Multi-model Analysis of Time of Emergence in Regional Precipitation Changes

Abstract

We have conducted an updated “Time of Emergence” (ToE) analysis of regional precipitation changes over the global land using multiple Global Climate Models in the Coupled Model Inter comparison Project Phase 5 (CMIP5). ToEs were estimated for 14 selected hotspots under two seasons [April to September (AS) and October to March (OM)] and we compared ToEs from three RCP scenarios representing low (RCP2.6), medium (RCP4.5), and high (RCP8.5) emissions. Results from RCP8.5 indicate that ToEs are expected to occur before 2040 over three northern high latitude regions, East Africa (OM wettening), and South Asia (AS wettening), and to occur in the mid-21st century (2040 2080) over Mediterranean (both OM and AS drying), South Africa (AS drying), and East Asia (AS wettening). In order to measure possible benefits from taking low emission scenarios, ToE differences were examined between RCP2.6 scenario and RCP4.5 and RCP8.5 scenarios. Significant ToE delay from 26 years to longer than 65 years was identified over East Africa (OM wettening), Mediterranean (both AS and OM drying), South Asia (AS wettening), and South Africa (AS wettening). We further investigated ToE differences between CMIP3 based and CMIP5 based models using the same number of models for the comparable scenario pairs (SRESA2 vs. RCP8.5, and SRESB1 vs. RCP4.5). Considerable differences in ToEs (more than 20 years) appeared in East Asia and South Asia (AS wettening) and South Africa (AS drying), which are found due to stronger signals in CMIP5 models than in CMIP3 models. Our results provide useful information on the timing of emerging signals in the regional and seasonal hydrological changes, having important implications for associated adaptation and mitigation plans.