Climate Change and...
- Climate Variability
- Climate Models
Effects of Climate Change
Aber, J. D., Ollinger, S. V., Federer, C. A., Reich, P. B., Goulden, M. L., Kicklighter, D. W., Melillo, J. M., Lathrop, R. G., Jr. (1995). Predicting the effects of climate change on water yield and forest production in the northeastern United States. Climate Research 5 (3): 207-222
ABSTRACT: Rapid and simultaneous changes in temperature, precipitation and the atmospheric concentration of CO2 are predicted to occur over the next century. Simple, well-validated models of ecosystem function are required to predict the effects of these changes This paper describes an improved version of a forest carbon and water balance model (PnET-II) and the application of the model to predict stand- and regional-level effects of changes in temperature, precipitation and atmospheric CO2 (gross and net) driven by nitrogen availability as expressed through foliar N concentration. Improvements was parameterized and run for 4 forest/site combinations and validated against available data for water yield, gross and net carbon exchange and biomass production. The validation exercise suggests that the determination of actual water availability to stands and the occurrence or non-occurrence of soil-based water stress are critical to accurate modeling of forest net primary production (NPP) and net ecosystem production (NEP). The model was then run for the entire New England/New York (USA) region using a 1 km resolution geographic information system. Predicted long-term NEP ranged from -85 to +275 g C m-2 yr-1 for the 4 forest/site combinations, and from -150 to 350 g cm-2 yr-1 for the region, with a regional average of 76 g C m-2 yr-1 . A combination of increased temperature (+6 degree C), decreased precipitation (-15%) and increased Water use efficiency (2x, due to doubling of CO2 ) resulted generally in increases in NPP and decreases in water yield over the region
ABSTRACT: The hydrological cycle has significant effects on the terrestrial carbon (C) balance through its controls on photosynthesis and C decomposition. A detailed representation of the water cycle in terrestrial C cycle models is essential for reliable estimates of C budgets. However, it is challenging to accurately describe the spatial and temporal variations of soil water, especially for regional and global applications. Vertical and horizontal movements of soil water should be included. To constrain the hydrology-related uncertainty in modelling the regional C balance, a three-dimensional hydrological module was incorporated into the Integrated Terrestrial Ecosystem Carbon-budget model (InTEC V3.0). We also added an explicit parameterization of wetlands. The inclusion of the hydrological module considerably improved the model's ability to simulate C content and balances in different ecosystems. Compared with measurements at five flux-tower sites, the model captured 85% and 82% of the variations in volumetric soil moisture content in the 0–10 cm and 10–30 cm depths during the growing season and 84% of the interannual variability in the measured C balance. The simulations showed that lateral subsurface water redistribution is a necessary mechanism for simulating water table depth for both poorly drained forest and peatland sites. Nationally, soil C content and their spatial variability are significantly related to drainage class. Poorly drained areas are important C sinks at the regional scale, however, their soil C content and balances are difficult to model and may have been inadequately represented in previous C cycle models. The InTEC V3.0 model predicted an annual net C uptake by Canada's forests and wetlands for the period 1901–1998 of 111.9 Tg C yr−1 , which is 41.4 Tg C yr−1 larger than our previous estimate (InTEC V2.0). The increase in the net C uptake occurred mainly in poorly drained regions and resulted from the inclusion of a separate wetland parameterization and a detailed hydrologic module with lateral flow in InTEC V3.0.
ABSTRACT: A coupled model of the hydrological and carbon cycles in the soil–vegetation–atmosphere system is suggested. The model describes the interception and evaporation of precipitation by canopy, transpiration, vertical transfer of soil moisture, photosynthesis, the interaction between transpiration and photosynthesis, and plant and soil respiration. The validation of this model was carried out using the FIFE measurements from a grassland site in Kansas, the BOREAS measurements from a jack pine forest site in Saskatchewan, and the observations conducted within a deciduous forest in the southeastern United States. The model results show a good agreement with experimental data. The model was shown to adequately describe the influence of soil moisture and atmospheric CO2 concentration on transpiration and net ecosystem CO2 exchange.
ABSTRACT: Hydrologic models provide a framework in which to conceptualize and investigate the relationships between climate and water resources. A review of current studies that assess the impacts of climate change using hydrologic models indicates a number of problem areas common to the variety of models applied. These problem areas include parameter estimation, scale, model validation, climate scenario generation, and data. Research needs to address these problems include development of (1) a more physically based understanding of hydrologic processes and their interactions; (2) parameter measurement and estimation techniques for application over a range of spatial and temporal scales; (3) quantitative measures of uncertainty in model parameters and model results; (4) improved methodologies of climate scenario generation; (5) detailed data sets in a variety of climatic and physiographic regions; and (6) modular modeling tools to provide a framework to facilitate interdisciplinary research. Solutions to these problems would significantly improve the capability of models to assess the effects of climate change.
M. Stieglitz, D. Rind, J. Famiglietti, C. Rosenzweig (1997). An efficient approach to modeling the topographic control of surface hydrology for regional and global climate modeling. Journal of Climate 10 (1): 118-137
ABSTRACT: The current generation of land-surface models used in GCMs view the soil column as the fundamental hydrologic unit. While this may be effective in simulating such processes as the evolution of ground temperatures and the growth/ablation of a snowpack at the soil plot scale, it effectively ignores the role topography plays in the development of soil moisture heterogeneity and the subsequent impacts of this soil moisture heterogeneity on watershed evapotranspiration and the partitioning of surface fluxes. This view also ignores the role topography plays in the timing of discharge and the partitioning of discharge into surface runoff and baseflow. In this paper an approach to land-surface modeling is presented that allows us to view the watershed as the fundamental hydrologic unit. The analytic form of TOPMODEL equations are incorporated into the soil column framework and the resulting model is used to predict the saturated fraction of the watershed and baseflow in a consistent fashion. Soil moisture heterogeneity represented by saturated lowlands subsequently impacts the partitioning of surface fluxes, including evapotranspiration and runoff. The approach is computationally efficient, allows for a greatly improved simulation of the hydrologic cycle, and is easily coupled into the existing framework of the current generation of single column land-surface models. Because this approach uses the statistics of the topography rather than the details of the topography, it is compatible with the large spatial scales of today’s regional and global climate models. Five years of meteorological and hydrological data from the Sleepers River watershed located in the northeastern United States where winter snow cover is significant were used to drive the new model. Site validation data were sufficient to evaluate model performance with regard to various aspects of the watershed water balance, including snowpack growth/ablation, the spring snowmelt hydrograph, storm hydrographs, and the seasonal development of watershed evapotranspiration and soil moisture.
Zhu, C., D.W. Pierce, T.P. Barnett, A.W. Wood, D.P. Lettenmaier (2004). Evaluation of hydrologically relevant PCM climate variables and large-scale variability over the western U.S.. Climatic Change 62 (1): 45-74
ABSTRACT: The ability of the Parallel Climate Model (PCM) to reproduce the mean and variability of hydrologically relevant climate variables was evaluated by comparing PCM historical climate runs with observations over temporal scales from sub-daily to annual. The domain was the continental U.S, and the model spatial resolution was T42 (about 2.8 degrees latitude by longitude). The climate variables evaluated include precipitation, surface air temperature, net surface solar radiation, soil moisture, and snow water equivalent. The results show that PCM has a winter dry bias in the Pacific Northwest and a summer wet bias in the central plains. The diurnal precipitation variation in summer is much stronger than observed, with an afternoon maximum in summer precipitation over much of the U.S. interior, in contrast with an observed nocturnal maximum in parts of the interior. PCM has a cold bias in annual mean temperature over most of the U.S., with deviations as large as –8 K. The PCM daily temperature range is lower than observed, especiallyin the central U.S. PCM generally overestimates the net solar radiation over most of the U.S, although the diurnal cycle is simulated well in spring, summer and winter. In autumn PCM has a pronounced noontime peak in solar radiation that differs by 5–10% from observations. PCM'ssimulated soil moisture is less variable than that of a sophisticated land-surface hydrology model, especially in the interior of the country. PCM simulates the wetter conditions over the southeastern U.S. and California during warm (El Niño) events, but shifts the drier conditions in the Pacific Northwest northward and underestimates their magnitude. The temperature response to the North Pacific Oscillation is generally captured by PCM, but the amplitude of this response is overestimated by a factor of about two.
ABSTRACT: Through its control on soil moisture patterns, topography’s role in influencing forest composition is widely recognized. This study addresses shortcomings in traditional moisture indices by employing a water balance approach, incorporating topographic and edaphic variability to assess fine-scale moisture demand and moisture availability. Using GIS and readily available data, evapotranspiration and moisture stress are modeled at a fine spatial scale at two study areas in the US (Ohio and North Carolina). Model results are compared to field-based soil moisture measurements throughout the growing season. A strong topographic pattern of moisture utilization and demand is uncovered, with highest rates of evapotranspiration found on south-facing slopes, followed by ridges, valleys, and north-facing slopes. South-facing slopes and ridges also experience highest moisture deficit. Overall higher rates of evapotranspiration are observed at the Ohio site, though deficit is slightly lower. Based on a comparison between modeled and measured soil moisture, utilization and recharge trends were captured well in terms of both magnitude and timing. Topographically controlled drainage patterns appear to have little influence on soil moisture patterns during the growing season. In addition to its ability to accurately capture patterns of soil moisture in both high-relief and moderate-relief environments, a water balance approach offers numerous advantages over traditional moisture indices. It assesses moisture availability and utilization in absolute terms, using readily available data and widely used GIS software. Results are directly comparable across sites, and although output is created at a fine-scale, the method is applicable for larger geographic areas. Since it incorporates topography, available water capacity, and climatic variables, the model is able to directly assess the potential response of vegetation to climate change.
D. Gerten, S. Schaphoff, U. Haberlandt, W. Lucht, S. Sitch (2004). Terrestrial vegetation and water balance—hydrological evaluation of a dynamic global vegetation model. Journal of Hydrology 286 (1-4): 249-270
ABSTRACT: Earth's vegetation plays a pivotal role in the global water balance. Hence, there is a need to model dynamic interactions and feedbacks between the terrestrial biosphere and the water cycle. Here, the hydrological performance of the Lund–Potsdam–Jena model (LPJ), a prominent dynamic global vegetation model, is evaluated. Models of this type simulate the coupled terrestrial carbon and water cycle, thus they are well suited for investigating biosphere–hydrosphere interactions over large domains. We demonstrate that runoff and evapotranspiration computed by LPJ agree well with respective results from state-of-the-art global hydrological models, while in some regions, runoff is significantly over- or underestimated compared to observations. The direction and magnitude of these biases is largely similar to those from other macro-scale models, rather than specific to LPJ. They are attributable primarily to uncertainties in the climate input data, and to human interventions not considered by the model (e.g. water withdrawal, land cover conversions). Additional model development is required to perform integrated assessments of water exchanges among the biosphere, the hydrosphere, and the anthroposphere. Yet, the LPJ model can now be used to study inter-relations between the world's major vegetation types and the terrestrial water balance. As an example, it is shown that a doubling of atmospheric CO2 content alone would result in pronounced changes in evapotranspiration and runoff for many parts of the world. Although significant, these changes would remain unseen by stand-alone hydrological models, thereby emphasizing the importance of simulating the coupled carbon and water cycle.
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 necessarily 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.
A. D. Ziegler, J. Sheffield, E. P. Maurer, B. Nijssen, E. F. Wood, D. P. Lettenmaier (2003). Detection of intensification in global- and continental-scale hydrological cycles: temporal scale of evaluation. Journal of Climate 16 (3): 535-547
ABSTRACT: Diagnostic studies of offline, global-scale Variable Infiltration Capacity (VIC) model simulations of terrestrial water budgets and simulations of the climate of the twenty-first century using the parallel climate model (PCM) are used to estimate the time required to detect plausible changes in precipitation (P), evaporation (E), and discharge (Q) if the global water cycle intensifies in response to global warming. Given the annual variability in these continental hydrological cycle components, several decades to perhaps more than a century of observations are needed to detect water cycle changes on the order of magnitude predicted by many global climate model studies simulating global warming scenarios. Global increases in precipitation, evaporation, and runoff of 0.6, 0.4, and 0.2 mm yr-1 require approximately 30–45, 25–35, and 50–60 yr, respectively, to detect with high confidence. These conservative detection time estimates are based on statistical error criteria (a = 0.05, ß = 0.10) that are associated with high statistical confidence, 1 - a (accept hypothesis of intensification when true, i.e., intensification is occurring), and high statistical power, 1 - ß (reject hypothesis of intensification when false, i.e., intensification is not occurring). If one is willing to accept a higher degree of risk in making a statistical error, the detection time estimates can be reduced substantially. Owing in part to greater variability, detection time of changes in continental P, E, and Q are longer than those for the globe. Similar calculations performed for three Global Energy and Water Experiment (GEWEX) basins reveal that minimum detection time for some of these basins may be longer than that for the corresponding continent as a whole, thereby calling into question the appropriateness of using continental-scale basins alone for rapid detection of changes in continental water cycles. A case is made for implementing networks of small-scale indicator basins, which collectively mimic the variability in continental P, E, and Q, to detect acceleration in the global water cycle.
Dolph, J., D. Marks, G.A. King, R.J. Naiman (1992). Sensitivity of the regional water balance in the Columbia River basin to climate variability: application of a spatially distributed water balance model. Springer-Verlag: 233-265
ABSTRACT: A one-dimensional water balance model was developed and used to simulate the water balance for the Columbia River Basin. The model was run over a 10 km digital elevation grid representing the U.S. portion of the basin. The regional water balance was calculated usign a monthly time step for a relatively wet year (1972 water year), a relatively dry year (1977 water year), and adouble (2xCO2 ) climate scenario. Input data, spatially distributed over the grid, included precipitation, maximum soil moisture storage capacity, potential evapotranspiration (PET) and threshold baseflow. The model output provides spatially distributed surfaces of actual evapotranspiration (ET), surface runoff, and soil storage. Model performance was assessed by comparing modelled ET and runoff with the input precipitation data, and by comparing modelled runoff with measured runoff. The model reasonably partitions incoming precipitation to evapotranspiration and runoff. However, modelled total annual runoff was significantly less than measured runoff, primarily because precipitation is underestimated by the network of measurement stations and because of limitations associated with the interpolation procedure used to distribute the precipitation across the grid. Estimated precipitation is less than measured runoff, a physical impossibility. Under warmer 2xCO2 climate conditions (January 4.0°K warmer, July 6.5°K warmer), the model predicts that PET increases by about 80%, ET increases, and runoff and soil moisture decrease. Under these climate conditions, the distribution and composition of forests in the region would change dramatically, and water resources would become more limited.
ABSTRACT: Water availability on the continents is important for human health economic activity, ecosystem function and geophysical processes. Because the saturation vapour pressure of water in air is highly sensitive to temperature, perturbations in the global water cycle are expected to accompany climate warming. Regional patterns of warming-induced changes in surface hydroclimate are complex and less certain than those in temperature, however, with both regional increases and decreases expected in precipitation and runoff. Here we show that an ensemble of 12 climate models exhibits qualitative and statistically significant skill in simulating observed regional patterns of twentieth-century multidecadal changes in streamflow. These models project 10–40% increases in runoff in eastern equatorial Africa, the La Plata basin and high-latitude North America and Eurasia, and 10–30% decreases in runoff in southern Africa, southern Europe, the Middle East and mid-latitude western North America by the year 2050. Such changes in sustainable water availability would have considerable regional-scale consequences for economies as well as ecosystems.
ABSTRACT: The projected response of coniferous forests to a climatic change scenario of doubled atmospheric CO2 , air temperature of +4 °C, and +10% precipitation was studied using a computer simulation model of forest ecosystem processes. A topographically complex forested region of Montana was simulated to study regional climate change induced forest responses. In general, increases of 10–20% in LAI, and 20–30% in evapotranspiration (ET) and photosynthesis (PSN) were projected. Snowpack duration decreased by 19–69 days depending on location, and growing season length increased proportionally. However, hydrologic outflow, primarily fed by snowmelt in this region, was projected to decrease by as much as 30%, which could virtually dry up rivers and irrigation water in the future. To understand the simulated forest responses, and explore the extent to which these results might apply continentally, seasonal hydrologic partitioning between outflow and ET, PSN, respiration, and net primary production (NPP) were simulated for two contrasting climates of Jacksonville, Florida (hot, wet) and Missoula, Montana (cold, dry). Three forest responses were studied sequentially from; climate change alone, addition of CO2 induced tree physiological responses of -30% stomatal conductance and +30% photosynthetic rates, and finally with a reequilibration of forest leaf area index (LAI), derived by a hydrologic equilibrium theory. NPP was projected to increase 88%, and ET 10%, in Missoula, MT, yet decrease 5% and 16% respectively for Jacksonville, FL, emphasizing the contrasting forest responses possible with future climatic change.
ABSTRACT: The sensitivity of streamflow to climate change was investigated in the American, Carson, and Truckee River Basins, California and Nevada. Nine gaging stations were used to represent streamflow in the basins. Annual models were developed by regressing 1961-1991 streamflow data on temperature and precipitation. Climate-change scenarios were used as inputs to the models to determine streamflow sensitivities. Climate-change scenarios were generated from historical time series by modifying mean temperatures by a range of +4°C to -4°C and total precipitation by a range of +25 percent to -25 percent. Results show that streamflow on the warmer, lower west side of the Sierra Nevada generally is more sensitive to temperature and precipitation changes than is streamflow on the colder, higher east side. A 2°C rise in temperature and a 25-percent decrease in precipitation results in streamflow decreases of 56 percent on the American River and 25 percent on the Carson River. A 2°C decline in temperature and a 25-percent increase in precipitation results in streamflow increases of 102 percent on the American River and 22 percent on the Carson River.
ABSTRACT: Changes in regional temperature and precipitation expected to occur as a result of the accumulation of greenhouse gases may have significant impacts on water resources. We use a conceptual hydrologic model, developed and operated by the National Weather Service, to study the sensitivity of surface runoff in several sub-basins of the Colorado River to these changes. Increases in temperature of 2°C decrease mean annual runoff by 4–12%. A temperature increase of 4°C decreases mean annual runoff by 9–21%. Increases or decreases in annual precipitation of 10–20% result in corresponding changes in mean annual runoff of approximately 10–20%. For the range of scenarios studied, these results suggest that runoff in the basin is somewhat more sensitive to changes in precipitation than to changes in temperature. Seasonal changes were also observed, with peak runoff shifting from June to April or May. Fall and winter flows generally increase, whereas spring and summer flows decrease in most of the scenarios studied. These changes are attributed to an increase of the ratio of rain to snow and to a higher snowline. Although these results suggest that streamflow in the Colorado Basin is less sensitive to climatic changes than previous statistical studies have indicated, the magnitude of possible changes is nonetheless sufficiently great to have significant environmental, economic, and political implications.
ABSTRACT: To evaluate the hydrologic and biogeochemical response of freshwater watersheds to climatic variability properly, a mathematical model with detailed parameterization in describing the hydrologic and thermal processes in a watershed is needed. For this purpose, the Enhanced Trickle Down model was modified to predict the hydrologic and thermal responses of freshwater watersheds to various climate change scenarios. Modifications of the model included the incorporation of an energy transfer submodel, an improved hydraulic conductivity scheme, and the coupling with a point source snowmelt model. The results of calibration and verification of the model using 8 years of field data collected at the Agricultural Research Service, W-3 watershed, located near Danville, Vermont, are presented.
A. Serrat-Capdevila, J. B. Valdés, J. González Péreze, K. Baird, L. J. Mata, Maddock, T., III (2007). Modeling climate change impacts – and uncertainty – on the hydrology of a riparian system: The San Pedro Basin (Arizona/Sonora). Journal of Hydrology 347 (1-2): 48-66
ABSTRACT: An assessment of climate change impacts in the water resources of a semi-arid basin in southeastern Arizona and northern Sonora is presented using results from an ensemble of 17 global circulation models (GCMs) and four different climate change scenarios from the Intergovernmental Panel on Climate Change (IPCC). Annual GCM precipitation data for the region is spatially downscaled and used to derive spatially distributed recharge estimates in the San Pedro Basin. A three dimensional transient groundwater-surface water flow model is used to simulate the hydrology of the current century, from 2000 to 2100, under different climate scenarios and model estimates. Groundwater extraction in the basin was maintained constant and equal to current. The use of multiple climate model results provides a highest-likelihood mean estimate as well as a measure of its uncertainty and a range of less probable outcomes. Results suggest that recharge in the San Pedro basin will decrease, affecting the dynamics of the riparian area in the long term. It is shown that mean net stream gain, i.e. base flow, will decrease and the effects on the riparian area could be significant. The results of this work provide a basis for the inclusion of representative climate scenarios into the basin’s existing decision support system model.