Climate Change and Hydrology/Water Resources

Global Studies

Nijssen, Bart, Greg M. O'Donnell, Alan F. Hamlet, and Dennis P. Lettenmaier. 2001. "Hydrologic Sensitivity of Global Rivers to Climate Change," Climatic Change, Vol. 50, No. 1-2, July, pp. 143-175.
ABSTRACT: Climate predictions from four state-of-the-art general circulation models (GCMs) were used to assess the hydrologic sensitivity to climate change of nine large, continental river basins (Amazon, Amur, Mackenzie, Mekong, Mississippi, Severnaya Dvina, Xi, Yellow, Yenisei). The four climate models (HCCPR-CM2, HCCPR-CM3, MPI-ECHAM4, and DOE-PCM3) all predicted transient climate response to changing greenhouse gas concentrations, and incorporated modern land surface parameterizations. Model-predicted monthly average precipitation and temperature changes were downscaled to the river basin level using model increments (transient minus control) to adjust for GCM bias. The variable infiltration capacity (VIC) macroscale hydrological model (MHM) was used to calculate the corresponding changes in hydrologic fluxes (especially streamflow and evapotranspiration) and moisture storages. Hydrologic model simulations were performed for decades centered on 2025 and 2045. In addition, a sensitivity study was performed in which temperature and precipitation were increased independently by 2 °C and 10%, respectively, during each of four seasons. All GCMs predict a warming for all nine basins, with the greatest warming predicted to occur during the winter months in the highest latitudes. Precipitation generally increases, but the monthly precipitation signal varies more between the models than does temperature. The largest changes in the hydrological cycle are predicted for the snow-dominated basins of mid to higher latitudes. This results in part from the greater amount of warming predicted for these regions, but more importantly, because of the important role of snow in the water balance. Because the snow pack integrates the effects of climate change over a period of months, the largest changes occur in early to mid spring when snow melt occurs. The climate change responses are somewhat different for the coldest snow dominated basins than for those with more transitional snow regimes. In the coldest basins, the response to warming is an increase of the spring streamflow peak, whereas for the transitional basins spring runoff decreases. Instead, the transitional basins have large increases in winter streamflows. The hydrological response of most tropical and mid-latitude basins to the warmer and somewhat wetter conditions predicted by the GCMs is a reduction in annual streamflow, although again, considerable disagreement exists among the different GCMs. In contrast, for the high-latitude basins increases in annual flow volume are predicted in most cases.

Arnell, Nigel W. 1999. "Climate change and global water resources," Global Environmental Change,
Vol. 9, Suppl. 1 , October, pp. S31-S49.
ABSTRACT: By 2025, it is estimated that around 5 billion people, out of a total population of around 8 billion, will be living in countries experiencing water stress (using more than 20% of their available resources). Climate change has the potential to impose additional pressures in some regions. This paper describes an assessment of the implications of climate change for global hydrological regimes and water resources. It uses climate change scenarios developed from Hadley Centre climate simulations (HadCM2 and HadCM3), and simulates global river flows at a spatial resolution of 0.5×0.5° using a macro-scale hydrological model. Changes in national water resources are calculated, including both internally generated runoff and upstream imports, and compared with national water use estimates developed for the United Nations Comprehensive Assessment of the Freshwater Resources of the World. Although there is variation between scenarios, the results suggest that average annual runoff will increase in high latitudes, in equatorial Africa and Asia, and southeast Asia, and will decrease in mid-latitudes and most subtropical regions. The HadCM3 scenario produces changes in runoff which are often similar to those from the HadCM2 scenarios -- but there are important regional differences. The rise in temperature associated with climate change leads to a general reduction in the proportion of precipitation falling as snow, and a consequent reduction in many areas in the duration of snow cover. This has implications for the timing of streamflow in such regions, with a shift from spring snow melt to winter runoff. Under the HadCM2 ensemble mean scenario, the number of people living in countries with water stress would increase by 53 million by 2025 (relative to those who would be affected in the absence of climate change). Under the HadCM3 scenario, the number of people living in countries with water stress would rise by 113 million. However, by 2050 there would be a net reduction in populations in stressed countries under HadCM2 (of around 69 million), but an increase of 56 million under HadCM3. The study also showed that different indications of the impact of climate change on water resource stresses could be obtained using different projections of future water use. The paper emphasises the large range between estimates of "impact", and also discusses the problems associated with the scale of analysis and the definition of indices of water resource impact.

Frederick, Kenneth D., and David C. Major. 1997. "Climate Change and Water Resources," Climatic Change, Vol. 37, No. 1, September, pp. 7-23.
ABSTRACT: Current perspectives on global climate change based on recent reports of the Intergovernmental Panel on Climate Change (IPCC) are presented. Impacts of a greenhouse warming that are likely to affect water planning and evaluation include changes in precipitation and runoff patterns, sea level rise, land use and population shifts following from these effects, and changes in water demands. Irrigation water demands are particularly sensitive to changes in precipitation, temperature, and carbon dioxide levels. Despite recent advances in climate change science, great uncertainty remains as to how and when climate will change and how these changes will affect the supply and demand for water at the river basin and watershed levels, which are of most interest to planners. To place the climate-induced uncertainties in perspective, the influence on the supply and demand for water of non-climate factors such as population, technology, economic conditions, social and political factors, and the values society places on alternative water uses are considered.

Major, David C., Kenneth D. Frederick. 1997. "Water Resources Planning and Climate Change Assessment Methods," Climatic Change, Vol. 37, No. 1, September, pp. 25-40.
ABSTRACT: This paper, which provides background for other papers in the volume, first reviews the nature and development of water resources planning and evaluation criteria at the Federal level in the United States. These criteria constitute a highly developed, complex set of guidelines for project planning and evaluation. The level of development of these criteria and their long historical development from theoretical foundations must be taken into account in relating global climate change to possible changes in planning criteria. Second, the essentials of water project planning and evaluation, including benefit-cost principles and more complex concepts of social decision-making, are outlined. Third, the paper provides an overview of global climate change assessment methods, including impact assessment and integrated assessment. Impact assessment uses a relatively straightforward comparison of with and without situations; integrated assessment attempts to improve on impact assessment by developing more complex models that incorporate a range of feedbacks and interrelationships.

Boorman, D. B., and C. E. M. Sefton. 1997. "Recognising the Uncertainty in the Quantification of the Effects of Climate Change on Hydrological Response," Climatic Change, Vol. 35, No. 4, April, pp. 415-434.
ABSTRACT: A widely used method of evaluating effects of climate change on flow regime is to perturb the climate inputs to a rainfall-runoff model and examine the effect on a statistic of the modelled flows. Such studies require four elements: a method of perturbing the climate, a rainfall-runoff model, a study catchment and a flow index. In practice the direction and magnitude of the estimated effects depend on each of the four elements, leading to concern over the usefulness and generality of the results. To investigate these uncertainties two climate scenarios and eight climate sensitivity tests have been applied to three UK catchments using two conceptual rainfall-runoff models in order to quantify effects of climate change on three flow indices representing mean runoff, flood magnitudes and low flows. The sensitivity tests were found to be useful to assess the suitability of the models to simulate flows outside the conditions experienced in their calibration. Both models gave internally consistent results but, on close examination, one model was found inappropriate for this application. Results show that the effect of climate change on flow varies between catchments and that different flow response indices can change in opposite directions, e.g. floods increased in magnitude while low flows reduced. Contrasting results were obtained from the two climate scenarios.

Rind, D., C. Rosenzweig, and R. Goldberg. 1992. "Modelling the hydrological cycle in assessments of climate change," Nature, 358, pp. 119-123.
ABSTRACT: Climate change caused by increasing atmospheric concentrations of greenhouse gases may have important effects on water circulation and availability and thus on agriculture, forestry and river flow, with significant economic consequences. A variety of models are being used to evaluate hydrological effects, but their hydrological responses to global warming are often inconsistent. Improved understanding of basic hydrological processes is needed if we are to assess the impact of future climate change.

Miscellaneous Hydrology Studies

Loáiciga H.A. 2003. "Climate Change and Ground Water," Annals of the Association of American Geographers, Vol. 93, No. 1, March, pp. 30-41.
ABSTRACT: This article summarizes the theory of climate change and the relationship of climate-change forcing to hydrologic and aquifer processes. It focuses on regional aquifer systems and on the methods to link large-scale climate-change processes to ground-water recharge and to simulate ground-water flow and solute transport in a warmer, 2xCO2 climate. The article reviews methods currently available to generate climate-change forcing and to simulate regional aquifer systems under ensuing hydrologic conditions. In addition, it outlines the development of a methodology to quantify the effects of climate change and of changes in ground-water use by population growth on hydrologic response. An example illustrates a specific procedure and our current capabilities and limitations to assess the potential impacts of a warming climate and population growth on regional-scale aquifer systems. The results indicate that aquifer exploitation strategies must take into account climatic variability and climate-change patterns. During protracted drought, the competition between human and ecological water uses is sharply accentuated. Changes in ground-water use may affect aquifer response more profoundly than climate change associated with modern global warming.

Stefan, H. G., X. Fang, and M. Hondzo. 1998. "Simulated Climate Change Effects on Year-Round Water Temperatures in Temperate Zone Lakes," Climatic Change, Vol. 40, No. 3-4, December, pp. 547-576.
ABSTRACT: A deterministic, one-dimensional model is presented to simulate daily water temperature profiles and associated ice and snow covers for dimictic and polymictic lakes of the temperate zone. The lake parameters required as model input are surface area (As), maximum depth (HMAX), and Secchi depth (zs), the latter, used as a measure of light attenuation and trophic state. The model is driven by daily weather data and operates year-round over multiple years. The model has been tested with extensive data (over 5,000 temperature points). Standard error between simulated and measured water temperatures is 1.4°C in the open water season and 0.5°C in the ice cover season. The model is applied to simulate the sensitivity of Minnesota lake water temperature characteristics to climate change. The projected climate changes due to a doubling of atmospheric CO2 are obtained from the output of the Canadian Climate Center General Circulation Model (CCC GCM) and the Goddard Institute of Space Studies General Circulation Model (GISS GCM). Simulated lake temperature characteristics have been plotted in a coordinate system with a lake geometry ratio (As0.25/HMAX) on one axis and Secchi depth on the other. The lake geometry ratio expresses a lake's susceptibility to stratification. By interpolation, the sensitivity of lake temperature characteristics to changes of water depth and Secchi depth under the projected climate scenarios can therefore be obtained. Selected lake temperature characteristics simulated with past climate conditions (1961-1979) and with a projected 2 × CO2 climate scenario as input are presented herein in graphical form. The simulation results show that under the 2 × CO2 climate scenario ice formation is delayed and ice cover period is shortened. These changes cause water temperature modifications throughout the year.

Qin Boqiang, and Qun Huang. 1998. "Evaluation of the Climatic Change Impacts on the Inland Lake - A Case Study of Lake Qinghai, China," Climatic Change, Vol. 39, No. 4, August, pp. 695-714.
ABSTRACT: A catchment model coupled with a lake thermal model has been used to simulate the lake water balance of Lake Qinghai, a large inland lake on the northeast Qinghai-Tibet Plateau in China. The sensitivity analyses show that changes in precipitation will produce larger changes in runoff than temperature and cloudiness, whereas changes in lake level are equally sensitive to changes in temperature and precipitation. With a doubling of CO2 in the atmosphere, four GCMs experiments predict warmer and wetter conditions in the Qinghai region than at present. The total runoff in the lake basin and evaporation will, in most cases, increase as conditions become warmer and wetter. The lake level changes would remain uncertain because the effects of an increase in precipitation are countered by the rise of temperature.

Bonell, M. 1998. "Possible Impacts of Climate Variability and Change on Tropical Forest Hydrology," Climatic Change, Vol. 39, No. 2-3, July, pp. 215-272.
ABSTRACT: The paper initially outlines selected uncertainties influencing climate change and their linkages with hydrology which have led to only a small section of the hydrological community (divided into 2 groups) being pro-active. Due to the foregoing uncertainties, the strategy adopted in this paper will be to focus on the principal conclusions from controlled experimental catchment studies and related process hydrology connected with land-use change arising from anthropogenic influences. The underlying philosophy is that even major natural disruptions to climate cause ecohydrological shifts in the response of landscapes and such changes may be indicated from recent hydrology research evaluating man-made impacts. The paper assesses the existing conclusions from hydrological work undertaken in both the closed forests of the humid tropics and the open forests of the tropical semi-arid regions based mostly from experimentation in headwater catchments. Such studies are concerned with the hydrological responses to the impacts of forest conversion on the change in total water yield and, in turn, the processes connected with dry weather flow (delayed flow) and storm runoff (quickflow). By taking the above approach, possible hydrological changes to climate change will be inferred, including some consideration given the outputs from atmospheric General Circulation Models (GCMs) using the Amazon basin as an example.