Natural Hazards

, Volume 29, Issue 2, pp 229–254

Changes in Global Monsoon Circulations Since 1950

  • T. N. Chase
  • J. A. Knaff
  • R. A. PielkeSr.
  • E. Kalnay

DOI: 10.1023/A:1023638030885

Cite this article as:
Chase, T.N., Knaff, J.A., Pielke, R.A. et al. Natural Hazards (2003) 29: 229. doi:10.1023/A:1023638030885


We examined changes in several independent intensity indices of four majortropical monsoonal circulations for the period 1950–1998. Theseintensity indices included observed land surface precipitation andobserved ocean surface pressure in the monsoon regions aswell as upper-level divergence calculated at severalstandard levels from the NCAR/NCEP reanalysis. These values wereaveraged seasonally over appropriate regions of southeastern Asian, western Africa, eastern Africa and the Australia/Maritime continent and adjacent ocean areas. Asa consistency check we also examined two secondary indices: mean sea level pressure trends and low level convergence both from theNCEP reanalysis.

We find that in each of the four regions examined, a consistentpicture emerges indicating significantly diminished monsoonalcirculations over the period of record, evidence of diminished spatialmaxima in the global hydrological cycle since 1950. Trends since 1979,the period of strongest reported surface warming, do not indicate any change inmonsoon circulations. When strong ENSO years are removed from each of the time series the trends still show a general, significant reduction of monsoon intensity indicating that ENSO variability is not the direct cause for the observed weakening.

Most previously reported model simulations of theeffects of rising CO2 show an increase in monsoonal activity withrising global surface temperature. We find no support in these datafor an increasing hydrological cycle or increasing extremes as hypothesized bygreenhouse warming scenarios.


Copyright information

© Kluwer Academic Publishers 2003

Authors and Affiliations

  • T. N. Chase
    • 1
  • J. A. Knaff
    • 2
  • R. A. PielkeSr.
    • 3
  • E. Kalnay
    • 4
  1. 1.Cooperative Institute for Research in Environmental SciencesUniversity of ColoradoBoulderUSA
  2. 2.Cooperative Institute for Research in the AtmosphereColorado State UniversityFt. CollinsUSA
  3. 3.Department of Atmospheric ScienceColorado State UniversityFt. CollinsUSA
  4. 4.Department of MeteorologyUniversity of MarylandCollege ParkUSA