Assessment of climate variability and trend on wheat productivity in West Bengal,India: crop growth simulation approach

Wheat is the second important cereal crop after rice in West Bengal. During last three decades, due to climate fluctuations and variability, the productivity of this crop remains almost constant, bringing the threat of food security of this State. The objectives of the present study were to assess the trend of climatic variables (rainfall, rainy days, and temperature) over six locations covering five major agro-climatic sub-zones of West Bengal and to estimate the variability of potential, simulated yield using crop simulation model (DSAATv4.5) and the yield gap with actual yield. There were no significant change of rainfall and rainy days in annual, seasonal and monthly scale at all the study sites. In general, the maximum temperature is decreasing throughout West Bengal. Except for Birbhum, the minimum temperature increased significantly in different study sites. District average yield of wheat varied from 1757 kg ha^?1 at Jalpaiguri to 2421 kg ha^?1at Birbhum. The actual yield trend ranged from ??4.7 kg ha^?1 year^?1 at Nadia to 32.8 kg ha^?1 year^?1 at Birbhum. Decreasing trend of potential yield was observed in Terai (Jalpaiguri), New Alluvial Zone (Nadia) and Coastal saline zone (South 24 Parganas), which is alarming for food security in West Bengal.     

Quantifying the effects of climate trends in the past 43 years (1961–2003) on crop growth and water demand in the North China Plain

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.     

Climate change,weather variability and corn yield at a higher latitude locale: Southwestern Quebec

Climate change has led to increased temperatures, and simulation models suggest that this should affect crop production in important agricultural regions of the world. Nations at higher latitudes, such as Canada, will be most affected. We studied the relationship between climate variability (temperature and precipitation) and corn yield trends over a period of 33 years for the Monteregie region of south-western Quebec using historical yield and climate records and statistical models. Growing season mean temperature has increased in Monterregie, mainly due to increased September temperature. Precipitation did not show any clear trend over the 33 year period. Yield increased about 118 kg ha⁻¹ year⁻¹ from 1973 to 2005 (under normal weather conditions) due mainly to changes in technology (genetics and management). Two climate variables were strongly associated with corn yield variability: July temperature and May precipitation. These two variables explain more than a half of yield variability associated with climate. In conclusion, July temperatures below normal and May precipitation above normal have negative effects on corn yield, and the growing seasons have warmed, largely due to increases in the September temperature.     

Assessment of future olive crop yield by a comparative evaluation of drought indices: a case study in western Turkey

A comparative performance analysis was studied on well-known drought indices (Standardized Precipitation Index, Palmer Drought Severity Index (PDSI) and its moisture anomaly index (Orig-Z), and self-calibrated Palmer Drought Severity Index (SC-PDSI) and its moisture anomaly index (SC-Z)) to determine the most appropriate index for assessing olive (O. europaea L.) yield for oil in seven crop regions (Mu?la, Ayd?n, ?zmir, Manisa, Bal?kesir, ?anakkale, and Bursa) in western Turkey and to evaluate the vulnerability of olive yield for oil to climate change with future projections provided by the Hadley Centre for Climate Prediction and Research ENSEMBLES project (HadCM3Q0). A series of curvilinear regression-based crop yield models were developed for each of the olive-growing regions based on the drought indices. The crop yield model that performed the best was the SC-PDSI model in Mu?la, Ayd?n, ?zmir, and Manisa regions and the PDSI model in ?anakkale, Bal?kesir, and Bursa regions. The SC-PDSI index-based model described 65%, 62%, 61%, and 62% of the measured variability of olive yield in Mu?la, Ayd?n, ?zmir, and Manisa regions, respectively. The PDSI index-based model explained 59%, 58%, and 64% of the measured variability of olive yield in Bal?kesir, ?anakkale, and Bursa regions, respectively. The vulnerability of the olive yield for oil to HadCM3Q0 future climate projections was evaluated for Ayd?n and ?anakkale regions due to the resolution of the regional climate model. In terms of the future scenarios, the expected decrease in olive yield residuals was 2.5?ton (10³ trees)^?1 and 1.78?ton (10³ trees)^?1 in Ayd?n and ?anakkale regions, respectively.     

Impacts of climate change on crop evapotranspiration with ensemble GCM projections in the North China Plain

As one of the key grain-producing regions in China, the agricultural system in the North China Plain (NCP) is vulnerable to climate change due to its limited water resources and strong dependence on irrigation for crop production. Exploring the impacts of climate change on crop evapotranspiration (ET) is of importance for water management and agricultural sustainability. The VIP (Vegetation Interface Processes) process-based ecosystem model and WRF (Weather Research and Forecasting) modeling system are applied to quantify ET responses of a wheat-maize cropping system to climate change. The ensemble projections of six General Circulation Models (GCMs) under the B2 and A2 scenarios in the 2050s over the NCP are used to account for the uncertainty of the projections. The thermal time requirements (TTR) of crops are assumed to remain constant under air warming conditions. It is found that in this case the length of the crop growth period will be shortened, which will result in the reduction of crop water consumption and possible crop productivity loss. Spatially, the changes of ET during the growth periods (ET_g) for wheat range from ?7 to 0 % with the average being ?1.5?±?1.2 % under the B2 scenario, and from ?8 to 2 % with the average being ?2.7?±?1.3 % under the A2 scenario/consistently, changes of ET_g for maize are from ?10 to 8 %, with the average being ?0.4?±?4.9 %, under the B2 scenario and from ?8 to 8 %, with the average being ?1.2?±?4.1 %, under the A2 scenario. Numerical analysis is also done on the condition that the length of the crop growth periods remains stable under the warming condition via breeding new crop varieties. In this case, TTR will be higher and the crop water requirements will increase, with the enhancement of the productivity. It is suggested that the options for adaptation to climate change include no action and accepting crop loss associated with the reduction in ET_g, or breeding new cultivars that would maintain or increase crop productivity and result in an increase in ET_g. In the latter case, attention should be paid to developing improved water conservation techniques to help compensate for the increased ET_g.     

Climate change impacts on sugarcane attainable yield in southern Brazil

This study evaluated the effects of climate change on sugarcane yield, water use efficiency, and irrigation needs in southern Brazil, based on downscaled outputs of two general circulation models (PRECIS and CSIRO) and a sugarcane growth model. For three harvest cycles every year, the DSSAT/CANEGRO model was used to simulate the baseline and four future climate scenarios for stalk yield for the 2050s. The model was calibrated for the main cultivar currently grown in Brazil based on five field experiments under several soil and climate conditions. The sensitivity of simulated stalk fresh mass (SFM) to air temperature, CO₂ concentration [CO₂] and rainfall was also analyzed. Simulated SFM responses to [CO₂], air temperature and rainfall variations were consistent with the literature. There were increases in simulated SFM and water usage efficiency (WUE) for all scenarios. On average, for the current sugarcane area in the State of São Paulo, SFM would increase 24 % and WUE 34 % for rainfed sugarcane. The WUE rise is relevant because of the current concern about water supply in southern Brazil. Considering the current technological improvement rate, projected yields for 2050 ranged from 96 to 129 t?ha^?1, which are respectively 15 and 59 % higher than the current state average yield.     

Simulating the impacts of climate change on cotton production in India

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.     

Impacts of climate change as a function of global mean temperature: maize productivity and water use in China

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.     

Effects of temperature rise and increase in CO2 concentration on simulated wheat yields in Europe

A crop-growth-simulation model based on SUCROS87 was used to study effects of temperature rise and increase of atmospheric CO₂ concentration on wheat yields in several regions in Europe. The model simulated potential and water-limited crop production (growth with ample supply of nutrients and in the absence of damage by pests, diseases and weeds). Historic daily weather data from 13 sites in Western Europe were used as starting point.For potential production (optimal water) a 3 °C temperature rise led to a yield decline due to a shortening of the growing period on all locations. Doubling of the CO₂ concentration caused an increase in yield of 40% due to higher assimilation rates. It was found that effects of higher temperature and higher CO₂ concentration were nearly additive and the combination of both led to a yield increase of 1–2 ton ha^-1. A very small CO₂-temperature interaction was found: the effect of doubled CO₂ concentration on crop yield was larger at higher temperatures. The inter-annual yield variability was hardly affected.When water was limiting crop-production effects of temperature rise and higher CO₂ levels were different than for the potential production. Rise in temperature led to a smaller yield reduction, doubled CO₂ concentration to a larger yield increase and combination of both led to a large yield increase (3 ton ha^-1) in comparison with yields simulated for the present situation. Both rise in temperature and increase in the CO₂ concentration reduced water requirements of the crop. Water shortages became smaller, leading to a reduction in inter-annual variability. It is concluded that when no major changes in precipitation pattern occur a climate change will not affect wheat yields since negative effects of higher temperatures are compensated by positive effects of CO₂ enrichment.     

Carbon for Farmers: Assessing the Potential for Soil Carbon Sequestration in the Old Peanut Basin of Senegal

Carbon sequestration in soil organic matter of degraded Sahelian agro-ecosystems could play a significant role in the global carbon (C) uptake through terrestrial sinks while, simultaneously, contributing to sustainable agriculture and desertification control. The paper documents the results of a two-year pilot project in Senegal assessing real project opportunities with main emphasis on the West-Central Agricultural Region (Old Peanut Basin). Current total system C content in this region, calculated on the basis of in situ soil and biomass carbon measurements, amounted to 28 t ha^–1 with 11 t C ha^–1 in soils (0–20 cm) and 6.3 t C ha^–1 in trees. Potential changes in soil C, simulated with CENTURY for a 25-year period, ranged from –0.13 t C ha^–1 yr^–1 under poor management to +0.43 t C ha^–1 yr^–1 under optimum agricultural intensification. Simulated changes in crop yields varied from –62% to +200% under worst and best management scenarios respectively. Best management practices that generate the highest sequestration rates are economically not feasible for the majority of local smallholders, unless considerable financial support is provided. Especially when applied on a larger scale, such packages risk to undermine local, opportunistic management regimes and, in the long run, also the beneficiaries capacity to successfully adapt to their constantly changing environment.     

Carbon for Farmers: Assessing the Potential for Soil Carbon Sequestration in the Old Peanut Basin of Senegal

Carbon sequestration in soil organic matter of degraded Sahelian agro-ecosystems could play a significant role in the global carbon (C) uptake through terrestrial sinks while, simultaneously, contributing to sustainable agriculture and desertification control. The paper documents the results of a two-year pilot project in Senegal assessing real project opportunities with main emphasis on the West-Central Agricultural Region (Old Peanut Basin). Current total system C content in this region, calculated on the basis of in situ soil and biomass carbon measurements, amounted to 28 t ha^–1 with 11 t C ha^–1 in soils (0–20 cm) and 6.3 t C ha^–1 in trees. Potential changes in soil C, simulated with CENTURY for a 25-year period, ranged from –0.13 t C ha^–1 yr^–1 under poor management to +0.43 t C ha^–1 yr^–1 under optimum agricultural intensification. Simulated changes in crop yields varied from –62% to +200% under worst and best management scenarios respectively. Best management practices that generate the highest sequestration rates are economically not feasible for the majority of local smallholders, unless considerable financial support is provided. Especially when applied on a larger scale, such packages risk to undermine local, opportunistic management regimes and, in the long run, also the beneficiaries capacity to successfully adapt to their constantly changing environment.     

Evaluating observed and projected future climate changes for the Arctic using the K?ppen-Trewartha climate classification

The ecosystems in the Arctic region are known to be very sensitive to climate changes. The accelerated warming for the past several decades has profoundly influenced the lives of the native populations and ecosystems in the Arctic. Given that the K?ppen-Trewartha (K-T) climate classification is based on reliable variations of land-surface types (especially vegetation), this study used the K-T scheme to evaluate climate changes and their impact on vegetation for the Arctic (north of 50°N) by analyzing observations as well as model simulations for the period 1900–2099. The models include 16 fully coupled global climate models from the Intergovernmental Panel on Climate Change Fourth Assessment. By the end of this century, the annual-mean surface temperature averaged over Arctic land regions is projected to increase by 3.1, 4.6 and 5.3°C under the Special Report on Emissions Scenario (SRES) B1, A1b, and A2 emission scenarios, respectively. Increasing temperature favors a northward expansion of temperate climate (i.e., Dc and Do in the K-T classification) and boreal oceanic climate (i.e., Eo) types into areas previously covered by boreal continental climate (i.e., Ec) and tundra; and tundra into areas occupied by permanent ice. The tundra region is projected to shrink by ?1.86?×?10⁶?km² (?33.0%) in B1, ?2.4?×?10⁶?km² (?42.6%) in A1b, and ?2.5?×?10⁶?km² (?44.2%) in A2 scenarios by the end of this century. The Ec climate type retreats at least 5° poleward of its present location, resulting in ?18.9, ?30.2, and ?37.1% declines in areal coverage under the B1, A1b and A2 scenarios, respectively. The temperate climate types (Dc and Do) advance and take over the area previously covered by Ec. The area covered by Dc climate expands by 4.61?×?10⁶?km² (84.6%) in B1, 6.88?×?10⁶?km² (126.4%) in A1b, and 8.16?×?10⁶?km² (149.6%) in A2 scenarios. The projected redistributions of K-T climate types also differ regionally. In northern Europe and Alaska, the warming may cause more rapid expansion of temperate climate types. Overall, the climate types in 25, 39.1, and 45% of the entire Arctic region are projected to change by the end of this century under the B1, A1b, and A2 scenarios, respectively. Because the K-T climate classification was constructed on the basis of vegetation types, and each K-T climate type is closely associated with certain prevalent vegetation species, the projected large shift in climate types suggests extensive broad-scale redistribution of prevalent ecoregions in the Arctic.     

Evaluation of three simulation approaches for assessing yield of rainfed sunflower in a Mediterranean environment for climate change impact modelling

The determination of the impact of climate change on crop yield at a regional scale requires the development of new modelling methodologies able to generate accurate yield estimates with reduced available data. In this study, different simulation approaches for assessing yield have been evaluated. In addition to two well-known models (AquaCrop and Stewart function), a methodological proposal considering a simplified approach using an empirical model (SOM) has been included in the analysis. This empirical model was calibrated using rainfed sunflower experimental field data from three sites located in Andalusia, southern Spain, and validated using two additional locations, providing very satisfactory results compared with the other models with higher data requirements. Thus, only requiring weather data (accumulated rainfall from the beginning of the season fixed on September 1st, and maximum temperature during flowering) the approach accurately described the temporal and spatial yield variability observed (RMSE?=?391 kg ha^?1). The satisfactory results for assessing yield of sunflower under semi-arid conditions obtained in this study demonstrate the utility of empirical approaches with few data requirements, providing an excellent decision tool for climate change impact analyses at a regional scale, where available data is very limited.     

Climatic constraints for the maize-soybean system in the humid subtropical region of Argentina

The implementation of two summer crops in the same growing season is a possible alternative for land intensification in areas with a long frost-free period. The aim of this study was to analyse the strategy of land intensification through the implementation of the maize-soybean succession at two locations (Reconquista, 29°09′S 59°40′W and Las Breñas, 27°05′S 61°5′W) of the humid subtropical region of Argentina. CERES-Maize and CROPGRO-Soybean models were used to evaluate the impact of inter-annual variability of climate (36 years) of both locations on rain-fed grain yields of the following productive alternatives: (i) monoculture of maize, (ii) monoculture of soybean and (iii) the succession of a short-cycle maize followed by soybean as the second summer crop (maize-soybean system). The maize-soybean system was evaluated by the method of land equivalent ratio (LER), based on the sum of the relative grain yields of its components. The impact of the inter-annual variability of climate and of “El Niño” or “La Niña” episodes (El Niño Southern Oscillation phenomenon (ENSO)) on LER values was analysed. Simulated yields of maize monoculture (5687 kg ha^?1; CV = 49.7% and 5637 kg ha^?1; CV = 57.6% at Reconquista and Las Breñas, respectively) were higher than those of the short-cycle maize, especially at Las Breñas (5448 kg ha^?1; CV = 49.3% and 2322 kg ha^?1; CV = 33.9% at Reconquista and Las Breñas, respectively). Simulated yields of the soybean monoculture were higher (3588 kg ha^?1; CV = 26.1% and 2883 kg ha^?1; CV = 20.7% at Reconquista and Las Breñas, respectively) that those of the soybean as the second crop (2634 kg ha^?1; CV = 38.1% and 2456 kg ha^?1; CV = 32.9% at Reconquista and Las Breñas, respectively) at both locations. Average LERs were 1.69 (CV = 11.4%) at Reconquista and 1.41 (CV = 26.1%) at Las Breñas, and the inter-annual variability of LER was mainly determined by grain yields of (i) soybean as the second crop at Reconquista and (ii) maize monoculture at Las Breñas. Soil water content after maize harvest and rainfalls during reproductive period of soybean as the second crop conditioned LER values, but they were generally greater than 1. At Reconquista, LER values were not affected by the different episodes of ENSO phenomenon. By contrast, at Las Breñas, LER values were higher during La Niña episodes (1.48; CV = 26.6%) than during El Niño episodes (1.32; CV = 23.7%) mainly by their effects on grain yields of maize monoculture. Therefore, crop simulation models demonstrate the possibility to intensify land use (40–70%) at two locations of the humid subtropical region of Argentina, by the implementation of the maize-soybean system.     

Climate Change Impacts and Adaptation Strategies in Spring Barley Production in the Czech Republic

The crop model CERES-Barley was used to assess the impacts of increased concentration of atmospheric CO₂ on growth and development of the most important spring cereal in Central and Western Europe, i.e., spring barley, and to examine possible adaptation strategies. Three experimental regions were selected to compare the climate change impacts in various climatic and pedological conditions. The analysis was based on multi-year crop model simulations run with daily weather series obtained by stochastic weather generator and included two yield levels: stressed yields and potential yields. Four climate change scenarios based on global climate models and representing 2 × CO₂ climate were applied. Results: (i) The crop model is suitable for use in the given environment, e.g., the coefficient of determination between the simulated and experimental yields equals 0.88. (ii) The indirect effect related to changed weather conditions is mostly negative. Its magnitude ranges from ?19% to +5% for the four scenarios applied at the three regions. (iii) The magnitude of the direct effect of doubled CO₂ on the stressed yields for the three test sites is 35–55% in the present climate and 25–65% in the 2 × CO₂ climates. (iv) The stressed yields would increase in 2 × CO₂ conditions by 13–52% when both direct and indirect effects were considered. (v) The impacts of doubled CO₂ on potential yields are more uniform throughout the localities in comparison with the stressed yields. The magnitude of the indirect and direct effects ranges from ?1 to ?9% and from +31 to +33%, respectively. Superposition of both effects results in 19–30% increase of the potential yields. (vi) Application of the earlier planting date (up to 60 days) would result in 15–22% increase of the yields in 2 × CO₂ conditions. (vii) Use of a cultivar with longer vegetation duration would bring 1.5% yield increase per one extra day of the vegetation season. (viii) The initial water content in the soil water profile proved to be one of the key elements determining the spring barley yield. It causes the yields to increase by 54–101 kg.ha^?1 per 1% increase of the available soil water content on the sowing day.     

Trends in carbon sink along the Belt and Road in the future under high emission scenario

Over the past three decades, the drawdown of atmospheric CO₂ in vegetation and soil has fueled net ecosystem production (NEP). Here, a global land-surface model (CABLE) is used to estimate the trend in NEP and its response to atmospheric CO₂, climate change, biological nitrogen (N) fixation, and N deposition under future conditions from 2031 to 2100 in the Belt and Road region. The trend of NEP simulated by CABLE decreases from 0.015 Pg carbon (C) yr^?2 under present conditions (1936–2005) to ?0.023 Pg C yr^?2 under future conditions. In contrast, the trend in NEP of the CMIP6 ensemble changes from 0.014 Pg C yr^?2 under present conditions to ?0.009 Pg C yr^?2 under future conditions. This suggests that the trend in the C sink for the Belt and Road region will likely decline in the future. The significant difference in the NEP trend between present and future conditions is mainly caused by the difference in the impact of climate change on NEP. Considering the responses of soil respiration (RH) or net primary production (NPP) to surface air temperature, the trend in surface air temperature changes from0.01°C yr^?1 under present conditions to 0.05°C yr^?1 under future conditions. CABLE simulates a greater response of RH to surface temperature than that of NPP under future conditions, which causes a decreasing trend in NEP. In addition, the greater decreasing trend in NEP under future conditions indicates that the C–climate–N interaction at the regional scale should be considered. It is important to estimate the direction and magnitude of C sinks under the C neutrality target.摘要目前, 在区域尺度, NEP趋势变化的强度和影响机制还存在很大的不确定性. 针对这一问题, 我们选取了一带一路覆盖的区域为研究对象, 基于全球陆面模式 (CABLE)和第六次国际耦合模式比较计划 (CMIP6), 评估了历史和未来NEP趋势的变化, 分析了影响的机制. 从过去到未来, CABLE结果表明NEP的趋势从 0.015 Pg C yr^?2 减少到 –0.023 Pg C yr^?2; CMIP6结果为从0.014 Pg C yr^?2转变为–0.009 Pg C yr^?2. 气候变化是引起这一变化的主因. 我们的研究结果强调了碳-气候-氮相互作用的重要性, 这对碳中和目标下碳汇潜力的准确估算尤为重要.     

Ecological limits to terrestrial biological carbon dioxide removal

Terrestrial biological atmospheric carbon dioxide removal (BCDR) through bioenergy with carbon capture and storage (BECS), afforestation/reforestation, and forest and soil management is a family of proposed climate change mitigation strategies. Very high sequestration potentials for these strategies have been reported, but there has been no systematic analysis of the potential ecological limits to and environmental impacts of implementation at the scale relevant to climate change mitigation. In this analysis, we identified site-specific aspects of land, water, nutrients, and habitat that will affect local project-scale carbon sequestration and ecological impacts. Using this framework, we estimated global-scale land and resource requirements for BCDR, implemented at a rate of 1 Pg C y^?1. We estimate that removing 1 Pg C y^?1 via tropical afforestation would require at least 7?×?10⁶ ha y^?1 of land, 0.09 Tg y^?1 of nitrogen, and 0.2 Tg y^?1 of phosphorous, and would increase evapotranspiration from those lands by almost 50 %. Switchgrass BECS would require at least 2?×?10⁸ ha of land (20 times U.S. area currently under bioethanol production) and 20 Tg y^?1 of nitrogen (20 % of global fertilizer nitrogen production), consuming 4?×?10¹²?m³ y^?1 of water. While BCDR promises some direct (climate) and ancillary (restoration, habitat protection) benefits, Pg C-scale implementation may be constrained by ecological factors, and may compromise the ultimate goals of climate change mitigation.     

Modelling the impacts of climate change on wheat yield and field water balance over the Murray�CDarling Basin in Australia

The study used a modelling approach to assess the potential impacts of likely climate change and increase in CO₂ concentration on the wheat growth and water balance in Murray?CDarling Basin in Australia. Impacts of individual changes in temperature, rainfall or CO₂ concentration as, well as the 2050 and 2070 climate change scenarios, were analysed. Along an E?CW transect, wheat yield at western sites (warmer and drier) was simulated to be more sensitive to temperature increase than that at eastern sites; along the S?CN transect, wheat yield at northern warmer sites was simulated to be more sensitive to temperature increase, within 1?C3°C temperature increase. Along the E?CW and S?CN transects, wheat at drier sites would benefit more from elevated [CO₂] than at wetter sites, but more sensitive to the decline in rainfall. The increase in temperature only did not have much impact on water balance. Elevated [CO₂] increased the drainage in all the sites, whilst rainfall reduction decreased evapotranspiration, runoff and drainage, especially at drier sites. In 2050, wheat yield would increase by 1?C10% under all climate change scenarios along the S?CN transect, except for the northernmost site (Dalby). Along the E?CW transect, the most obvious increase of wheat yields under all climate change scenarios occurred in cooler and wetter eastern sites (Yass and Young), with an average increase rate of 7%. The biggest loss occurred at the driest sites (Griffith and Swan Hill) under A1FI and B2 scenarios, ranging from ?5% to ?16%. In 2070, there would be an increased risk of yield loss in general, except for the cool and wet sites. Water use efficiency was simulated to increase at most of the study sites under all the climate change scenarios, except for the driest site. Yield variability would increase at drier sites (Ardlethan, Griffith and Swan Hill). Soil types would also impact on the response of wheat yield and water balance to future climate change.     

Thermal Climate Variations and Potential Modification of the Cropping Pattern in Bangladesh

Summary Changes in the thermal climate due to inter-annual climatic variability can potentially modify existing cropping pattern by forcing farmers to rearrange transplanting and harvesting dates. In the present study, a crop climate model, the YIELD, has been applied to 12 meteorological stations located in major rice growing regions in Bangladesh to estimate the effect of thermal climate variations on the transplanting and harvesting dates of boro rice and the resultant potential changes in cropping pattern and spatial shift. The abnormal thermal climate scenarios have been created by synthetically perturbing mean air temperatures (T_air) up to −5 °C to +5 °C with an interval of 1 °C for each of these stations. Historical meteorological records of air temperature in Bangladesh have been used to prepare these scenarios. The study finds that under abnormally cool conditions transplanting dates will be pushed well into February to avoid plant injury and harvesting dates will be moved into the monsoon. The growing seasons will be longer under cooler than normal thermal conditions. Under abnormally warm conditions harvesting dates will be established well into March and will cause reduction of yield due to a shorter growing season. These conditions will also cause spatial shift in crop potential and changes in the cropping pattern. Due to a longer boro rice growing season farmers will lose a significant amount of cropping land which is usually used for low and deep water rice cultivation. New crops will need to be introduced during the beginning of a year to overcome the loss of production under abnormally cool conditions. Wheat and potato can be good options for the farmers for such conditions. New aus rice variety needs to be introduced after the boro harvesting under warmer than the normal conditions to overcome the loss of yield due to a shorter growing season. Received September 16, 1996 Revised September 8, 1997     

Carbon sequestration potential of parkland agroforestry in the Sahel

Establishing parkland agroforestry on currently treeless cropland in the West African Sahel may help mitigate climate change. To evaluate its potential, we used climatically suitable ranges for parklands for 19 climate scenarios, derived by ecological niche modeling, for estimating potential carbon stocks in parkland and treeless cropland. A biocarbon business model was used to evaluate profitability of hypothetical Terrestrial Carbon Projects (TCPs), across a range of farm sizes, farm numbers, carbon prices and benefit sharing mechanisms. Using climate analogues, we explored potential climate change trajectories for selected locations. If mature parklands covered their maximum range, carbon stocks in Sahelian productive land would be about 1,284?Tg, compared to 725?Tg in a treeless scenario. Due to slow increase rates of total system carbon by 0.4?Mg?C?ha^?1 a^?1, most TCPs at carbon prices that seem realistic today were not feasible, or required the participation of large numbers of farmers. For small farms, few TCP scenarios were feasible, and low Net Present Values for farmers made it unlikely that carbon payments would motivate many to participate in TCPs, unless additional benefits were provided. Climate analogue locations indicated an uncertain climate trajectory for the Sahel, but most scenarios projected increasing aridity and reduced suitability for parklands. The potentially severe impacts of climate change on Sahelian ecosystems and the uncertain profitability of TCPs make the Sahel highly risky for carbon investments. Given the likelihood of degrading environmental conditions, the search for appropriate adaptation strategies should take precedence over promoting mitigation activities.