Changes in the characteristics of ‘wet’ and ‘dry’ Red Sea Trough over the Eastern Mediterranean in CMIP5 climate projections

Abstract

The Eastern Mediterranean resides on the border between the temperate and semi-arid and arid climate zones, and is thus influenced by both mid-latitude and sub-tropical weather systems. Precipitation and extreme weather in this region are mainly associated with either Cyprus Lows or the “wet” Red Sea Troughs. Current regional climate projections indicate that the region may become warmer and drier in future decades. Here, we analyze the influence of enhanced greenhouse gas forcing on the climatological properties of the ‘wet’ and ‘dry’ Red Sea Trough (WRST & DRST, respectively). With this aim, a regional synoptic classification and a downscaling algorithm based on past analogs are applied to eighteen rain stations over the main ground water basins in Israel. The algorithms are applied to the NCEP/NCAR reanalysis data for 1986–2005 and to eight CMIP5 model simulations for the historical (1986–2005) and end of the century (2081–2100) climate conditions according to the RCP8.5 scenario. For the historical period, the CMIP5 models are largely able to represent the characteristics of the Red Sea Trough. Based on the multi-model mean, significant changes are found for WRST and DRST for the late XXI Century. First, an increase in the meridional pressure gradient is found for both the WRST and the DRST, implying stronger horizontal winds. Furthermore, a significant decrease in the occurrence of the WRST (− 20%) and a significant increase in the frequency of the DRST (+ 19%) are identified. Accordingly, the persistence of the WRST decreases (− 9%), while for DRST increases (+ 9%). The decline in the frequency of WRST occurs primarily in the transition seasons, while the increase for DRST is found throughout the wet season. In total, the daily rainfall associated with the WRST system is projected to significantly decline (− 37%) by the end of the XXI century. These results document the projected changes in a dominant synoptic system in this area, which can facilitate a better estimation of the arising challenges, e.g., related to shortage of water resources and associated political unrest, reduced agricultural potential, and increased air pollution and forest fires. Such a pathway can ultimately foster novel mitigation strategies for water resources management and regional climate change adaptation.

ESD Reviews: Extreme Weather and Societal Impacts in the Eastern Mediterranean

“…Climate models consistently project a substantial decrease in the number of Mediterranean cyclones reaching the south-eastern portion of the Mediterranean basin (up to 35% decrease by the end of the 21 st century under the RCP8.5 scenario), along with a decrease in their mean daily precipitation yield (Pinto et al, 2007;Kelley et al, 2012;Zappa et al, 2015a;Hochman et al, 2018aHochman et al, , 2018bHochman et al, , 2020bSamuels et al, 2018). A slight increase in the occurrence frequency of Red Sea Troughs has been reported, accompanied by a decrease of their typical intensities (Zappa et al, 2015a;Hochman et al, 2018aHochman et al, , 2021bSaaroni et al, 2020), although there is still a debate on whether the number of Active Red Sea Troughs is actually decreasing (Hochman et al, 2021b). A decrease in the occurrence frequency of Medicanes is also estimated, together with some evidence for an increase in their intensity (Cavicchia et al, 2014;Romera et al, 2016;Tous et al, 2016;González-Alemán et al, 2019), with yet to be studied impacts on the emerging extremes (e.g., Hosseini et al, 2020).…”

“…5 c, d; e.g., Berkovic, 2017). This situation, often denominated Active Red Sea Trough, has recently received ample attention, particularly since there is an ongoing debate on how an increase in greenhouse gas concentrations will influence the frequency and intensity of this system (Alpert et al, 2004;Peleg et al, 2015a;Saaroni et al, 2020;Hochman et al, 2021b;Marra et al, 2021a). We note here that there is relatively little literature related to the physical understanding, observed trends, and future projections of wind extremes in the southeastern part of the eastern Mediterranean.…”

Identification and classification of the wet Red Sea Trough over Israel

“…These variables were used in previous studies (Kahana et al, 2004 andKrichak et al, 2012, Table 1) but they were effective only in identifying major floods associated with ARSTs, with an annual occurrence of <1 day. Another automatic identification method for WRSTs, relying on analogue fitting, was applied by Hochman et al (2021). Their RST identification was based on the synoptic classification of Alpert et al (2004), upgraded by Saaroni et al (2020) and their study area was the Mediterranean climate region in Israel, not the arid region.…”

“…Two fully automatic methods were developed to identify a WRST. Hochman et al (2021) started with a set of RST days from the period 1986 to 2005, 'the learning period'. The WRST days were selected as a subset, based on rain observations.…”

Evaluation of Geopotential Height at 500 hpa with Rainfall Events: A Case Study of Iraq

“…Rainfall over Iraq is comparable to rainfall in mid-latitudes in that it is mostly influenced by upper-level weather patterns (trough, cut-off low, rex block) that boost the weather system at the surface [6]. Due to global warming, there is a change in the behavior of the synoptic system in the middle east, where there is a decrease in the mid-latitude cyclone [7]. South West Asia countries face a downward trend in annual rainfall, where Iraq is the most affected country and can be regarded as in crisis due to the lack of rainfall [8].…”