小型水体对气温观测环境影响的初步模拟分析

为研究水体对气温观测环境的影响,应用WRF中尺度模式,通过对四季晴天小风、阴天大风背景天气下有无水体算例模拟结果的比较,分析了浙江青山湖水体(6.5 km2)对周边2 m高度处气温的影响。模拟结果表明:(1)冬季天气条件通常较稳定,水体对下风方的影响最为明显;春、秋季节水体对下风方的影响次之,夏季局地热力环流复杂,水体对下风方气温影响不若其他季节明显。(2)青山湖水体对下风方约5 km内的气温可能产生明显影响,非下风方缩短为0.4 km。(3)水体面积越大,对周边气温影响距离越大。(4)当风速大于6.2 m·s-1时,水陆热力性质差异迅速被平流项输送携带走,水体对下风方气温影响不明显。而湍流扩散项则将水体与陆面热力性质的差异向上传递,湍流强度大于0.5 m2·s-2时,水体对下风方气温的影响不明显。     

Spatiotemporal distributions of δD in atmospheric water vapor based on TES Data during 2004–2009

The spatial and temporal distributions of the stable isotopes such as HD¹⁶O (or ¹H²H¹⁶O, or HDO) and H₂ ¹⁸O in atmospheric water vapor are related to evaporation in source places, vapor condensation during transport, and vapor convergence and divergence, and thus provide useful information for investigation and understanding of the global water cycle. This paper analyzes spatiotemporal variations of the content of isotope HDO (i.e., δ _D), in atmospheric water vapor, namely, δ _{D v}, and the relationship of δ _{D v} with atmospheric humidity and temperature at different levels in the troposphere, using the HDO and H₂O data retrieved from the Tropospheric Emission Spectrometer (TES) at seven pressure levels from 825 to 100 hPa. The results indicate that δ _{D v} has a clear zonal distribution in the troposphere and a good correspondence with atmospheric precipitable water. The results also show that δ _{D v} decreases logarithmically with atmospheric pressure and presents a decreasing trend from the equator to high latitudes and from lands to oceans. Seasonal changes of δ _{D v} exhibit regional differences. The spatial distribution and seasonal variation of δ _{D v} in the low troposphere are consistent with those in the middle troposphere, but opposite situations occur from the upper troposphere to the lower stratosphere. The correlation between δ _{D v} and temperature has a similar distribution pattern to the correlation between δ _{D v} and precipitable water in the troposphere. The stable isotope HDO in water vapor (δ _{D v}), compared with that in precipitation (δ _{D p}), is of some differences in spatial distribution and seasonal variation, and in its relationship with temperature and humidity, indicating that the impacts of stable isotopic fractionation and atmospheric circulation on the two types of stable isotopes are different.     

博斯腾湖面积定量遥感

采用NOAA/AVHRR资料, 利用水体与地物光谱特性的差异, 结合通道2方案和通道2/通道1方案, 对4月博斯腾湖水体进行判识, 而利用通道2、通道2/通道1并结合通道4的方案判识了10月博斯腾湖水体, 在此基础上利用线性混合模式对混合像元做了处理, 定量估算了1990—1998年4月和10月博斯腾湖的面积, 调研了9年来博斯腾湖面积变化情况, 表明9年间博斯腾湖面积呈增加趋势。进一步采用主成分分析方法对博斯腾湖面积增大原因做了初步的气候分析, 表明1988年以来博斯腾湖地区气温升高、蒸发量减少、降水有所增加, 而人类活动用水和出流稳定并有减少是博斯腾湖面积增加的主要原因。而博斯腾湖及上游地区季节性积雪的特征, 使冬季积雪水资源注入博斯腾湖, 导致春季博斯腾湖面积较秋季大。     

Methane emission from rice paddies

Methane release rates from rice paddies have been measured in Andalusia, Spain, during almost a complete vegetation period in 1982 using the static box system. The release rates ranged between 2 and 14 mg/m²/h and exhibited a strong seasonal variation with low values during the tillering stage and shortly before harvest, while maximum values were observed at the end of the flowering stage. The CH₄ release rate, averaged over the complete vegetation period, accounted for 4 mg/m²/h which results in a worldwide CH₄ emission from rice paddies of 35–59×10¹² g/yr if we assume that the observed CH₄ release rates are representative of global conditions. The CH₄ release rates showed diurnal variations with higher values late in the afternoon which were most likely caused by temperature variations within the upper layers of the paddy soils. Approximately 95% of the CH₄ emitted into the atmosphere by rice paddies was due to transport through the rice plants. Transport by bubbles or diffusion through the paddy water was of minor importance. Incubation experiments showed that CH₄ was neither produced nor consumed in the paddy water. The relase of CH₄ from rice paddies caused a diurnal variation of CH₄ in ambient air within the rice-growing area with maximum values of up to 2.3 ppmv during the early morning, compared to average daytime values of 1.75 ppmv.     

南四湖对鲁西南气温分布的影响

利用1981—2015年鲁西南25个气象站35 a整编资料及2015—2019年部分区域气象站逐小时数据资料,系统分析了鲁西南气温分布特征及南四湖在其分布中的贡献,揭示出：年平均气温在东南部湖区呈现出与南四湖东南—西北走向一致的暖舌,南四湖改变了气温通常的南高北低态势,使得鲁西南的月平均气温分布呈现出了东高西低型和过渡调整型;湖区是最高气温分布的低值区,最低气温分布的高值区,年气温日较差平均值偏小;相对于鲁西南同经度和同纬度区域,湖区的月气温日较差平均值和月气温日较差最大值均偏小,秋季差异最明显,夏季差异最小,气温日变化曲线较平稳,白天气温较高时段偏低,夜间气温较低时段偏高,日最高气温出现时间约迟1 h,在同一天气条件下,湖区气温日变幅总是偏小,不同天气条件下,日最高气温的差值和日最低气温的差值表现为晴天最大、阴天次之、雨天最小。     

Chemical composition of rain water and influence of airmass trajectories at a rural site in an ecological sensitive area of Western Ghats (India)

Samples of rain water were collected during monsoon season (June to September) of 2006 and 2007 at Hudegadde, a rural site located in an ecological sensitive area of Western Ghats. The collected samples were analyzed for pH, conductivity and major ions. At this site, rainwater pH varied from 4.20 to 7.39 with 5.65 as volume weighed mean. The observed mean was slightly lower than the average pH reported at most of the Indian continental sites. Monthly variation showed that average pH of rain water was the lowest during September (end of monsoon) and the highest during July (peak of monsoon). Overall, marine sources had dominating influence at this site. However, significant influence of anthropogenic and crustal sources from local as well as inter-continental regions was also noticed. As compared to NO₃⁻, higher concentration of SO₄²⁻ was noticed which might be due to contribution from industrial activities responsible for SO₂ emission. At this site, influence of five types of airmass trajectories was noticed i.e. i) C.I.O. (Central part of Indian Ocean)-when air masses blown from Maldives and nearby region of central Indian ocean. These airmasses had higher concentrations of nss Ca²⁺ which did not show any adverse impact on the pH; ii) N.W.I.O.(North-West Indian Ocean)-when airmasses travelled from oceanic region close to north-east Africa. These airmassses had higher concentrations of nss sulphate and nitrate and gave rise to acid rain; iii) S.W.I.O. (South -West Indian Ocean)- when airmasses came from southern part of Indian ocean (close to Mauritius). During these airmasses, rain water samples had almost equal ratio of nss SO₄²⁻ and nss Ca²⁺ similar to N.W.I.O but very low NO₃⁻ ; iv) Gulf-when airmasses were observed coming from Gulf region. Although these airmasses contributed only 2% of the total number of samples but carried high amount of nss SO₄²⁻ which gave rise to acid rain. The second lowest pH was observed during these airmasses which might be due to very high nssSO₄²⁻/nssCa²⁺ ratios; v) N.W.I.O. + S.W.I.C. (North-West Indian Ocean+South-West Indian Continental)- when airmasses originated from north-west Indian Ocean travelling towards south continental part of India and then arriving to the site. During these airmasses, samples showed typical influence of urban activities having high concentrations of nss SO₄²⁻ and NO₃⁻ leading to the lowest pH of rain water.     

博斯腾湖水位变化特征及其可能影响机制分析

应用开都河下游大山口水文站径流和博斯腾湖1956-2009年的逐月水位数据和流域内各气象站的气象数据,通过模糊聚类等统计方法,分析了博斯腾湖水位变化趋势及其可能影响因子.结果表明:博斯腾湖的水位年际变化受开都河流域径流的影响很大,当开都河流域径流量大时博湖水位较高,且开都河径流与其上、下游气温和降水关系密切.博斯腾湖水位逐年的月变化基本上可以分为5类,其中最主要的为第一类型和第二类型:第一类为递减型,特征为季节变化不明显,水位在春季较高,以后逐渐降低;第二类为递增型,特点是季节变化较第一大类明显,水位在夏末秋初的时候较高,整体呈现上升趋势.递增、递减型出现的主要原因是受上下游降水和大山口径流的影响,当上下游降水和径流偏多时水位月际变化出现递增型,反之易出现递减型.     

MEASUREMENT OF pH AND CHEMICAL ANALYSIS OF RAIN WATER IN RURAL AREA OF INDIA

Large number of rain water samples, at 7 rural locations in the semi-arid region of the DeccanPlateau were collected during 4 consecutive monsoon seasons (1979-1982).pH, conductivityand the major ionic components (C1~-, SO_4~= , NO_3~- , NH_4~+ , Na~+, K~+, Ca~(++), Mg~(++) of the abovesamples were determined. The pH of rain water was found to be highly alkaline and the valuesvaried from 6.4 to 7.8. Soil-oriented elements showed good correltioan (r~0.6) with pH valuesof rain water. The high concentration of soil-oriented elements, specially Ca~(++), is found to play animportant role in neutralizing the acidity of rain water and maintaining high alkaline pH. The studysuggested that the contribution of atmospheric aerosol of natural sources (sea and soil) to thechemical composition of rain water is more than that of anthropogenic origin.     

长江三角洲地区净生态系统二氧化碳通量及浓度的数值模拟

净生态系统碳通量(NEE)的计算对于准确模拟区域碳通量和大气CO₂浓度的时空变化至关重要。本文利用中尺度大气-温室气体耦合模式WRF-GHG(Weather Research and Forecasting Model with Greenhouse Gases Module),对2010年7月28日至2010年8月2日期间影响长江三角洲地区大气CO₂浓度及时空分布的各种过程进行了详尽模拟。结果表明,植被光合呼吸模型(VPRM)能模拟不同植被下垫面NEE的日变化;WRF-GHG模拟的大气CO₂浓度日变化与观测相吻合,但低估了大气CO₂浓度5~15 ppm(ppm表示10-6),这可能与人为排放源的低估、VPRM参数的不确定性以及气象场模拟的不准确性有关。太湖和植被覆盖较好的地区如浙江北部山区是该地区的主要碳汇,而城市为CO₂的主要排放源。太湖和陆地生态系统对区域内碳循环起到一定的调节作用,减缓区域大气CO₂浓度的升高。此外,局地气象条件如湖陆风对太湖周边地区大气CO₂浓度有显著影响。     

锡林浩特草原CO2通量特征及其影响因素分析

利用锡林浩特国家气候观象台开路涡度相关系统、辐射土壤观测系统,测得的长期连续通量观测数据,对锡林浩特草原2009—2011年期间的CO₂通量观测特征进行了分析。结果表明:CO₂通量存在明显的年际、季节和日变化特征。3 a中NEE年际变率达到200 g·m^-2,季节变率最大达到460 g·m^-2,日变化幅度生长季最大达到0.25 mg·m^-2·s^-1。通过不同时间尺度碳通量与温度、水分、辐射等环境因子的分析,认为CO₂通量日变化主要受温度和光合有效辐射影响,而季节变化和年变化主要受降水和土壤含水量的影响。降水强度及时间分布是制约牧草CO₂吸收的关键因素,大于15%的土壤含水量有利于促进牧草生长。     

The chemical composition of rainwater over Büyükçekmece Lake, Istanbul

In the present study, the precipitation near Büyükçekmece Lake, which is one of the important drinking water sources of Istanbul city, was studied during October 2001–July 2002. Seventy-nine bulk precipitation samples were collected at two sampling stations near the Lake (41°2′35″N, 28°35′25″E and 41°5′30″N, 28°37′7″E). The study comprised the determination of H⁺, Cl⁻, NO₃⁻, SO₄²⁻, NH₄⁺, Na, K, Mg, Ca, Al, Ba, Fe, Cu and Mn concentrations in bulk deposition rain event samples. The average volume-weighted pH value was found to be 4.81, which points out that the rain is slightly acidic. High sulfate concentrations were observed together with high H⁺ ion values. Sulfur emissions were the major cause for the observed high hydrogen ion levels. On the basis of factor analysis and correlation matrix analysis, it has been found that in this region, acid neutralization is brought about by calcium rather than the ammonium ion. The varimax rotated factor analysis grouped the variables into four factors, which are crustal, marine and two anthropogenic sources.     

Effects of increased CO2 on land water balance from 1850 to 1989

Numerous studies have shown that increased atmospheric CO₂ concentration is one of the most important factors altering land water balance. In this study, we investigated the effects of increased CO₂ on global land water balance using the dataset released by the Coupled Model Intercomparison Project Phase 5 derived from the Canadian Centre for Climate Modelling and Analysis second-generation Earth System Model. The results suggested that the radiative effect of CO₂ was much greater than the physiological effect on the water balance. At the model experiment only integrating CO₂ radiative effect, the precipitation, evapotranspiration (ET) and runoff had significantly increased by 0.37, 0.12 and 0.31 mm year^?2, respectively. Increases of ET and runoff caused a significant decrease of soil water storage by 0.05 mm year^?2. However, the results showed increases of runoff and decreases of precipitation and ET in response to the CO₂ fertilisation effect, which resulted into a small, non-significant decrease in the land water budget. In the Northern Hemisphere, especially on the coasts of Greenland, Northern Asia and Alaska, there were obvious decreases of soil water responding to the CO₂ radiative effect. This trend could result from increased ice–snow melting as a consequence of warmer surface temperature. Although the evidence suggested that variations in soil moisture and snow cover and vegetation feedback made an important contribution to the variations in the land water budget, the effect of other factors, such as aerosols, should not be ignored, implying that more efforts are needed to investigate the effects of these factors on the hydrological cycle and land water balance.     

Effects of changes in temperature and CO2 concentration on simulated spring wheat yields in The Netherlands

A crop growth simulation model based on SUCROS87 was constructed to study the effects of temperature rise and increase of the atmospheric CO₂ concentration on spring wheat yields in The Netherlands. The model simulated potential production (limited by crop characteristics, temperature and radiation but without any stress from water or nutrient shortages or pests, diseases and weeds) and water-limited production in which growth is also limited by water shortage. The model was validated for the present climatic conditions. When daily weather data from a nearby station were used, the model was well able to simulate yields obtained in field experiments.Effects of several combinations of temperature rise and atmospheric CO₂ concentration on simulated yields were studied. A temperature rise resulted in a reduction in simulated yield due to shortening of the growing period. Large variations existed in the magnitude of this reduction. Increases in atmospheric CO₂ concentration led to yield increases due to higher assimilation rates and to increase of the water use efficiency. Combination of temperature rise and higher CO₂ concentration resulted in small yield increases in years in which water was not limiting growth and large yield increases in dry years.Change of variety or of sowing date could not reduce the negative effects of temperature rise on simulated yields.     

Global transport and inter-reservoir exchange of carbon dioxide with particular reference to stable isotopic distributions

A two-dimensional model of global atmospheric transport is used to relate estimated air-to-surface exchanges of carbon dioxide (CO₂) to spatial and temporal variations of atmospheric CO₂ concentrations and isotopic composition. The atmospheric model coupled with models of the biosphere and mixed layer of the ocean describes the gross features of the global carbon cycle. In particular this paper considers the change in isotopic composition due to interreservoir exchanges and thus the potential application and measurement requirements of new isotopic observational programs.A comparison is made between the model-generated CO₂ concentration variation and those observed on secular, interannual and seasonal time scales and spatially through the depth of the troposphere and meridionally from pole-to-pole.The relationship between isotopic and concentration variation on a seasonal time-scale is discussed and it is shown how this can be used to quantitatively estimate relative contributions of biospheric and oceanic CO₂ exchange. Further, it is shown that the interhemispheric gradient of concentration and isotopic ratio results primarily from the redistribution of fossil fuel CO₂. Both isotopic and concentration data indicate that tropical deforestation contributes less than 2 Gt yr^-1 of carbon to the atmosphere.The study suggests that changes in the rate of change of the ratio of ¹³C to ¹²C in the atmosphere of less than 0.03 yr^-1 might be expected if net exchanges with the biosphere are the cause of interannual variations of CO₂ concentrations.     

Atmospheric Turbulence Characteristics Over a Temperature-Inhomogeneous Land Surface. Part I: Statistical Characteristics of Small-Scale Spatial Inhomogeneities of Land Surface Temperature

The results of our 1993 and 1994 experiments at the Tsimlyansk experimental site are given. Spatial variations of small-scale (0.1 m < l < 100 m) temperature inhomogeneities of a steppe surface have been measured. Considerable variations in surface radiation temperature T_r, with variances up to 5 K², have been found. The spectra of T_r variations are of a one-mode character. The position of the spectral maximum on the wavenumber scale depends on the surface characteristics and may change from year-to-year. Probability density distributions for steppe surface radiation temperature variations are close to a normal distribution.     

Thermal features of the Mackenzie basin from NOAA AVHRR observations for summer 1994

Abstract

A series of mid‐afternoon Advanced Very High Resolution Radiometer (AVHRR) thermal radiance scenes were assembled in order to develop a better understanding of the complex energy and water processes leading to variations in surface temperature. An in‐depth knowledge of the temperature variability is of interest to land surface process modelling and its application to the Mackenzie Global Energy and Water Cycle Experiment (GEWEX) Study (MAGS).

Clear‐sky land surface temperatures are estimated by applying a split window technique to remove atmospheric effects. A maximum land surface temperature map of the Mackenzie basin at 1‐km scale for summer 1994 is produced. The patterns are related to land surface features and elevation. The basin's maximum land surface temperature patterns can be subdivided into three land zones (≥ 35°C, 33–34°C and 27–32°C) and a water dominated zone (20.5°C on average). The highest maximum temperature zone (≥35°C) corresponds to a combination of minimal vegetation, drier soils and low terrain. This zone is not in the southern part of the basin as might be speculated in the absence of these data, but in a wide low elevation corridor from west of Great Bear Lake along the Mackenzie River down to 50°N, 120°W. The maximum land surface temperatures tend to decrease with increasing vegetation density and surface moisture; they also decrease with elevation at a rate of –4.5°C km^–1. This is confirmed by weather station data. The AVHRR data extend this relationship to the 1200 – 2200 m altitude ranges, where there are no station data. The data suggest that elevation and land cover should be taken into account in the objective analysis (spatial interpolation) of station data.     

Humidity Effect and Its Influence on the Seasonal Distribution of Precipitation δ18O in Monsoon Regions

The humidity effect, namely the markedly positive correlation between the stable isotopic ratio in precipitation and the dew-point deficit △Td in the atmosphere, is put forward firstly and the relationships between the δ18O in precipitation and △Td are analyzed for the Urumqi and Kunming stations, which have completely different climatic characteristics. Although the seasonal variations in δ18O and △Td exhibit differences between the two stations, their humidity effect is notable. The correlation coefficient and its confidence level of the humidity effect are higher than those of the amount effect at Kunming, showing the marked influence of the humidity conditions in the atmosphere on stable isotopes in precipitation.Using a kinetic model for stable isotopic fractionation, and according to the seasonal distribution of meanmonthly temperature at 500 hPa at Kunming, the variations of the δ18O in condensate in cloud aresimulated. A very good agreement between the seasonal variations of the simulated mean δ18O and themean monthly temperature at 500 hPa is obtained, showing that the oxygen stable isotope in condensateof cloud experiences a temperature effect. Such a result is markedly different from the amount effect atthe ground. Based on the simulations of seasonal variations of δ18O in falling raindrops, it can be foundthat, in the dry season from November to April, the increasing trend with falling distance of δ18O in fallingraindrops corresponds remarkably to the great ATd, showing a strong evaporation enrichment function infalling raindrops; however, in the wet season from May to October, the δ18O in falling raindrops displaysan unapparent increase corresponding to the small ATd, except in May. By comparing the simulated meanδ18O at the ground with the actual monthly δ18O in precipitation, we see distinctly that the two monthlyδ18O variations agree very well. On average, the δ18O values are relatively lower because of the highlymoist air, heavy rainfall, small △Td and weak evaporation enrichment function of stable isotopes in thefalling raindrops, under the influence of vapor from the oceans; but they are relatively higher because of the dry air, light rainfall, great △Td and strong evaporation enrichment function in falling raindrops, under the control of the continental air mass. Therefore, the δ18O in precipitation at Kunming can be used to indicate the humidity situation in the atmosphere to a certain degree, and thus indicate the intensity of the precipitation and the strength of the monsoon indirectly. The humidity effect changes not only the magnitude of the stable isotopic ratio in precipitation but also its seasonal distribution due to its influence on the strength of the evaporation enrichment of stable isotopes in falling raindrops and the direction of the net mass transfer of stable isotopes between the atmosphere and the raindrops. Consequently, it is inferred that the humidity effect is probably one of the foremost causes generating the amount effect.     

Low-frequency and high-frequency changes in temperature and effective humidity during the Holocene in south-central Sweden: implications for atmospheric and oceanic forcings of climate

An integrated use of independent palaeoclimatological proxy techniques that reflect different components of the climate system provides a potential key for functional analysis of past climate changes. Here we report a 10,000 year quantitative record of annual mean temperature (T _ann), based on pollen-climate transfer functions and pollen-stratigraphical data from Lake Flarken, south-central Sweden. The pollen-based temperature reconstruction is compared with a reconstruction of effective humidity, as reflected by a δ¹⁸O record obtained on stratigraphy of lacustrine carbonates from Lake Igelsjön, c. 10 km from Lake Flarken, which gives evidence of pronounced changes in effective humidity. The relatively low T _ann, and high effective humidity as reflected by a low evaporation/inflow ratio suggest a maritime early Holocene climate (10,000–8,300 cal year BP), seemingly incompatible with the highly seasonal solar insolation configuration. We argue that the maritime climate was due to the stronger-than-present zonal flow, enhanced by the high early Holocene sea-surface temperatures in the North Atlantic. The maritime climate mode was disrupted by the abrupt cold event at 8,200 cal year BP, followed at 8,000 cal year BP by a stable Holocene Thermal Maximum. The latter was characterized by T _ann values about 2.5°C higher than at present and markedly dry conditions, indicative of stable summer-time anti-cyclonic circulation, possibly corresponding with modern blocking anticyclonic conditions. The last 4,300 year period is characterized by an increasingly cold, moist, and unstable climate. The results demonstrate the value of combining two independent palaeoclimatic proxies in enhancing the reliability, generality, and interpretability of the palaeoclimatic results. Further methodological refinements especially in resolving past seasonal climatic contrasts are needed to better understand the role of different forcing factors in driving millennial-scale climate dynamics.     

A sodar study of the temperature structure parameter in the convective boundary layer

From sodar measurements gathered during the Voves experiment (France, summer 1977), the variations of the temperature structure parameter C _T ² were studied in the morning planetary boundary layer. Dimensionless profiles of C _T ² are consistent with the mixed-layer scaling of Kaimal et al. (1976); however, for z < 0,5 z _i, the decrease of C _T ² as z ^4/3 should be weighted according to Frisch and Ochs (1975).When the final breakup of the nocturnal inversion is achieved, the variations of the maximum of the C _T ² profile are in good agreement with those predicted by Wyngaard and Le Mone (1980). Discrepancies are observed mainly when the mixed layer is shallow and mechanical turbulence is important compared with buoyancy-driven turbulence.     

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.