东亚水循环中水稳定同位素的GCM模拟和相互比较

利用引入稳定同位素循环的ECHAM4、GISS E和HadCM3模式的模拟,对东亚降水中年平均δD和过量氘d的空间分布以及大气水线（MWL）进行了分析.根据模拟的空间分布,降水同位素在很大程度上反映不同气团的地理背景以及它们之间的相互作用,模拟结果很好地再现了由GNIP实测资料得到的降水稳定同位素的纬度效应、大陆效应和...     

季风区降水δ18O与云顶气压关系

不同于高纬地区, 中低纬度季风区降水稳定同位素变化较复杂, 降水稳定同位素 "温度效应"不明显, 而出现显著的"降水量效应"。而通过地表的数据分析很难解释影响季风区降水稳定同位素变化的过程与机制, 这使得对于季风区稳定同位素气候记录的解释存在不同认识。本文利用GNIP降水稳定同位素数据和ISCCP D2云气候资料, 通过分析降水 δ18O与云顶气压的关系, 试图从降水过程中的水汽传输来解释季风区降水稳定同位素的变化特征。研究发现季风区降水 δ18O与云顶气压在局地和区域尺度上均有显著正相关关系, 夏季风爆发时云顶气压和降水 δ18O都显著降低, 表明云抬升高度对降水 δ18O的重要影响。这种关系表明季风区降水 δ18O除受局地过程的影响外, 还受大尺度对流活动的影响。本研究从不同角度证明了对流降水是季风区降水稳定同位素出现"降水量效应"的重要因素。季风活动越强, 云顶高度越高, 凝结温度越低, 从而导致降水中 δ18O越低, 是出现同位素"降水量效应"的机制。     

Stable water isotopes of precipitation in China simulated by SWING2 models

The stable water isotope ratio in precipitation is a useful tracer of atmospheric circulation. Such observations, however, are very limited in space and time. To solve this problem, many isotope-enabled general circulation models (GCMs) are used to help the interpretation of isotope proxies. In this paper, several isotope-enabled GCMs released by the second Stable Water Isotope Intercomparison Group (SWING2) were selected to assess the spatial pattern of deuterium (δD) and the deuterium excess (d) of precipitation in China. The isotopic data of the Global Network of Isotopes in Precipitation (GNIP) and the Chinese Network of Isotopes in Precipitation (CHNIP) were also applied to verify the simulations. The results indicate that these models accurately simulate the spatial characteristics of δD and d of precipitation in China. The correlation between the observations and simulations for LMDZ is the highest among these models, while the root-mean-square (RMS) and standard deviation are not perfect. In addition, LMDZ is worse than other models in capturing the low signal in certain regions, such as CAM, GISS_E, and MIROC. For the monthly variation, most SWING2 models underestimate δD of the precipitation but overestimate the value of d, except for isoGSM. The simulated monthly variation of the water isotopes from SWING2 models is in general similar to the observations, and the trend corresponds to the monthly variation in the Northern Hemisphere. Moreover, all models are good at illustrating the temperature and precipitation amount effects, while they exhibit varying skills in interpreting the altitude and continental effects.     

应用统计降尺度方法预估江淮流域未来降水

统计降尺度方法广泛应用于弥补大气环流模式(GCM)模拟区域气候变化能力较弱的不足。利用1960~2009年的NCEP/NCAR再分析资料和江淮流域52个站点降水观测资料,通过敏感性分析,针对4个季节分别选择10个大尺度预测因子,采用主成分分析(PCA)和支持向量机(SVM)相结合的方法,建立了江淮流域降水统计降尺度模型。检验结果表明,该模型获取的江淮流域降水的偏差显著减小,能够描述降水在月、年尺度的变化,适用于HadCM3输出的大尺度气候场,具有预测未来降水变化的能力。将统计降尺度模型应用于HadCM3在A2情景下输出的2020~2099年大尺度预测因子,分3个时段:2020~2039年,2050~2069年和2080~2099年,从年和季节两个时间尺度分析江淮流域未来降水变化。结果表明,相对1960~1999年,未来3个时段的降水有小幅增加,其中2080~2099年增幅最大,为3.6 mm;在未来3个时段的不同季节,降水变化呈现出不同特征。     

A comparative study on isotopic composition of precipitation in wet tropic and semi-arid stations across southern India

Isotopic composition of monthly composite precipitation samples from Kozhikode (n = 31), a wet tropic station and Hyderabad (n = 25), a semi-arid station across southern India were studied for a period of four years from 2005 to 2008. During the study period, the Kozhikode station recorded an average rainfall of 3500 mm while the Hyderabad station showed an average rainfall of 790 mm. The average stable isotope values in precipitation at the Kozhikode station were δ ¹⁸O = −3.52‰, d-excess = 13.72‰; δ ¹⁸O = −2.94‰, d-excess = 10.57‰; and δ ¹⁸O = −7.53‰, d-excess = 13.79‰, respectively during the pre-monsoon (March–May), monsoon (June–September) and post-monsoon (October–February) seasons. For the Hyderabad station, the average stable isotope values were δ ¹⁸O = −5.88‰, d-excess = 2.34‰; δ ¹⁸O = −4.39‰, d-excess = 9.21‰; and δ ¹⁸O = −8.69‰, d-excess = 14.29‰, respectively for the three seasons. The precipitation at the two stations showed distinctive isotopic signatures. The stable isotopic composition of precipitation at the Hyderabad station showed significant variations from the global trend while the Kozhikode station almost followed the global value. These differences are mainly attributed to the latitudinal differences of the two stations coupled with the differences in climatic conditions.     

Ambiguity in the altitude effect of precipitation isotopes for estimating groundwater recharge elevation and paleoelevation reconstruction in the leeward side of a mountain

The altitude effect of isotopes in precipitation is not as significant on the leeward side of a mountain as it is on the windward side, which makes it difficult to use isotopes at leeward sites, especially if estimating elevation of groundwater recharge or reconstructing paleoelevations. Samples of precipitation were taken at three stations with different elevations—2,306–3,243 m above mean sea level (asl)—on the leeward side of the Meili Snow Mountains on the southeastern Tibetan Plateau from August 2017 to July 2018. The isotope vs. altitude gradients were calculated based on two adjacent stations at the daily, monthly, and annual scales. Most of the gradients are beyond the global ranges of –0.5 to –0.1‰ per 100 m for δ¹⁸O and –5 to –1‰ per 100 m for δ²H, and some of the gradients are even positive. Local processes of sub-cloud evaporation and mixing with recycled moisture are identified for the ambiguous altitude effect, while regional atmospheric circulation processes dominate the major patterns of stable isotope variation at the three stations. The groundwater recharge elevation is estimated to be in a very large range, 2,562–6,321 m asl, which could be caused by the differences in isotope vs. altitude gradient in the studied catchments. Considering the complex atmospheric processes affecting precipitation isotopes, sampling of event-based/monthly precipitation at more than two altitudes for at least one complete hydrological year is a minimum requirement to establish a reasonable isotope vs. altitude gradient.

     

亚洲季风区降水中稳定同位素气候意义研究进展

文章回顾了过去30多年围绕亚洲季风区,特别是青藏高原降水与冰芯同位素现代过程研究,对季风区稳定同位素气候意义的认识过程。降水及不同介质氧稳定同位素研究从最早聚焦于降水同位素与当地气候因子之间的关系,即"温度效应"与"降水量效应",发展到大尺度大气环流过程对降水同位素时空变化的影响,进而否定了局地气候因子的控制作用。近些年重要的研究进展之一是明确了与赤道海洋温度变化相关的ENSO对整个亚洲季风区同位素年际年代际波动的影响过程与机制,发现了大尺度大气环流在不同时间尺度稳定同位素记录中的显著信号。这些认识对于亚洲季风区冰芯、石笋、树轮同位素气候意义的解释都具有重要意义。但在不同时间尺度上,影响降水同位素的主导控制因素不同,导致对于解释长时间尺度同位素记录仍存在挑战,有待于从机制和结合同位素分馏的大气环流模型模拟研究中取得新的突破。     

湿度效应及其对降水中δ18O季节分布的影响

提出了湿度效应的概念,即降水中稳定同位素比率与大气的温度露点差ΔT_d存在显著的正相关关系.对两个气候特征完全不同的取样站乌鲁木齐和昆明降水中δ¹⁸O与温度露点差之间的关系进行了分析,尽管两站的δ¹⁸O与ΔT_d的季节变化存在差异,但它们的湿度效应是显著的.利用稳定同位素动力分馏模型并根据500hPa月平均温度的季节分布对昆明站云中凝结物中δ¹⁸O进行了模拟,模拟的月平均δ¹⁸O与月平均温度的变化具有非常好的一致性,说明昆明站云中凝结物中的氧稳定同位素具有温度效应.这个结果与地面降水中氧稳定同位素的降水量效应截然不同.昆明站降水中δ¹⁸O一定程度上指示大气的干湿状况,同时也间接地指示降水量的多寡或季风的强弱.湿度效应的存在,影响降落雨滴中稳定同位素蒸发富集的强度以及雨滴与大气之间稳定同位素物质迁移的方向.它不仅改变降水中稳定同位素比率的大小,也改变其季节分布的特点.     

不同时间尺度氢氧稳定同位素效应的比较——以长沙降水为例

基于长沙2010年1月~2019年12月日降水中氢、氧稳定同位素以及相应日平均温度和日降水量的监测数据,利用数理统计方法对该站在日、月、年三类时间尺度下以及在不同降水强度条件下的降水中δ¹⁸O与降水量、δ¹⁸O与温度之间的关系以及局地大气水线（LMWL）变化特征进行分析和比较,其目的在于揭示在不同时间尺度下和不同降水强度条件下降水中稳定同位素效应的差异,深化对季风区降水稳定同位素变化规律的认识。结果表明：在长沙,降水中δ¹⁸O的变化范围随时间尺度的增大而减小;在日时间尺度下,降水量效应稳定存在,受雨滴下降过程中蒸发富集的影响,5.0 mm/d以下的小降水事件明显改变δ¹⁸O-P回归线的斜率。在月和年时间尺度下,降水中稳定同位素均不存在显著的降水量效应;在雨热同期的气候背景下,除冷半年外,在日和月时间尺度下,降水中δ¹⁸O与温度均存在显著的负相关关系。在年时间尺度下,降水中年加权平均δ¹⁸O与温度之间不存在显著的相关关系;对应于不同的时间尺度、不同的季节和不同的降水强度,LMWL均具有显著的差异。在日和月的时间尺度下,冷半年LMWL的斜率和截距分别小于和大于暖半年LMWL的斜率和截距,且随降水强度的增加呈先明显增加（日时间尺度在5.0 mm/d以下,月时间尺度在50.0 mm/month以下）、然后保持基本不变的态势。在年时间尺度下,冷半年LMWL的斜率和截距均大于暖半年。

     

下垫面蒸发和云中凝结分馏对降水稳定同位素影响的数值试验——时间变化的比较(以长沙降水同位素为例)

利用稳定同位素大气水平衡模式（iAWBM）的模拟数据,分析了在不同的下垫面蒸发和不同的凝结分馏条件下降水中δ¹⁸O的时间变化、降水量效应、负温度效应和大气水线。并通过与长沙站5年实测数据的比较以及模拟试验结果之间的相互比较,揭示下垫面蒸发水汽中稳定同位素的季节性变化和云中稳定同位素分馏对降水中稳定同位素变化的可能影响,增进对季风区水稳定同位素效应的理解和认识。iAWBM给出的4个模拟试验均很好地再现了监测站降水中δ¹⁸O的时间变化,模拟出季风区降水中稳定同位素在暖半年被贫化、在冷半年被富集的基本特点。与平衡分馏相比,动力分馏下降水中稳定同位素被贫化的程度加强、季节差和离散程度减小;由下垫面蒸发水汽中稳定同位素δ_e季节性变化所引起的降水中稳定同位素的变化在不同季节完全相反：在长沙,暖半年降水中δ¹⁸O更低,冷半年降水中δ¹⁸O更高,使得降水中稳定同位素季节差和离散程度增大。4个模拟试验均很好地再现了季风区的降水量效应和负温度效应。与平衡分馏相比,动力分馏下模拟的降水量效应和负温度效应的斜率相对较小;δ_e季节性变化导致模拟的降水量效应和负温度效应的斜率增大。利用iAWBM,模拟出季风区湿热气候条件下的MWL。动力分馏以及δ_e季节变化均使模拟得到的MWL的斜率和截距减小。     

Moisture source in the Hyblean Mountains region (south-eastern Sicily, Italy): Evidence from stable isotopes signature

Here the authors present results of an isotope study on precipitation collected during a 2-a period from a rain-gauge network consisting of 6 stations located at different elevations in the Hyblean Mountains (HM) region, in south-eastern Sicily. The slope of the local meteoric water line (δD = 6.50 δ¹⁸O + 9.87) obtained for the region suggests that precipitation is affected by evaporation during rainfall events. The main variations in rainwater isotope composition are due to seasonal effects and elevation. An average ²H excess value of +21.2‰ was found for precipitation events less affected by evaporation (i.e. when the rainfall was >65 mm/month). The spatial distribution of O isotope composition of precipitation shows a negative gradient from east and south to the inner areas. The depositional rate of Cl, used as a tracer of the origin of air masses, is highest at the coastal rain-gauges (SR and MRG stations) and lowest on the northern flank of the HM region (SC station). Based on these findings, a model is proposed for the origin of precipitation in the HM region, which assumes that a Mediterranean-derived component is the main source of moisture in the studied area. D/H and ¹⁸O/¹⁶O ratios of inferred meteoric recharge waters were also compared with the isotope composition of waters collected from the main local springs and wells. The best linear fit of the δ¹⁸O vs δD relationship for Hyblean groundwater is δD = 4.85 δ¹⁸O–2.01. The enrichment of heavy isotopes in Hyblean groundwater is probably due to evaporation occurring after precipitation events or to a recharging contribution from surface waters (lakes or rivers) enriched in heavy isotopes.     

Performance of general circulation models and their ensembles for the prediction of drought indices over India during summer monsoon

The drought during the months of June to September (JJAS) results in significant deficiency in the annual rainfall and affects the hydrological planning, disaster management, and the agriculture sector of India. Advance information on drought characteristics over the space may help in risk assessment over the country. This issue motivated the present study which deals with the prediction of drought during JJAS through standardized precipitation index (SPI) using nine general circulation models (GCM) product. Among these GCMs, three are the atmospheric and six are atmosphere–ocean coupled models. The performance of these GCM’s predicted SPI is examined against the observed SPI for the time period of 1982–2010. After a rigorous analysis, it can be concluded that the skill of prediction by GCM is not satisfactory, whereas the ability of the coupled models is better than the atmospheric models. An attempt has been made to improve the accuracy of predicted SPI using two different multi-model ensemble (MME) schemes, viz., arithmetic mean and weighted mean using singular value decomposition-based multiple linear regressions (SVD-MLR) of GCMs. It is found that among these MME techniques, SVD-MLR-based MME has more skill as compared to simple MME as well as individual GCMs.     

Controls on the isotopic composition of surface water and precipitation in the Northern Andes, Colombian Eastern Cordillera

Empirical datasets provide the constraints on the variability and causes of variability in stable isotope compositions (δD or δ¹⁸O) of surface water and precipitation that are essential not only for models of modern and past climate but also for investigations of paleoelevation. This study presents stable isotope data for 76 samples from four elevation transects and three IAEA GNIP stations in the Eastern Cordillera of Colombia and the northern Andean foreland. These data are largely consistent with theories of stable isotope variability developed based on a global dataset. On a monthly basis, the precipitation-amount effect exerts the dominant control on δD_p and δ¹⁸O_p values at the IAEA GNIP stations. At the Bogotá station (2547 m), the δD_p and δ¹⁸O_p values vary seasonally, with isotopic minima correlating with maxima in precipitation-amount. Although surface water samples from Eastern Cordilleran streams and rivers fall on the Global Meteoric Water Line, samples from three of four lakes (2842–3459 m) have evaporatively elevated δD_sw and δ¹⁸O_sw values. The IAEA GNIP station data averaged over multiple years, combined with stream and river water data, define vertical lapse rates of −1.8‰ km⁻¹ for Δδ¹⁸O and −14.6‰ km⁻¹ for ΔδD, and are a close fit to a common thermodynamically based Rayleigh distillation model. Elevation uncertainties for these relationships are also evaluated. Comparison of this Colombian dataset with the elevation uncertainties generated by the thermodynamically based model shows that the model underestimates uncertainty at high Δδ¹⁸O and ΔδD values while overestimating it for low Δδ¹⁸O and ΔδD values. This study presents an independent, empirical assessment of stable isotope-based elevation uncertainties for the northern Andes based on a dataset of sufficient size to ensure statistical integrity. These vertical lapse rates and associated uncertainties form the basis for stable isotope paleoelevation studies in the northern Andes.     

变化环境下降雨集中度的变异与驱动力探究

降雨的时空分布过于集中会诱发洪旱灾害。研究降雨集中度的变异及其驱动力有助于全面掌握降雨对变化环境的响应特征,为区域水资源的综合利用与灾害预警提供依据。以汉江流域为研究对象,选取月降雨集中度指数(CIM)和日降雨集中度指数(CID)表征降雨集中度,并采用Mann-Kendall趋势检验法与启发式分割算法对降雨集中度进行变异分析,利用交叉小波变换探究太阳黑子与大气环流异常因子对降雨集中度变化的影响。结果表明:①汉江流域CIM北大南小,呈不显著的下降趋势;CID东大西小,在6个站呈显著上升趋势;②流域部分站点CID发生突变,而CIM序列较为平稳,表明CID相比CIM对变化环境的响应更为敏感;③太阳黑子和大气环流异常因子对降雨集中度的变化有较强的影响,其中太阳黑子的影响最大,它通过影响大气环流异常因子间接影响汉江流域的降雨集中度。     

Circulation and representativeness of precipitation and air temperature in the southeast of the Quinghai-Xizang Plateau

Based on time series of 98 stations from the Qinghai-Xizang Plateau, the Indo-Gagnetic Plains, the River Gorge Country and Eastern China, the representativeness of the locally observed interannual variations of temperature and precipitation was analyzed by a statistical method. After an overview, which regards the main circulation patterns as well as the spatial distribution of temperature and precipitation in winter (January) and summer (July), the monthly distribution of the representativeness is discussed in a climato-genetic context. The monthly temperature representativeness is characterized by strong spatial and seasonal contrasts. The values range from less than 200 km in the basins and valley bottoms of NW Sichuan, caused by local summer circulation patterns, and more than 1600 km in the lower areas of E China, affected by the far reaching influence of the winter monsoonal surges of cold continental airmasses. With only a few exceptions mainly occurring in December, the precipitation representativeness does not exceed a 300 km limit. Due to the comparatively modest spatial disparities — except December when a steep rise, greater than 600 km occurs in the upper Tsangpo valley and adjacent areas — it can only be concluded, that a tendency of higher (lower) representativeness is predominantly related to advective (convective) regimes.     

Isotopic features of rivers and groundwater of the Parma Province (Northern Italy) and their relationships with precipitation

The Enza, Parma, Baganza, Taro and Po rivers and several waters from aquifers of the area of the Parma town (northern Italy) have been investigated for oxygen and hydrogen isotopes. Enza, Parma, Baganza and Taro differ from Po in having higher isotope ratios and the Taro River exhibits an isotope ratio higher than those of Enza, Parma and Baganza. The low values of Po are due to the dominant contribution of waters coming from glaciers and precipitation occurring along the Alps. The high values of the Taro River are probably due to the fact that its catchment basin extends close to the Tyrrhenian sea and is well opened to perturbations coming from the west. The isotopic values of the present day precipitations occurring along the northern Apennine piedmont area are lower than in rivers. On the contrary, the rivers resemble waters issuing from springs located close the Apennine ridge; the isotopic values of the last waters probably approach those in the precipitation occurring at present along the Apennine ridge. Reasonably, the low isotope values recorded in precipitation of the Apennines piedmont area are due to cold air masses invading the Po plain from N or NE rather than only to the change in the regime of precipitation (higher amount in cold periods, lower amount in the hot periods). Waters of the aquifer of the Po plain have been investigated in the Priorato, Parola and Parma fields (Parma Province). The aquifers are largely fed by the surface hydrographic system: their waters have constant isotopic composition and resemble waters of the Apennines rivers. They are also isotopically similar to the average precipitation occurring from 1995 to 2006, but differ largely from recent (2003–2005) precipitation. Minor isotopic variations recorded in a well of the Priorato field suggest that this well is partly fed by local precipitation.     

Late Quaternary behavior of the East African monsoon and the importance of the Congo Air Boundary

Both Atlantic and Indian Ocean climate dynamics exert influence over tropical African hydroclimate, producing complex patterns of convergence and precipitation. To isolate the Indian Ocean influence on African paleohydrology, we analyzed the deuterium/hydrogen ratio of higher plant leaf waxes (δD_wax) in a 25 000-year sediment record from Lake Challa (3° S, 38° E) in the easternmost area of the African tropics. Whereas both the seismic record of inferred lake level fluctuations and the Branched and Isoprenoidal Tetraether (BIT) index proxy record changes in hydrology within the Challa basin, δD_wax, as a proxy for the isotopic composition of precipitation (δD_P) is interpreted as a tracer of large-scale atmospheric circulation that integrates the history of the moisture transported to the Lake Challa area. Specifically, based on modern-day isotope–rainfall relationships, we argue that Lake Challa δD_wax reflects the intensity of East African monsoon circulation. The three hydrological proxy records show generally similar trends for the last 25 000 years, but there are important differences between them, primarily during the middle Holocene. We interpret this deviation of δD_wax from local hydrological history as a decoupling of East African monsoon intensity – which heavily influences the isotopes of precipitation in East Africa today – from rainfall amount in the Challa basin. In combination, the hydrological proxy data from Lake Challa singularly highlight zonal gradients in tropical African climate that occur over a variety of timescales, suggesting that the Congo Air Boundary plays a fundamental role in controlling hydroclimate in the African tropics.     

新疆阿尔泰山额尔齐斯河源区不同降水观测方法对比分析及1980-2015年降水变化研究

合理评估不同降水观测仪器的精度是评价区域降水变化的前提。基于阿尔泰山额尔齐斯河源区库威水文站ø20 cm标准雨量筒的人工降水观测和库威积雪站T-200b的自动降水观测,对比分析了T-200b和ø20 cm标准雨量筒的观测精度,在此基础上,基于1980-2015年库威水文站的降水观测,分析了阿尔泰山额尔齐斯河源区的降水变化。结果表明：两种方法观测的日降水、月降水和年降水量均具有良好的相关性;两种方法观测液态降水相关性要明显优于固态降水;随着降雨强度的增加,两种观测方法的相关性显著增强。总体上,T-200b观测的降水量较ø20 cm标准雨量筒偏高。1980-2015年间额尔齐斯河源区的年降水量以2005年为转折点呈现"先增加后减小"的变化趋势,且冷季（11月至次年3月）的降水增加显著,冷季的降水占年降水量的比例呈现逐渐增加的变化趋势。降水和融雪过程的变化已导致春季融雪水文过程发生改变,进一步合理评估地表可利用水资源的年内重分配是该地区水安全的重要保障。     

The impact of ENSO and macrocirculation patterns on precipitation under climate change

The possible impact of El Niño-Southern Oscillation (ENSO) and macrocirculation patterns (CPs) on local precipitation are examined and analyzed here under climate change conditions. First the relationship between the input and output variables under present conditions is established using two models, a fuzzy rule-based model (FRBM) and a multivariate linear regression model (MLRM), then this historical relationship is extended under climate change conditions. The input variables for these models consist of lagged ENSO-data (represented by the Southern Oscillation Index, SOI) and 500 hPa height data clustered into macrocirculation patterns over the western United States, while the output is an estimate of monthly local precipitation at selected Arizona stations. To overcome the lack of SOI data under climate change, several scenarios are constructed by perturbing the historical SOI data in a design of experiments framework. The results of the experimental design show that, in general, the precipitation amount seems to decrease under climate change. While the stations and months have differences, as expected, the perturbed scenarios do not show significant differences.     

Potential impacts of global warming on the frequency and magnitude of heavy precipitation

It is now widely recognised that the most significant impacts of global warming are likely to be experienced through changes in the frequency of extreme events, including flooding. This paper reviews physical and empirical arguments which suggest that global warming may result in a more intense hydrological cycle, with an associated increase in the frequency and/or magnitude of heavy precipitation. Results derived from enhanced-greenhouse experiments using global climate models (GCMs) are shown to be consistent with these physical and empirical arguments. Detailed analysis of output from three GCMs indicates the possibility of substantial increases in the frequency and magnitude of extreme daily precipitation, with amplification of the effect as the return period increases. Moreover, return period analyses for locations in Australia, Europe, India, China and the USA indicate that the results are global in scope. Subsequent discussion of the limitations of GCMs for this sort of analysis highlights the need for caution when interpreting the precipitation results presented here. However, the consistency between physically-based expectations, empirical observations, and GCM results is considered sufficient for the GCM results to be taken seriously, at least in a qualitative sense, especially considering that the alternative seems to be reliance by planners on the fundamentally flawed concept of a stationary climate.