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1.
Methods have been designed to calculate orographic and frictional influences on precipitation in coastal regions. A model computes the vertical fluxes of water vapor at the top of the planetary boundary layer due to these two effects. The horizontal downwind displacement of falling precipitation is also allowed for. The procedures are applied over southwestern British Columbia to monthly amounts and maximum 24-h rainfalls for return periods of 2–50 yr. Correlation coefficients between observed and computed precipitation vary from 0.65 to 0.97, the average being 0.84.  相似文献   

2.
Annual precipitation for the last 2,500 years was reconstructed for northeastern Qinghai from living and archaeological juniper trees. A dominant feature of the precipitation of this area is a high degree of variability in mean rainfall at annual, decadal, and centennial scales, with many wet and dry periods that are corroborated by other paleoclimatic indicators. Reconstructed values of annual precipitation vary mostly from 100 to 300 mm and thus are no different from the modern instrumental record in Dulan. However, relatively dry years with below-average precipitation occurred more frequently in the past than in the present. Periods of relatively dry years occurred during 74–25 BC, AD 51–375, 426–500, 526–575, 626–700, 1100–1225, 1251–1325, 1451–1525, 1651–1750 and 1801–1825. Periods with a relatively wet climate occurred during AD 376–425, 576–625, 951–1050, 1351–1375, 1551–1600 and the present. This variability is probably related to latitudinal positions of winter frontal storms. Another key feature of precipitation in this area is an apparently direct relationship between interannual variability in rainfall with temperature, whereby increased warming in the future might lead to increased flooding and droughts. Such increased climatic variability might then impact human societies of the area, much as the climate has done for the past 2,500 years.  相似文献   

3.
We present an analysis of climate change over Europe as simulated by a regional climate model (RCM) nested within time-slice atmospheric general circulation model (AGCM) experiments. Changes in mean and interannual variability are discussed for the 30-year period of 2071–2100 with respect to the present day period of 1961–1990 under forcing from the A2 and B2 IPCC emission scenarios. In both scenarios, the European region undergoes substantial warming in all seasons, in the range of 1–5.5°C, with the warming being 1–2°C lower in the B2 than in the A2 scenario. The spatial patterns of warming are similar in the two scenarios, with a maximum over eastern Europe in winter and over western and southern Europe in summer. The precipitation changes in the two scenarios also show similar spatial patterns. In winter, precipitation increases over most of Europe (except for the southern Mediterranean regions) due to increased storm activity and higher atmospheric water vapor loadings. In summer, a decrease in precipitation is found over most of western and southern Europe in response to a blocking-like anticyclonic circulation over the northeastern Atlantic which deflects summer storms northward. The precipitation changes in the intermediate seasons (spring and fall) are less pronounced than in winter and summer. Overall, the intensity of daily precipitation events predominantly increases, often also in regions where the mean precipitation decreases. Conversely the number of wet days decreases (leading to longer dry periods) except in the winter over western and central Europe. Cloudiness, snow cover and soil water content show predominant decreases, in many cases also in regions where precipitation increases. Interannual variability of both temperature and precipitation increases substantially in the summer and shows only small changes in the other seasons. A number of statistically significant regional trends are found throughout the scenario simulations, especially for temperature and for the A2 scenario. The results from the forcing AGCM simulations and the nested RCM simulations are generally consistent with each other at the broad scale. However, significant differences in the simulated surface climate changes are found between the two models in the summer, when local physics processes are more important. In addition, substantial fine scale detail in the RCM-produced change signal is found in response to local topographical and coastline features.  相似文献   

4.
There is an ongoing important debate about the role of water vapour in climate change. Predictions of future climate change depend strongly on the magnitude of the water vapour feedback and until now models have almost exclusively been relied upon to quantify this feedback. In this work we employ observations of water vapour changes, together with detailed radiative calculations to estimate the water vapour feedback for the case of the Mt. Pinatubo eruption. We then compare our observed estimate with that calculated from a relatively large ensemble of simulations from a complex coupled climate model. We calculate an observed water vapour feedback parameter of –1.6 Wm–2 K–1, with uncertainty placing the feedback parameter between –0.9 to –2.5 Wm–2 K–1. The uncertain is principally from natural climate variations that contaminate the volcanic cooling. The observed estimates are consistent with that found in the climate model, with the ensemble average model feedback parameter being –2.0 Wm–2 K–1, with a 5–95% range of –0.4 to –3.6 Wm–2 K–1 (as in the case of the observations, the spread is due to an inability to separate the forced response from natural variability). However, in both the upper troposphere and Southern Hemisphere the observed model water vapour response differs markedly from the observations. The observed range represents a 40%–400% increase in the magnitude of surface temperature change when compared to a fixed water vapour response and is in good agreement with values found in other studies. Variability, both in the observed value and in the climate models feedback parameter, between different ensemble members, suggests that the long-term water vapour feedback associated with global climate change could still be a factor of 2 or 3 different than the mean observed value found here and the model water vapour feedback could be quite different from this value; although a small water vapour feedback appears unlikely. We also discuss where in the atmosphere water vapour changes have their largest effect on surface climate.  相似文献   

5.
Extreme climate index is one of the useful tools to monitor and detect climate change. The primary objective of this study is to provide a more comprehensively the changes in extreme precipitation between the periods of 1954–1983 and 1984–2013 in Shaanxi province under climate change, which will hopefully provide a scientific understanding of the precipitation-related natural hazards such as flood and drought. Daily precipitation from 34 surface meteorological stations were used to calculated 13 extreme precipitation indices (EPIs) generated by the joint World Meteorological Organization Commission for Climatology (CCI)/World Climate Research Programme (WCRP) project on Climate Variability and Predictability (CLIVAR) expect Team on climate change Detection, Monitoring and Indices (ETCCDMI). Two periods including 1954–1983 and 1984–2013 were selected and five types of precipitation days (R10mm-R100mm) were defined, to provide more evidences of climate change impacts on the extreme precipitation events, and specially, to investigate the changes in different types of precipitation days. The EPIs were generated using RClimRex software, and the trends were analyzed using Mann-Kendall nonparametric test and Sen’s slope estimator. The relationships between the EPIs and the impacts of climate anomalies on typical EPIs were investigated using correlation and composite analysis. The mainly results include: 1) Thirteen EPIs, except consecutive dry day (CDD), were positive trends dominated for the period of 1984–2013, but the trends were not obvious for the period of 1954–1983. Most of the trends were not statistically significant at 5 % significance level. 2) The spatial distributions of stations that exhibited positive and negative trends were scattered. However, the stations that had negative trends mainly distributed in the north of Shaanxi province, and the stations that had positive trends mainly located in the south. 3) The percentage of stations that had positive trends had increased from the period of 1954–1983 to 1984–2013 for all the 13 EPIs except CDD, indicating the possible climate change impacts on extreme precipitation events. 4) The correlations between annual total wet-day precipitation (PRCPTOT) and other 12 EPIs varied for different indices and stations. The composite analysis found that El Niño Southern Oscillation (ENSO) exerted greater impacts on PRCPTOT than other EPIs and greater in the Guanzhong Plain (GZP) than Qinling-Dabashan Mountains (QDM) and Shanbei Plateau (SBP) of Shaanxi province.  相似文献   

6.
Potential effects of climate change on a semi-permanent prairie wetland   总被引：4，自引：0，他引：4  
We assessed the potential effects of a greenhouse gas-induced global climate change on the hydrology and vegetation of a semi-permanent prairie wetland using a spatially-defined, rule-based simulation model. An 11-yr simulation was run using current versus enhanced greenhouse gas climates. Projections of climatic change were from the Goddard Institute for Space Studies (GISS) general circulation model. Simulations were also run using a range of temperature (+2 and +4 °C) and precipitation change values (–20, –10, 0, +10, +20%) to determine the responsiveness of wetland vegetation and hydrology to a variety of climate scenarios.Maximum water depths were significantly less under the enhanced greenhouse gas scenario than under the current climate. The wetland dried in most years with increased temperature and changes in precipitation. Simulations also revealed a significant change in the vegetation, from a nearly balanced emergent cover to open water ratio to a completely closed basin with no open water areas. Simulations over a range of climate change scenarios showed that precipitation changes (particularly increases) had a greater impact on water levels and cover ratios when the temperature increase was moderate (+2 °C).These potential changes in wetland hydrology and vegetation could result in a dramatic decline in the quality of habitat for breeding birds, particularly waterfowl. Continued research on climate and wetland modeling is needed.  相似文献   

7.
This paper presents probable effects of climate change on soil moisture availability in the Southeast Anatolia Development Project (GAP) region of Turkey. A series of hypothetical climate change scenarios and GCM-generated IPCC Business-as-Usual scenario estimates of temperature and precipitation changes were used to examine implications of climate change for seasonal changes in actual evapotranspiration, soil moisture deficit, and soil moisture surplus in 13 subregions of the GAP. Of particular importance are predicted patterns of enhancement in summer soil moisture deficit that are consistent across the region in all scenarios. Least effect of the projected warming on the soil moisture deficit enhancement is observed with the IPCC estimates. The projected temperature changes would be responsible for a great portion of the enhancement in summer deficits in the GAP region. The increase in precipitation had less effect on depletion rate of soil moisture when the temperatures increase. Particularly southern and southeastern parts of the region will suffer severe moisture shortages during summer. Winter surplus decreased in scenarios with increased temperature and decreased precipitation in most cases. Even when precipitation was not changed, total annual surplus decreased by 4 percent to 43 percent for a 2°C warming and by 8 percent to 91 percent for a 4°C warming. These hydrologic results may have significant implications for water availability in the GAP as the present project evaluations lack climate change analysis. Adaptation strategies – such as changes in crop varieties, applying more advanced dry farming methods, improved water management, developing more efficient irrigation systems, and changes in planting – will be important in limiting adverse effects and taking advantage of beneficial changes in climate.  相似文献   

8.
The impact of future climate change on sugar beet yields is assessed over western Europe using future (2021–2050) climate scenario data from a General Circulation Model (GCM) and the Broom's Barn simulation model of rain-fed crop growth and yield. GCM output for the 1961–1990 period is first compared with observed climate data and shown to be reliable for regions west of 24° E. Comparisons east of this meridian were less reliable with this GCM (HadCM2) and so were omitted from simulations of crop yield. Climate change is expected to bring yield increases of around 1 t/ha of sugar in northern Europe with decreases of a similar magnitude in northern France, Belgium and west/central Poland, for the period 2021–2050. Averaged for the study area (weighted by current regional production), yields show no overall change due to changed climate. However, this figure masks significant increases in yield potential (due to accelerated growth in warmer springs) and in losses due to drought stress. Drought losses are predicted to approximately double in areas with an existing problem and to become a serious new problem in NE France and Belgium. Overall west and central Europe simulated average drought losses rise from 7% (1961–1990) to 18% (2021–2050). The annual variability of yield (as measured by the coefficient of variation) will increase by half, from 10% to 15% compared to 1961–1990, again with potentially serious consequences for the sugar industry. The importance of crop breeding for drought tolerance is further emphasised. These changes are independent of the 9% yield increase which we estimate, on the basis of work by Demmers-Derks et al. (1998), is the likely direct effect of the increase in atmospheric CO2 concentration by 2021–2050.  相似文献   

9.
We document the characteristic time scales of variability for seven climate indices whose time-dependent behavior is sensitive to some aspect of the El Niño/Southern Oscillation (ENSO). The ENSO sensitivity arises from the location of these long-term records on the periphery of the Indian and Pacific Oceans. Three of the indices are derived principally from historical sources, three others consist of tree-ring reconstructions (one of summer temperature, and the other two of winter rainfall), and one is an annual record of oxygen isotopic composition for a high-elevation glacier in Peru. Five of the seven indices sample at least portions of the Medieval Warm Period (~ A.D. 950 to 1250).Time series spectral analysis was used to identify the major time scales of variability among the different indices. We focus on two principal time scales: a high frequency band (~ 2–10 yr), which comprises most of the variability found in the modern record of ENSO activity, and a low frequency band to highlight variations on decadal to century time scales (11 <P < 150 yr). This last spectral band contains variability on time scales that are of general interest with respect to possible changes in large-scale air-sea exchanges. A technique called evolutive spectral analysis (ESA) is used to ascertain how stable each spectral peak is in time. Coherence and phase spectra are also calculated among the different indices over each full common period, and following a 91-yr window through time to examine whether the relationships change.In general, spectral power on time scales of ~ 2–6 yr is statistically significant and persists throughout most of the time intervals sampled by the different indices. Assuming that the ENSO phenomenon is the source of much of the variability at these time scales, this indicates that ENSO has been an important part of interannual climatic variations over broad areas of the circum-Pacific region throughout the last millennium. Significant coherence values were found for El Niño and reconstructed Sierra Nevada winter precipitation at ~ 2–4 yr throughout much of their common record (late 1500s to present) and between 6 and 7 yr from the mid-18th to the early 20th century.At decadal time scales each record generally tends to exhibit significant spectral power over different periods at different times. Both the Quelccaya Ice Cap 18O series and the Quinn El Niño event record exhibit significant spectral power over frequencies ~ 35 to 45 yr; however, there is low coherence between these two series at those frequencies over their common record. The Sierra Nevada winter rainfall reconstruction exhibits consistently strong variability at periods of ~ 30–60 yr.  相似文献   

10.
F. Giorgi  X. Bi  J. S. Pal 《Climate Dynamics》2004,22(6-7):733-756
We present an analysis of a multidecadal simulation of present-day climate (1961–1990) over Europe with the regional climate model RegCM nested within the global atmospheric model HadAMH. Climatic means, interannual variability and trends are examined, with focus on surface air temperature and precipitation. The RegCM driven by HadAMH fields is able to reproduce the basic features of the observed mean surface climate over Europe, its seasonal evolution and the regional detail due to topographic forcing. Surface air temperature biases are mostly less than 1–2 °C and precipitation biases mostly within 10–20%. The RegCM has more intense vertical transport of temperature and water vapor than HadAMH, which results in lower surface air temperatures and greater precipitation than found in the HadAMH simulation. In some cases this is in the direction of greater agreement with observations, while in others it is in the opposite direction. The simulation shows a tendency to overestimate interannual variability of temperature and precipitation compared to observations, particularly during summer and over the Mediterranean regions. It is shown that in DJF, MAM and SON the RegCM interannual variability is primarily determined by the boundary forcing from HadAMH, while in JJA the internal model physics and resolution effects dominate over many subregions of the domain, and the RegCM has higher interannual variability than HadAMH. The precipitation trends simulated by the nested modeling system for the period 1961–1990 capture some features of the observed trends, in particular the cold season drying over the Mediterranean regions. Ensembles of simulations are, however, needed for a more robust assessment of the models capability to simulate climatic trends. Overall, this simulation is of good quality compared with previous nested RegCM experiments and will constitute the basis for the generation of climate change scenarios over the European region to be reported in future work.  相似文献   

11.
The Mediterranean area is one of the regions of the world where GCMs agree the most on precipitation changes due to climate change. In this study we aim to assess the impact of recent climate change on drought features of Mediterranean ecosystems in Southern France. Regional climatic trends for the 1971–2006 period are compared to drought trends based on a water balance model accounting for soil properties, vegetation structure and functioning. Drought, defined here as periods when soil water potentials drop below ??0.5 MPa, is described in terms of intensity, duration and timing, which are integrative of both climate variability and site conditions. Temporal trends in precipitation, temperature and solar radiation lead altogether to drier and warmer conditions over the region but with a high spatial heterogeneity; for similar climatic trends, a significant increase in drought intensity was detected in the wettest areas of the region, whereas drought intensity in the driest areas did not change. Indeed, in the wettest areas, we observed an earlier onset of drought by about 1 month, but a constant end of drought. In the driest areas of the region, we observed the same earlier onset of drought but combined with an earlier end of drought, thus leading to a shift of the dry season without increasing its duration. The definition of drought features both in terms of intensity but also of seasonal timing appears relevant to capture historical or forecasted changes in ecosystem functioning. Studies concerning climate change impacts on forested ecosystems should be interpreted with caution when using climate proxies alone.  相似文献   

12.
Nel Caine 《Climatic change》2002,54(4):463-470
A 20-year record of ice thickness in late-March on an alpine lake in the Colorado Front Range shows a consistent thinning of the ice cover at 2.0 cm/yr(r = –0.931; N = 16; p < 0.01) during a period of increasing precipitation. The correlation between ice thickness and precipitation in the preceding Oct.–Mar. period is –0.439 (N = 16; p < 0.10),reflecting the insulating effect of an increase in snow cover on the lake. A second effect derived from increased precipitation occurs through additional water storage in the lake's catchment during the previous summer. This leads to a corresponding increase in groundwater flow to the lake during the winter, with a correlation between ice thickness and groundwater storage at the end of the preceding September of –0.656 (N = 16; p < 0.01). Whencombined, these two effects account for 50% of the variability in ice thickness(R = 0.714; N = 16; p < 0.01). Thus, much of the decline in ice thicknessin March is explained by two influences derived from an increase in winter precipitation: one associated with the current winter's precipitation and one with that of the previous winter.  相似文献   

13.
Earlywood width chronologies from Douglas-fir tree rings were used to reconstruct winter (November–March) precipitation for more than 600 years over Durango, Mexico. The tree-ring data were obtained from two sites of long-lived Douglas-fir in northern and southern Durango and the seasonal climatic precipitation data were regionally averaged from five weather stations well distributed across the state. The averaged earlywood chronology accounted for 56% of the variance in instrumental November–March precipitation 1942–1983. We validated the reconstruction against independent precipitation records. The worst winter drought of the 20th century in Durango occurred 1950–1965. However, the reconstruction indicates droughts more severe than any witnessed in the 20th century, e.g., the 1850s–1860s, and the megadrought in the mid- to late-16th century. Reconstructed winter precipitation 1540–1579 shows 33 of 40 years were dry. Persistent drought may be linked to extended La Niña episodes. The Tropical Rainfall Index (TRI) correlates well with instrumental and reconstructed winter precipitation (r = 0.49 and 0.55, respectively), reflecting the strong ENSO modulation of cool season climate over northern Mexico. The ENSO teleconnection varies through time, with TRI-reconstructed precipitation correlations ranging from 0.78 to 0.27 in five periods 1895–1993. The 1942–1983 winter observed and reconstructed Durango data correlate well with the corresponding seasonalization of the All-Mexico Rainfall Index (AMRI; r=0.68, P<0.0001 and r=0.70, P<0.001, respectively), indicating that both the observed and the reconstructed precipitation often reflect broad-scale precipitation anomalies across Mexico. New long Douglas-fir and baldcypress tree-ring chronologies are now available for central and southern Mexico near major population centers, allowing the exploration of relationships between drought, food scarcity, and social and political upheaval in Mexican history.  相似文献   

14.
Maximum Entropy Spectral Analysis of the annual mean surface temperature series for land masses and sea in the northern and southern hemispheres indicated long-term linear warming trends of (0.12 to 0.56) °C/century with superposed significant periods in the ranges T = 5–6 yr, 10–11 yr, 15 yr, 20 yr, 28–32 yr, and 55–80 yr. Extrapolation in future indicated for 2000–2030 a departure of (+0.4 °C) above the 1950–70 level. However, for the 1980s, the observed values are above the expected level, probably indicating large greenhouse effects due to human intervention. In that case, our predictions would be underestimates.  相似文献   

15.
A model to calculate the water balance of a hummocky sedge fen in the northern Hudson Bay Lowland is presented. The model develops the potential latent heat flux (evaporation) as a function of net radiation and atmospheric temperature. It is about equally sensitive to a 2% change in net radiation and a 1°C change in temperature. The modelled potential evaporation agrees well with the Priestley–Taylor formulation of evaporation under conditions of a non-limiting water supply. The actual evaporative heat flux is modelled by expressing actual/potential evaporation as a function of potential accumulated water deficit. Model evaporation agrees well with energy balance calculations using 7 years of measured data including wet and dry extremes. Water deficit is defined as the depth of water below reservoir capacity. Modelled water table changes concur with measurements taken over a 4 year period. When net radiation, temperature and precipitation measurements are available the water balance can be projected to longer time periods. Over a 30 year interval (1965–1994) the water balance of the sedge fen showed the following. During the growing season, there was an increase in precipitation, no change in temperature and a decrease in net radiation, evapotranspiration and water deficit. There was also a decrease in winter snow depths. The fen was brought back to reservoir capacity during final snowmelt every year but one. Summer rainfall was the most important single factor affecting the water balance and the ratio actual/potential evaporation emerged as a linear function of rainfall amount. A 2 × CO2 climate warming scenario with an annual temperature increase of 4°C and no precipitation change indicates lesser snow amounts and a shorter snow cover period. A greater summer water deficit, triggered mainly by greater evaporation during the month of May, is partially alleviated by lesser evaporation magnitudes in July. The greater water deficit would be counterbalanced by a 23% increase in summer rainfall. On average, the fen's water reservoir would still be recharged after winter snowmelt but the ground would remain at reservoir capacity for a shorter time. The warming scenario with a 10% decline in summer rainfall would create a large increase in the longevity and severity of the water deficit and this would be particularly evident during drier years. The carbon budget and peat accumulation and breakdown rates are strongly affected by changes in the water balance. Some evidence implies that greater water deficits lead to an increase in net carbon emissions. This implies that the sedge peatland could lose biomass under such conditions. An example is given where increased water deficit results in large decreases in local wetland streamflow.  相似文献   

16.
RHINEFLOW is a GIS based water balance model that has been developed to study the changes in the water balance compartments of the river Rhine basin on a monthly time basis. The model has been designed to study the sensitivity of the Rhine discharge to a climate change. The calculated discharge has been calibrated and validated on the period 1956 to 1980. For this period the model efficiency of RHINEFLOW is between 0.74 and 0.81 both for the entire Rhine and for its tributaries. Also calculated values for variations in other compartments, e.g. snow storage and actual evapotranspiration, were in good agreement with the measured values.Since a high correlation between monthly discharge and peak discharge was found for the period 1900–1980 The RHINEFLOW model is used to assess the probability of exceedence for discharge peaks under possible future climate conditions.The probabilities of exceedence were calculated from the conditional probabilities of peak discharges for a series of 15 classes of monthly discharges. Comparison of a calculated frequency distribution of high discharge peaks with observed peaks in a test series showed that the method performs well.Scenarios for temperature changes between 0 °C and plus 4 °C and precipitation changes between plus 20% and minus 20% have been applied. Within this range flood frequencies are more sensitive for a precipitation change than for a temperature change. The present two-year return period peak flow (6500–7000 m3/s) decreases by about 6% due to a temperature rise of 4 °C; a precipitation decrease of 20% leads to 30% lower two-year peaks whilst 20% precipitation increase raises them by approximately 30%.Application of a Business As Usual (BAU) and an Accelerated Policy (AP) climate scenario resulted in a significant increase in probability of peak flows for the BAU scenario, while for the AP scenario no significant change could be found. Due to sampling errors, accurate estimations of recurrence times of discharge peaks7000 m3/s require a longer sampling time series than 90 years. For management purposes the method can be applied to estimate changes of probabilities of events with a relatively long recurrence time.  相似文献   

17.
Detection of effects of changing climate on the hydrologic responses of rivers can be further complicated by changes in land use, drainage, and water use. To discern effects of human-caused changes in a basin and those due to precipitation over time, a comparison was made of annual mean flows and peakflows in Midwestern basins that experienced increases in annual precipitation and heavy rain events during 1940–1990. Two pairs of basins, one pair in a rural area and one pair in an urbanized area, were selected for in-pair comparisons, with one basin in each pair experiencing more land use and drainage changes during 1940–1990 than the other basin. All basins experienced significant upward trends in annual precipitation and annual mean flows. Human-produced changes affecting runoff in both rural basins accounted for about two-thirds of the fluctuations in the mean flows, and precipitation changes accounted for the other third. However, much of the change in peakflows in the rural basin undergoing sizable changes in drainage was due to these changes (85%) versus 75% in the rural basin without comparable shifts in drainage. The mean and peak flows of the two urban basins showed considerably more response to precipitation shifts than those of the two rural basins. The urbanized area doubled within one urban basin during 1940–1990, and these land use changes explained much more of the increase in mean flows and peakflows there than in the urban basin with less change in land use. By 1990 precipitation accounted for 69% of the upward trend in mean flows since 1941 in the heavily developed urban basin, as compared to 37% of the trend in the less settled urban basin. For purposes of assessing climate change, the precipitation changes over fifty years in all basins produced marked uptrends in basin streamflow, but the magnitude of the precipitation effect was masked by the land use and drainage changes. The results illustrate the need for careful analysis of natural basin characteristics (soils and basin shape), land use and drainage changes, and of various precipitation conditions if the influence of shifting precipitation on hydrologic conditions is to be detected, accurately measured, and correctly interpreted. For such studies the paired basin comparison techniques appears to be a valuable approach.  相似文献   

18.
Hydrological models of the Great Lakes basin were used to study the sensitivity of Great Lakes water supplies to climate warming by driving them with meteorological data from four U.S. climate zones that were transposed to the basin. Widely different existing climates were selected for transposition in order to identify thresholds of change where major impacts on water supplies begin to occur and whether there are non-linear responses in the system. The climate zones each consist of 43 years of daily temperature and precipitation data for 1,000 or more stations and daily evaporation-related variables (temperature, wind speed, humidity, cloud cover) for approximately 20–35 stations. A key characteristic of these selected climates was much larger variability in inter-annual precipitation than currently experienced over the Great Lakes. Climate data were adjusted to simulate lake effects; however, a comparison of hydrologic results with and without lake effects showed that there was only minor effects on water supplies.  相似文献   

19.
Summary Daily precipitation amounts from the meteorological station at Kaédi (Mauritania) are available since 1904, the country's longest record. The series constitutes an excellent tool for studying variations in the precipitation climate. Analysis of the annual precipitation amounts reveals the existence of a statistically highly significant downward trend which started in the sixties and is still continuing at present.It was further found that the entire reference period 1904–1988 needs, for reasons of data stationarity, to be split into two parts, corresponding respectively to the periods 1904–1967 and 1968–1988, the year 1967 being estimated as the change-point. The latter period corresponds to the drought which has prevailed over the Sahel region since 1968. The jump disclosed in the hydroclimatic system is indicative of the existence of multiple stable climate regimes.With 7 Figures  相似文献   

20.
Jinwon Kim 《Climatic change》2005,68(1-2):153-168
The effects of increased atmospheric CO2 on the frequency of extreme hydrologic events in the Western United States (WUS) for the 10-yr period of 2040–2049 are examined using dynamically downscaled regional climate change signals. For assessing the changes in the occurrence of hydrologic extremes, downscaled climate change signals in daily precipitation and runoff that are likely to indicate the occurrence of extreme events are examined. Downscaled climate change signals in the selected indicators suggest that the global warming induced by increased CO2 is likely to increase extreme hydrologic events in the WUS. The indicators for heavy precipitation events show largest increases in the mountainous regions of the northern California Coastal Range and the Sierra Nevada. Increased cold season precipitation and increased rainfall-portion of precipitation at the expense of snowfall in the projected warmer climate result in large increases in high runoff events in the Sierra Nevada river basins that are already prone to cold season flooding in todays climate. The projected changes in the hydrologic characteristics in the WUS are mainly associated with higher freezing levels in the warmer climate and increases in the cold season water vapor influx from the Pacific Ocean.  相似文献   

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