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1.
This study simulates water resources in the Tien Shan alpine basins to forecast how global and regional climate changes would affect river runoff. The model employed annual mean values for the major characteristics of the water cycle: annual air temperature, precipitation, evapotranspiration and river runoff. The simulation was based on 304 hydro-meteorological stations, 23 precipitation sites, 328 high altitudinal points with glaciological measurements, 123 stream-gauges, and 54 evaporation sites, and it took into account topography. The findings were simulated over Tien Shan relief using a 1:500,000 scale 100 m grid resolution Digital Elevation Model. An applicable GIS-based distributed River Runoff Model was implemented in regional conditions and tested in the Tien Shan basins. The annual evapotranspiration exceeds the river runoff in the Tien Shan watersheds particularly up to 3700 m. Hypothetical climate-change scenarios in the Tien Shan predict that by 2100 river runoff will increase by 1.047 times with an increase in air temperature averaging 3 °C and an increase in precipitation averaging 1.2 times the current levels. Change in precipitation, rather than temperature, is the main parameter determining river runoff in the Tien Shan. The maximum ratio for predicted river runoff could reach up to 2.2 and the minimum is predicted to be 0.55 times current levels. This possibly dramatic change in river runoff indicates on non-linear system response caused mainly by the non-linear response of evapotranspiration from air temperature and precipitation changes. In the frame of forecasted possible climate change scenarios the probability of river runoff growth amounts 83–87% and probability of this decline is 17–13% by 2100 in the Tien Shan River basins.  相似文献   

2.
Past and present glacier changes have been studied at Cordón Martial, Cordillera Fueguina Oriental, Tierra del Fuego, providing novel data for the Holocene deglaciation history of southern South America and extrapolating as well its future behavior based on predicted climatic changes. Regional geomorphologic and stratigraphic correlations indicate that the last glacier advance deposited the ice-proximal (“internal”) moraines of Cordón Martial, around 330 14C yr BP, during the Late Little Ice Age (LLIA). Since then glaciers have receded slowly, until 60 years ago, when major glacier retreat started. There is a good correspondence for the past 100 years between the surface area variation of four small cirque glaciers at Cordón Martial and the annual temperature and precipitation data of Ushuaia. Between 1984 and 1998, Martial Este Glacier lost 0.64 ± 0.02 × 106 m3 of ice mass (0.59 ± 0.02 × 106 m3 w.e.), corresponding to an average ice thinning of 7.0 ± 0.2 m (6.4 ± 0.2 m w.e), according to repeated topographic mapping. More detailed climatic data have been obtained since 1998 at the Martial Este Glacier, including air temperature, humidity and solar radiation. These records, together with the monthly mass balance measured since March 2000, document the annual response of the Martial Este Glacier to the climate variation. Mass balances during hydrological years were positive in 2000, negative in 2001 and near equilibrium in 2002. Finally, using these data and the regional temperature trend projections, modeled for different future scenarios by the Atmosphere-Ocean Model (GISS-NASA/GSFC), potential climatic-change effects on this mountain glacier were extrapolated. The analysis shows that only the Martial Este Glacier may survive this century.  相似文献   

3.
Cryospheric change in China   总被引：16，自引：0，他引：16  
This paper provides an overview of the current status of the cryosphere in China and its changes. Up-to-date statistics of the cryosphere in China are summarized based on the latest available data. There are 46,377 glaciers in China, covering an area of 59,425 km2. The glacier ice reserve is estimated to be about 5600 km3 and the annual glacier runoff is about 61.6 × 109 m3. The continuous snow cover extent (> 60 days) in China is about 3.4 × 106 km2 and the maximum water equivalent is 95.9 × 109 m3 yr− 1. The permafrost area in China is about 1.72 × 106 km2. The total ground ice reserve on the Qinghai–Tibetan Plateau is estimated to be about 10,923 km3. Recent investigations indicated that glacier areas in China have shrunk about 2–10% over the past 45 yr. Total glacier area has receded by about 5.5%. Snow mass has increased slightly. Permafrost is clearly degrading, as indicated by shrinking areas of permafrost, increasing depth of the active layer, rising of lower limit of permafrost, and thinning of the seasonal frost depth. Some models predict that glacier area shrinkage could be as high as 26.7% in 2050, with glacier runoff increasing until its maximum in about 2030. Although snow mass shows an increasing trend in western China, in eastern China the trend is toward decreasing snow mass, with increasing interannual fluctuations. Permafrost degradation is likely to continue, with one-third to one-half of the permafrost on the Qinghai–Tibetan Plateau anticipated to degrade by 2100. Most of the high-temperature permafrost will disappear by then. The permafrost in northeastern China will retreat further northward.  相似文献   

4.
Evidence for Late Pleistocene glaciers and rock glaciers in the Pindus Mountains, Greece, is used to reconstruct palaeoclimate for this part of the Mediterranean during the last cold stage (Tymphian/ Würmian). Mean annual precipitation was c. 2300 ± 200 mm and the mean summer temperature (June/July/August) was c. 4.9 °C at 2174 m a.s.l., the equilibrium line altitude of the former glaciers, at the last local glacier maximum. The glacier–climate relationship in the northern Pindus Mountains during the local glacier maximum of the Tymphian Stage closely resembled that found today at the equilibrium line altitude of Norwegian glaciers. The local glacier maximum on Mount Tymphi is likely to have preceded both the most severe phase of climate indicated in the pollen record at nearby Ioannina and also the global last glacial maximum. Major stadials, including the most severe phase of the last cold stage, were characterised by cold sea surfaces temperatures, which inhibited atmospheric moisture supply creating unfavourable conditions for glacier formation. Such stadial conditions are likely to have favoured periglacial conditions and the formation of features such as rock glaciers. Conversely, warm summer temperatures during major interstadials would have promoted glacier ablation, offsetting increased precipitation enabled by warmer sea surface temperatures. Thus, the most favourable conditions for glacier formation would have occurred during intermediate conditions between major stadials and interstadials. It is clear that former glacier behaviour in the mountains of this region is best understood with reference to temporally dynamic glacier–climate models, which take into account millennial-scale changes in both precipitation and temperature.  相似文献   

5.
Climatic changes of the 20th century have altered the water cycle in the Andean basins of central Argentina. The most visible change is seen in the mountain glaciers, with loss of part of their mass due to decreasing thickness and a substantial recession in the last 100 years. This paper briefly describes the results of glacier mass balance research since 1979 in the Piloto Glacier at the Cajón del Rubio, in the headwaters of Las Cuevas River, presenting new results for the period 1997–2003. Very large interannual variability of net annual specific balance is evident, due largely to variations in winter snow accumulation, with a maximum net annual value of + 151 cm w.e. and a minimum value of - 230 cm w.e. Wet El Niño years are normally associated with positive net annual balances, while dry La Niña years generally result in negative balances. Within the 24-year period, 67% of the years show negative net annual specific balances, with a cumulative mass balance loss of - 10.50 m water equivalent (w.e.). Except for exceptions normally related to El Niño events, a general decreasing trend of winter snow accumulation is evident in the record, particularly after 1992, which has a strong effect in the overall negative mass balance values. The glacier contribution to Las Cuevas River runoff is analysed based on the Punta de Vacas River gauge station for a hypothetical year without snow precipitation (YWSP), when the snowmelt component is zero. Extremely dry years similar to a YWSP have occurred in 1968–1969, 1969–1970 and 1996–1997. The Punta de Vacas gauge station is located 62 km downstream from Piloto Glacier, and the basin contains 3.0% of uncovered glacier ice and 3.7% of debris-covered ice. The total glacier contribution to Las Cuevas River discharge is calculated as 82 ± 8% during extremely dry years. If glacier wastage continues at the present trend as observed during the last 2 decades, it will severely affect the water resources in the arid central Andes of Argentina.  相似文献   

6.
Although several proxies have been proposed to trace the course of environmental and climatological fluctuations, precise paleoclimate records from the tropics, notably from Africa are still sorely lacking today. Stable carbon isotopes (δ13C) in tree rings are an attractive record of climate. In this study, the patterns and climatic signals of δ13C ratios were determined on tree rings of deciduous (Acacia senegal, Acacia tortilis, Acacia seyal) and an evergreen (Balanites aegyptiaca) species, from a semi-arid Acacia Woodland in Ethiopia. δ13C inter-annual patterns are synchronous among the co-occurring species. A declining trend with time was observed in δ13C, notably for B. aegyptiaca, which could be due to anthropogenic increases in atmospheric CO2 concentration and decrease in atmospheric δ13C. Tree ring δ13C values of all the species revealed significant negative correlation with precipitation amount but not with temperature and relative humidity. The δ13C series of the deciduous species shows a higher correlation (r = − 0.70 to − 0.78) with precipitation than the evergreen species (r = − 0.55). A master δ13C series, composed of the average of the three Acacia species, displayed stronger significant correlation (r = − 0.82) than any of the individual species δ13C series. The weak relationship between temperature and δ13C in this study indicates that photosynthetic rate is not a significant factor. Moisture stress, however, may have a direct impact on the stomatal conductance and explain the strong negative relationship between δ13C and precipitation. The results demonstrate the potential of δ13C in tree rings to reflect physiological responses to environmental changes as a vehicle for paleoclimatic reconstruction, which is important to understand tree response to past and future climate change.  相似文献   

7.
A 41-year-long reconstructed annual mean glacier mass balance record from the Cordillera Blanca, Peru, was investigated for its climate sensitivity toward temperature, humidity and precipitation, and its links with the large-scale atmospheric circulation. On interannual timescales precipitation variability appears to be the main driver for glacier mass balance fluctuations in the Cordillera Blanca. This is corroborated by an analysis of the relationship between mass balance variations and local- to regional-scale precipitation variability. Temperature tends to enhance precipitation in driving the mass balance signal, as dry years are often characterized by warm conditions, while wet years usually coincide with cold anomalies. In some years, however, warm and wet or cold and dry conditions coincide, under which circumstances temperature minimizes or even neutralizes the effects of precipitation. Surface energy balance studies have shown that changes in atmospheric humidity significantly affect the melt rates of tropical glaciers, but the lack of long and high-quality in-situ measurements precludes a detailed quantitative assessment of its role on interannual timescales in the Cordillera Blanca. Sea surface temperature anomalies (SSTA) in the tropical Pacific exert the dominant large-scale forcing on interannual time scales, leading to negative mass balance anomalies during El Niño and above average mass balance during La Niña episodes. In general the teleconnection mechanism linking ENSO with glacier mass balance is similar to what has previously been described for the Bolivian Altiplano region. Changes in the upper-tropospheric zonal flow aloft associated with ENSO conditions determine the amount of snowfall during the wet season and thereby significantly affect the glacier mass balance. Because this teleconnection mechanism is spatially unstable and oscillates latitudinally along the subtropical Andes, it affects the Cordillera Blanca in most, but not all years. The relationship between ENSO and glacier mass balance is therefore characterized by occasional ‘break downs’, more common since the mid-1970's, when El Niño years with above average mass balance and La Niña events with negative mass balance have been observed.  相似文献   

8.
The growth of two high-elevation inland lakes (at 4600 m) was analyzed using satellite imagery (2000–2005) and data were collected over the last decade (1997–2006) at a plateau meteorological station (at 4820 m) and stream gauging data from a station (at 4250 m) in central Tibet. We examined the lake water balance responses to meteorological and hydrological variables. The results show that the lake areas greatly expanded by a maximum of 27.1% (or 43.7 km2) between 1998 and 2005. This expansion appears to be associated with an increase in annual precipitation of 51.0 mm (12.6%), mean annual and winter mean temperature increases of 0.41 °C and 0.71 °C, and an annual runoff increase of 20% during the last decade. The changes point to an abrupt increase in the annual precipitation, mean temperature and runoff occurring in 1996, 1998 and 1997, respectively, and a decrease in the annual pan evaporation that happened in 1996. The timing of lake growth corresponds closely with abrupt increases in the annual precipitation and runoff and with the decrease in the annual evaporation since the mid-1990s. This study indicates a strong positive water balance in these permafrost highland lakes, and provides further evidence of lake growth as a proxy indicator of climate variability and change.  相似文献   

9.
Changes in the extent of glaciers and rates of glacier termini retreat in the eastern Terskey–Alatoo Range, the Tien Shan Mountains, Central Asia have been evaluated using the remote sensing techniques. Changes in the extent of 335 glaciers between the end of the Little Ice Age (LIA; mid-19th century), 1990 and 2003 have been estimated through the delineation of glacier outlines and the LIA moraine positions on the Landsat TM and ASTER imagery for 1990 and 2003 respectively. By 2003, the glacier surface area had decreased by 19% of the LIA value, which constitutes a 76 km2 reduction in glacier surface area. Mapping of 109 glaciers using the 1965 1:25,000 maps revealed that glacier surface area decreased by 12.6% of the 1965 value between 1965 and 2003. Detailed mapping of 10 glaciers using historical maps and aerial photographs from the 1943–1977 period, has enabled glacier extent variations over the 20th century to be identified with a higher temporal resolution. Glacial retreat was slow in the early 20th century but increased considerably between 1943 and 1956 and then again after 1977. The post-1990 period has been marked by the most rapid glacier retreat since the end of the LIA. The observed changes in the extent of glaciers are in line with the observed climatic warming. The regional weather stations have revealed a strong climatic warming during the ablation season since the 1950s at a rate of 0.02–0.03 °C a− 1. At the higher elevations in the study area represented by the Tien Shan meteorological station, the summer warming was accompanied by negative anomalies in annual precipitation in the 1990s enhancing glacier retreat. However, trends in precipitation in the post-1997 period cannot be evaluated due to the change in observational practices at this station. Neither station in the study area exhibits significant long-term trends in precipitation.  相似文献   

10.
Climate changes and recent glacier behaviour in the Chilean Lake District   总被引：1，自引：1，他引：0  
Atmospheric temperatures measured at the Chilean Lake District (38°–42°S) showed contrasting trends during the second half of the 20th century. The surface cooling detected at several meteorological stations ranged from − 0.014 to − 0.021 °C a− 1, whilst upper troposphere (850–300 gpm) records at radiosonde of Puerto Montt (41°26′S/73°07′W) revealed warming between 0.019 and 0.031 °C a− 1. Regional rainfall data collected from 1961 to 2000 showed the overall decrease with a maximum rate of − 15 mm a− 2 at Valdivia st. (39°38′S/73°05′W). These ongoing climatic changes, especially the precipitation reduction, seem to be related to El Niño–Southern Oscillation (ENSO) phenomena which has been more frequent after 1976. Glaciers within the Chilean Lake District have significantly retreated during recent decades, in an apparent out-of-phase response to the regional surface cooling. Moreover, very little is known about upper troposphere changes and how they can enhance the glacier responses. In order to analyse their behaviour in the context of the observed climate changes, Casa Pangue glacier (41°08′S/71°52′W) has been selected and studied by comparing Digital Elevation Models (DEMs) computed at three different dates throughout the last four decades. This approach allowed the determination of ice elevation changes between 1961 and 1998, yielding a mean thinning rate of − 2.3 ± 0.6 m a− 1. Strikingly, when ice thinning is computed for the period between 1981 and 1998, the resulting rate is 50% higher (− 3.6 ± 0.6 m a− 1). This enhanced trend and the related area loss and frontal retreat suggests that Casa Pangue might currently be suffering negative mass balances in response to the upper troposphere warming and decreased precipitation of the last 25–30 yr, as well as debris cover would not prevent the glacier from a fast reaction to climate forcing. Most of recent glaciological studies regarding Andean glaciers have concentrated on low altitude changes, namely frontal variations, however, in order to better understand the regional glacier changes, new data are necessary, especially from the accumulation areas.  相似文献   

11.
Mendenhall Glacier is a dynamic maritime glacier in southeast Alaska that is undergoing substantial recession and thinning. The terminus has retreated 3 km during the 20th century and the lower part of the glacier has thinned 200 m or more since 1909. Glacier-wide volume loss between 1948 and 2000 is estimated at 5.5 km3. Wastage has been the strongest in the glacier's lower reaches, but the glacier has also thinned at higher elevations. The shrinkage of Mendenhall Glacier appears to be due primarily to surface melting and secondarily to lake calving. The change in the average rate of thinning on the lower glacier, <1 m a−1 between 1948 and 1982 and >2 m a−1 since 1982, agrees qualitatively with observed warming trends in the region. Mean annual temperatures in Juneau decreased slightly from 1947 to 1976; they then began to increase, leading to an overall warming of ∼1.6 °C since 1943. Lake calving losses have periodically been a small but significant fraction of glacier ablation. The portion of the terminus that ends in the lake is becoming increasingly vulnerable to calving because of a deep pro-glacial lake basin. If current climatic trends persist, the glacier will continue to shrink and the terminus will recede onto land at a position about 500 m inland within one to two decades. The glacier and the meltwaters that flow from it are integral components of the Mendenhall Valley hydrologic system. Approximately 13% of the recent average annual discharge of the Mendenhall River is attributable to glacier shrinkage. Glacier melt contributes 50% of the total river discharge in summer.  相似文献   

12.
A glaciological program has been undertaken since 1991 on Zongo glacier in Bolivia (6000–4850 m asl, 2.4 km2, 16°S). This program involves mass balance measurements, hydrological studies and energy balance investigations. On outer-tropical glaciers, melting and snow accumulation are both maximum in the wet season (austral summer), whereas the dry season (winter) is a period of low ablation. Errors on each term of the glaciological (stakes, snow-pits and integration method of the measurements) and hydrological (precipitation, discharge and runoff coefficient of free ice areas) methods are investigated to estimate the overall accuracy of the mass balance measurements. The hydrological budget is less than the glaciological one (mean difference: 60 cm w.e. per year), but both methods reproduce similar inter-annual variations. Errors in assessment of evaporation or water storage inside the glacier cannot explain the discrepancy. Errors using the glaciological method are large (around ± 40 cm w.e. per year), but no bias can explain the departure from the hydrological balance. Errors on discharge measurements are small and the uncertainty on the runoff coefficient has a minor effect on the mass balance. We concluded that hydrological budgets are too low due to the catch deficiency of rain gauges and absence of precipitation measurements at high altitudes, emphasizing the difficulty to assess snowfall distribution in high mountainous basins.  相似文献   

13.
This paper presents data concerning recent (1990–2007) surface morphological and ice-dynamical changes on the Tasman Glacier, New Zealand. We use remote-sensing data to derive rates of lake growth, glacier velocities and rates of glacier surface lowering. Between 1990 and 2007, the glacier terminus receded ~ 3.5 km and a large ice-contact proglacial lake developed behind the outwash head. By 2007 the lake area was ~ 6 km2 and had replaced the majority of the lowermost 4 km of the glacier tongue. There is evidence that lake growth is proceeding at increasing rates — the lake area doubled between 2000 and 2007 alone. Measured horizontal glacier velocities decline from 150 m a− 1 in the upper glacier catchment to almost zero at the glacier terminus and there is a consequent down-glacier increase in surface debris cover. Surface debris mapping shows that a large catastrophic rockfall onto the glacier surface in 1991 is still evident as a series of arcuate debris ridges below the Hochstetter icefall. Calculated glacier surface lowering is most clearly pronounced around the terminal area of the glacier tongue, with down-wasting rates of 4.2 ± 1.4 m a− 1 in areas adjacent to the lateral moraine ridges outside of the current lake extent. Surface lowering rates of approximately 1.9 ± 1.4 m a− 1 are common in the upper areas of the glacier. Calculations of future lake expansion are dependent on accurate bathymetric and bed topography surveys, but published data indicate that a further 8–10 km of the glacier is susceptible to calving and further lake development in the future.  相似文献   

14.
The 395 late-type spiral galaxies brighter than 15m in r-band are selected from the Data Release 2 of Sloan Digital Sky Survey and the colormagnitude relations of these galaxies and their disks are investigated. It is found that the colors g − r, r − z and g − z of these galaxies and their disks are strongly correlated with the r-band absolute magnitudes, i.e., the more luminous galaxies (or disks) have the redder colors than the less luminous galaxies (or disks). And the correlation of galaxies is stronger than that of their disks.  相似文献   

15.
Field investigations in the eroded central uplift of the ≤30 km Keurusselkä impact structure, Finland, revealed a thin, dark melt vein that intersects the autochthonous shatter cone‐bearing target rocks near the homestead of Kirkkoranta, close to the center of the impact structure. The petrographic analysis of quartz in this melt breccia and the wall rock granite indicate weak shock metamorphic overprint not exceeding ~8–10 GPa. The mode of occurrence and composition of the melt breccia suggest its formation as some kind of pseudotachylitic breccia. 40Ar/39Ar dating of dark and clast‐poor whole‐rock chips yielded five concordant Late Mesoproterozoic miniplateau ages and one plateau age of 1151 ± 10 Ma [± 11 Ma] (2σ; MSWD = 0.11; P = 0.98), considered here as the statistically most robust age for the rock. The new 40Ar/39Ar age is incompatible with ~1.88 Ga Svecofennian tectonism and magmatism in south‐central Finland and probably reflects the Keurusselkä impact, followed by impact‐induced hydrothermal chloritization of the crater basement. In keeping with the crosscutting relationships in the outcrop and the possible influence of postimpact alteration, the Late Mesoproterozoic 40Ar/39Ar age of ~1150 Ma should be treated as a minimum age for the impact. The new 40Ar/39Ar results are consistent with paleomagnetic results that suggested a similar age for Keurusselkä, which is shown to be one of the oldest impact structures currently known in Europe and worldwide.  相似文献   

16.
We utilize a regional climate model with detailed land surface processes (RegCM2) to simulate East Asian monsoon climates at 0 ka, 6 ka and 21 ka BP, and evaluate the changes in hydrology process, including vapor transportation, precipitation, evapotranspiration and runoff in the eastern and western China during these periods. Results indicate that the Tibetan Plateau climate presents a wet–cold status during the LGM while it exhibits a wet–warm climate at 6 ka BP. The LGM wetter climate over the Tibetan Plateau mainly results from the increased vapor inflow through its south boundary, while the increase in the vapor import over the Tibetan Plateau at 6 ka BP mostly sources from its west boundary. The increase in the LGM runoff over the Tibetan Plateau is mainly caused by the decrease in evapotranspiration, while the increase in runoff at the 6 ka BP mainly by the enhanced precipitation. Eastern China (including southern China) presents a dry status during the LGM, which precipitation and runoff decreases significantly due largely to weakened Asian summer monsoon that results in the decreased vapor inflow through the south boundary of eastern China. The variation pattern in the hydrological cycle in eastern China is contrary to that in western China during the LGM. The increase in precipitation and runoff at 6 ka BP in eastern China is tightly related to the strong Asian summer monsoon that leads to increased vapor import through the south boundary. Long term decrease trend in precipitation and runoff in northern China since the last 20 000 years may be attributed to the steady increase in vapor export through the east boundary as a result of the changes of East Asian monsoon and the adjustments of local atmospheric circulations in this area.  相似文献   

17.
Increased melting on glaciers and ice sheets and rising sea level are often mentioned as important aspects of the anticipated greenhouse warming of the earth's atmosphere. This paper deals with the sensitivity of Greenland's ice mass budget and presents a tentative projection of the Greenland component of future sea level rise for the next few hundred years. To do this, the ‘Villach II temperature scenario’ is prescribed,output from a comprehensive mass balance model is used to drive a high-resolution 3-D thermomechanic model of the ice sheet.The mass balance model consists of two parts: the accumulation part is based on presently observed values and is forced by changes in mean anr tempeerature. The ablation model is based on the degree-day method and accounts for daily and annual temperature cycle, a different degree-day factor for ice and snow melting and superimposed ice formation. Under present-day climatic conditions, the following total mass balance results (in ice equivalent per years): 599.3 × 109 m3 of accumulation, 281.7 × 109m3 of runoff assuming a balanced budget, 317.6 × 109m3 of iceberg calving. A 1K uniform warming is then calculated to increase the runoff by 119.5 × 109 m3. Since accumulation also increases by 32 × 109 m3, this leads to reduction of the total mass balance by 887.5 × 109 m3 of ice, corresponding to a sea level rise of 0.22 mm/yr. For temperature increase larger than 2.7 K, runoff, exceeds accumulation, and if ice sheet dynamics were to remain unchanged, this would add an extra amount of 0.8 mmyr to the worl's oceans.Imposing the Villach II scenario (warming up to 4.23 K) and accumulating mass balance changes forward in time (static response) would then result in a global sea level rise of 7.1 cm by 2100 AD, but this figure may go up to as much as 40 cm per century in case the warming is doubled. In a subsequent dynamic model involving the ice flow, the ice sheet is found to produce a counteracting effect by dynamically producing steeper slopes at the margin, thereby reducing the area over which runoff can take place. This effect is particularly apparent in the northeastern part of the ice sheet, and is also more pronounced for the smaller temperature perturbations. Nevertheless, all these experiments certainly highlight the vulnerability of the Greenland ice sheet with respect to a climatic warming.  相似文献   

18.
The possible effects of trace-gas induced climatic changes on Pyramid and Yellowstone Lakes are assessed using a model of lake temperature. The model is driven by years of hourly meteorological data obtained directly from the output of double-CO2 experiments (2 × CO2) conducted with a regional climate model nested in a general circulation model. The regional atmospheric model is the climate version of the National Center for Atmospheric Research/Pennsylvania State University mesoscale model, MM4.Average annual surface temperature of Pyramid Lake for the 2 × CO2 climate is 15.5 ± 5.4°C (±1 σ), 2.8°C higher than the control. Annual overturn of the lake ceases as a result of these higher temperatures for the 2 × CO2 climate. Evaporation increases from 1400 mm yr−1 in the control to 1595 mm yr−1 in the 2 × CO2 simulation, but net water supplied to the Pyramid Lake basin increases from −6 mm yr−1 in the control to +27 mm yr−1 in the 2 × CO2 simulation due to increased precipitation.For the open water periods, the average annual surface temperature of Yellowstone Lake is 13.2 ± 5.1°C for the 2 × CO2 climate, a temperature 1.6°C higher than the control. The annual duration of ice cover on the lake is 152 days in the 2 × CO2 simulation, a reduction of 44 days relative to the control. Warming of the lake for the 2 × CO2 climate is mostly confined to the near-surface. Simulated spring overturn for the 2 × CO2 climate occurs earlier in the year and fall overturn later than in the control. Evaporation increases from 544 mm yr−1 to 600 mm yr−1 in the 2 × CO2 simulation, but net water supplied to the Yellowstone Lake basin increases from +373 mm yr−1 in the control to +619 mm yr−1 due to increased precipitation. The effects of these climatic changes suggest possible deterioration of water quality and productivity in Pyramid Lake and possible enhancement of productivity in Yellowstone Lake.  相似文献   

19.
The role of tropical ecosystems in global carbon cycling is uncertain, at least partially due to an incomplete understanding of climatic forcings of carbon fluxes. To reduce this uncertainty, we simulated and analyzed 1982–1999 Amazonian, African, and Asian carbon fluxes using the Biome-BGC prognostic carbon cycle model driven by National Centers for Environmental Prediction reanalysis daily climate data. We first characterized the individual contribution of temperature, precipitation, radiation, and vapor pressure deficit to interannual variations in carbon fluxes and then calculated trends in gross primary productivity (GPP) and net primary productivity (NPP). In tropical ecosystems, variations in solar radiation and, to a lesser extent, temperature and precipitation, explained most interannual variation in GPP. On the other hand, temperature followed by solar radiation primarily determined variation in NPP. Tropical GPP gradually increased in response to increasing atmospheric CO2. Confirming earlier studies, changes in solar radiation played a dominant role in CO2 uptake over the Amazon relative to other tropical regions. Model results showed negligible impacts from variations and trends in precipitation or vapor pressure deficits on CO2 uptake.  相似文献   

20.
The observed rapid glacier wastage in the European Alps during the past 20 years already has strong impacts on the natural environment (rock fall, lake formation) as well as on human activities (tourism, hydro-power production, etc.) and poses several new challenges also for glacier monitoring. With a further increase of global mean temperature in the future, it is likely that Alpine glaciers and the high-mountain environment as an entire system will further develop into a state of imbalance. Hence, the assessment of future glacier geometries is a valuable prerequisite for various impact studies. In order to calculate and visualize in a consistent manner future glacier extent for a large number of individual glaciers (> 100) according to a given climate change scenario, we have developed an automated and simple but robust approach that is based on an empirical relationship between glacier size and the steady-state accumulation area ratio (AAR0) in the Alps. The model requires digital glacier outlines and a digital elevation model (DEM) only and calculates new glacier geometries from a given shift of the steady-state equilibrium line altitude (ELA0) by means of hypsographic modelling. We have calculated changes in number, area and volume for 3062 individual glacier units in Switzerland and applied six step changes in ELA0 (from + 100 to + 600 m) combined with four different values of the AAR0 (0.5, 0.6, 0.67, 0.75). For an AAR0 of 0.6 and an ELA0 rise of 200 m (400 m) we calculate a total area loss of − 54% (− 80%) and a corresponding volume loss of − 50% (− 78%) compared to the 1973 glacier extent. In combination with a geocoded satellite image, the future glacier outlines are also used for automated rendering of perspective visualisations. This is a very attractive tool for communicating research results to the general public. Our study is illustrated for a test site in the Upper Engadine (Switzerland), where landscape changes above timberline play an important role for the local economy. The model is seen as a first-step approach, where several parts can be (and should be) further developed.  相似文献   

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