Regional climate changes and river runoff in Azerbaijan

Urgent current problems, namely, the climate change and its effects on river runoffare considered. The regional climate change at different altitudes and in separate regions of Azerbaijan is studied using long-term data of hydrometeorological observations. The trend towards the decrease in annual river runoff and peak flood discharge as well as towards the increase in winter (low-water) runoff is observed due to the influence of regional climate change.     

Simulation of the effect of doubled atmospheric CO2 on the climate of northern and central California

A Local Climate Model (LCM) is described that can provide a high-resolution (10 km) simulation of climate resulting from a doubling of atmospheric CO₂ concentrations. A canonicalregression function is used to compute the monthly temperature (mean of daily-maximum-temperature) and precipitation for any point, given a set of predictor variables. Predictor variables represent the influence of terrain, sea-surface temperature (SST), windfields, CO₂ concentration, and solar radiation on climate. The canonical-regression function is calibrated and validated using empirical windfield, SST, and climate data from stations in the western U.S. To illustrate an application of the LCM, the climate of northern and central California is simulated for a doubled CO₂ (600 ppmv) and a control scenario (300 ppmv CO₂). Windfields and SSTs used to compute predictor variables are taken from general circulation model simulations for these two scenarios. LCM solutions indicate that doubling CO₂ will result in a 3 C° increase in January temperature, a 2 C° increase in July temperature, a 16 mm (37%) increase in January precipitation, and a 3 mm (46%) increase in July precipitation.     

Estimation of large intermountain depression river runoff response to global climate warming

The response of runoff of rivers of large intermountain depressions to global warming is estimated (case study of the Fergana Valley). It is established that warming has led to runoff changes in certain rivers, from 18% decrease to 38% increase in mid-mountain rivers and glacier- and snow-fed rivers.     

Bayesian prediction of minimum river runoff under nonstationary conditions of future climate change

The problem of runoff prediction taking into account the possible climate change is considered using the Bayesian approach. The proposed technique is applied to the probabilistic forecasting of minimum runoff variations on the rivers of the Volga River basin.     

The Siberian High and climate change over middle to high latitude Asia

Summary The Siberian High is the most important atmospheric centre of action in Eurasia during the winter months. Here its variability and relationship with temperature and precipitation is investigated for the period 1922 to 2000. The pronounced weakening of the Siberian High during the last ∼ 20 years is its most remarkable feature. Mean temperature, averaged over middle to high latitude Asia (30° E–140° E, 30° N–70° N), is correlated with the Siberian High central intensity (SHCI) with correlation coefficient of − 0.58 (1922–1999), and for precipitation, the correlation coefficient is − 0.44 (1922–1998). Taking the Arctic Oscillation (AO), the SHCI, the Eurasian teleconnection pattern (EU), and the Southern Oscillation (SO) index into account, 72 percent of the variance in temperature can be explained for the period 1949–1997 (for precipitation the variance is 26 percent), with the AO alone explaining 30 percent of the variance, and the Siberian High contributing 24 percent. The precipitation variance explained by the Siberian High is only 9.8 percent of the total. Received January 2, 2001 Revised November 24, 2001     

Analysis of variability and diurnal range of daily temperature in a nested regional climate model: comparison with observations and doubled CO2 results

Analysis of daily variability of temperature in climate model experiments is important as a model diagnostic and for determination of how such variability may change under perturbed climate conditions. The latter could be important from a climate impacts perspective. We analyze daily mean, diurnal range and variability of surface air temperature in two continuous 3 1/2 year long climate simulations over the continental USA, one for present day conditions and one for conditions under doubled carbon dioxide concentration, conducted with a regional climate model (RegCM), on a 60 km grid, nested in a general circulation model (GCM). Model output is compared with a 30-year daily observational data set for various regions of the USA. In comparison with observations the diurnal range in the model control run is somewhat too low although the daily temperature mean is often well reproduced. The daily variability of temperature is underestimated by the model in all areas, but particularly when and where the observed variability is relatively high. Causes for these underestimations are traced to deficiencies in the general circulation of the driving GCM. With doubled CO₂, both maximum and minimum temperatures increase, but the change in the diurnal temperature range (DTR) varies spatially and seasonally. On an annual average over the land domain, the DTR decreases by 0.25'C. Changes in DTR are most strongly correlated with changes in absorbed shortwave radiation at the surface, which explains 72% of the variance in DTR on an annual basis. Change in evaporation was a factor affecting DTR only in the summer when it explained 52% of the variance. The most significant findings with CO₂ doubling are substantial decreases in daily variability in winter over large portions of the domain, and localized increases in summer. Causes for these changes are traced to fluctuations in the intensity and position of the jet stream.     

Effects of freshwater runoff on a tropical pacific climate in the HadGEM2

This paper investigates the effects of river discharge on simulated climatology from 1979 to 1988 using the Hadley Centre Global Environmental Model version 2. Two experiments are performed with and without the inclusion of Total Runoff Integrating Pathways. The results show that the inclusion of flow routing can lead to the decrease of salinity over the coastal region due to freshwater. This reduction results in a shallower mixed layer depth, which in turn leads to the weakening of trade winds and a decrease in vertical mixing in the ocean. The enhanced sensible and latent heat fluxes over warmed SST improve the simulated precipitation and thermodynamic circulation. As a result, the experiment with flow routing is capable of improving the large-scale climate feature with an increase in precipitation over the eastern tropical equatorial Pacific region.     

The CO2 climate response problem a statistical approach

Summary The anthropogenic increase of the atmospheric carbon dioxide (CO₂) concentration leads to a global warming of the atmospheric surface layer, whereas the stratosphere is cooled. This greenhouse effect postulated by a number of climate models (on a physical basis) can be conditionally verified by statistical multiple regression techniques. In this study the following climatic time series are used (all data yearly averages): northern hemisphere mean temperatures near surface 1781–1980 (alternatively since 1851 or 1881) and corresponding stratospheric data 1958–1983, sea surface temperatures 1856–1980, northern hemisphere or global average, alternatively, and the global mean sea level fluctuations 1881–1980. In order to account for an appropriate part of explained variance, volcanic and solar forcing parameters are implied and the data are low-pass filtered suppressing variations of the period rangeT < 10 years. Based on the recently assessed preindustrial CO₂ concentration of c. 280 ppm and the Mauna Loa value of c. 344 ppm in 1984 this industrial CO₂ increase reveals a northern hemisphere temperature increase near surface of c. (.7±.1) K (average and standard deviation of all statistical regression runs), statistically significant at the 95% level. A CO₂ doubling (300 to 600 ppm) leads to a statistically derived signal of (3.1±.6) K, satisfactorily congruent with the results of most of the (deterministic) climate models: c. (3±1.5)K. A stratospheric cooling trend in recent time may be existent but is highly non-significant. Similarly, the SST data do not allow to evaluate a significant CO₂ signal to noise ratio. In contrast to that the observed long-term global mean sea level increase (9.3 cm) can be predominantly attributed to the CO₂ effect (99.9% level).

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Zusammenfassung Der anthropogen bedingte Anstieg der atmosphärischen Kohlendioxid-(CO₂-)Konzentration führt zu einer Erwärmung der bodennahen Luftschicht, während die Stratosphäre abgekühlt wird. Dieser Glashauseffekt, von zahlreichen Klimamodellierungen (auf physikalischer Basis) postuliert, kann auf statistischem Weg durch multiple Regressionsrechnungen bedingt verifiziert werden. Die vorliegende Studie basiert auf den folgenden Klima-Zeitreihen (alle Daten in Form von Jahresmittelwerten): nordhemisphärische Mitteltemperatur in Bodennähe 1781–1980 (alternativ seit 1851 bzw. 1881) und in der Stratosphäre 1958–1983, Meeresoberflächentemperatur 1956–1980, nordhemisphärisch bzw. global gemittelt, und mittlere globale Meeresspiegelschwankungen 1881–1980. Um einen angemessenen Teil erklärter Varianz zu erfassen, wurden vulkanische und solare Parameter mit einbezogen und eine Tiefpaßfilterung mit Unterdrückung des PeriodenbereichsT < 10 Jahre zugrunde gelegt. Auf der Basis des kürzlich abgeschätzten vorindustriellen CO₂-Konzentrationswertes von ca. 280 ppm und dem Mauna Loa Wert des Jahres 1984 von ca. 344 ppm entspricht dieser industrielle CO₂-Anstieg einer Erhöhung der bodennahen nordhemisphärischen Mitteltemperatur von ca. (0.7±0.1) K (Mittelwert und Standardabweichung aller Regressionsrechnungen), was einen auf dem 95%-Niveau signifikanten Temperaturanstieg darstellt. Eine CO₂-Verdoppelung (300 auf 600 ppm) führt, ebenfalls auf statistischem Weg, zu einem Temperatursignal von (3.1±0.6) K, in befriedigender Übereinstimmung mit den meisten der (deterministischen) Klimamodelle: ca. (3±1.5) K. In der Stratosphäre könnte in letzter Zeit ein Abkühlungstrend aufgetreten sein, der aber höchst insignifikant ist. Auch die SST-Daten erlauben keine signifikanten Schätzungen des Signal-Rausch-Verhältnisses. Im Gegensatz dazu kann der langfristige Trend des globalen Meeresspiegelanstiegs (9.3 cm) weitgehend dem CO₂-Effekt zugeschrieben werden (99.9%-Signifikanzniveau).

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With 7 Figures     

Long-term forecasting of characteristics of minimal river runoff discharges in Russia in case of possible climate change

A technique of long-term forecasting of outliers of a random runoff process in the low-water period in case of possible climate change is proposed. A stochastic model of runoff formation based on the Fokker-Plank-Kolmogorov equation (FPK) was used to estimate hydrological implications of climate change. The frequency and duration of a 30-day runoff below 80% probability were considered as principal characteristics of the forecast. They substantially influence the development of the strategy of water resources management in perspective and can be used for an environmental estimate of implications of changes in the hydrological regime in low-water periods. The forecast results are generalized in the form of maps.     

Influences on surface energy fluxes in simulated present and doubled CO2 climates

The surface energy fluxes simulated by the CSIRO9 Mark 1 GCM for present and doubled CO₂ conditions are analyzed. On the global scale the climatological flux fields are similar to those from four GCMs studied previously. A diagnostic calculation is used to provide estimates of the radiative forcing by the GCM atmosphere. For 1 × CO₂, in the global and annual mean, cloud produces a net cooling at the surface of 31 W m^–2. The clear-sky longwave surface greenhouse effect is 311 W m^–2, while the corresponding shortwave term is –79 W m^–2. As for the other GCM results, the CSIRO9 CO₂ surface warming (global mean 4.8°C) is closely related to the increased downward longwave radiation (LW ). Global mean net cloud forcing changes little. The contrast in warming between land and ocean, largely due to the increase in evaporative cooling (E) over ocean, is highlighted. In order to further the understanding of influences on the fluxes, simple physically based linear models are developed using multiple regression. Applied to both 1 × CO₂ and CO₂ December–February mean tropical fields from CSIRO9, the linear models quite accurately (3–5 W m^–2 for 1 × CO₂ and 2–3 W m^–2 for CO₂) relate LW and net shortwave radiation to temperature, surface albedo, the water vapor column, and cloud. The linear models provide alternative estimates of radiative forcing terms to those from the diagnostic calculation. Tropical mean cloud forcings are compared. Over land, E is well correlated with soil moisture, and sensible heat with air-surface temperature difference. However an attempt to relate the spatial variation of LWt within the tropics to that of the nonflux fields had little success. Regional changes in surface temperature are not linearly related to, for instance, changes in cloud or soil moisture.     

Response of the East Asian summer monsoon to doubled atmospheric CO2: Coupled climate model simulations and projections under IPCC AR4

Summary The East Asian (China, Korea and Japan) summer monsoon precipitation and its variability are examined from the outputs of the coupled climate models performing coordinated experiments leading to the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4). Out of the 22 models examined, 14 reproduce the observed shape of the annual cycle well with peak during the boreal summer (June through August), but with varying magnitude. Three models simulate the maximum a month later and with lower magnitudes. Only one model considerably underestimates the magnitude of the annual cycle. The remaining 4 models show some deviations from the observed. Models are unable to simulate the minimum in July with peaks in June and August associated with northward shifts of the Meiyu-Changma-Baiu precipitation band. The realistic simulation of the annual cycle does not appear to depend on the model resolution. The inter-model variation is slightly larger during summer, implying larger diversity of the models in simulating summer monsoon precipitation. The spatial rainfall patterns are reasonably well simulated by most of the models, with several models able to simulate the precipitation associated with the Meiyu-Changma-Baiu frontal zone and that associated with the location of the subtropical high over the north Pacific. Simulated spatial distribution could be sensitive to model resolution as evidenced by two versions of MIROC3.2 model. The multi-model ensemble (MME) pattern reveals an underestimation of seasonal precipitation over the east coast of China, Korea-Japan peninsular and the adjoining oceanic regions. This may be related with the mass-flux based scheme employed for convective parameterization by majority of the models. Further the inter-model variation of precipitation is about 2 times stronger south of 30° N, than north of this latitude, indicating larger diversity of the coupled models in simulating low latitude precipitation. The simulated inter-annual variability is estimated by computing the mean summer monsoon seasonal rainfall and the coefficient of variability (CV). In general the mean observed seasonal precipitation of 542 mm and CV of 6.7% is very well simulated by most of the models. Except for one model mean seasonal precipitation varies from 400 to 650 mm. However the CV varies from 2 to 9%. Future projections under the radiative forcing of doubled CO₂ scenario are examined for individual models and by the MME technique. Changes in mean precipitation and variability are tested by the t-test and F-ratio respectively to evaluate their statistical significance. The changes in mean precipitation vary from −0.6% (CNRM-CM3) to about 14% (ECHO-G; UKMO-HadCM3). The MME technique reveals an increase varying from 5 to 10%, with an average of 7.8% (greater than the observed CV of 6.7%) over the East Asian region. However the increases are significant over the Korea-Japan peninsula and the adjoining north China region only. The increases may be attributed to the projected intensification of the subtropical high, Meiyu-Changma-Baiu frontal zone and the associated influx of moist air from the Pacific inland. The projected changes in the amount of precipitation are directly proportional to the projected changes in the strength of the subtropical high. Further the MME suggests a possible increase in the length of the summer monsoon precipitation period from late spring through early autumn. The changes in precipitation could be stabilized by controlling the CO₂ emissions.     

Incorporating groundwater dynamics and surface/subsurface runoff mechanisms in regional climate modeling over river basins in China

To improve the capability of numerical modeling of climate-groundwater interactions, a groundwater component and new surface/subsurface runoff schemes were incorporated into the regional climate model RegCM3, renamed RegCM3_Hydro. 20－year simulations from both models were used to investigate the effects of groundwater dynamics and surface/subsurface runoff parameterizations on regional climate over seven river basins in China. A comparison of results shows that RegCM3_Hydro reduced the positive biases of annual and summer (June, July, August) precipitation over six river basins, while it slightly increased the bias over the Huaihe River Basin in eastern China. RegCM3_Hydro also reduced the cold bias of surface air temperature from RegCM3 across years, especially for the Haihe and the Huaihe river basins, with significant bias reductions of 0.80C and 0.88C, respectively. The spatial distribution and seasonal variations of water table depth were also well captured. With the new surface and subsurface runoff schemes, RegCM3_Hydro increased annual surface runoff by 0.11－0.62 mm d－1 over the seven basins. Though previous studies found that incorporating a groundwater component tends to increase soil moisture due to the consideration of upward groundwater recharge, our present work shows that the modified runoff schemes cause less infiltration, which outweigh the recharge from groundwater and result in drier soil, and consequently cause less latent heat and more sensible heat over most of the basins.     

Basic physical processes and regularities of winter and spring river runoff formation under climate warming conditions

A mechanism of climate change influence on the Medvenka River runoff in the winter- and springtime is revealed based on the generalized long-term observations carried out at the Podmoskovnaya water-balance station. It is demonstrated that average increase in the monthly mean temperature in January and February 1981–2008 of 2.8°C resulted in 1.9-time increase in the runoff over these months and its 15% decrease in April compared to the period of 1958–1980. The analysis of the observation materials and mathematical modeling of processes of migration and moisture infiltration in freezing and thawing soils allows establishing the fact that a decrease in the depth of soil freezing and, correspondingly, in moisture migration in the wintertime towards the freezing front and its accumulation in the frozen layer (a 56% increase in the runoff), available thaws (38%), and the fall increase in the soil moistening (6%) are major factors influencing the winter runoff increase.     

CO2 equivalences for short-lived climate forcers

With advancing climate change there is a growing need to include short-lived climate forcings in cost-efficient mitigation strategies to achieve international climate policy targets. Tools are required to compare the climate impact of perturbations with distinctively different atmospheric lifetimes and atmospheric properties. We present a generic approach for relating the climate effect of short-lived climate forcers (SLCF) to that of CO₂ emissions. We distinguish between three alternative types of metric-based factors that can be used to derive CO₂ equivalences for SLCF: based on forcing, activity and fossil fuel consumption. We derive numerical values for a wide range of parameter assumptions and apply the resulting generalised approach to the practical example of aviation-induced cloudiness. The evaluation of CO₂ equivalences for SLCF tends to be more sensitive to SLCF specific physical uncertainties and the normative choice of a discount rate than to the choice of a physical or economic metric approach. The ability of physical metrics to approximate economic-based metrics alters with changing atmospheric concentration levels and trends. Under reference conditions, physical CO₂ equivalences for SLCF provide sufficient proxies for economic ones. The latter, however, allow detailed insight into structural uncertainties. They provide CO₂ equivalences for SLCF in short term strategies in the face of failing climate policies, and a temporal evolution of CO₂ equivalences over time that is noticeably better in line with cost-efficient climate stabilisation.     

辽河流域气候变化及对径流影响预估与评估分析

辽河流域属于气候变暖较为显著区域,增温幅度比全球和全国的增温幅度都要高。同时辽河流域也是水资源较为匮乏且需求量大的地区,因此气候变化对水资源影响问题也更值得关注。基于长期历史观测气象水文数据和未来不同情景下气候变化预估资料,建立评估气候变化与径流量的关系,预估未来气候变化对径流量的可能影响,为辽河流域应对气候变化决策提供科学依据。结果表明：1961—2020年,辽河流域气温为持续上升趋势,降水没有明显的增减趋势,但存在阶段性变化;辽河流域降水量与径流量有较好的相关关系,具有较为一致的长期变化趋势与特征,年降水量与径流量相关数达到0.6以上。日降水量与径流量相关分析表明,降水发生后次日且为大雨降水等级(即日降水量≥25 mm)时,两者相关系数可高达0.85;敏感性试验和模式模拟试验表明,径流量对气候变化有明显的响应,降水增加(减少)、气温降低(升高),则径流量增加(减少);在未来RCP8.5排放情景下气温升高趋势最为明显,未来径流量也为显著增加趋势;RCP2.6排放情景下气温增加的幅度最小,未来径流量也表现为无明显增减趋势;RCP4.5情景下,气温增加的幅度居中,未来径流量则为减少趋势。     

The diurnal cycle of surface air temperature in simulated present and doubled CO2 climates

 The diurnal range of surface air temperature (rT _a ) simulated for present and doubled CO₂ climates by the CSIRO9 GCM is analysed. Based on mean diurnal cycles of temperature and surface heat fluxes, a theory for understanding the results is developed. The cycles are described as the response to a diurnal forcing which is represented well by the diurnal mean flux of net shortwave radiation at the surface (SW) minus the evaporative (E) and sensible (H) fluxes. The response is modified by heat absorbed by the ground, and by the cycle in downward longwave (LW) radiation, but these effects are nearly proportional to the range in surface temperature. Thus in seasonal means, rT _a is approximately given by SW–E–H divided by 6 W m^-2/^°C. A multiple regression model for (rT _a ) is developed, based on quantities known to influence SW, E and H, and applied to both spatial variation in seasonal means, and day-to-day variation at a range of locations. In both cases, rT _a is shown to be influenced by cloud cover, snow extent and wind speed. It is influenced by soil moisture, although this effect is closely tied to that of cloud. In seasonal means rT _a is also well correlated with precipitable water, apparently because of the latter’s influence on E+H. The regression model describes well the spatial variation in the doubled CO₂ change in rT _a . The annual mean change in rT _a over land on doubling CO₂ was −0.36 ^°C, partly because of a decrease in the mean diurnal forcing (as defined in the theory), but also apparently because of the effect of nonlinearity in T _s of the upward longwave emission. A diagnostic radiation calculation indicates that the CO₂ and water vapour provide a small increase in rT _a through the downward LW response, which partially counters a decrease due to a reduction of SW by the gases. Received: 8 November 1995 / Accepted: 3 January 1997     

Low-frequency variability and CO2 transient climate change

Results from a global coupled ocean-atmosphere general circulation model (GCM) are used to perform the first in a series of studies of the various time and space scales of climate anomalies in an environment of gradually increasing carbon dioxide (CO₂) (a linear transient increase of 1% per year in the coupled model). Since observed climate anomaly patterns often are computed as time-averaged differences between two periods, climate-change signals in the coupled model are defined using differences of various averaging intervals between the transient and control integrations. Annual mean surface air temperature differences for several regions show that the Northern Hemisphere warms faster than the Southern Hemisphere and that land areas warm faster than ocean. The high northern latitudes outside the North Atlantic contribute most to global warming but also exhibit great variability, while the high southern latitudes contribute the least. The equatorial tropics warm more slowly than the subtropics due to strong upwelling and mixing in the ocean. The globally averaged surface air temperature trend computed from annual mean differences for years 23–60 is 0.03 C per year. Projecting this trend to the time of CO₂ doubling in year 100 produces a warming of 2.3° C. By chance, one particular northern winter five-year average geographical difference pattern in the Northern Hemisphere from the coupled model resembles the recent observed pattern of surface temperature and sea-level pressure anomalies. This pattern is not consistent from one five-year period to the next in any season in the model. However, multidecadal averages in the coupled model show that the North Atlantic warms less than the rest of the high northern latitudes, and recent observations may be a manifestation of this phenomenon. Consistent geographic patterns of climate anomalies forced by increased CO₂ in the model are more evident with a longer averaging interval. There is also the possibility that the CO₂ climate-change signal may itself be a function of time and space. The general pattern of zonal mean temperature anomalies for all periods in the model shows warming in the troposphere and cooling in the stratosphere. This pattern (or one similar to it taking into account the rest of the trace gases) could be looked for in observations to verify the enhanced greenhouse effect. A zonal mean pattern, however, could prove scientifically satisfactory but of little value to policymakers seeking regional climate-change forecasts. These results from the coupled model underscore the difficulty in identifying a time- and space-dependent fingerprint of greenhouse warming that has some practical use from short climatic records and point to the need to understand the mechanisms of decadal-scale variability.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

气侯变化对东部季风区赣江和官厅流域径流的影响

选取中国东部季风区南方赣江流域和北方官厅流域,基于逐日气象和水文观测数据率定和验证了HBV水文模型,并以国际耦合模式比较计划第五阶段（CMIP5）中输出要素最多的5个全球气候模式在3种典型浓度路径（RCP2.6、RCP4.5和RCP8.5）下的预估结果驱动HBV模型,预估了气候变化对21世纪两个流域径流的影响。结果表明：(1) 1961—2017年,赣江和官厅流域年平均气温均呈显著上升趋势,升温速率分别为0.17℃/(10 a)和0.28℃/(10 a);同期,赣江流域降水显著增加,官厅流域降水微弱下降。不同RCP情景下,21世纪两个流域均将持续变暖、降水有所增加,北方官厅流域的气温和降水增幅均大于南方赣江流域。(2) 21世纪,官厅流域年、季径流增幅远大于赣江流域。官厅流域年径流在近期（2020—2039年）、中期（2050—2069年）、末期（2080—2099年）均呈增加趋势,RCP8.5情景下增幅最大、RCP4.5最小。赣江流域在RCP4.5下,近期、中期年径流相对基准期略有减少,但在整个21世纪径流呈上升趋势;RCP2.6和RCP8.5下,21世纪中期以后径流增幅下降。(3) 21世纪,东部季风区北部的官厅流域发生洪涝、南方赣江流域发生干旱的可能性增大,不同RCP情景预估得到相同的结论。