Jun 20, 1990

Potential evapotranspiration and the likelihood of future drought

by
Rind, D., Goldberg, R., Hansen, J., Rosenzweig, C., Ruedy, R.
,
Journal of Geophysical Research: Atmospheres
  • Studies the likelihood of drought based on two drought indices calculated from the Goddard Institute for Space Studies general circulation model (GISS GCM) transient and doubled CO2 climate changes
  • Uses the Palmer drought severity index (PDSI) and a supply-demand index (SDDI), the latter being the difference between the precipitation and potential evapotranspiration Ep, i.e., the difference between atmospheric supply of and demand for moisture
  • Finds that both indices show increasing drought for the United States during the next century, with effects becoming apparent in the 1990s
  • Model results suggest that if greenhouse gas emissions continue to increase rapidly, severe drought (5% frequency today) will occur about 50% of the time by the 2050s
  • Results are driven by the large increase in EP, associated with the simulated climate warming. EP increases most where the temperature is highest, at low to mid-latitudes, while precipitation increases most where the air is coolest and easiest to saturate by the additional moisture, at higher latitudes
  • Finds atmospheric demand becomes greater than supply for most of the globe by the latter half of next century
  • Shows that large EP changes can lead to soil moisture deficits, as in the PDSI hydrologic budget, and vegetation desiccation, as is implied by vegetation and climate models
  • Suggests that drought intensification has been understated in most GCM simulations, including the GISS GCM, because of their lack of realistic land surface models
  • Reviews paleoclimate analogues in the Mesozoic and Cenozoic, which imply that arid conditions can result from either increased temperatures or decreased precipitation, consistent with the SDDI
  • ​States the results depend primarily on the temperature increase, in particular the model sensitivity of 4°C warming for doubled CO2
  • States global precipitation cannot keep pace with increased demand over land because the land surface warms more than the ocean surface; this effect, along with greater atmospheric opacity, reduces low level gradients and evaporation from the ocean
  • States that if the forecast temperature changes come to pass, these conclusions suggest that drought conditions will increase dramatically