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Climate change is likely to severely affect the economies of countries in the Arabian Peninsula and make their populations vulnerable to weather extremes. This study aimed to investigate the changes in future temperature and precipitation extreme indices over the Arabian Peninsula using regional climate model simulations for the future time slices mid-century (2036-2065) and end-century (2071-2100) with respect to the reference period (1976-2005). For this purpose, three Global Climate Models (GCMs) simulations from the WCRP Coupled Model Intercomparison Project phase 5 (CMIP5) are downscaled over the Arabian Peninsula using the International Centre for Theoretical Physics (ICTP) Regional Climate Model (RegCM4). The results show that the warm days/nights (TX90p/TN90p) will increase more than 50% over most parts of the Arabian Peninsula. Warm spell duration index (WSDI) will increase over the Arabian Peninsula while the cold spell duration index (CSDI) will decrease in the mid-century under the high-emission scenario. The number of cold days/nights (TX10p/TN10p) will decrease over most parts of the Arabian Peninsula in the middle of the 21st century. The number of very wet days will increase over the whole Arabian Peninsula under both scenarios (RCP4.5 and RCP8.5). Towards the end-century, it will decrease in the central and southern regions under both scenarios. Heavy rainfall days will increase over the Arabian Peninsula in the mid-century. By the end-century, the number of heavy-precipitation days will mix of decrease and increase depending on region to region and model to model. Overall, the extreme precipitation is projected to increase rather than decrease at the endcentury under both scenarios. The number of consecutive dry days (CDD) will increase over a large area of central and western Arabian Peninsula under the moderate scenario in the mid-century while it will decrease under the high-emission scenario. The present findings indicate that a careful interpretation of climate projections is needed for policy purposes as well as for climate change impact and adaptation related studies. [ABSTRACT FROM AUTHOR]

Sudan is one of the most vulnerable countries to climate change in the African Sahel region. Given the urgent need to understand the potential behaviour of the future climate, this study assessed the skill of 32 global climate models (GCMs) from the fifth (CMIP5) and the sixth (CMIP6) phases of the Coupled Model Intercomparison Project (CMIP) in simulating summer monsoon precipitation over Sudan for the period 1946–2005. The models were ranked based on the Skills Score, estimated using three statistical metrics, correlation coefficient, index of agreement, and normalized root mean square error. The best performing models and their ensembles were used for long‐term trend quantification, empirical orthogonal function (EOF) analysis, and assessment of precipitation associations with atmospheric circulation. GISS‐E2‐H, IPSL‐CM5A‐MR, and MPI‐ESM‐LR of CMIP5 and BCC‐CSM2‐MR, INM‐CM4‐8, and MPI‐ESM1‐2‐LR of CMIP6 showed the best performance in Sudan. Instead of August's unimodal peak rainfall, the GCMs, especially the CMIP5 GCMs, showed an unrealistic rainfall peak in May and a shift of the August rainfall peak to September. Only the CMIP6 multi‐model ensemble reliably reproduced the unimodal rainfall property. All models of both phases failed to reconstruct the dominant mode of monsoon precipitation as determined using EOF analysis, particularly in the country's southern parts. The models also failed to reproduce the long‐term rainfall trends in different climate zones. Only MPI‐ESM‐LR (CMIP5) and MPI‐ESM1‐2‐LR (CMIP6) were successful in simulating monsoon rainfall associations with sea surface temperature, El Niño‐Southern Oscillation teleconnection, and winds components at 850 hPa. [ABSTRACT FROM AUTHOR]

The potential predictability and skill of boreal winter (December to February: DJF) precipitation over central-southwest Asia (CSWA) is explored in six models of the North American Multimodel Ensemble project for the period 1983–2018. The seasonal prediction data for DJF precipitation initialized at Nov. (Lead-1) observed initial condition is utilized. The potential skill is estimated by perfect model correlation (PMC) method, while observed real skill is calculated by the temporal anomaly correlation coefficient (TCC). The main focus is over the Northern Pakistan (NP: 68°–78°E, 31°–37°N), which is a dominant winter precipitation sub-region in CSWA. All participating models generally capture the observed climatological pattern and variation in winter precipitation over the region. However, there are some systematic biases in the prediction of the climatological mean DJF precipitation, specifically an overestimation of precipitation over the foothills of the Himalayas in all models. The substantial internal atmospheric variability (noise) in the seasonal mean (signal) means that the regional winter precipitation is poorly predictable. The NCEP climate forecast system (CFSv2) and two Geophysical Fluid Dynamics Laboratory models (FLOR-A and FLOR-B) show the lowest potential and real skill. The COLA and NASA models show moderate but statistically significant PMC and TCC values. Each model captures the observed relationship between spatially averaged DJF precipitation over NP, with sea surface temperature (SST) and 200 hPa geopotential height (Z200), in varying details. The COLA and NASA models skillfully matched the observed teleconnection patterns, which could be a reason for their good performance as compared to other models. It also found that SSTs in the tropical oceans are relatively well predicted by NASA model when compared with other models. A critical outcome of the predictive analysis is that the multimodel ensemble (MME: A combination of six models and 79 members) does not show many advantages over the individual models in predicting boreal winter precipitation over the region of interest. Together, these results indicate that reliable prediction of the boreal winter precipitation over CSWA remains a big challenge in initialized models. [ABSTRACT FROM AUTHOR]

The interannual precipitation variability over Western Himalaya–Karakoram–Hindukush (WHKH) region has a significant impact on the freshwater resources, energy and agriculture sectors. Midlatitude storms play the role of an atmospheric bridge between large-scale circulation patterns and regional precipitation distributions during the winter (December–April) season. In this study, we investigated long-term changes between El Niño Southern Oscillation (ENSO) and storm activity as well as between ENSO and for precipitation, over WHKH for the period 1950–2015. The Melbourne University Objective Cyclone Identification and Tracking Scheme is used to track the midlatitude storms. A non-linear relationship is identified between the storm track frequency and precipitation over the WHKH region. The correlation between the storm frequency and precipitation increases significantly (95%) after the 1980s and reaches a maximum value of 0.53. Furthermore, 21-year running correlations also show non-linear relationships between ENSO and WHKH's precipitation as well as for storm tracks frequency. The simultaneous correlation between storm tracks frequency (precipitation) and Niño3.4 index was insignificant 0.03 (0.25) in the earlier period from 1950 to 1979, which surged to 0.47 (0.60) in recent 30-years period from 1986 to 2015. Composites and regression analysis illustrate that ENSO modulated the midlatitude storm tracks over the WHKH region, which in turns impact more precipitation anomalies in the recent 30-years period. Moreover, Saudi King Abdulaziz University Atmospheric General Circulation Model (Saudi-KAU AGCM) also confirms the change in the relationship between ENSO and WHKH precipitation variability during the winter season between the two periods. These findings may have important implications for the seasonal rainfall predictability of the WHKH region. [ABSTRACT FROM AUTHOR]

In this study, we examined the relationship between the mid-latitude circulation and the extended winter (November–February) precipitation over the Arabian Peninsula by using observational and NCEP/NCAR reanalysis data (1948–2012). Special emphasis is given to a mid-latitude circumglobal wave train (CGT) that is known to influence the precipitation in the northern hemisphere during both winter and summer seasons. We found a linkage between mid-latitude CGT and winter precipitation over the Arabian Peninsula. The CGT wavelike pattern is associated with anomalous trough above western parts and high pressure over eastern parts of Arabian Peninsula. At lower levels, the CGT is associated with anomalous low over northwestern and high over southeastern parts of the Arabian Peninsula and adjacent parts of the Arabian Sea. The anomalous circulation is further associated with a precipitation pattern over the Arabian Peninsula entailing significantly enhanced precipitation over the central and northwestern parts and reduced precipitation over southeastern parts of the Arabian Peninsula. We further examined the global teleconnection pattern using a precipitation index summarizing winter precipitation over the Arabian Peninsula. The upper-level signature associated with the precipitation index resembles the CGT-like wave pattern with anomalous low over northwestern parts and high over southeastern parts of the Arabian Peninsula. The imprint of the CGT on winter precipitation over the Arabian Peninsula is distinct from that of the North Atlantic Oscillation (NAO), despite the two modes of variability bear some similarities in their upper-level atmospheric pattern above the Arabian Peninsula. [ABSTRACT FROM AUTHOR]

In this paper, a nonhydrostatic Weather Research and Forecasting (WRF) model has been used to simulate the extreme precipitation event of 25 November 2009, over Jeddah, Saudi Arabia. The model is integrated in three nested (27, 9, and 3 km) domains with the initial and boundary forcing derived from the NCEP reanalysis datasets. As a control experiment, the model integrated for 48 h initiated at 0000 UTC on 24 November 2009. The simulated rainfall in the control experiment depicts in well agreement with Tropical Rainfall Measurement Mission rainfall estimates in terms of intensity as well as spatio-temporal distribution. Results indicate that a strong low-level (850 hPa) wind over Jeddah and surrounding regions enhanced the moisture and temperature gradient and created a conditionally unstable atmosphere that favored the development of the mesoscale system. The influences of topography and heat exchange process in the atmosphere were investigated on the development of extreme precipitation event; two sensitivity experiments are carried out: one without topography and another without exchange of surface heating to the atmosphere. The results depict that both surface heating and topography played crucial role in determining the spatial distribution and intensity of the extreme rainfall over Jeddah. The topography favored enhanced uplift motion that further strengthened the low-level jet and hence the rainfall over Jeddah and adjacent areas. On the other hand, the absence of surface heating considerably reduced the simulated rainfall by 30% as compared to the observations. [ABSTRACT FROM AUTHOR]

This study examines the influence of mid-latitude circulation on the wet season (October-May) Dust Storm Activity (DSA) over the northern Arabian Peninsula for the period of 1983-2013, using observational and reanalysis gridded datasets. Dusty and clear days composites of the 200 hPa geopotential height anomalies reveal a pattern in the upper-levels which is strongly correlated with the mid-latitude circumglobal wave train (CGT) and exists 3 days prior to the outbreak of dust storms. The regional surface conditions (such as the mean sea level pressure; low-level temperature and winds, etc.) that favor the DSA over the northern Arabian Peninsula display significant correlations with the CGT on intraseasonal time scale. A time-lagged analysis reveals that the eastward propagating CGT influences the surface pressure over the northern Arabian Peninsula and adjacent areas—hence the DSA. The DSA over the northern Arabian Peninsula is found to be more frequent during the positive phase of the North Atlantic Oscillation (NAO) and the cold phase of the El Niño-Southern Oscillation (La Niña), and less frequent during the negative phase of NAO and the warm phase of the El Niño-Southern Oscillation (El Niño). [ABSTRACT FROM AUTHOR]

ABSTRACT: This study examines the effects of convective parameterization schemes (CPSs) on the simulated June–September (JJAS) precipitation climatology, variability and predictability over southwestern Arabian Peninsula and northeast Africa during 1981–2014 within an atmospheric global climate model framework. The three CPSs used are: the simplified Arakawa–Schubert (SAS) scheme; the SAS scheme with Tokioka modification (STOK) and the Emanuel (EMAN) scheme coupled with a probability distribution function‐based cloud parameterization scheme. SAS and STOK overestimate JJAS total precipitation over the selected domain compared to observations, while EMAN underestimates. EMAN provides the most realistic distribution of precipitation and spatial distribution of convective precipitation despite the tendency for underestimating the total precipitation. The principal patterns of precipitation variability (as measured by the leading empirical orthogonal functions) in EMAN and STOK are clearly related to the observed pattern, while the maximum variability in SAS occurs in a completely different location. The El Niño Southern Oscillation‐related JJAS precipitation teleconnection simulated by the SAS scheme is very weak as compared to observations and other two CPSs. The signal‐to‐noise ratio estimated by SAS and STOK is very low as compared to EMAN. Correlation analysis shows that EMAN performs better than the other two CPSs. Low (high) outgoing longwave radiation (OLR) values are indicative of enhanced (suppressed) convection and hence more (less) cloud coverage. The root mean square error estimated for OLR in EMAN is lower than that of the other two CPSs. The vertical structure of specific humidity and temperature shows less error in EMAN than that of the other two CPSs, which could be a reason for better predictability over the region of interest. [ABSTRACT FROM AUTHOR]

Durations of monthly precipitation wet and dry spells are calculated using historical records and regional climate model (RCM) simulations for the Wadi Al-Lith basin in western Saudi Arabia. The characteristics of durations of wet and dry spells are based on the 50% risk level corresponding to the monthly records for average regional precipitation. The duration of wet spells in the model data is compared with observations for the base period 1971–2000. The impact of climate change on the durations of wet and dry spells is obtained using three global climate models projections with RCP4.5 and RCP8.5 scenarios downscaled by RCM. The probability distribution functions (PDFs) of the climate model scenarios and the precipitation records for the base period prove that climate change has a clear impact on the durations of wet and dry spells over the study area. There is an increase in wet spells frequency in the far future (2070–2099) compared to the near future (2020–2049). The increase in wet spells can be partly explained by the increase in extreme rainfall events and by the decrease in dry spells expected to occur over the study area towards the end of 21st century. [ABSTRACT FROM AUTHOR]

The current study presents the future projection of temperature and precipitation based on ensemble from Couple Model Intercomparison Project 5 (CMIP5) at seasonal and annual time scales over the Arabian Peninsula. Various analysis methods and techniques including spatial plots with robustness analysis, line plots with likelihood spread, and bar plots as well as annual cycles with likelihood ranges of both temperature and precipitation have been employed. The Northern Arabian Peninsula (NAP) region shows an increase in projected signal of temperature higher than the Southern Arabian Peninsula (SAP). Moreover, the northwestern part of NAP shows a large decrease in precipitation for both the RCP4.5 and RCP8.5 scenarios. However, the SAP region shows a great increase in precipitation for both the scenarios. Further, the central, southern and eastern parts of Saudi Arabia also show a tendency of increase in precipitation. Moreover at annual time scale, NAP shows a consistent statistically significant (95% level) decreasing trend of precipitation at the rate of 0.66% (− 1.18/− 0.14 for RCP4.5/RCP8.5) per decade, whereas SAP shows statistically significant (99% level) increasing trend in precipitation at the rate of 1.67% (0.34/2.99 for RCP4.5/RCP8.5) per decade, while the precipitation significant (99% level) increasing trend 0.86% (− 0.27/2.00 for RCP4.5/RCP8.5) per decade over the Arabian Peninsula. The significant (99% level) warming is projected 0.42 °C (0.23 °C/0.60 °C for RCP4.5/RCP8.5) and 0.37 °C (0.20 °C/0.53 °C for RCP4.5/RCP8.5) per decade over NAP and SAP respectively, which is 0.39 °C (0.22 °C/0.57 °C for RCP4.5/RCP8.5) per decade over the whole Peninsula. Our results call for the development of immediate actions and policies in order to combat negative impacts of climate change over the Arabian Peninsula. [ABSTRACT FROM AUTHOR]

Northern Hemisphere winter precipitation reforecasts from the European Centre for Medium Range Weather Forecast System-4 and six of the models in the North American Multi-Model Ensemble are evaluated, focusing on two regions (Region-A: 20°N-45°N, 10°E-65°E and Region-B: 20°N-55°N, 205°E-255°E) where winter precipitation is a dominant fraction of the annual total and where precipitation from mid-latitude storms is important. Predictability and skill (deterministic and probabilistic) are assessed for 1983-2013 by the multimodel composite (MME) of seven prediction models. The MME climatological mean and variability over the two regions is comparable to observation with some regional differences. The statistically significant decreasing trend observed in Region-B precipitation is captured well by the MME and most of the individual models. El Niño Southern Oscillation is a source of forecast skill, and the correlation coefficient between the Niño3.4 index and precipitation over region A and B is 0.46 and 0.35, statistically significant at the 95 % level. The MME reforecasts weakly reproduce the observed teleconnection. Signal, noise and signal to noise ratio analysis show that the signal variance over two regions is very small as compared to noise variance which tends to reduce the prediction skill. The MME ranked probability skill score is higher than that of individual models, showing the advantage of a multimodel ensemble. Observed Region-A rainfall anomalies are strongly associated with the North Atlantic Oscillation, but none of the models reproduce this relation, which may explain the low skill over Region-A. The superior quality of multimodel ensemble compared with individual models is mainly due to larger ensemble size. [ABSTRACT FROM AUTHOR]

A new closure and a modified detrainment for the simplified Arakawa-Schubert (SAS) cumulus parameterization scheme are proposed. In the modified convective scheme which is named as King Abdulaziz University (KAU) scheme, the closure depends on both the buoyancy force and the environment mean relative humidity. A lateral entrainment rate varying with environment relative humidity is proposed and tends to suppress convection in a dry atmosphere. The detrainment rate also varies with environment relative humidity. The KAU scheme has been tested in a single column model (SCM) and implemented in a coupled global climate model (CGCM). Increased coupling between environment and clouds in the KAU scheme results in improved sensitivity of the depth and strength of convection to environmental humidity compared to the original SAS scheme. The new scheme improves precipitation simulation with better representations of moisture and temperature especially during suppressed convection periods. The KAU scheme implemented in the Seoul National University (SNU) CGCM shows improved precipitation over the tropics. The simulated precipitation pattern over the Arabian Peninsula and Northeast African region is also improved. [ABSTRACT FROM AUTHOR]

An ensemble from different climate projections is essential for attaining robust climate change information in a particular region. To achieve this purpose, the results of an ensemble combining the Global Climate Models data from Couple Model Intercomparison Project 3 (CMIP3), have been employed for the Arabian Peninsula region. Different analysis methods comprising spatial plots with robustness analysis, bar plots with likelihood ranges, as well as line plots with likelihood spread along with decadal trend analysis have been carried out at annual as well as seasonal time scales for temperature and precipitation. Results of CMIP3 data for the B1, A1B and A2 scenarios indicate robust changes in temperature and precipitation in the future climate. Spatial plots show a robust summer temperature increase over the whole Peninsula which is higher in the summer season as compared to the winter. The Northern Arabian Peninsula (NAP) region also shows a higher temperature increase in comparison with the Southern Arabian Peninsula (SAP) during the summer season. Moreover the NAP region, which generally comes under the influence of disturbances originating from the Mediterranean Sea region during the winter season, has shown a robust decrease in precipitation during the winter season. Contrarily the SAP region, which remains dry during the winter season and comes under the influence of South Asian Summer Monsoon in the summer season, indicates a robust increase in precipitation during the summer season. This behavior is also obvious from bar plots, which show a gradual decrease (increase) in median precipitation values towards the end of the 21st century for all the three scenarios over the NAP (SAP) region during the winter (summer) season. Moreover, smaller lengths of full as well as likely ranges in the bar plot for NAP (SAP) shows that these precipitation projections are less uncertain as compared to SAP (NAP) for the winter (summer) season. Furthermore from the line plots, a consistent decreasing trend in precipitation (1.35% per decade, significant at 99%) can be observed, while SAP shows an increasing trend in precipitation (1.21% per decade, significant at 99%). Similarly for the case of temperature, a significant (99% level) increase is projected over NAP and SAP regions with values of 0.37 and 0.35 °C per decade respectively. Considering the vulnerability of the region to climate change impacts, these results call for immediate actions in developing the long-term strategies to deal with the adverse impacts of climate change up-to the end of the 21st century at a regional level. [ABSTRACT FROM AUTHOR]

ABSTRACT A climatic regionalization of Saudi Arabia that aims to classify the country into several homogenous groups is carried out, by grouping similar long-term climatological features for precipitation and air temperature. Twenty-seven stations are selected across Saudi Arabia for the analysis and 1985-2010 (26 years) is chosen as the common period. The employed methodology is a combination of mathematical and statistical techniques (principal components analysis and correlation); and a rather subjective physically detailed comparison with the long-term climatology and topography for Saudi Arabia. Five groups have been identified: group A (Northern), B (Red Sea Coastal), C (Interior), D (Highland) and E (Southern). Each of the climatic groups exhibits a unique feature (with strong similarities among stations that belong to the same group), especially in terms of inter-annual fluctuations and the degree of seasonality. This simplified overview of climatic characteristics is beneficial for assisting with economic planning, especially for any semi-arid or arid land that is naturally vulnerable to climatic variability and extremes. The classification method used in this study, however, would be applicable for similar studies on regionalization in other regions. [ABSTRACT FROM AUTHOR]

Multidecadal variations in the relationship between El Niño-Southern Oscillation (ENSO) and the Arabian Peninsula rainfall are investigated using observed data for the last 60 years and various atmospheric general circulation model (AGCM) experiments. The wet season in the Arabian Peninsula from November to April was considered. The 6-month averaged Arabian rainfall was negatively correlated with ENSO for an earlier 30-yr period from 1950 to 1979 and positively correlated to ENSO for a more recent period from 1981 to 2010. The multidecadal variations can be attributed to the variations in Indian Ocean SST anomalies accompanied by ENSO. In the early 30-yr period, ENSO accompanied relatively large SST anomalies in the Indian Ocean, whereas in the recent 30-yr period it accompanied relatively small SST anomalies in the Indian Ocean. The atmospheric anomalies in the Arabian region during ENSO are combined responses to the Pacific and Indian Ocean SST anomalies, which offset each other during ENSO. The recent El Niño events accompanied negative 200-hPa geopotential height (GH) anomalies over the Arabian region, mainly forced by the Pacific SST anomalies, resulting in an increase of precipitation over the region. In contrast, in the early 30-yr period, Indian Ocean SST anomalies played a dominant role in the atmospheric responses over the Arabian region during ENSO, and the negative GH anomalies and more precipitation over the Arabian region were mainly forced by the negative SST anomalies over the Indian Ocean, which appeared during La Niña. These observed findings are confirmed by various AGCM experiments. [ABSTRACT FROM AUTHOR]

A mass flux closure in a general circulation model (GCM) was developed in terms of the mean gradient Richardson number (GRN), which is defined as the ratio between the buoyancy and the shear-driven kinetic energy in the planetary boundary layer. The cloud resolving model (CRM) simulations using the tropical ocean and global atmosphere-coupled ocean-atmosphere response experiment forcing show that cloud-base mass flux is well correlated with the GRN. Using the CRM simulations, a mass flux closure function is formulated as an exponential function of the GRN and it is implemented in the Arakawa-Schubert convective scheme. The GCM simulations with the new mass flux closure are compared to those of the GCM with the conventional mass flux closure based on convective available potential energy. Because of the exponential function, the new closure permits convective precipitation only when the GRN has a sufficiently large value. When the GRN has a relatively small value, the convection is suppressed while the convective instability is released by large-scale precipitation. As a result, the ratio of convective precipitation to total precipitation is reduced and there is an increase in the frequency of heavy precipitation, more similar to the observations. The new closure also improves the diurnal cycle of precipitation due to a time delay of the large GRN with respect to convective instability. [ABSTRACT FROM AUTHOR]

ABSTRACT In this article, climate parameters (rainfall and temperature) are simulated for Saudi Arabia by downscaling the European Centre for Medium-Range Weather Forecasts ( ECMWF) 40-year reanalysis ( ERA40) and the European Community − Hamburg Atmospheric Model ( ECHAM5) data using the UK Met Office Regional Climate Model PRECIS (Providing REgional Climates for Impacts Studies). Simulations are performed for a present climate of 30 years (1971-2000) using ERA40 and ECHAM5, and future climate is predicted for a period of 50 years (2021-2070) using ECHAM5 A1B emissions scenario. The results show that the spatial distribution of the present-day rainfall and temperature simulated by PRECIS are consistent with the observed dataset. In addition, their annual cycle and interannual variability are reasonably well reproduced. The dry precipitation and warm temperature biases exhibited in the driving fields (compared with the observations) are reduced because of the improvements in specific humidity and in the wind field within the PRECIS simulations compared with the driving fields. The projection using the calibrated national average temperature exhibits a positive trend in mean temperature of around 0.65 °C per decade. For rainfall projection, the results show that the coastal areas along the central parts of the Red Sea and the south-southwestern areas of Saudi Arabia may experience more extreme rainfall events, whereas the northern and central parts of the country may undergo a drying trend. © 2013 The Authors. International Journal of Climatology published by John Wiley & Sons Ltd on behalf of the Royal Meteorological Society. [ABSTRACT FROM AUTHOR]

We investigate the dust radiative forcing and its feedback on the Arabian Peninsula's wet season climate using the International Centre for Theoretical Physics-Regional Climate Model (ICTP-RegCM4). We have found that the dust plumes exert a negative (positive) radiative forcing at the surface (top of the atmosphere) by reducing incoming solar radiation reaching the ground and locally heating up the atmosphere column. Consequently, the surface air temperature is cooler, hence indicating a decrease in the warm bias and an increase in the temperature gradient. This reduces the geopotential heights and enhances the low-level wind convergence, suggesting stronger upward motion. These changes increase evaporation, the difference between precipitation and evaporation in the atmosphere and rainfall over the Peninsula, indicating an intensification of the hydrologic cycle. The decrease in the precipitation dry bias and the large reduction in the temperature warm bias caused by the impact of dust over the entire Peninsula represent a significant success for the RegCM4 simulation. Therefore, the inclusion of dust in the simulation of the Arabian Peninsula's climate for the wet season contributes to an improved performance of this regional climate model over the region. [ABSTRACT FROM AUTHOR]

Abstract: Attempts are made to study the seasonal climatology of the Arabian Peninsula, including the regional to station level information for Saudi Arabia for the period 1979–2009. The wet (November to April) and dry (June to September) season rainfall and temperature climatology are obtained from various data sources, namely, surface observations, CPC Merged Analysis of Precipitation (CMAP), Climatic Research Unit (CRU) and Tropical Rainfall Measuring Mission (TRMM). These gridded datasets detect the dry zone over the Rub Al-Khali, the world''s largest sand desert, during the wet season. In this season, large rain belts exist north of 30°N and south of 15°N. During the dry season, the Arabian Peninsula is almost entirely dry north of 15°N but rain belts exist below this latitudinal boundary. Irrespective of the season or dataset used, a relatively heavy-rain area is obtained for the southwest of the Peninsula. The wet (dry) season temperature is highest over the western (middle to the northern) parts of the Peninsula. Surface observations indicate that, irrespective of season, rainfall insignificantly increased in the first period (1979–1993), and then significantly decreased in the second period (1994–2009). The decrease rate is 35.1mm (5.5mm) per decade during the wet (dry) season. The temperature over Saudi Arabia has increased significantly, and the increase rate is faster (0.72°C per decade) in the dry season compared to the wet season (0.51°C per decade). [Copyright &y& Elsevier]

This study examines the relative contribution of extreme daily precipitation events (RR > 99th percentile) to accumulated rainfall over the Arabian Peninsula in current and future climates. Both gridded observations and model simulation data are analyzed. Observations reveal that the extreme daily precipitation events contribute nearly 40% (70%) to the accumulated amount of rainfall in the wet (dry) regions of the Peninsula for the period 1970–1999. The regional climate model simulations show a large overestimation of the annual mean rainfall in the present climate. However, the model data also depicts almost an enhanced contribution of extreme daily precipitation events to the accumulated rainfall over the Peninsula. In agreement with observations, the simulated extreme precipitation events show a small (large) contribution to total rainfall in the wet (dry) regions. The relative contribution of extreme daily precipitation events to total rainfall increases over the southern and central parts of the Peninsula in case of the future climate. We also found an increase in the accumulated amount of simulated precipitation associated with extreme events in the future climate when compared to the reference period. This indicates that extreme events are likely to become more intense over the Peninsula in the future. The results indicate an increase in daily precipitation intensities over the Arabian Peninsula in the future. The results presented in this study highlight that a better understanding of extreme precipitation events and their regional distribution over the Arabian Peninsula currently and in the future is essential for judicious socio-economic planning for the region. Contribution of extreme precipitation events (RR > 99th percentile) to the total precipitation amount over four sub-regions in the Arabian Peninsula at the present and future climate under two RCPs. Unlabelled Image • Analyzed the contribution of extreme daily precipitation to total amount over the Arabian Peninsula. • Extreme precipitations are obtained from observed and climate model simulations. • Contribution of extreme daily precipitation to total amount will increases over southern/central Arabian Peninsula. • Extreme events are likely to become more intense over the Arabian Peninsula in the future. • An increase in daily precipitation intensities over the Arabian Peninsula in the future. [ABSTRACT FROM AUTHOR]

An assessment of the Extreme Precipitation Events (EPEs) is important because of their potential impacts on the local livelihood, ecosystem, and water resource management. In the present study, the EPEs are defined by applying a non-parametric (95th percentile) approach over different climatic regions of Saudi Arabia using observed daily precipitation data for the period 1984–2016 obtained from 27 meteorological stations. The frequency, composite and correlation analyses are performed to evaluate the statistics of EPEs and their teleconnections. During the wet season (Nov-Apr), the frequency of the EPEs (≥25 mm/day) are higher over northeastern, central and southwestern coastal parts of Saudi Arabia. The composites and correlation analyses show that the EPEs over Saudi Arabia are associated with mid-latitude circumglobal wave train (CGT), which evolves a few days before the onset of EPEs and decays afterwards. The CGT modulates the upper-level trough over the Arabian Peninsula (AP) along with the surface anomalous low-pressure system that enhances moisture convergence, favoring the occurrence of EPEs over the region. The EPEs over Saudi Arabia are also associated with El Niño Southern Oscillation (ENSO), which shows that during the positive (negative) ENSO phase the frequency of EPEs increases (decreases) over the country. Moreover, the El Niño (with positive CGT) enhances the EPEs frequency over Saudi Arabia while vice-versa happens for La Niña (with negative CGT) phase. Unlabelled Image • EPEs are defined using observed station data over Saudi Arabia during wet season. • Frequency, composite and correlation analysis performed for the identified EPEs. • EPEs are higher over northeastern, central and southwestern parts of Saudi Arabia. • EPEs over Saudi Arabia are associated with circumglobal wave train (CGT). • ENSO also influences EPEs by altering moisture dynamics. [ABSTRACT FROM AUTHOR]