Changes in precipitation extremes projected by a 20-km mesh global atmospheric model

摘要

Abstract High-resolution modeling is necessary to project weather and climate extremes and their future changes under global warming. A global high-resolution atmospheric general circulation model with grid size about 20?km is able to reproduce climate fields as well as regional-scale phenomena such as monsoonal rainfall, tropical and extratropical cyclones, and heavy precipitation. This 20-km mesh model is applied to project future changes in weather and climate extremes at the end of the 21st century with four different spatial patterns in sea surface temperature (SST) changes: one with the mean SST changes by the 28 models of the Coupled Model Intercomparison Project Phase 5 (CMIP5) under the Representative Concentration Pathways (RCP)-8.5 scenario, and the other three obtained from a cluster analysis, in which tropical SST anomalies derived from the 28 CMIP5 models were grouped. Here we focus on future changes in regional precipitation and its extremes. Various precipitation indices averaged over the Twenty-two regional land domains are calculated. Heavy precipitation indices (maximum 5-day precipitation total and maximum 1-day precipitation total) increase in all regional domains, even where mean precipitation decrease (Southern Africa, South Europe/Mediterranean, Central America). South Asia is the domain of the largest extreme precipitation increase. In some domains, different SST patterns result in large precipitation changes, possibly related to changes in large-scale circulations in the tropical Pacific. Keywords Heavy precipitation ; Climate change ; High-resolution ; GCM prs.rt("abs_end"); 1. Introduction Both too much water and too little water are of great concern for human life because the contrasts in precipitation between wet and dry regions and between wet and dry seasons are projected to increase in a coming future world (Intergovernmental Panel on Climate Change (IPCC), 2013 ). Warmer climate should theoretically lead to more precipitation extremes due to increasing atmospheric water vapor content ( Allen and Ingram, 2002 and Allan and Soden, 2008 ). The intensity of precipitation extremes, however, depends on not only water vapor content but also on atmospheric environmental changes ( O'Gorman and Schneider, 2009 ). Based on global climate model (GCM) simulations of the Coupled Model Intercomparison Project Phase 3 (CMIP3, Meehl et al., 2007 ), it is assessed that the frequency of heavy precipitation or the proportion of total rainfall from heavy rainfalls will likely increase in the 21st century over many areas of the globe ( IPCC, 2012 ). The same assessment was made with the CMIP5 ( Taylor et al., 2012 ) models under Representative Concentration Pathways (RCPs) such that extreme precipitation events over most of the mid-latitude land masses and over wet tropical regions will very likely become more intense and more frequent by the end of this century, as global mean surface temperature increases ( IPCC, 2013 ). The CMIP5 models have better performance than the previous CMIP3 models in simulating precipitation extremes in the present climate ( Sillmann et al., 2013a ). A part of this improvement may come from increasing horizontal resolution, about 280?km in CMIP3 versus about 200?km in CMIP5. Spatial distribution of precipitation indices is reasonably reproduced but differences are still found in precipitation intensity where the magnitude of precipitation extremes is underestimated by climate models ( Sillmann et al., 2013a and Mehran et al., 2014 ). In a future warming world, change rate of heavy precipitation amounts will generally increase more than that of annual mean precipitation ( Tebaldi et al., 2006 , Sun et al., 2007 and Sillmann et al., 2013b ). The increasing rate of annual mean precipitation at the end of the 21st century projected by CMIP5 models in RCP8.5 scenario is 9% (median value), while that in simple daily intensity index (SDII) defined as annual total precipitation divided by the number of wet days is 12% and that in annual maximum 5-day precipitation total (R5d) is 20% ( Sillmann et al., 2013b ). This increasing rate depends on the scenario, where the change ratio of R5d is 6% in RCP2.6 and 10% in RCP4.5, respectively. Similarly, 20-year or 50-year return values of daily precipitation are projected to increase and 20-year or 50-year return periods for the present precipitation events will reduce in the future almost everywhere except for subtropical dry regions ( Kharin et al., 2013 and Toreti et al., 2013 ). The 20-year return values increase about 6% per a degree change in annual mean surface temperature, but with considerable inter-model variability ( Kharin et al., 2013 ). Large variability is also known among models in simulated increase of precipitation extremes, particularly in summer when organized convection matters ( Toreti et al., 2013 ). Both thermodynamical and dynamical factors are responsible for regional precipitation changes, with the former