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1.
The study evaluates statistical downscaling model (SDSM) developed by annual and monthly sub-models for downscaling maximum temperature, minimum temperature, and precipitation, and assesses future changes in climate in the Jhelum River basin, Pakistan and India. Additionally, bias correction is applied on downscaled climate variables. The mean explained variances of 66, 76, and 11 % for max temperature, min temperature, and precipitation, respectively, are obtained during calibration of SDSM with NCEP predictors, which are selected through a quantitative procedure. During validation, average R 2 values by the annual sub-model (SDSM-A)—followed by bias correction using NCEP, H3A2, and H3B2—lie between 98.4 and 99.1 % for both max and min temperature, and 77 to 85 % for precipitation. As for the monthly sub-model (SDSM-M), followed by bias correction, average R 2 values lie between 98.5 and 99.5 % for both max and min temperature and 75 to 83 % for precipitation. These results indicate a good applicability of SDSM-A and SDSM-M for downscaling max temperature, min temperature, and precipitation under H3A2 and H3B2 scenarios for future periods of the 2020s, 2050s, and 2080s in this basin. Both sub-models show a mean annual increase in max temperature, min temperature, and precipitation. Under H3A2, and according to both sub-models, changes in max temperature, min temperature, and precipitation are projected as 0.91–3.15 °C, 0.93–2.63 °C, and 6–12 %, and under H3B2, the values of change are 0.69–1.92 °C, 0.56–1.63 °C, and 8–14 % in 2020s, 2050s, and 2080s. These results show that the climate of the basin will be warmer and wetter relative to the baseline period. SDSM-A, most of the time, projects higher changes in climate than SDSM-M. It can also be concluded that although SDSM-A performed well in predicting mean annual values, it cannot be used with regard to monthly and seasonal variations, especially in the case of precipitation unless correction is applied.  相似文献   

2.
Soil temperature (T s) and its thermal regime are the most important factors in plant growth, biological activities, and water movement in soil. Due to scarcity of the T s data, estimation of soil temperature is an important issue in different fields of sciences. The main objective of the present study is to investigate the accuracy of multivariate adaptive regression splines (MARS) and support vector machine (SVM) methods for estimating the T s. For this aim, the monthly mean data of the T s (at depths of 5, 10, 50, and 100 cm) and meteorological parameters of 30 synoptic stations in Iran were utilized. To develop the MARS and SVM models, various combinations of minimum, maximum, and mean air temperatures (T min, T max, T); actual and maximum possible sunshine duration; sunshine duration ratio (n, N, n/N); actual, net, and extraterrestrial solar radiation data (R s, R n, R a); precipitation (P); relative humidity (RH); wind speed at 2 m height (u 2); and water vapor pressure (Vp) were used as input variables. Three error statistics including root-mean-square-error (RMSE), mean absolute error (MAE), and determination coefficient (R 2) were used to check the performance of MARS and SVM models. The results indicated that the MARS was superior to the SVM at different depths. In the test and validation phases, the most accurate estimations for the MARS were obtained at the depth of 10 cm for T max, T min, T inputs (RMSE = 0.71 °C, MAE = 0.54 °C, and R 2 = 0.995) and for RH, V p, P, and u 2 inputs (RMSE = 0.80 °C, MAE = 0.61 °C, and R 2 = 0.996), respectively.  相似文献   

3.
This study investigates atmospheric conditions’ influence on the mean and extreme characteristics of PM10 concentrations in Poznań during the period 2006–2013. A correlation analysis was carried out to identify the most important meteorological variables influencing the seasonal dynamics of PM10 concentrations. The highest absolute correlation values were obtained for planetary boundary layer height (r = ?0.57), thermal (daily minimum air temperature: r = ?0.51), anemological (average daily wind speed: r = ?0.37), and pluvial (precipitation occurrence: r = ?0.36) conditions, however the highest correlations were observed for temporal autocorrelations (1 day lag: r = 0.70). As regulated by law, extreme events were identified on the basis of daily threshold value i.e. 50 μg m?3. On average, annually there are approximately 71.3 days anywhere in the city when the threshold value is exceeded, 46.6 % of those occur in winter. Additionally, 83.7 % of these cases have been found to be continuous episodes of a few days, with the longest one persisting for 22 days. The analysis of the macro-scale circulation patterns led to the identification of an easy-to-perceive seasonal relations between atmospheric fields that favour the occurrence of high PM10 concentration, as well as synoptic situations contributing to the rapid air quality improvement. The highest PM10 concentrations are a clear reaction to a decrease in air temperature by over 3 °C, with simultaneous lowering of PBL height, mean wind speed (by around 1 m s?1) and changing dominant wind directions from western to eastern sectors. In most cases, such a situation is related to the expansion of a high pressure system over eastern Europe and weakening of the Icelandic Low. Usually, air quality conditions improve along with an intensification of westerlies associated with the occurrence of low pressure systems over western and central Europe. Opposite relations are distinguishable in summer, when air quality deterioration is related to the inflow of tropical air masses originating over the Sahara desert.  相似文献   

4.
Uncertainty assessments of climate change projections over South America   总被引：2，自引：0，他引：2  
This paper assesses the uncertainties involved in the projections of seasonal temperature and precipitation changes over South America in the twenty-first century. Climate simulations generated by 24 general circulation models are weighted according to the reliability ensemble averaging (REA) approach. The results show that the REA mean temperature change is slightly smaller over South America compared to the simple ensemble mean. Higher reliability in the temperature projections is found over the La Plata basin, and a larger uncertainty range is located in the Amazon. A temperature increase exceeding 2 °C is found to have a very likely (>90 %) probability of occurrence for the entire South American continent in all seasons, and a more likely than not (>50 %) probability of exceeding 4 °C by the end of this century is found over northwest South America, the Amazon Basin, and Northeast Brazil. For precipitation, the projected changes have the same magnitude as the uncertainty range and are comparable to natural variability.  相似文献   

5.
Based on homogenized land surface air temperature (SAT) data (derived from China Homogenized Historical Temperature (CHHT) 1.0), the warming trends over Northeast China are detected in this paper, and the impacts of urban heat islands (UHIs) evaluated. Results show that this region is undergoing rapid warming: the trends of annual mean minimum temperature (MMIT), mean temperature (MT), and mean maximum temperature (MMAT) are 0.40 C decade?1, 0.32 C decade?1, and 0.23 C decade?1, respectively. Regional average temperature series built with these networks including and excluding “typical urban stations” are compared for the periods of 1954–2005. Although impacts of UHIs on the absolute annual and seasonal temperature are identified, UHI contributions to the long-term trends are less than 10% of the regional total warming during the period. The large warming trend during the period is due to a regime shift in around 1988, which accounted for about 51% of the regional warming.  相似文献   

6.
Effects of global warming on radial growth were examined for the subalpine tree species Abies veitchii (1600–2200 m?a.s.l.), A. mariesii (2000–2500 m?a.s.l.) and Betula ermanii (1600–2500 m?a.s.l.) in central Japan, by using dendrochronological techniques. Chronologies of tree-ring widths were examined for the three species and of maximum latewood densities for the two Abies species at their upper and lower distribution limits (total 10 chronologies). We developed multiple regression models to reproduce these chronologies from the monthly mean temperature and sum of precipitation. Of the 10 chronologies, growth-climate relations could not be modeled for tree-ring width chronologies of the three species at their lower distribution limits because of low correlation. Annual mean temperature and annual sum of precipitation will increase about 3 °C and 100 mm, respectively, by 2100 in central Japan, according to 18 climatic change scenarios (6 general circulation models ×3 greenhouse gasses emission scenarios). We predicted tree-ring widths and maximum latewood densities by substituting 18 climatic change scenarios into the growth-climate models. Maximum latewood densities and tree-ring widths of A. mariesii at the upper and lower distribution limits increased by 2100. The rates of the increase tended to be greater for scenarios with more greenhouse gas emission. By contrast, maximum latewood densities of A. veitchii and tree-ring widths of B. ermanii were unchanged by 2100, irrespective of the three greenhouse gas emission scenarios. This study showed that radial growth of the three species responds differently to global warming and their responses are predictable by dendrochronological models.  相似文献   

7.
Much research focuses on how the terrestrial biosphere influences climate through changes in surface albedo (reflectivity), stomatal conductance and leaf area index (LAI). By using a fully-coupled GCM (HadCM3LC), our research objective was to induce an increase in the growth of global vegetation to isolate the effect of increased LAI on atmospheric exchange of heat and moisture. Our Control simulation had a mean global net primary production (NPP) of 56.3 GtCyr?1 which is half that of our scenario value of 115.1 GtCyr?1. LAI and latent energy (Q E) were simulated to increase globally, except in areas around Antarctica. A highly productive biosphere promotes mid-latitude mean surface cooling of ~2.5°C in the summer, and surface warming of ~1.0°C in the winter. The former response is primarily the result of reduced Bowen ratio (i.e. increased production of Q E) in combination with small increases in planetary albedo. Response in winter temperature is likely due to decreased planetary albedo that in turn permits a greater amount of solar radiation to reach the Earth’s surface. Energy balance calculations show that between 75° and 90°N latitude, an additional 2.4 Wm?2 of surface heat must be advected into the region to maintain energy balance, and ultimately causes high northern latitudes to warm by up to 3°C. We postulate that large increases in Q E promoted by increased growth of terrestrial vegetation could contribute to greater surface-to-atmosphere exchange and convection. Our high growth simulation shows that convective rainfall substantially increases across three latitudinal bands relative to Control; in the tropics, across the monsoonal belt, and in mid-latitude temperate regions. Our theoretical research has implications for applied climatology; in the modeling of past “hot-house” climates, in explaining the greening of northern latitudes in modern-day times, and for predicting future changes in surface temperature with continued increases in atmospheric CO2.  相似文献   

8.
Drought is one of the crucial environmental factors affecting crop production. Synchronizing crop phenology with expected or predicted seasonal soil moisture supply is an effective approach to avoid drought impact. To assess the potential for drought avoidance, this study investigated the long-term climate data of four locations (Bojnourd, Mashhad, Sabzevar, and Torbat Heydarieh) in Khorasan province, in the northeast of Iran, with respect to the four dominant crops (common bean, lentil, peanut, and potato). Weekly water deficit defined as the difference between weekly precipitation and weekly potential evapotranspiration was calculated. Whenever the weekly water deficit was larger than the critical water demand of a crop, the probability for drought was determined. Results showed that Sabzevar has the highest average maximum temperature (24.6 °C), minimum temperature (11.7 °C), weekly evapotranspiration (32.1 mm), and weekly water deficit (28.3 mm) and has the lowest average weekly precipitation (3.8 mm). However, the lowest mean maximum temperature (19.7 °C), minimum temperature (6.9 °C), weekly evapotranspiration (22.5 mm), and weekly water deficit (17.5 mm) occur in Bojnourd. This location shows the shortest period of water deficit during the growing season for all crops except potato, which also experienced drought at the end of the growing season. Sabzevar and Torbat Heydarieh experienced the highest probability of occurrence and longest duration of drought during the growing season for all crops. The result of this study will be helpful for farmers in order to reduce drought impact and enable them to match crop phenology with periods during the growing season when water supply is more abundant.  相似文献   

9.
Changes over the twentieth century in seasonal mean potential predictability (PP) of global precipitation, 200 hPa height and land surface temperature are examined by using 100-member ensemble. The ensemble simulations have been conducted by using an intermediate complexity atmospheric general circulation model of the International Center for Theoretical Physics, Italy. Using the Hadley Centre sea surface temperature (SST) dataset on a 1° grid, two 31 year periods of 1920–1950 and 1970–2000 are separated to distinguish the periods of low and high SST variability, respectively. The standard deviation values averaged for the (“Niño-3.4”; 5°S–5°N, 170°W–120°W) region are 0.71 and 1.15 °C, for the periods of low and high SST variability, respectively, with a percentage change of 62 % during December–January–February (DJF). The leading eigenvector and the associated principal component time series, also indicate that the amplitude of SST variations have positive trend since 1920s to recent years, particularly over the El Niño Southern Oscillation (ENSO) region. Our hypothesis states that the increase in SST variability has increased the PP for precipitation, 200 hPa height and land surface temperature during the DJF. The analysis of signal and noise shows that the signal-to-noise (S/N) ratio is much increased over most of the globe, particularly over the tropics and subtropics for DJF precipitation. This occurs because of a larger increase in the signal and at the same time a reduction in the noise, over most of the tropical areas. For 200 hPa height, the S/N ratio over the Pacific North American (PNA) region is increasing more than that for the other extratropical regions, because of a larger percentage increase in the signal and only a small increase in noise. It is also found that the increase in seasonal mean transient signal over the PNA region is 50 %, while increase in the noise is only 12 %, during the high SST variability period, which indicates that the increase in signal is more than the noise. For DJF land surface temperature, the perfect model notion is utilized to confirm the changes in PP during the low and high SST variability periods. The correlation between the perfect model and the other members clearly reveal that the seasonal mean PP changed. In particular, the PP for the 31 years period of 1970–2000 is higher than that for the 31 years period of 1920–1950. The land surface temperature PP is increased in northern and southern Africa, central Europe, southern South America, eastern United States and over Canada. The increase of the signal and hence the seasonal mean PP is coincides with an increase in tropical Pacific SST variability, particularly in the ENSO region.  相似文献   

10.
Climate records of air temperature (AT) and total precipitation (TP) are standard inputs for soil carbon dynamic models, i.e., for calculating temperature and moisture effects on soil biological activity. In this study our objective was to determine both spatial and temporal differences in soil biological activity in the Province of Québec, Canada. Soil biological activity was here calculated on a daily basis with the ICBM re_clim parameter using data from weather stations. When keeping soil and crop properties constant, re_clim (unitless) allows us to assess relative differences in soil biological activity. The magnitude of the temporal changes in re_clim, AT and TP were analyzed using Sen’s slope, which is a nonparametric method used to determine the presence of a trend component. The re_clim varied across Québec from 0.50 (58 °N) to a high of 1.66 (45 °N). Considering only the area with significant agricultural production, re_clim varied from 0.99 at Gaspé (48 °N) to 1.66 at Philipsburg (45 °N), i.e., soil organic carbon (SOC) decomposition rate is 68 % higher at the latter site (1.66/0.99) and correspondingly more C input is needed to maintain SOC. Soil biological activity increased from 1960 to 2009, with a mean slope variation in re_clim of about +10 %. The temporal variation in AT had more influence than that of TP. For 1980–2009 the mean annual slope of re_clim was significantly different from zero for 29 out of 49 climate records (mean?=?+14 %; N?=?29). We also emphasize that analysis of seasonal changes in AT is an issue that needs further attention, as well as modeling climate-induced changes in SOC dynamics based on future climate scenarios.  相似文献   

11.
D. M. Volobuev 《Climate Dynamics》2014,42(9-10):2469-2475
Antarctic “Vostok” station works most closely to the center of the ice cap among permanent year-around stations. Climate conditions are exclusively stable: low precipitation level, cloudiness and wind velocity. These conditions can be considered as an ideal model laboratory to study the surface temperature response on solar irradiance variability during 11-year cycle of solar activity. Here we solve an inverse heat conductivity problem: calculate the boundary heat flux density (HFD) from known evolution of temperature. Using meteorological temperature record during (1958–2011) we calculated the HFD variation about 0.2–0.3 W/m2 in phase with solar activity cycle. This HFD variation is derived from 0.5 to 1 °C temperature variation and shows relatively high climate sensitivity per 0.1 % of solar radiation change. This effect can be due to the polar amplification phenomenon, which predicts a similar response 0.3–0.8 °C/0.1 % (Gal-Chen and Schneider in Tellus 28:108–121, 1975). The solar forcing (TSI) is disturbed by volcanic forcing (VF), so that their linear combination TSI + 0.5VF empirically provides higher correlation with HFD (r = 0.63 ± 0.22) than TSI (r = 0.50 ± 0.24) and VF (r = 0.41 ± 0.25) separately. TSI shows higher wavelet coherence and phase agreement with HFD than VF.  相似文献   

12.
Daily gridded (1°×1°) temperature data (1969–2005) were used to detect spatial patterns of temporal trends of maximum and minimum temperature (monthly and seasonal), growing degree days (GDDs) over the crop-growing season (kharif, rabi, and zaid) and annual frequencies of temperature extremes over India. The direction and magnitude of trends, at each grid level, were estimated using the Mann–Kendall statistics (α = 0.05) and further assessed at the homogeneous temperature regions using a field significance test (α=0.05). General warming trends were observed over India with considerable variations in direction and magnitude over space and time. The spatial extent and the magnitude of the increasing trends of minimum temperature (0.02–0.04 °C year?1) were found to be higher than that of maximum temperature (0.01–0.02 °C year?1) during winter and pre-monsoon seasons. Significant negative trends of minimum temperature were found over eastern India during the monsoon months. Such trends were also observed for the maximum temperature over northern and eastern parts, particularly in the winter month of January. The general warming patterns also changed the thermal environment of the crop-growing season causing significant increase in GDDs during kharif and rabi seasons across India. The warming climate has also caused significant increase in occurrences of hot extremes such as hot days and hot nights, and significant decrease in cold extremes such as cold days and cold nights.  相似文献   

13.
In order to investigate the physical structure characteristics of the clouds and precipitation over the Tianshan Mountains in summer, the Urumqi Institute of Desert Meteorology of China Meteorological Administration (CMA) carried out an atmospheric detection experiment in Bayanbulak from 1st to 31st August 2012 by means of a wind-profiling radar and a Doppler weather radar. Using the radar observation data, this paper analyzes the dynamic, thermodynamic, radar echo intensity and macro-micro structure characteristics of the 2–3 August precipitation process. The results show that: (1) The radar echo intensity of this rainfall process changes within 5–38 dBZ, and the precipitation cloud system is under the height of 6500 m, with notable 0 °C level echo bright band between 1200 m and 2000 m height. NCEP analysis data shows that the cloud top temperature ranges from ?25 °C to ?32 °C. These indicate the features of typical stratiform cold cloud precipitation. (2) Atmospheric motion during the precipitation process presents the multi-layer structure with wind velocity varying within the range of 3.0–8.0 m/s. The temperature advection is presented with the vertical structure distribution of “cold-warm-cold”, which indicates relative stability of the atmospheric stratification. (3) By retrieving and analyzing the raindrop size distributions below 0 °C level bright band within 600–1200 m height, when the precipitation evolve from early stage to its peak stage, the concentration of the tiny particle zone (D?≤?2.5 mm) changes a little while the concentration of the medium particle zone (2.5?<?D?≤?4 mm) and the concentration of the large particle(D?>?4 mm) increase considerably; but after peak stage the concentration in the medium particle zone and the concentration in the large particle zone decline first, then the concentration in the tiny particle zone reduces. (4) Raindrop size distribution data is used to calculate the precipitation intensity and the liquid water content, whose spatial-temporal variation characteristics are the same. During peak stage of the precipitation, the instantaneous precipitation intensity reaches 5.0 mm/h, and the liquid water content reaches 0.35 g/m3. This study would help deepen the understanding on the physical structure of the clouds and precipitation over the Tianshan Mountains in summer, and also provide some scientific basis for cloud seeding operation over this area.  相似文献   

14.
In this analysis, the weather research and forecasting model coupled with a single-layer urban canopy model is used to simulate the climatic impacts of urbanization in the Beijing–Tianjin–Hebei metropolitan area, which has experienced significant expansion in its urban areas. Two cases examining current landscapes and the sensitivity test of urban areas replaced by cropland have been carried out to explore the changes in the surface air and atmospheric boundary structure. The impact of urbanization on annual mean surface air temperature has been found to be more than 1 °C in urban areas, and the maximum difference is almost 2 °C. The change in near-surface level temperature is most pronounced in winter, but the area influenced by urbanization is slightly larger in summer. The annual mean water vapor mixing ratio and wind speed are both reduced in the urban area. The effect of urbanization can only heat the temperature inside the urban boundary layer, below 850 hPa. The modeling results also indicate that the underlying surface thermal forces induced by the “urban heat island” effect enhance vertical air movement and engenders a convergence zone over urban areas. The convergence at low level together with the moisture increases in the layer between 850 and 700 hPa triggered the increase of convective precipitation.  相似文献   

15.
C. Hatté  J. Guiot 《Climate Dynamics》2005,25(2-3):315-327
A modified version of the Biome4 vegetation model for simulation of the mean δ13C of plant communities is presented, and used to reconstruct palaeoprecipitation. We treat all fractionations by C3 and C4 plants in all coexistent Plant Functional Types, weighted by their respective net primary production. We constrain the range of variation in the intracellular versus atmospheric CO2 concentration by fixing a lower limit. Finally, we replace some constant parameters by functions of external forcing to account for their responses to environmental variation. The new version of Biome4 was applied as an inverse model and tested on three modern data sets. The fit between observations and simulations is very close to the 1:1 relationship, with respective slopes of 0.90±0.02 (r 2=0.98, n=29) for δ13C and 0.97±0.06 (r 2=0.90, n=29) for precipitation. Inverse modelling was applied using the Metropolis-Hastings algorithm to the Nußloch loess sequence. Over the last glaciation, simulated palaeoprecipitation varies between 240 mm year?1 and 400 mm year?1. This study clearly demonstrates atmospheric teleconnections with the Greenland ice-sheet extension, by matching Dansgaard-Oeschger events with precipitation increase of ca. 100–200 mm year?1.  相似文献   

16.
Daily precipitation forecast of ECMWF verified over Iran   总被引：1，自引：0，他引：1  
In this paper, the performance of the Centre for Medium Range Weather Forecast (ECMWF) model (t?+?27 h to t?+?51 h) in predicting precipitation is discussed. This model is the first, which has been verified over Iran. The spatial resolution of the model is 0.351° and the 24-h forecasts are compared with daily observations. The study concentrates on year 2001 and the precipitation measurements were collected from the data of 2,048 rain gauges in Iran. The accuracy of four different interpolation methods (nearest neighborhood, inverse distance, kriging, and upscaling) was investigated. Using cross-validation, the inverse distance method (IDM) with minimum mean error was applied. Verification results are given in terms of difference fields (mean error?=?0.46 mm/day), rank–order correlation coefficients (0.70), as well as accuracy scores (false alarm ratio?=?0.50 and probability of detection?=?0.60) and skill scores (true skill statistics [TSS]?=?0.45) in year 2001. The position of the rain band was only partly captured by the ECMWF model; however, the position of maximum precipitations agrees with the observations well. The results show that the high values of TSS are associated with the large amounts of precipitation (over 25 mm). Slight to moderate precipitation events have been underforecasted by the model (bias?<?1) and it leads to a small value of TSS for these thresholds (5–25 mm/day). The ECMWF model has better performance in high and mountainous regions than over flat terrain and in deserts. Comparing TSS over the Alborz and the Zagros Mountains, it is obvious that the ability of the model to predict the convective precipitation events needs some improvement. The amount of daily precipitation has been also slightly overestimated over Iran. From the beginning of January up to 21 March 2001, the ECMWF time series indicates an obvious phase shift of 1 day, although in other months, no phase shift is noticed.  相似文献   

17.
We investigate the future changes of Asian-Australian monsoon (AAM) system projected by 20 climate models that participated in the phase five of the Coupled Model Intercomparison Project (CMIP5). A metrics for evaluation of the model’s performance on AAM precipitation climatology and variability is used to select a subset of seven best models. The CMIP5 models are more skillful than the CMIP3 models in terms of the AAM metrics. The future projections made by the selected multi-model mean suggest the following changes by the end of the 21st century. (1) The total AAM precipitation (as well as the land and oceanic components) will increase significantly (by 4.5 %/°C) mainly due to the increases in Indian summer monsoon (5.0 %/°C) and East Asian summer monsoon (6.4 %/°C) rainfall; the Australian summer monsoon rainfall will increase moderately by 2.6 %/°C. The “warm land-cool ocean” favors the entire AAM precipitation increase by generation of an east-west asymmetry in the sea level pressure field. On the other hand, the warm Northern Hemisphere-cool Southern Hemisphere induced hemispheric SLP difference favors the ASM but reduces the Australian summer monsoon rainfall. The combined effects explain the differences between the Asian and Australian monsoon changes. (2) The low-level tropical AAM circulation will weaken significantly (by 2.3 %/°C) due to atmospheric stabilization that overrides the effect of increasing moisture convergence. Different from the CMIP3 analysis, the EA subtropical summer monsoon circulation will increase by 4.4 %/°C. (3) The Asian monsoon domain over the land area will expand by about 10 %. (4) The spatial structures of the leading mode of interannual variation of AAM precipitation will not change appreciably but the ENSO-AAM relationship will be significantly enhanced.  相似文献   

18.
An approach to mitigate global warming via sulphur loading in the stratosphere (geoengineering) is studied, employing a large ensemble of numerical experiments with the climate model of intermediate complexity IAP RAS CM. The model is forced by the historical+SRES A1B anthropogenic greenhouse gases+tropospheric sulphates scenario for 1860–2100 with additional sulphur emissions in the stratosphere in the twenty-first century. Different ensemble members are constructed by varying values of the parameters governing mass, horizontal distribution and radiative forcing of the stratospheric sulphates. It is obtained that, given a global loading of the sulphates in the stratosphere, among those studied in this paper latitudinal distributions of geoengineering aerosols, the most efficient one at the global basis is that peaked between 50°N and 70°N and with a somewhat smaller burden in the tropics. Uniform latitudinal distribution of stratospheric sulphates is a little less efficient. Sulphur emissions in the stratosphere required to stop the global temperature at the level corresponding to the mean value for 2000–2010 amount to more than 10 TgS/year in the year 2100. These emissions may be reduced if some warming is allowed to occur in the twenty-first century. For instance, if the global temperature trend S g in every decade of this century is limited not to exceed 0.10 K/decade (0.15 K/decade), geoengineering emissions of 4–14 TgS/year (2–7 TgS/year) would be sufficient. Even if the global warming is stopped, temperature changes in different regions still occur with a magnitude up to 1 K. Their horizontal pattern depends on implied latitudinal distribution of stratospheric sulphates. In addition, for the stabilised global mean surface air temperature, global precipitation decreases by about 10%. If geoengineering emissions are stopped after several decades of implementation, their climatic effect is removed within a few decades. In this period, surface air temperature may grow with a rate of several Kelvins per decade. The results obtained with the IAP RAS CM are further interpreted employing a globally averaged energy–balance climate model. With the latter model, an analytical estimate for sulphate aerosol emissions in the stratosphere required climate mitigation is obtained. It is shown that effective vertical localisation of the imposed radiative forcing is important for geoengineering efficiency.  相似文献   

19.
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20.
Observed climate variability and change in Urmia Lake Basin, Iran   总被引：4，自引：2，他引：2  
This paper analyzes climate variability and change in the Urmia Lake Basin, northwest of Iran. Annual average of the following data time series has been analyzed by statistical methods: dry bulb temperature, maximum and minimum temperature, precipitation, and number of rainy and snowy days. We have also used mean monthly temperature and precipitation data for analysis of drought spells for the period 1964–2005 to find out whether fluctuations in the lake level are attributable to natural drought. Our results indicate that mean precipitation has decreased by 9.2 % and the average maximum temperature has increased by 0.8°C over these four decades. The seasonal changes are particularly visible in winter and spring. Results of the Palmer Drought Severity Index show that on average, drought episodes have hit the Urmia Lake Basin every 5 years and most of them reached severe levels, but recent droughts have become more intense and last longer.  相似文献   

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