ESSL LAR

Kevin Trenberth

 

Senior Scientist
TIIMES - CGD
WCAS

 

Contact Information:
PO Box 3000, Boulder, CO 80307-3000
Office: ML - 120a
Telephone: 303-497-1318
Email: trenbert@ucar.edu
Home Page | FY07 Abstracts

Kevin Trenberth
 

Project Summary:

 

Large-scale moisture in the climate system and models

Components of the hydrological cycle studied include water vapor, precipitation (amount, frequency, intensity, type), evapotranspiration (evaporation plus transpiration from plants), soil moisture, runoff, streamflow and river discharge into the oceans (Qian et al. 2006, 2007), atmospheric moisture flows and divergence, and atmospheric moisture storage.  The historical records and model simulations were analyzed to examine any changes associated with global warming in the water cycle, such as potential drying over land.   

Hydrological CycleClick on picture to view the entire figure.


Fig. 1. The hydrological cycle. Estimates of the main water reservoirs, given in plain font in 103 km3, and the flow of moisture through the system, given in slant font in103 km3/yr, equivalent to Exagrams (1018 g) per year. (Trenberth et al. 2006a).

 A detailed study of the hydro-meteorology of the Mississippi river basin (Qian et al. 2007) utilizes both the energy and water budget constraints to put together a physically consistent picture of trends in the region.  Trends from 1948 to 2004 in cloud and precipitation have reduced the solar energy available for evaporation (“dimming”) and thus potential evaporation (or pan evaporation), but increased soil moisture has increased evapotranspiration as the actual evaporation has risen to become closer to the potential amount, even as runoff and streamflow have also increased.  Diminished solar radiation is offset by reduced outgoing longwave radiation and the increased surface wetness has led to an increase in latent at the expense of a decrease in sensible surface heat flux.

A new estimate has been made of the global hydrological cycle for long-term annual means that includes estimates of the main reservoirs of water as well as the flows of water among them (Trenberth et al. 2007), see Fig. 1.  In addition, the mean annual cycle of the atmospheric hydrological cycle based on 1979 to 2000 data includes monthly estimates of P, evapotranspiration E, atmospheric moisture convergence over land, and changes in atmospheric storage, for the major continental land masses, zonal means over land, hemispheric land means and global land means.  The evapotranspiration was computed from the Community Land Model run with realistic atmospheric forcings, including precipitation constrained by observations for monthly means but with high frequency information taken from atmospheric reanalyses.  Results for P-E from ERA-40 reanalyses show physically unrealistic results, especially in the tropics and subtropics.  Effects of climate change on the hydrological cycle and precipitation are explored in Rasmussen et al. (2007). An analysis of time series after 1948 reveals that the Mount Pinatubo volcanic eruption in 1991 was followed by record low land precipitation and river runoff (Trenberth and Dai 2007) that was so low it must have been associated with the volcanic aerosol forcing.

 

Tropical cyclones and climate

Hurricane KatrinaClick on picture to view the entire figure.

Fig. 2. For 1800 UTC 28 August to 0600 UTC 29 August 2005, hours 42 to 54 of the simulation, given are (left) the azimuthally-averaged precipitation (mm/h), and (right) column integrated moisture convergence and surface latent heat flux as a function of radius for the control (red) and changes in SST of +1°C (blue) and -1°C (green). The precipitation and latent heat fluxes are area averages from the eye to the radius plotted to be compatible with the moisture convergence across that cylinder radius. (Trenberth et al. 2007b).

Another major topic has been the energy and water cycles of hurricanes and their role in the climate system.

One study has computed how much moisture that ends up as rain in hurricanes comes from local evaporation in the storm versus large-scale convergence (Trenberth et al. 2007a).  This has been analyzed in a model framework using WRF at high resolution for realistic simulations run for observed storms, in particular Ivan in 2004 and Katrina in 2005.

Tropical cyclones - Hurricane KatrinaClick on picture to view the entire figure.


Fig. 3. Based on best track data for the tropical cyclones observed each year classified by maximum wind speed, the total surface energy loss by the global ocean is given based on Katrina simulated fluxes within 400 km of the eye of the storms as given by (2) as latent (blue), sensible (cyan) and total enthalpy (black) flux in 1021 Joules per year. Also given in green (right hand scale) is the precipitation in the same units. The dotted lines are linear trends. Trenberth and Fasullo (2007).

Models sensitivity runs have also been made with SSTs increased and decreased by 1°C.  Results demonstrate the overwhelming dominance of moisture convergence into the storms, in spite of the critical role of the surface evaporative source (see Fig. 2), and have implications for the changing environment on hurricanes as climate changes.  These model results have been related empirically to the maximum sustained wind in the model and the results used with the “best track” global observed data on tropical cyclones to deduce how surface fluxes and precipitation in  hurricanes have changed since 1970 (Trenberth and Fasullo 2007), see Fig. 3.  Hurricanes play a key role in climate and that role is increasing over time as SSTs rise.

 

References
Qian, T., A. Dai, K. E. Trenberth, K. W. Oleson, 2006: Simulation of global land surface conditions from 1948 to 2004: Part I: Forcing Data and Evaluations. J. Hydrometeorol., 7, 953-975.

Qian, T., A. Dai, and K. E. Trenberth, 2007: Hydroclimatic trends in the Mississippi river basin from 1948 to 2004.  J. Climate, 20, 4599-4614.

Rasmussen, R., A. Dai, K. E. Trenberth, 2007: Impact of climate change on precipitation. Chapter 16. Large-scale Disasters: Prediction, Control and Mitigation, Gad-el-Hak, Ed., Cambridge University Press, 453-472.

Trenberth, K. E., and A. Dai, 2007: Effects of Mount Pinatubo volcanic eruption on the hydrological cycle as an analog of geoengineering.  Geophys. Res. Lett., 34, L15702, doi:10.1029/2007GL030524.

Trenberth, K. E., C. A. Davis and J. Fasullo, 2007a: The water and energy budgets of hurricanes: Case studies of Ivan and Katrina . J.  Geophys. Res., in press.

Trenberth, K. E., L. Smith, T. Qian, A. Dai and J. Fasullo, 2007b: Estimates of the global water budget and its annual cycle using observational and model data. J. Hydrometeor., 8, 758–769.

Trenberth, K. E., and J. Fasullo, 2007: The water and energy budgets of hurricanes and implications for climate change. J. Geophys. Res., in press.
 

Publications:

Serreze, M. C., A. P. Barrett, A. J. Slater, M. Steele, J. Zhang, K. E. Trenberth, 2007: The large-scale energy budget of the Arctic. J. Geophys. Res., 112, D11122, doi: 10.1029/2006JD008230.

Trenberth, K. E., 2007: Climate Feedback: the climate change blog. Nature.com.

Qian, T., A. Dai, K. E. Trenberth, 2007: Hydroclimatic trends in the Mississippi River Basin from 1948-2004. J. Climate, 20, 4599-4614.

Trenberth, K. E., 2007: The climate in 2057: hot and dry with occasional outpourings of conscience. The Way We Will Be 50 Years From Today, Mike Wallace, Ed., Adler and Robin Books, Inc. (In Press)

Trenberth, K. E., L. Smith, T. Qian, A. Dai, J. Fasullo, 2007: Estimates of the global water budget and its annual cycle using observational and model data. J. Hydrometeorol., 8, 758-769.

Trenberth, K. E., A. Dai, 2007: Effects of Mount Pinatubo volcanic eruption on the hydrological cycle as an analog of geoengineering. Geophys. Res. Lett., 34, L15702, doi: 10.1029/2007GL030524.

Trenberth, K. E., 2007: Warmer oceans, stronger hurricanes. Sci. Amer., 297 (1), 26-33.

Trenberth, K. E., P. D. Jones, P. Ambenje, R. Bojariu, D. Easterling, A. K. Tank, D. Parker, F. Rahimzadeh, J. A. Renwick, M. Rusticucci, B. Soden, P. Zhai, 2007: Observations: Surface and Atmospheric Climate Change. Chapter 3. Climate Change 2007: The Physical Science Basis, IPCC AR4 WG1 Final Report, S. Solomon, D. Qin, M. Manning, Z. Chen, M. C. Marquis, K. B. Avery, M. Tignor, and H. L. Miller, Eds., IPCC, Cambridge University Press, 235-236.

Forster, P., R. Somerville, N. Bindoff, J. Christensen, K. Denman, G. Hegerl, B. Hewitson, E. Jansen, P. Jones, P. Lemke, G. A. Meehl, J. Overpeck, V. Ramaswamy, D. Randall, T. Stocker, K. Trenberth, H. Le Treut, J. Willebrand, R. Wood, F. Zwiers, 2007: Climate with care. New Scientist, 193 (2596), 27, doi: 10.1016/S0262-4079(07)60732-5.

Rasmussen, R., A. Dai, K. E. Trenberth, 2007: Impact of climate change on precipitation. Chapter 16. Large-scale Disasters: Prediction, Control and Mitigation, Mohamed Gad-el-Hak, Ed., Cambridge University Press, 453-472.

Simmons, A., K. E. Trenberth, S. Uppala, 2006: Future needs in atmospheric reanalysis. EOS Trans. Amer. Geophys. Union, 87, 583, 587.

Trenberth, K. E., 2006: Observed changes to the climate and their causes. Chapter 9. Confronting Climate Change: Critical Issues for New Zealand, R. Chapman, J. Boston, and M. Schwass, Eds., Victoria University Press, 93-102, doi: ISBN 0 86473 546 4.

Trenberth, K. E., 2006: The role of the oceans in climate. Flotsam and Jetsam, 35, 1, 5-7.

Trenberth, K. E., B. Moore, T. R. Karl, C. Nobre, 2006: Monitoring and prediction of the Earth's climate: A future perspective. J. Climate (CLIVAR special issue), 19, 5001-5008, doi: 10.1175/JCLI3897.1.

Qian, T., A. Dai, K. E. Trenberth, K. W. Oleson, 2006: Simulation of global land surface conditions from 1948 to 2004. Part I: Forcing data and evaluation. J. Hydrometeorol., 7, 953-975, doi: 10.1175/JHM540.1.

Trenberth, K. E., A. Dai, 2006: Evaluation of the atmospheric water cycle in ERA-40 using observationally-constrained land model results. GEWEX News, 16(2), 8-10, 20.