Jeremy S. Pal

Projected changes in mean and extreme precipitation over the Mediterranean region from a high resolution double nested RCM simulation

[1]xa0Results are presented from high resolution climate change simulations over the Mediterranean region using the ICTP Regional Climate Model, RegCM3. Two sets of multi-decadal simulations are performed at 20-km grid spacing for present day and future climate (IPCC A2 scenario). We analyze changes in precipitation mean and extremes and find that the change signal shows seasonally dependent fine scale structure in response to the topographic forcing and changes in circulation, especially over the Alpine region and the Iberian, Italian and Hellenic peninsulas. In winter, the mean precipitation change is positive in the Northern Mediterranean regions and negative in the Southern Mediterranean, while precipitation in the other seasons mostly decreases (especially in summer), except over some localized areas. Changes in extreme precipitation events and dry spells suggest not only shifts, but also a broadening, of the precipitation distribution, with an increased probability of occurrence of events conducive to both floods and droughts.

Consistency of recent European summer precipitation trends and extremes with future regional climate projections

[1]xa0Summer climate over Europe in recent decades has been characterized by a drying trend and by the occurrence of especially devastating drought and flood events, such as in the summers of 2002 and 2003. We compare these trends with results from regional climate model simulations of future climate over Europe under increased greenhouse gas concentrations (GHG). We find that the projected changes in mean summer precipitation and large-scale circulations are remarkably consistent with the observed changes in recent decades. Although we cannot directly attribute the observed changes to an anthropogenic GHG forcing, this result suggests that the observed drying trend over most of Europe might continue in the future. Our experiments additionally indicate substantial changes in the intensity and persistence of summer drought and flood. We identify the Central Mediterranean and Central/Western Europe to be especially vulnerable to increases in both summer drought and flood.

Convection suppression criteria applied to the MIT cumulus parameterization scheme for simulating the Asian summer monsoon

[1]xa0It is shown in this study that applying some convection suppression criteria to the MIT or Emanuel cumulus parameterization scheme may significantly improve the performance of a regional climate model to simulate the Asian summer monsoon precipitation, particularly the precipitation over southeastern China and the Mei-yu rainband over the East Asian region. With the original MIT cumulus scheme, the precipitation over the ocean particularly the South China Sea (SCS) region is generally over-estimated, which may result in the under-estimation of precipitation over China. It is found that the relative vorticity criterion (which shuts down the convection when the low-level flow is anticyclonic and stronger than a certain threshold value) has the largest impact on suppressing the over-estimated precipitation over the SCS.