Uniform TitleUnderstanding soil moisture dynamics using observations and climate models
NameLi, Haibin (author), Robock, Alan (chair), Reinfelder, Ying Fan (internal member), Broccoli, Anthony (internal member), Milly, Christopher (outside member), Rutgers University, Graduate School-New Brunswick,
DescriptionWith the objective to improve our understanding of soil moisture and its long term changes, I analyzed and compared climate model simulations with in situ soil moisture observations. Three studies were conducted to investigate soil moisture variations on seasonal to interannual scales and its long term changes.
To investigate soil moisture evolutions on seasonal to interannual scales and the capacity of reanalysis systems to capture the observed characteristics, I analyzed newly updated 19 yr of Chinese soil moisture data and evaluated ERA40, NCEP/NCAR reanalysis (R-1), and NCEP/DOE reanalysis 2 (R-2). Over this region, soil moisture seasonality is in general not strong. Seasonal cycles and interannual variations exhibit considerably spatial diversity. R-2 generally exhibits improved interannual variability and better seasonal patterns of soil moisture than R-1 as a result of incorporating observed precipitation. ERA40 produces a better mean value of soil moisture for most Chinese stations and good interannual variability. In terms of temporal scale - an indicator of anomaly persistence, R-2 has a memory about twice that of the observations for the growing season. The unrealistic long temporal scale of R-2 can be attributed to the deep layer of the land surface model, which is too thick and dominates the soil moisture variability. The analysis highlights the importance of correct soil parameters to land surface processes and points out possible directions in which the reanalysis can be continuously improved to provide more realistic soil moisture outputs.
Observations from Ukraine and Russia show significant increases in summer for the period from 1958-1999 that seem contradictory to the classic summer drying issue from early modeling studies. To see whether the latest climate models can capture the observed patterns, I calculated trends in soil moisture simulations from Intergovernmental Panel on Climate Change Fourth Assessment climate models. The upward trends in observations, which cannot be explained by precipitation and temperature changes alone, were found to be much larger than most trends in model realizations. Solar dimming is proposed to have played an important role in modulating soil moisture variations for these two regions.
Further, a series off-line sensitivity experiments with a sophisticated land surface model were conducted to investigate possible contribution from solar dimming and elevated CO2 to the observed soil moisture trends for Ukraine and Russia. I demonstrate, by imposing a downward trend to shortwave radiation forcing to mimic the dimming, the observed soil moisture pattern can be essentially reproduced. On the other hand, the effects of elevated CO2 are relatively small for the study period. The results support the hypothesis that solar dimming may have played an important role in regional soil moisture changes.
Note[bibliography] Includes bibliographical references (p. 68-79).
CollectionGraduate School - New Brunswick Electronic Theses and Dissertations
Organization NameRutgers, The State University of New Jersey
RightsThe author owns the copyright to this work.