Aiguo Dai

Scientist II
TIIMES - CGD
WCAS

Contact Information:
PO Box 3000, Boulder, CO 80307-3000
Office: ML-274
Telephone: 303-497-1357
Email: adai@ucar.edu
Home Page

Project Summary:

Click on picture to view the entire figure.

Top: Adapted time series of 20°N to 20°S ERBS non-scanner wide-field-of-view broadband shortwave, longwave and net radiation anomalies from 1985 to 1999 [Wielicki et al., 2002a, 2002b] where the anomalies are defined with respect to the 1985 to1989 period with Edition 3_Rev 1 data [Wong et al., 2006]. Bottom: Time series of the annual water year (Oct. to Sep.); note slight offset of points plotted vs tick marks indicating January) continental freshwater discharge and land precipitation (from Fig. 1) for the 1985 to 1999 period. In both panels, the period clearly influenced by the Mount Pinatubo eruption is indicated by grey shading. (From Trenberth and Dai 2007, GRL)

Aiguo Dai’s TIIMES research is largely through the Water Cycle Program (WCP) under TIIMES. It focuses on the global, continental, and large-scale aspects of the water cycle, such as the variations and changes in precipitation, water vapor, cloudiness, evaporation, soil moisture, streamflow and continental discharge. Another area tied to the focus of the WCP is the diurnal cycle of warm-season precipitation and convection over the U.S. and other continents, and its representation in climate models.

During FY07, Dai authored or co-authored eight refereed journal articles and one book chapter (see CGD Catalog for the abstract and one figure from each paper). Almost all of these studies are related to WCP. Components of the hydrological cycle studied include water vapor (Wang et al., 2006), precipitation (amount, frequency, intensity, type) (Dai et al. 2007, Tian et al. 2007), evapotranspiration, soil moisture, runoff, streamflow and river discharge into the oceans (Qian et al. 2006, 2007; Trenberth and Dai 2007). 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. Major findings from these studies include

1) spatial variations in mean precipitation amount come largely from precipitation frequency rather than intensity;

2) the diurnal cycle of precipitation amount comes mostly from its frequency rather than its intensity over most low and mid-latitudes, with the intensity has only about half of the strength of the diurnal cycle in the frequency and amount;

3) IPCC AR4 models show decreased daily precipitation frequency and increased daily precipitation intensity under CO2-induced global warming, and there is a shift in precipitation frequency distribution towards extremes, resulting in large increases in very heavy precipitation events (>50 mm/day);

4) Analyses of both surface water and energy budgets show that evapotranspiration has increased in the Mississippi River basin from 1948-2004 mainly due to increased precipitation and soil moisture;

5) enhanced snowfall induced by the bias corrections (for under-catch errors) to high-latitude raing-gauge observations increases snow accumulation on the ground (by 6–18 cm for December to February), which in turn increases May to July runoff by 0.4–0.6 mm/day and streamflow by 5–25% for most major rivers in the northern latitudes (north of 45 deg.N); and

6) The eruption of Mount Pinatubo in June 1991 induced a large reduction in precipitation over land and a record decrease in runoff and river discharge into the ocean from October 1991-September 1992, which suggests that major adverse effects, including wide-spread drought and reduced water resources, could arise from geoengineering solutions emulating volcanic eruptions to battle global warming.

For the near future, Dai’s research will continue to focus on precipitation variability including those in satellite observations, streamflow and discharge changes, trends in evapotranspiration, historical and future droughts, and cumulus parameterizations in climate models.

Community Service:

• Advisor on Graduate Research: Hongmei Li, , Institute of Atmospheric Research, Chinese Academy of Sciences, Beijing, PRC
• Advisor on Graduate Research: Xiangjun Tian, , Institute of Atmospheric Research, Chinese Academy of Sciences, Beijing, PRC
• Chair - Organizing Committee for AMS 20th Symposium on Climate Variability and Change, American Meteorological Society (AMS)
• Co-Chair - Organizing Committee for AMS 19th Symposium on Climate Variability and Change, American Meteorological Society (AMS)
• K-12 Activiy: Science Fair Judge, Bear Creek Elementary, Boulder, CO, USA
• Member - AMS Committee on Climate Variability and Change, American Meteorological Society (AMS)
• Member - NASA's Precipitation Science Team, NASA
• Member - NRC's Committee to Review of CCSP Report SAP 1.3, The National Research Council (NRC)
• Member - Overseas Team on Coupled Model Development, Chinese Academy of Sciences

Presentations:

• A Comparison of the Diurnal Cycle of Precipitation in Several High-resolution Satellite Datasets and Surface Observations, San Antonio USA, January 2007
• Applications of Historical Land Simulations for Climate Studies, Beijing CHN, July 2007
• Changes in Continental Freshwater Discharge from 1949-2004, Qingdao CHN, July 2007
• Direct Effects of Modifications to the Cumulus Parameterizations in CAM3, Boulder USA, August 2007
• Drought Research, Boulder USA,August 2007
• Increased Arctic Discharge Linked to Thawing of Permafrost Caused by Surface Warming, Boulder USA, January 2007
• Precipitation Frequency, Intensity and Diurnal Cycle in Satellite and Surface Observations, Atlanta USA, May 2007
• Precipitation Simulations in Global Models, Atlanta USA, May 2007
• The 20th century East Asian summer monsoon simulated by coupled climate models of IPCC AR4, San Antonio USA, January 2007
• The global precipitation diurnal cycle: observations vs. model simulations, Changdu CHN, October 2006
• The Water Cycle in a Warming Climate, Boulder USA, August 2007
• Variations in global freshwater discharge during 1948-2004, Boulder USA, December 2006

TIIMES External Collaborators:

Alan Betts, Atmospheric Research
Paul Dirmeyer, National Science Foundation
John Finnigan, Commonwealth Scientific and Industrial Research Organisation (CSIRO) - Centre for Complex System Science
Kou-Lin Hsu, University of California, Irvine
Anthony Illingworth, University of Reading
Anne Jost, Universite Pierre et Marie Curie
Christian Kummerow, Colorado State University
Xin-Zhong Liang, University of Illinois & Illinois State Water Survey
David Maidment, University of Texas at Austin
Sumant Nigam, University of Maryland
Ronald Smith, Yale University
Daqing Yang, University of Alaska, Fairbanks
Song Yang, George Mason University - NASA
Xiangdong Zhang, University of Alaska, Fairbanks
Tianjun Zhou, Chinese Academy of Science, Institute of Atmospheric Phys.

Publications:

Sun, Y., S. Solomon, A. Dai, R. Portmann, 2007: How often will it rain? J. Climate. (In Press)3

Wang, J., L. Zhang, A. Dai, T. VanHove, J. Van Baelen, 2007: A near-global, 2-hourly data set of atmospheric precipitable water from ground-based GPS measurements. J. Geophys. Res., 112, D11107, doi: 10.1029/2006JD007529.2

Tian, X., A. Dai, D. Yang, Z. Xie, 2007: Effects of precipitation-bias corrections on surface hydrology over northern latitudes. J. Geophys. Res., 112, D14101, doi: 10.029/2007JD008420.

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

Dai, A., X. Lin, K.-Y. Hsu, 2007: The frequency, intensity, and diurnal cycle of precipitation in surface and satellite observations over low- and mid-latitudes. Clim. Dyn., doi: 10.1007/s00382-007-0260-y. (In Press)2

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.

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.