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1.
    
ABSTRACT: Climatic variation and the possibility of anthropogenically-caused climatic change have emphasized the need for global hydrological cycle models able to simulate the impacts of climate on the atmosphere, continents and oceans. To date, global atmospheric and oceanic models have been developed but, to the best of the author's knowledge, there are no continental hydrological models. Instead, hydrological models continue to develop at the catchment scale and the land phase component of the global hydrologic cycle is modeled as parameterizations within atmospheric models. The author argues that this is not the best solution; that the present land surface components of atmospheric models do not accurately model land phase hydrology and that, instead, atmospheric and oceanic models should be linked to continental-scale hydrological models to form a true model of the global hydrological cycle.  相似文献   

2.
ABSTRACT: A review of literature pertaining to the relative rates of evaporation from vegetation covered and open water bodies is presented. The review indicates that the only reliable experiments capable of correctly addressing this question are those conducted in situ. Experiments of this nature show the ratio of vegetation covered (swamp) evaporation to open water evaporation to generally be less than unity over extensive surfaces and to only approach unity for vegetation that is young and vigorous. Recent experimental evidence presented within a theoretical context, however, indicates that even in the latter situation the ratio may never reach unity. Consequently, over large lakes and reservoirs, the presence of vegetation may actually be a water conservation mechanism, with the eradication of the vegetation leading to significantly increased evaporative water losses.  相似文献   

3.
ABSTRACT: Air temperatures are sometimes used as substitutes for stream temperatures. To examine the errors associated with this procedure, linear relationships between stream temperatures, T, and air temperatures, Ta, recorded for 11 streams in the central U.S. (Mississippi River basin) were analyzed. Weather stations were an average 42 miles (range 0 to 144 miles) from the rivers. The general equations, Tw= 5.0 + 0.75 Ta and Tw= 2.9 + 0.86 Ta with temperatures in °C, were derived for daily and weekly water temperatures, respectively, for the 11 streams studied. The simulations had a standard deviation between measurements and predictions of 2.7°C (daily) and 2.1°C (weekly). Equations derived for each specific stream individually gave lower standard deviations, i.e., 2.1°C and 1.4°C, respectively. Small, shallow streams had smaller deviations than large, deep rivers. The measured water temperatures follow the air temperatures closely with some time lag. time lags ranged from hours to days, increasing with stream depth. Taking into account these time lags improved the daily temperature predictions slightly. Periods of ice cover were excluded from the analysis.  相似文献   

4.
    
ABSTRACT: Two general circulation models (GCMs) used in the U.S. national assessment of the potential consequences of climate variability and change (CGCM1 and HadCM2) show a large increase in precipitation in the future over the southwestern U.S., particularly during winter. This precipitation increase is an extension of a larger region of increased precipitation in the Pacific Ocean off the west coast of North America that is associated with a deepened and southward-shifted Aleutian Low, a weaker subtropical high, and warmer sea surface temperatures (SSTs). The models differ in their simulation of precipitation anomalies over the southeastern U.S., with CGCM1 showing drier conditions and HadCM2 showing wetter conditions in the future. While both models show decreased frequency of Atlantic storms, consistent with decreased meridional and land/sea temperature gradients, the more coastal position of the storm track in CGCM1 results in less precipitation than modern along the eastern seaboard of the U.S. During summer, differences in land surface models within the two GCMs sometimes lead to differences in soil moisture that feed back to the precipitation over land due to available moisture.  相似文献   

5.
    
ABSTRACT: The Great Plains of the United States, drained primanly by the Missouri River, are very sensitive to shifts in climate. The six main stem dams on the Missouri River control more than one‐half of the nearly 1.5 million square kilometer basin and can store three times the annual inflow from upstream. The dams are operated by the U.S. Army Corps of Engineers using a Master Manual that describes system priorities and benefits. The complex operational rules were incorporated into the Soil and Water Assessment Tool computer model (SWAT). SWAT is a distributed parameter rainfall‐runoff model capable of simulating the transpiration suppression effects of CO2 enrichment. The new reservoir algorithms were calibrated using a 25‐year long historic record of basin climate and discharge records. Results demonstrate that it is possible to incorporate the operation of a highly regulated river system into a complex rainfall‐runoff model. The algorithms were then tested using extreme climate scenarios indicative of a prolonged drought, a short drought, and a ten percent increase in basin‐wide precipitation. It is apparent that the rules for operating the reservoirs will likely require modification if, for example, upper‐basin precipitation were to increase only ten percent under changed climate conditions.  相似文献   

6.
    
ABSTRACT: Granular matrix soil moisture sensors were used to control urban landscape irrigation in Boulder, Colorado, during 1997. The purpose of the study was to evaluate the effectiveness and reliability of the technology for water conservation. The 23 test sites included a traffic median, a small city park, and 21 residential sites. The results were very good. The system limited actual applications to an average of 73 percent of the theoretical requirement. This resulted in an average saving of $331 per installed sensor. The sensors were highly reliable. All 23 sensors were placed in service at least three years prior to the 1997 study during earlier studies. Of these, only two had failed by the beginning of the 1997 study, both due to external factors. Including replacement of these failed sensors, the total repair cost for the 1997 irrigation season was less than $270. The effort required to maintain each system was small, only about 6–7 minutes per visit. Each site was visited weekly for this study, but less frequent visits could be made in practice. The sensors observed in this study performed well, significantly reduced water consumption, and were easy to monitor and maintain. Soil moisture sensors appear to be a useful and economical tool for urban water conservation.  相似文献   

7.
    
For water‐resource planning, sensitivity of freshwater availability to anthropogenic climate change (ACC) often is analyzed with “offline” hydrologic models that use precipitation and potential evapotranspiration (Ep) as inputs. Because Ep is not a climate‐model output, an intermediary model of Ep must be introduced to connect the climate model to the hydrologic model. Several Ep methods are used. The suitability of each can be assessed by noting a credible Ep method for offline analyses should be able to reproduce climate models’ ACC‐driven changes in actual evapotranspiration in regions and seasons of negligible water stress (Ew). We quantified this ability for seven commonly used Ep methods and for a simple proportionality with available energy (“energy‐only” method). With the exception of the energy‐only method, all methods tend to overestimate substantially the increase in Ep associated with ACC. In an offline hydrologic model, the Ep‐change biases produce excessive increases in actual evapotranspiration (E), whether the system experiences water stress or not, and thence strong negative biases in runoff change, as compared to hydrologic fluxes in the driving climate models. The runoff biases are comparable in magnitude to the ACC‐induced runoff changes themselves. These results suggest future hydrologic drying (wetting) trends likely are being systematically and substantially overestimated (underestimated) in many water‐resource impact analyses.  相似文献   

8.
ABSTRACT: The effects of changes in the landscape and climate over geological time are plain to see in the present hydrological regime. More recent anthropogenic changes may also have effects on our way of life. A prerequisite to predicting such effects is that we understand the interactions between climate, landscape and the hydrological regime. A semi-distributed hydrological model (SLURP) has been developed which can be used to investigate, in a simple way, the links between landscape, climate and hydrology for watersheds of various sizes. As well as using data from the observed climate network, the model has been used with data from atmospheric models to investigate possible changes in hydrology. A critical input to such a model is knowledge of the links between landscape and climate. While direct anthropogenic effects such as changes in forested area may presently be included, the indirect effects of climate on landscape and vice versa are not yet modeled well enough to be explicitly included. The development of models describing climate-landscape relationships such as regeneration, development and breakup, water and carbon fluxes at species, ecosystem and biome level is a necessary step in understanding and predicting the effects of changes in climate on landscape and on water resources. Forest is the predominant land cover in Canada covering 453 Mha and productivity/succession models for major forest types should be included in an integrated climate-landscape-water simulation.  相似文献   

9.
    
ABSTRACT: The effects of potential climate change on mean annual runoff in the conterminous United States (U.S.) are examined using a simple water-balance model and output from two atmospheric general circulation models (GCMs). The two GCMs are from the Canadian Centre for Climate Prediction and Analysis (CCC) and the Hadley Centre for Climate Prediction and Research (HAD). In general, the CCC GCM climate results in decreases in runoff for the conterminous U.S., and the HAD GCM climate produces increases in runoff. These estimated changes in runoff primarily are the result of estimated changes in precipitation. The changes in mean annual runoff, however, mostly are smaller than the decade-to-decade variability in GCM-based mean annual runoff and errors in GCM-based runoff. The differences in simulated runoff between the two GCMs, together with decade-to-decade variability and errors in GCM-based runoff, cause the estimates of changes in runoff to be uncertain and unreliable.  相似文献   

10.
    
ABSTRACT: Recent work has found that a one-parameter Weibull model of wet day precipitation amount based on the Weibull distribution provides a better fit to historical daily precipitation data for eastern U.S. sites than other one-parameter models. The general two-parameter Weibull distribution was compared in this study to other widely used distributions for describing the distribution of daily precipitation event sizes at 99 sites from the U.S. Pacific Northwest. Surprisingly little performance was sacrificed by reducing the two-parameter Weibull to a single-parameter distribution. Advantages of the single-parameter model included requiring only the mean wet day precipitation amount for calibration, invertibility for simulation purposes, and ease of analytical manipulation. The fit of the single-parameter Weibull to the 99 stations included in this study was significantly better than other single-parameter models tested, and performed as well as the widely endorsed, more cumbersome, two-parameter gamma model. Both the one-and two-parameter Weibull distributions are shown to have b-moments that are consistent with historical precipitation data, while the ratio of b-skew and b-variance in the gamma model is inconsistent with the historical recerd by this measure. In addition, it was found that the two-parameter gamma distribution was better fit using the method of moments estimators than maximum likelihood estimates. These findings suggested that the distribution in precipitation among sites in the Pacific Northwest with dramatically different settings are nearly identical if expressed in proportion to the mean site event size.  相似文献   

11.
    
ABSTRACT: A time series of annual flow of the Sacramento River, California, is reconstructed to A.D. 869 from tree rings for a long‐term perspective on hydrologic drought. Reconstructions derived by principal components regression of flow on time‐varying subsets of tree‐ring chronologies account for 64 to 81 percent of the flow variance in the 1906 to 1977 calibration period. A Monte Carlo analysis of reconstructed n‐year running means indicates that the gaged record contains examples of drought extremes for averaging periods of perhaps = 6 to 10 years, but not for longer and shorter averaging periods. For example, the estimated probability approaches 1.0 that the flow in A.D. 1580 was lower than the lowest single‐year gaged flow. The tree‐ring record also suggests that persistently high or low flows over 50‐year periods characterize some parts of the long‐term flow history. The results should contribute to sensible water resources planning for the Sacramento Basin and to the methodology of incorporating tree‐ring data in the assessment of the probability of hydrologic drought.  相似文献   

12.
    
ABSTRACT: Downscaling coarse resolution climate data to scales that are useful for impact assessment studies is receiving increased attention. Basin-scale hydrologic processes and other local climate impacts related to water resources such as reservoir management, crop and forest productivity, and ecosystem response require climate information at scales that are much finer than current and future GCM resolutions. The Regional Climate System Model (RCSM) is a dynamic downscaling system that has been used since 1994 for short-term precipitation and streamflow predictions and seasonal hindcast analysis with good skill. During the 1997–1998 winter, experimental seasonal forecasts were made in collaboration with the NOAA Climate Prediction Center and UCLA with promising results. Preliminary studies of a control and 2°CO2 perturbation for the southwestern U.S. have been performed.  相似文献   

13.
ABSTRACT: The meteorology flood hydroclimatolog and socioeconomic impacts of the Flood of January 1996 in the Susquehanna River Basin are explored. The analysis explains how an unusual storm system brought high humidities, high temperatures, strong winds, and heavy rain to the basin. The rapid melt of the deep snowpack, combined with the heavy rainfall, produced the sudden release of large volumes of water. Because the ground surface was frozen or saturated, this water moved primarily as overland flow. Thus, the flood waters were not restricted to areas immediately adjacent to stream channels and, consequently, some of the largest impacts were on people, property, and infrastructure in areas not normally prone to flooding. Socioeconomic patterns of flooding over time and space are investigated to put this flood into context and to highlight its impacts. The analysis concludes that if such overland flooding is a more common feature of climate change, then the current vulnerability to this form of flooding and its economic implications must be considered carefully.  相似文献   

14.
    
ABSTRACT: Where data are available, hydrologic studies may use precipitation's stable oxygen and hydrogen isotope composition to investigate streamflow, ground water/surface water interaction, and ground water recharge. Paleoclimate studies utilize the δ18Oprecipitation‐Tair relationship, in conjunction with lake sediments, fossils, or old ground waters, for example, to estimate pale‐otemperatures. Ecological studies utilize precipitation and soil water isotope composition to track moisture uptake in plants, and to trace species migration patterns. Such studies require that the isotopic composition of precipitation be known. Oxygen‐18 (δ18O) and deuterium (δ2H) data for precipitation are lacking in the semi‐arid portion of the north‐central U.S. Great Plains, and thus there is a need to establish additional meteoric water lines as isotope input functions across the region, as well as to develop better understanding of the isotopic climate linkages that control oxygen and hydrogen isotope ratios in precipitation. This study determined the δ18O and δ2H composition of precipitation in the Pawnee Grasslands of northeastern Colorado from 1994 through 1998 using archived National Atmospheric Deposition Program samples. The resulting local water line follows the relationship δ2H = 7.86 δ18O‐7.66, and the data show a δ18Oweekly ‐ Tweekly relationship of δ18O = 0.560‐T (°C)‐18.8.  相似文献   

15.
    
ABSTRACT: A 2xCO2 climate and runoff in the Upper Deschutes Basin in central Oregon is simulated using a mesoscale atmospheric model and a watershed model that incorporates spatial variability of the runoff process. A nine‐year control climate monthly time series provides a benchmark for assessing changes related to a warmer and wetter 2xCO2 climate. Potential evapotranspiration is increased by 23 percent and snow water equivalent is reduced by 59 percent in the 2xCO2 climate. Annual runoff increases by 23 percent, while November runoff increases by 55 percent. The average maximum monthly runoff is in May for both the control climate and 2xCO2 climate, but in five of the nine years the monthly maximum runoff for the 2xCO2 climate occurs two to five months earlier than for the control climate. The minimum runoff month is one to five months earlier in the 2xCO2 climate in seven of the nine years, and the month of average minimum runoff is March in the control climate and November in the 2xCO2 climate. Since precipitation is greatest in December in both the control climate and 2xCO2 climate, the earlier maximum and minimum runoff for a 2xCO2 climate indicates greater watershed sensitivity to temperature than to precipitation.  相似文献   

16.
    
ABSTRACT: April 1 snowpack accumulations measured at 311 snow courses in the western United States (U.S.) are grouped using a correlation-based cluster analysis. A conceptual snow accumulation and melt model and monthly temperature and precipitation for each cluster are used to estimate cluster-average April 1 snowpack. The conceptual snow model is subsequently used to estimate future snowpack by using changes in monthly temperature and precipitation simulated by the Canadian Centre for Climate Modeling and Analysis (CCC) and the Hadley Centre for Climate Prediction and Research (HADLEY) general circulation models (GCMs). Results for the CCC model indicate that although winter precipitation is estimated to increase in the future, increases in temperatures will result in large decreases in April 1 snowpack for the entire western U.S. Results for the HADLEY model also indicate large decreases in April 1 snowpack for most of the western US, but the decreases are not as severe as those estimated using the CCC simulations. Although snowpack conditions are estimated to decrease for most areas of the western US, both GCMs estimate a general increase in winter precipitation toward the latter half of the next century. Thus, water quantity may be increased in the western US; however, the timing of runoff will be altered because precipitation will more frequently occur as rain rather than as snow.  相似文献   

17.
    
ABSTRACT: Point rainfall intensities for a given return period are often used to formulate design storms for rainfall/runoff models to simulate design floods. These design floods are in turn used to design bridges, culverts, and a variety of drainage and flood control structures. The projected rapid growth in the southwestern United States will require very substantial monetary investments in drainage infrastructure. Accurate estimates of point rainfall intensities are critical to ensure both safe designs while not wasting dollars in overdesign. Rainfall point intensities (accumulated rainfall depth over a specified duration) for 5‐, 15‐, 30‐, and 60‐minute durations for the 2‐, 5‐, 10‐, 25‐, 50‐, and 100‐year return periods were determined for southeast Arizona. Thirty‐five years of rainfall record (1961 to 1995) were used in this study. The records came from 20 stations that were grouped into five sets of four independent stations to extend the rainfall records. The stations are in the USDA‐ARS Walnut Gulch Experimental Watershed (WGEW), which is representative of large portions of the Southwest whose runoff generation is dominated by air‐mass thunderstorms. The 5‐, 15‐, 30‐, and 60‐minute maximum intensities per year followed log‐normal distributions. The mean point rainfall intensities of the five sets of gages are very close (between 0 and 11 percent) to the NOAA values of the 5‐, 15‐, 30‐, and 60‐minute durations for all return periods. Much larger differences between the mean point rainfall intensities for all durations were found when these results were compared to those of a previous study done with a shorter rainfall record (between 14 and 33 percent for the 25‐, 50‐, and 100‐year return‐periods). The difference between the largest and the smallest values of point rainfall intensities recorded by each group, for all durations, usually increases as the return period increases.  相似文献   

18.
    
ABSTRACT: Air temperatures are sometimes used as easy substitutes for stream temperatures. To examine the errors associated with this substitution, linear relationships between 39 Minnesota stream water temperature records and associated air temperature records were analyzed. From the lumped data set (38,082 daily data pairs), equations were derived for daily, weekly, monthly, and annual mean temperatures. Standard deviations between all measured and predicted water temperatures were 3.5°C (daily), 2.6°C (weekly), 1.9°C (monthly), and 1.3°C (annual). Separate analyses for each stream gaging station gave substantially lower standard deviations. Weather monitoring stations were, on average, 37.5 km from the stream. The measured water temperatures follow the annual air temperature cycle closely. No time lags were taken into account, and periods of ice cover were excluded from the analysis. If atmospheric CO2 doubles in the future, air temperatures in Minnesota are projected (CCC GCM) to rise by 4.3°C in the warm season (April-October). This would translate into an average 4.1°C stream temperature rise, provided that stream shading would remain unaltered.  相似文献   

19.
    
ABSTRACT: Solar exposure profoundly affects stream processes and species composition. Despite this, prominent stream monitoring protocols focus on canopy closure (obstruction of the sky as a whole) rather than on measures of solar exposure or shading. We identify a candidate set of solar exposure metrics that can be derived from hemispheric images. These metrics enable a more mechanistic evaluation of solar exposure than can be achieved with canopy closure metrics. Data collected from 31 stream reaches in eastern Oregon enable us to quantify and compare metrics of solar exposure from hemispheric images and a metric of canopy closure with a concave densiometer. Repeatability of hemispheric metrics is generally as good as or better than the densiometer closure metric, and variation in the analysis of hemispheric images attributable to differences between analysts is negligibly small. Metrics from the hemispheric images and the densiometer are typically strongly correlated, at the scale of an individual observation and for 150 m stream reaches, but not always in a linear fashion. We quantify the character of the uncertainty in the relationship between the densiometer and the hemispheric metrics. Hemispheric imagery produces repeatable metrics representing an important ecological attribute; thus those researching the effects of solar exposure on stream ecosystems should consider the use of hemispheric imagery.  相似文献   

20.
    
ABSTRACT: In 1996, the Illinois State Geological Survey began an investigation of fluctuating water levels in a pond in Cary, Illinois. The cause of the fluctuations appeared to be ground water discharge into a storm sewer recently installed by the Illinois Department of Transportation. However, analysis of climatic data provided an equally likely explanation of the fluctuations. Distinguishing the effect of climatic variations from the effect of the storm sewer was hampered by the lack of antecedent ground water and surface water data. In similar settings, it is recommended that ground water and surface water data be collected prior to initiating any infrastructure improvements.  相似文献   

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