Robust late twenty-first century shift in the regional monsoons in RegCM-CORDEX simulations

Abstract

We use an unprecedented ensemble of regional climate model (RCM) projections over seven regional CORDEX domains to provide, for the first time, an RCM-based global view of monsoon changes at various levels of increased greenhouse gas (GHG) forcing. All regional simulations are conducted using RegCM4 at a 25 km horizontal grid spacing using lateral and lower boundary forcing from three General Circulation Models (GCMs), which are part of the fifth phase of the Coupled Model Inter-comparison Project (CMIP5). Each simulation covers the period from 1970 through 2100 under two Representative Concentration Pathways (RCP2.6 and RCP8.5). Regional climate simulations exhibit high fidelity in capturing key characteristics of precipitation and atmospheric dynamics across monsoon regions in the historical period. In the future period, regional monsoons exhibit a spatially robust delay in the monsoon onset, an increase in seasonality, and a reduction in the rainy season length at higher levels of radiative forcing. All regions with substantial delays in the monsoon onset exhibit a decrease in pre-monsoon precipitation, indicating a strong connection between pre-monsoon drying and a shift in the monsoon onset. The weakening of latent heat driven atmospheric warming during the pre-monsoon period delays the overturning of atmospheric subsidence in the monsoon regions, which defers their transitioning into deep convective states. Monsoon changes under the RCP2.6 scenario are mostly within the baseline variability.

Assessing mean climate change signals in the global CORDEX-CORE ensemble

“…Based on the CORDEX-CORE ensemble, increases as well as decreases are projected for the far future, highlighting the large uncertainty for precipitation changes in this region. Additionally, a robust shift in the timing of monsoon is noted, which is attributed to pre-monsoon drying (Ashfaq et al 2020). Similarly, Dash et al (2015) linked the decreases in a previous RegCM experiment to weaker monsoon circulations.…”

Topographic Controls on the Distribution of Summer Monsoon Precipitation over South Asia

“…It is important to note that MTD remains negative in all months in a given year except during summer season. Before the onset of rainy season in South Asia, rate of tropospheric warming in the north exceeds than that in the south due to pre-monsoon precipitation (Ashfaq et al 2017(Ashfaq et al , 2020. As a result, the difference between north and south starts diminishing.…”

“…All modified topography experiments exhibit weaker MTD right from the beginning of the summer monsoon season (June 1). It should be noted that pre-monsoon precipitation is mostly convective, which is distributed along the slopes of HKH (Ashfaq et al, 2017), in contrast to the monsoon season where precipitation is widespread and the fraction of stratiform precipitation also increases due to the presence of organized precipitation systems (Ashfaq et al, 2020;Schumacher and Houze, 2003). An obvious impact of the removal of the TP and other elevated surfaces is the entertainment of dry and cold air, which makes conditions inefficient for moist convection.…”

“…Numerical modeling studies demonstrate that land-sea thermal contrast is often sufficient for the arrival of monsoon rains over land (e.g., Wu et al 2012); however, a multitude of factors may determine the extent of subsequent meridional progression. Take an example of West and East African (Australian) monsoons that extend up to ~ 20° N (~ 20° S) (Ashfaq et al 2020;Almazroui et al 2020b) and do not have any elevated surfaces in their north (south). The northward extent of South Asian monsoon is not very different from these monsoons when it is stripped of its elevated surfaces (Figs.…”

Projected Changes in Temperature and Precipitation Over the United States, Central America, and the Caribbean in CMIP6 GCMs

“…An anthropogenic footprint is also detectable in the greater frequency of multivariate extremes, such as droughts (Diffenbaugh et al 2015) and wildfires (Radeloff et al 2018;Abatzoglou and Williams 2016). Studies suggest that continued greenhouse gas emissions will lead to further warming, along with long-term changes in all components of the climate system, increasing the likelihood of widespread and potentially irreversible impacts on social and ecological Published in partnership with CECCR at King Abdulaziz University systems (IPCC 2014;Sillmann et al 2013;Pu et al 2020;Christensen et al 2013;Fischer and Knutti 2016;Easterling et al 2017;Diaconescu et al 2018;Giorgi et al 2018;Moreno et al 2019;Veas-Ayala et al 2018;Oppenheimer et al 2019;Ashfaq et al 2020;Cook et al 2020;Wang et al 2020a, b). These expected changes in climate characteristics will likely intensify the regional hydrological cycle (Ashfaq et al 2013;Naz et al 2016), exacerbate the risk of water stress in the regions where river runoff is dominated by snowmelt (Pagan et al 2016), and increase the population's exposure to climate extremes (Batibeniz et al 2020).…”