This is one of 16 Rapid Response (RAPID) projects funded as the result of a Dear Colleague Letter (NSF 11-006) encouraging diagnostic analyses of climate model simulations prepared for the Intergovernmental Panel on Climate Change Fifth Assessment Report (IPCC AR5). Research conducted in these projects is expected to lead to more detailed model intercomparisons, better understanding of robust model behaviors, and better understanding and quantification of uncertainty in future climate simulations.
This project examines the simulation of the American Monsoon System (AMS) in simulations of the recent past from the Climate Model Intercomparison Project verson 5 (CMIP5). The main goals are to develop an extensive assessment of how realistic simulations are in representing the observed characteristics of the American Monsoon System (AMS) in the recent past, and to assess uncertainties in projected decadal climate changes in the AMS. More specifically, the project
1) Assesses the skill of CMIP5 model simulations in representing the climatological and statistical characteristics of the monsoons in the Americas including: circulation and precipitation features, subseasonal variance, onsets and demises, amplitudes and cross equatorial transitions.
2) Determines which CMIP5 models realistically represent the spatiotemporal variability of the monsoons in the present climate including near-term trends, frequency of very dry/wet seasons and statistical distributions of extreme precipitation events.
3) Examines which CMIP5 models skillfully represent the observed relationships between remote forcings and the American monsoons. These include the Madden-Julian Oscillation (MJO), El Niño/Southern Oscillation (ENSO), North Atlantic Oscillation (NAO), Pacific Decadal Oscillation (PDO), Antarctic Oscillation (AAO), Atlantic Ocean and Intra-Americas Sea forcings.
4) Seeks to determine how much of the climate changes projected for the next decades in the Americas are explained by natural decadal variability and how much by greenhouse gases increases.
The broader impact of the project lies in its support of the IPCC AR5, which is intended to provide information on climate change and its consequences to decision makers worldwide. The AMS affects water resources, agriculture, human health, ecosystems and biodiversity throughout a large and densely populated portion of the Americas. The impact of climate change on the AMS is not known, and this research will help to determine the extent to which models used to project climate change are capable of accurately representing the AMS system and its variability and change over the observed record.
The presence of a monsoonal type of circulation involving intense convective activity and heavy precipitation is the dominant climatic feature in the tropical Americas during the respective summer seasons. The North American monsoon system (NAMS) and the South American monsoon system (SAMS) are often interpreted as the two extremes of the seasonal cycle of heat, moisture transport and precipitation over the Americas. Agriculture, water reservoirs, and hydropowers depend largely on precipitation from the monsoon systems. NAMS peaks between June-August (JJA) and SAMS between December-February (DJF). The SAMS and NAMS seasonal cycles are essentially driven by the differential heating between continent and ocean. The global mean concentration of carbon dioxide and associated atmospheric radiative forcing has dramatically increased in the last decades. These changes have modified the distribution of the atmospheric heating and altered ocean-continent contrasts with consequences to the monsoon circulation and hydrological cycle. The availability of the fifth phase of the Coupled Model Intercomparison Project (CMIP5) simulations provided invaluable data sets to further investigate the future projections of climate change in American monsoon regions. Carvalho and Jones (2013) investigated multiannual changes in the low troposphere (850hPa) temperature (T850), specific humidity (Q850) and daily precipitation over SAMS and NAMS using the National Centers for Environmental Prediction/National Center for Atmospheric Research (2.5o lat/lon grid spacing and during 1 January 1948 to 31 December 2010, NCEP/NCAR-1) and the Climate Forecast System Reanalysis (0.5o lat/lon grid spacing during 1 January 1979-31 December 2010 - CFSR) in addition to CMIP5 simulations for two scenarios: "historic" and high emission representative concentration pathways "RCP8.5". The focus of these analyses was on the magnitude and area extent of the warming and moistening of the tropical Americas. Thus they investigated theT850 and Q850 85th percentiles because these high values are observed in tropical continental areas in the present climate. North America (NA) and South America (SA) were distinctly examined during the peak of the respective monsoon season. The historic simulations (1951-2005) and the two reanalyses agree well and indicate that significant warming has already occurred over tropical SA with the most remarkable increase in the area and magnitude of the 85th percentile in the 1996-2005 decade. The warming is more extensive over eastern Brazil in the region formerly occupied by savanna, which has been consistently replaced by crops and pasture. Most importantly, the RCP8.5 CMIP5 ensemble mean projects a remarkable increase in the T850 85th percentile over SA: about 2.5oC by 2050 and 4.8oC by 2095 relative to 1955. In contrast, the 85th percentile of T850 and Q850 has not significantly increased over the NAMS domain during the 1950-2005 period. However, the RCP8.5 projects that T850 will increase 2.8oC by 2050 and 5.5oC by 2095 relative to 1955. The area of SA (NA) that is observed with T850 ≥ the 85th percentile is projected to increase from ~10% (15%) in 1955 to ~58% (~33%) by 2050 and ~80% (~50%) by 2095. The respective increase in the 85th percentile of Q850 is about 3g/kg over SAMS and NAMS by 2095. CMIP5 models project variable changes in daily precipitation over tropical Americas. The most consistent is increased rainfall in the intertropical convergence zone in DJF and JJA and decreased precipitation over NAMS in JJA. Jones and Carvalho (2013) examined the large-scale characteristics of the SAMS seasonal amplitudes, onset and demise dates, duration and total seasonal precipitation (from the onset to the demise). Changes in the SAMS characteristics were investigated with CFSR reanalyses and CMIP5 simulations for the "historic" and RCP8.5. CMIP5 model simulations for the historical experiment show signals of climate change in South America. The RCP8.5 simulations show significant increases in seasonal amplitudes, early onsets, late demises, and durations of the SAMS. This scenario projects an ensemble mean decrease of 14 days in the onset and 17-day increase in the demise date of the SAMS by 2045–50. However, there is a lack of spatial agreement in model projections of changes in total wet-season precipitation over SA during 2070–2100. The most consistent CMIP5 projections are the increase in the total monsoon precipitation over southern Brazil, Uruguay, and northern Argentina. All these climatic changes will significant impact water resources in SA with implications for agriculture and energy. These researches contributed to the Chapter 14 of the 5th assessment report (AR5) of the International Panel on Climate Change (IPCC). The PIs have incorporated these results into the curriculum of climate classes at UCSB (graduate and undergraduate levels). They convened sessions on climate change in the American Geophysical Union fall and the Meeting of the Americas. They participated in outreach activities directed to 7th grade students in Santa Barbara to increase awareness on climate change and have been invited to give talks in several universities (Alabama at Tuscaloosa, Indiana at Bloomington, San Diego State University, University of Sao Paulo, Brazil) and meetings.
