model simulated carbon fluxes, soil carbon dynamics, soil CO2, N2O, and NO emissions with the changes of temperature and precipitation conditions. The results showed that with variation in the baseline temperature from –2℃ to +2℃, the gross primary production (GPP) and soil organic carbon (SOC) increased, and the net primary production (NPP) and net ecosystem production (NEP) decreased because of higher respiration rate. With increasing baseline precipitation the GPP and NPP increased slightly, and the NEP and SOC showed decreasing trend. Soil CO2 emissions increased with the increase of temperature, and CO2 emissions changed little with increased baseline precipitation. With increased temperature and decreased baseline temperature, the total annual soil N2O emissions increased.With the variation of baseline temperature from –2℃ to +2℃, the total annual soil NO emissions increased. The total annual N2O and NO emissions showed increasing trends with the increase of precipitation. The biogeochemical simulation of the typical forest indicated that temperature changes strongly a ected carbon fluxes, soil carbon dynamics, and soil GHGs emissions. The precipitation was not a principal factor a ecting carbon fluxes, soil carbon dynamics, and soil CO2 emissions, but changes in precipitation could exert strong e ect on soil N2O and NO emissions.     

Modeling effects of temperature and precipitation on carbon characteristics and GHGs emissions in Abies fabric forest of subaipine

Abies fabric forest in the eastern slope of Gongga mountain is one type of subalpine dark coniferous forests of southwestern China. It is located on the southeastern edge of the Qinghai-Tibet plateau and is sensitive to climatic changes. A process-oriented biogeochemical model, Forest-DNDC, was applied to simulate the effects of climatic factors, temperature and precipitation changes on carbon characteristics, and greenhouse gases （GHGs） emissions in A. fabric forest. Validation indicated that the Forest-DNDC could be used to predict carbon characteristics and GHGs emissions with reasonable accuracy. The model simulated carbon fluxes, soil carbon dynamics, soil CO2, N2O, and NO emissions with the changes of temperature and precipitation conditions. The results showed that with variation in the baseline temperature from -2℃ to ＋2℃, the gross primary production （GPP） and soil organic carbon （SOC） increased, and the net primary production （NPP） and net ecosystem production （NEP） decreased because of higher respiration rate. With increasing baseline precipitation the GPP and NPP increased slightly, and the NEP and SOC showed decreasing trend. Soil CO2 emissions increased with the increase of temperature, and CO2 emissions changed little with increased baseline precipitation. With increased temperature and decreased baseline temperature, the total annual soil N2O emissions increased. With the variation of baseline temperature from -2℃ to ＋2℃, the total annual soil NO emissions increased. The total annual N2O and NO emissions showed increasing trends with the increase of precipitation. The biogeochemical simulation of the typical forest indicated that temperature changes strongly affected carbon fluxes, soil carbon dynamics, and soil GHGs emissions. The precipitation was not a principal factor affecting carbon fluxes, soil carbon dynamics, and soil CO2 emissions, but changes in precipitation could exert strong effect on soil N2O and NO emissions.     

Simulating global soil-CO2 flux and its response to climate change

It has been argued that increased soil respiration would become a major atmospheric source of CO2 in the event of global warming. The simple statistical models were developed based on a georeferenced database with 0.5° × 0.5° longitude/latitude resolution to simulate global soil-CO2 fluxes, to investigate climatic effects on these fluxes using sensitivity experiments, and to assess possible responses of soil-CO2 fluxes to various climate change scenarios. The statistical models yield a value of 69 PgC/a of global soil CO2 fluxes for current condition. Sensitivity experiments confirm that the fluxes are responsive to changes in temperature,precipitation and actual evapotranspiration, but increases in temperature and actual evapotranspiration affect soil-CO2 fluxes more than increases in precipitation. Using climatic change projections from four global circulation models, each corresponding to an equilibrium doubling of CO2, it can be found that the largest increases in soil-CO2 fluxes were associated with the boreal and tundra regions. The globally averaged soil-CO2 fluxes were estimated to increase by about 35 ％ above current values, providing a positive feedback to the greenhouse effect.     

Soil temperature and moisture sensitivities of soil CO2 e ux before and after tillage in a wheat field of Loess Plateau, China

As a conventional farming practice, tillage has lasted for thousands of years in Loess Plateau, China. Although recent studies show that tillage is a prominent culprit to soil carbon loss in croplands, few studies have investigated the influences of tillage on the responses of soil CO2 e ux (SCE) to soil temperature and moisture. Using a multi-channel automated CO2 e ux chamber system, we measured SCE in situ continuously before and after the conventional tillage in a rain fed wheat field of Loess Plateau, China. The changes in soil temperature and moisture sensitivities of SCE, denoted by the Q10 value and linear regression slope respectively, were compared in the same range of soil temperature and moisture before and after the tillage. The results showed that, after the tillage, SCE increased by 1.2–2.2 times; the soil temperature sensitivity increased by 36.1%–37.5%; and the soil moisture sensitivity increased by 140%–166%. Thus, the tillage-induced increase in SCE might partially be attributed to the increases in temperature and moisture sensitivity of SCE.     

Combined and synergistic effects of climate change and urbanization on water quality in the Wolf Bay watershed, southern Alabama

This study investigated potential changes in flow, total suspended solid(TSS) and nutrient(nitrogen and phosphorous) loadings under future climate change, land use/cover(LULC)change and combined change scenarios in the Wolf Bay watershed, southern Alabama,USA. Four Global Circulation Models(GCMs) under three Special Report Emission Scenarios(SRES) of greenhouse gas were used to assess the future climate change(2016–2040). Three projected LULC maps(2030) were employed to reflect different extents of urbanization in future. The individual, combined and synergistic impacts of LULC and climate change on water quantity/quality were analyzed by the Soil and Water Assessment Tool(SWAT).Under the "climate change only" scenario, monthly distribution and projected variation of TSS are expected to follow a pattern similar to streamflow. Nutrients are influenced both by flow and management practices. The variation of Total Nitrogen(TN) and Total Phosphorous(TP) generally follow the flow trend as well. No evident difference in the N:P ratio was projected. Under the "LULC change only" scenario, TN was projected to decrease,mainly due to the shrinkage of croplands. TP will increase in fall and winter. The N:P ratio shows a strong decreasing potential. Under the "combined change" scenario, LULC and climate change effect were considered simultaneously. Results indicate that if future loadings are expected to increase/decrease under any individual scenario, then the combined change will intensify that trend. Conversely, if their effects are in opposite directions, an offsetting effect occurs. Science-based management practices are needed to reduce nutrient loadings to the Bay.     

Effects of seasonal climatic variability on several toxic contaminants in urban lakes: Implications for the impacts of climate change

Climate change is supposed to have influences on water quality and ecosystem. However, only few studies have assessed the effect of climate change on environmental toxic contaminants in urban lakes. In this research, response of several toxic contaminants in twelve urban lakes in Beijing, China, to the seasonal variations in climatic factors was studied. Fluorides, volatile phenols, arsenic, selenium, and other water quality parameters were analyzed monthly from2009 to 2012. Multivariate statistical methods including principle component analysis, cluster analysis, and multiple regression analysis were performed to study the relationship between contaminants and climatic factors including temperature, precipitation, wind speed, and sunshine duration. Fluoride and arsenic concentrations in most urban lakes exhibited a significant positive correlation with temperature/precipitation, which is mainly caused by rainfall induced diffuse pollution. A negative correlation was observed between volatile phenols and temperature/precipitation, and this could be explained by their enhanced volatilization and biodegradation rates caused by higher temperature. Selenium did not show a significant response to climatic factor variations, which was attributed to low selenium contents in the lakes and soils. Moreover, the response degrees of contaminants to climatic variations differ among lakes with different contamination levels. On average, temperature/precipitation contributed to 8%, 15%, and 12% of the variations in volatile phenols, arsenic, and fluorides,respectively. Beijing is undergoing increased temperature and heavy rainfall frequency during the past five decades. This study suggests that water quality related to fluoride and arsenic concentrations of most urban lakes in Beijing is becoming worse under this climate change trend.     

Study on climate-vegetation interaction in China

The climate-vegetation interaction of China is mainly controlled by the atmospheric circulations and topographic characteristics. The distribution and NPP of vegetation zones show a close relationship with a series of climatological indexes, such as annual mean temperature, precipitation, various thermal indexes, and potential evapotranspiration rates. The multivariate analysis (DCA) for climate and vegetation, zones in China provides quantitative environmental interpretation for two significant ecological gradients. The first gradient is mainly a thermal gradient, it can be displayed by latitude, altitude, biotemperature, and annual mean temperature. The second gradient is basically a moisture gradient, it correlated highly with longitude and potential evaportranspiration. The quantitative interaction or statistical models between vegetation zones and climato-geographical indexes can provide a fundamental scenario and comparative parameters for the study on climate and vegetation changes in China.     

Response of soil CO2 efflux to precipitation manipulation in a semiarid grassland

Soil CO_2efflux(SCE) is an important component of ecosystem CO_2 exchange and is largely temperature and moisture dependent, providing feedback between C cycling and the climate system. We used a precipitation manipulation experiment to examine the effects of precipitation treatment on SCE and its dependences on soil temperature and moisture in a semiarid grassland. Precipitation manipulation included ambient precipitation, decreased precipitation(- 43%), or increased precipitation(+ 17%). The SCE was measured from July2013 to December 2014, and CO_2 emission during the experimental period was assessed.The response curves of SCE to soil temperature and moisture were analyzed to determine whether the dependence of SCE on soil temperature or moisture varied with precipitation manipulation. The SCE significantly varied seasonally but was not affected by precipitation treatments regardless of season. Increasing precipitation resulted in an upward shift of SCE–temperature response curves and rightward shift of SCE–moisture response curves,while decreasing precipitation resulted in opposite shifts of such response curves. These shifts in the SCE response curves suggested that increasing precipitation strengthened the dependence of SCE on temperature or moisture, and decreasing precipitation weakened such dependences. Such shifts affected the predictions in soil CO_2 emissions for different precipitation treatments. When considering such shifts, decreasing or increasing precipitation resulted in 43 or 75% less change, respectively, in CO_2 emission compared with changes in emissions predicted without considering such shifts. Furthermore, the effects of shifts in SCE response curves on CO_2 emission prediction were greater during the growing than the non-growing season.     

Interannual variability of carbon cycle implied by a 2-d atmospheric transport model

A 2-dimensional atmospheric transport model is deployed in asimplified CO2 inverse study. Calculated carbon flux distribution for the interval from 1981 to 1997 confirms the existence of a terrestrial carbon sink in mid-high latitude area of North Hemisphere. Strong interannual variability exists in carbon flux patterns, implying a possible link with ENSO and other natural episodes such as Pinatubo volcano eruption in 1991. Mechanism of this possible link was investigated with statistic method. Correlation analysis indicated that in North Hemisphere, climatic factors such as temperature and precipitation, to some extend, could influence the carbon cycle process of land and ocean, thus cause considerable change in carbon flux distribution. In addition, correlation study also demonstrated the possible important role of Asian terrestrial ecosystems in carbon cycle.     

Flux characteristics of total dissolved iron and its species during extreme rainfall event in the midstream of the Heilongjiang River

The occurrence of extreme rainfall events and associated flooding has been enhanced due to climate changes, and is thought to influence the flux of total dissolved iron(TDI) in rivers considerably. Since TDI is a controlling factor in primary productivity in marine ecosystems, alteration of riverine TDI input to the ocean may lead to climate change via its effect on biological productivity. During an extreme rainfall event that arose in northeastern China in 2013, water samples were collected in the midstream of the Heilongjiang River to analyze the concentration and species of TDI as well as other basic parameters. The speciation of TDI was surveyed by filtration and ultrafiltration methods.Compared with data monitored from 2007 to 2012, the concentration of TDI increased significantly during this event, with an average concentration of 1.11 mg/L, and the estimated TDI flux reached 1.2 × 105 tons, equaling the average annual TDI flux level.Species analysis revealed that low-molecular-weight complexed iron was the dominant species, and the impulse of TDI flux could probably be attributed to the hydrological connection to riparian wetlands and iron-rich terrestrial runoff. Moreover, dissolved organic matter played a key role in the flux, species and bioavailability of TDI. In addition,there is a possibility that the rising TDI flux could further influence the transport and cycling of nutrients and related ecological processes in the river, estuary coupled with the coastal ecosystems, which merits closer attention in the future.     

Effect of temperature and moisture on soil organic carbon mineralization of predominantly permafrost peatland in the Great Hing’an Mountains, Northeastern China

Boreal peatlands represent a large global carbon pool.The relationships between carbon mineralization,soil temperature and moisture in the permafrost peatlands of the Great Hing'an Mountains,China,were examined.The CO2 emissions were measured during laboratory incubations of samples from four sites under different temperatures(5,10,15,and 20°C) and moisture contents(0%,30%,60%,100% water holding capacity(WHC) and completely water saturated).Total carbon mineralization ranged from 15.51 to 112.92 mg C under the treatments for all sites.Carbon mineralization rates decreased with soil depth,increased with temperature,and reached the highest at 60% WHC at the same temperature.The calculated temperature coefficient(Q10) values ranged from 1.84 to 2.51 with the soil depths and moisture.However,the values were not significantly affected by soil moisture and depth for all sites due to the different peat properties(P 0.05).We found that the carbon mineralization could be successfully predicted as a two-compartment function with temperature and moisture(R2 0.96) and total carbon mineralization was significantly affected by temperature and moisture(P 0.05).Thus,temperature and moisture would play important roles in carbon mineralization of permafrost peatlands in the Great Hing'an Mountains,indicating that the permafrost peatlands would be sensitive to the environment change,and the permafrost peatlands would be potentially mineralized under future climate change.     

Modeling soil conservation, water conservation and their tradeoffs:A case study in Beijing

Natural ecosystems provide society with important goods and services. With the rapid increase in human populations and excessive utilization of natural resources, humans frequently enhance the production of some services at the expense of the others. Although the need for tradeoffs between conservation and development is urgent, the lack of efficient methods to assess such tradeoffs has impeded progress. Three land use strategy scenarios (development scenario, plan trend scenario and conservation scenario) were created to forecast potential changes in ecosystem services from 2007 to 2050 in Beijing, China. GIS-based techniques were used to map spatial and temporal distribution and changes in ecosystem services for each scenario. The provision of ecosystem services differed spatially, with significant changes being associated with different scenarios. Scenario analysis of water yield (as average annual yield) and soil retention (as retention rate per unit area) for the period 2007 to 2050 indicated that the highest values for these parameters were predicted for the forest habitat under all three scenarios. Annual yield/retention of forest, shrub, and grassland ranked the highest in the conservation scenario. Total water yield and soil retention increased in the conservation scenario and declined dramatically in the other two scenarios, especially the development scenario. The conservation scenario was the optimal land use strategy, resulting in the highest soil retention and water yield. Our study suggests that the evaluation and visualization of ecosystem services can effectively assist in understanding the tradeoffs between conservation and development. Results of this study have implications for planning and monitoring future management of natural capital and ecosystem services, which can be integrated into land use decision-making.     

Effects of temperature change and tree species composition on N2O and NO emissions in acidic forest soils of subtropical China

Tree species and temperature change arising from seasonal variation or global warming are two important factors influencing N2O and NO emissions from forest soils. However, few studies have examined the effects of temperatures(5–35℃) on the emissions of forest soil N2O and NO in typical subtropical region. A short-term laboratory experiment was carried out to investigate the influence of temperature changes(5–35℃) on soil N2O and NO emissions under aerobic conditions in two contrasting(broad-leaved and coniferous) subtropical acidic forest types in China. The results showed that the temporal pattern of N2O and NO emissions between the three lower temperatures(5℃, 15℃, and 25℃) and 35℃ was significantly different for both broad-leaved and coniferous forest soils. The effects of temperature on soil N2O and NO emission rates varied between broad-leaved and coniferous forest soils. Both N2O and NO emissions increased exponentially with an increase in temperature in the broad-leaved forest soil. However, N2O and NO emissions in the coniferous forest soil were not sensitive to temperature change between 5℃ and 25℃. N2O and NO emission rates were significantly higher in the broad-leaved forest soil as compared with the coniferous forest soil at all incubation temperatures except 5℃. These results suggest that the broad-leaved forest could contribute more N2O and NO emissions than the coniferous forest for most of the year in the subtropical region of China.     

The role of atmospheric aerosol composition in climate change

The chemical composition of atmospheric aerosols has been investigated. Contributions ofsulfate and soot in aerosols to the atmospheric extinction are studied. Discussions are made on the problems of aerosol emitted from volcano, forest fires in northern China, 1987 and oil field fires in Kuwait, 1991. It is indicated that the changes in concentration, particle size, and chemical composition of aerosol after those events could have impacts on the climate change either regionally or globally and that the impact of aerosol particles on climate change could compensate for some temperature increase caused by greenhouse gases and the increase of surface intensity of ultraviolet radiation due to ozone layer depletion.     

Changes in groundwater levels and the response of natural vegetation to transfer of water to the lower reaches of the Tarim River

Restoration and reconstruction of the degraded Tarim River ecosystem is an important challenge.A goal of an ecological water conveyance project is to protect and restore the natural vegetation in the lower reaches of Tarim River by transferring water from Bosten Lake,through the river channel,to the lower reaches.This study describes the changes in groundwater depth during the water transfer and the respondence of riparian vegetation to alterations in groundwater levels.The results indicate that groundwater depth along the Tarim River channel has a significant spatial-temporal component.Groundwater levels closest to the river channel show the most immediate and pronounced changes as a response to water transfer while those further away respond more slowly,although the observed change appears to be longer in duration.With a rise in the groundwater level,natural vegetation responded with higher growth rates,biomass and biodiversity.These favorable changes show that it is feasible to protect and restore the degraded natural vegetation by raising the groundwater depth.Plant communities are likely to reflect the hysteresis phenomenon,requiring higher water levels to initiate and stimulate desired growth than what may be needed to maintain the plant community.Because different species have different ecologies,including different root depths and densities and water needs,their response to increasing water availability will be spatially and temporally heterogenous.The response of vegetation is also influenced by microtopography and watering style.This paper discusses strategies for the protection and restoration of the degraded vegetation in the lower reaches of the Tarim River and provides information to complement ongoing theoretical research into ecological restoration in arid or semi-arid ecosystems.