Simulation of Seasonal and Decadal-Scale Variability in the Caspian Sea

W. Paul Budgell
Dept. of Physics and Physical Oceanography, Memorial University of Newfoundland, Canada

Ralf Toumi, Catherine Reifen, Andrew Singleton, and James Farley Nicholls
Department of Physics, Imperial College, United Kingdom

The Caspian Sea, the world’s largest enclosed water body, has exhibited dramatic variations in sea level over the past century. Future climate projections from IPCC AR4 model results indicate that the Caspian Sea Level (CSL) may fall by as much as 8 m. Such a drop in the CSL would dry nearly the whole Northern Basin of the Caspian, with dire environmental implications.

Before attempting to downscale future climate scenarios for the Caspian, we wish to understand previous swings in the CSL and to develop confidence that we can reproduce the variability in the Caspian Sea physical environment under existing climate conditions. To examine seasonal and decadal-scale behaviour of the Caspian Sea, a hindcast simulation is conducted for the period 1958-2001 using the coupled ice-ocean Regional Ocean Modelling System (ROMS) forced with ERA40 atmospheric reanalysis data. Using available river disharge data and a conventional bulk flux algorithm for latent heat transfer produced a bias in CSL trend of +6 cm/yr. The sensitivity of the Caspian water balance to evaporation of river runoff downstream of gauging stations, enhanced evaporation due to wave action, mesoscale variability in air-sea fluxes and changes in Caspian surface area are addressed.