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Featured Application: The present work studies the difference when assessing the solar energy potential of Saudi Arabia by using the Liu–Jordan (isotropic) and Hay (anisotropic) models. The present work investigated the performance of an isotropic (Liu–Jordan, L–J) and an anisotropic (Hay) model in assessing the solar energy potential of Saudi Arabia. Three types of solar collectors were considered: with southward fixed-tilt (mode (i)), with fixed-tilt tracking the Sun (mode (ii)), and with varying-tilt tracking the Sun (mode (iii)). This was the first time such a study was conducted for Saudi Arabia. The average annual difference between anisotropic (Hay) and isotropic (L–J) estimates is least ≈38 kWhm−2 year−1 over Saudi Arabia for mode (i), and therefore, the L–J model can be used effectively. In modes (ii) and (iii), the difference is greater (≈197 and ≈226 kWhm−2 year−1, respectively). It is, then, up to the solar energy engineer to decide which model is to be used, but it is recommended that the Hay model be utilised for mode-(iii) solar collectors. These results fill a research gap about the suitability of models in practice. An interesting feature for the ratio of the annual mean solar energy yield of Hay over L–J as function of the latitude, φ, and the ground albedo, ρr, is the formation of a "well" for 29° ≤ φ ≤ 31° and 1.15 ≤ ρr ≤ 1. [ABSTRACT FROM AUTHOR]

The objective of the present work is to investigate the optimally performing tilt angles in Saudi Arabia of solar panels that follow the daily motion of the Sun. To that end, the annual energy sums are estimated for surfaces with tilt angles in the range 5°–55° at 82 locations covering all Saudi Arabia. All calculations use a surface albedo of 0.2 and a near-real value, too. It is found that tilt angles of 40°, 45°, and 50°, respectively, are optimal for the three recently defined solar energy zones in Saudi Arabia. The variation of the energy sums in each energy zone on annual, seasonal and monthly basis is given for near-real ground albedos; the analysis provides regression equations for the energy sums as functions of time. A map of the annual global inclined solar energy for Saudi Arabia is derived and presented. The annual energy sums are found to vary between 2159 kWhm−2year−1 and 4078 kWhm−2year−1. Finally, a correction factor, introduced in a recent publication, is used; it is confirmed that the relationship between the correction factor and either the tilt angle or the ground-albedo ratio has a general application and it may constitute a nomogram. [ABSTRACT FROM AUTHOR]

The major objective of the present work is to investigate into the appropriate tilt angles of south-oriented solar panels in Saudi Arabia for maximum performance. This is done with the estimation of the annual energy sums received on surfaces with tilt angles in the range 15°–55° inclined to south at 82 locations covering all Saudi Arabia. The analysis shows that tilt angles of 20°, 25° and 30° towards south are the optimum ones depending on site. These optimum tilt angles define three distinct solar energy zones in Saudi Arabia. The variation of the energy sums in each energy zone on annual, seasonal and monthly basis is given; the analysis provides regression equations for the energy sums as function of time in each case. Furthermore, the spatial distribution of the annual global inclined solar energy in Saudi Arabia is shown in a solar map specially derived. The annual energy sums are found to vary between 1612 kWhm−2year−1 and 2977 kWhm−2year−1 across the country. Finally, the notion of a correction factor is introduced, defined, and employed. This factor can be used to correct energy values estimated by a reference ground albedo to those based on near-real ground albedo. [ABSTRACT FROM AUTHOR]

The summer season (June–July–August) surface air temperatures (SATs) over Saudi Arabia and its association with the atmospheric circulation cells were identified and analysed using the NCEP‐NCAR reanalyses and the NOAA extended reconstructed sea surface temperature (SST) datasets from 1948 to 2016. The pressure vertical velocity and divergent wind were utilized to determine the atmospheric circulation cells such as Hadley, Walker, and Ferrel cells. Possible mechanisms associated with changes in Saudi Arabia summer SAT were investigated, with particular focus on the uppermost and lowermost summers. Changes in SAT are mainly linked to the significant changes in the meridional and zonal atmospheric circulations. Partial correlations between SAT and atmospheric circulation showed that the effect of the Hadley and Walker circulations on the SAT was significant. There is no obvious connection between either the Hadley East Pacific circulation or the Ferrel circulation and SAT. Moreover, there is no dependency between summer SAT and the Atlantic Hadley and Atlantic Walker circulations, which could be detected in the summer season. The Hadley circulation may affect the Indian monsoon depression, whereas the Walker circulation has less effect. Also, a strong relationship between the Indian‐Pacific warm pool (IPWP) and both the Hadley and Walker circulations were found. Simultaneously, IPWP SST influenced Indian monsoon depression. Therefore, the Hadley circulation, Walker circulation, and IPWP all play key roles in the displacement and intensity of the Indian monsoon, which in turn strongly influences SAT variability over Saudi Arabia during summertime. [ABSTRACT FROM AUTHOR]

Climate change is posing severe threats to human health through its impacts on food, water supply, and weather. Saudi Arabia has frequently experienced record-breaking climate extremes over the last decade, which have had adverse socioeconomic effects on many sectors of the country. The present study explores the changes in average temperature and temperature extremes over Saudi Arabia using an updated daily temperature dataset for the period 1978–2019. Also, changes in frequency and percentile trends of extreme events, as well as in absolute threshold-based temperature extremes, are analyzed at seasonal and annual time scales. The results are robust in showing an increase in both temperature trends and temperature extremes averaged over the second period (2000–2019) when compared to the first period (1980–1999). Over the period 1978–2019, the minimum temperature for the country increased (0.64°C per decade) at a higher rate than the maximum temperature (0.60°C per decade). The rate of increase in the minimum and maximum temperatures was reported as 0.48 and 0.71°C per decade, respectively, for the period 1978–2009. The minimum temperature increased by 0.81°C per decade for the second period compared to an increase of 0.47°C per decade for the first period. The significant increase in minimum temperature has resulted in a decreasing linear trend in the diurnal temperature range over recent decades. The maximum (minimum) temperature increased at a higher rate for Jan-Mar (Jun-Nov) with the highest increase of 0.82 (0.89)°C per decade occurring in March (August). The analysis shows a substantial increase (decrease) in the number of warm (cold) days/nights over the second period compared to the first period. The number of warm days (nights) significantly increased by about 13 (21) days per decade, and there is a significant decrease of about 11 (13) days per decade of cold days (nights). The seasonal analysis shows that this increase in warm days/nights is enhanced in boreal summer, with a reduction in the number of cold days/nights in winter. These results indicate that the warming climate of Saudi Arabia is accelerating in recent decades, which may have severe socioeconomic repercussions in many sectors of the country. [ABSTRACT FROM AUTHOR]

The present study evaluates the potential predictability, and prediction skill of surface air temperature (SAT) over the Arabian peninsula (AP) referred to as AP-SAT hereafter, during boreal summer (June–July–August: JJA) from 1982 through 2017. The study was made by considering the single model, and a multimodel ensemble (MME) approach. The seasonal prediction data for JJA SAT initialized at May (Lead-1), and April (Lead-2) observed initial conditions, from six coupled atmosphere–ocean global circulation models included in the North American Multimodel Ensemble, is utilized. The potential predictability (PP) is estimated through the estimation of the signal-to-noise ratio (S/N ratio) and perfect model correlation (PMC), while prediction skill is computed by the temporal anomaly correlation coefficient (TCC). All models show a decrease in potential predictability and prediction skill with an increase in lead time. The CFSv2 and NASA models show higher PP, which indicates a high potential predictive skill for summer AP-SAT in these models. However, both models show quite low values of TCC all over the AP domain, which is an indication of overconfident predictions. The three geophysical fluid dynamics laboratory models show high prediction skill at both leads. An essential finding of the predictive analysis (PMC and TCC) is that the MME does outperform the individual model at both leads for summer AP-SAT. Each model captures the observed relationship between spatially averaged AP-SAT with sea surface temperature (SST) and 200 hPa geopotential height (Z200) during JJA, with varying details. Persistent model biases impact negatively model predictability and skill, and better AP-SAT and SST teleconnection pattern in models lead to higher predictability. Improvements in initial conditions, model physics, and larger ensemble size are necessary elements to enhance the summer AP-SAT potential predictability and skill. [ABSTRACT FROM AUTHOR]

This study compares the precision of the satellite-based Moderate Resolution Imaging Spectroradiometer (MODIS) Deep Blue (DB) Collection–51 (C–51) and Collection–06 (C–06) Aerosol Optical Depth (AOD, at 550 nm) products with surface-based aerosol robotic network (AERONET) observations for the period 2002–2013 at the Solar Village, Saudi Arabia. In general, MODIS captures the patterns of AERONET AOD although C−51 tends to underestimate them while C−06 overestimates them. We found a slightly higher correlation for C–06 (0.79) than for C–51 (0.74) over the Solar Village. The C–06 retrievals are typically of better quality than those of C−51 with a smaller root mean square error (RMSE) and mean absolute error (MAE) and more AODs fall within the expected error range and relative mean bias. Overall, both the C–51 and C–06 MODIS DB algorithms show significant uncertainties and errors. The errors in AOD measurements arise due to imperfect aerosol model schemes and underestimation of surface reflectance over the Solar Village. This study suggests that further quantitative research is required to provide better estimates of satellite-based AOD over Saudi Arabia. • An inter-comparison of MODIS DB C−51 and –06 AOD has been studied. • The AOD data have been taken from 2002 to 2013 over the Solar Village and KAUST. • Both the C–51 and –06 show the significant uncertainties and errors. • The inappropriate aerosol model selection is responsible for the error. • The underestimation of surface reflectance is also responsible for the error. [ABSTRACT FROM AUTHOR]

This paper examined the temperature changes from the COordinated Regional climate Downscaling Experiment (CORDEX) over the Middle East and North Africa (MENA) domain called CORDEX-MENA. The focus is on the Arabian Peninsula in the 21st century, using data from three Coupled Model Intercomparison Project Phase 5 (CMIP5) models downscaled by RegCM4, a regional climate model. The analysis includes surface observations along with RegCM4 simulations and changes in threshold based on extreme temperature at the end of the 21st century relative to the base period (1971–2000). Irrespective of the driving CMIP5 models, the RegCM4 simulations show enhanced future temperature changes for RCP8.5 as compared to RCP4.5. The Arabian Peninsula will warm at a faster rate (0.83°C per decade) as compared to the entire domain (0.79°C per decade) for RCP8.5 during the period 2071–2100. Moreover, the number of hot days (Tmax ≥ 50°C) (cold nights: Tmin ≤ 5°C) will increase (decrease) faster in the Arabian Peninsula as compared to the entire domain. This increase (decrease) of hot days (cold nights) will be more prominent in the far future (2071–2100) as compared to the near future (2021–2050) period. Moreover, the future changes in temperature over the main cities in Saudi Arabia are also projected. The RegCM4-based temperature simulation data from two suitable CMIP5 models are recommended as a useful database for further climate-change-related studies. [ABSTRACT FROM AUTHOR]

Due to the scarcity, randomness, and extremity of rainfall events in arid regions, planning and management of water resources are essential. Rainfall in many arid regions such as Saudi Arabia is characterized by high intensity and short duration during which flash floods occur and cause not only major loss in life and structures but also a huge loss of clean water. Understanding the relationship between rainfall and runoff is the key issue in the management and control of water resources. In this study, two approaches have been applied using Hydrologic Engineering Center’s Hydraulic Modeling System model to simulate flood hydrographs of a mountainous watershed located on the west side of Saudi Arabia. The first approach was based on incorporating losses through the soil conservation service (SCS) curve number and SCS unit hydrograph. The second approach was based on effective rainfall in which excess rainfall was computed by Horton’s infiltration method and the Phi index method. Results revealed that the performance of losses incorporation approach was poor in simulating runoff hydrographs in all studied storms. Its main drawback was the ineffective representation of flow mass conservation and the early generation of runoff due to rainfall input. In contrast, the effective rainfall approach simulated runoff hydrographs efficiently; moreover, results were comparable with many of those reported in the literature. The two critical hydrograph parameters of peak flow and time to peak were simulated accurately by Phi index method and Horton’s infiltration method. The sensitivity analysis showed that the peak flow is directly proportional to the curve number and inversely proportional to the initial abstraction. From water management point of view, the simulated hydrographs added a valuable piece of information about the quantification of lost and stored rainwater. About 55%–70% of rainwater infiltrates through the soil profile and recharges the underlined groundwater reservoir, hence becomes a major source of water in the region. [ABSTRACT FROM AUTHOR]

Groundwater reservoirs are important water resources all over the world. Especially, they are of utmost significance for arid and semi-arid regions, and therefore, a sustainable exploitation of these reservoirs needs to be ensured. The natural and most exclusive water supplier to groundwater reservoirs in Saudi Arabia is rainfall, which is characterized by sporadic and random temporal and spatial distributions, particularly under the impacts of climate change; giving rise to uncertainty in groundwater recharge quantification. Although in Saudi Arabia, intense and frequent rainfall events are rare, but they generate significant flash floods with huge amounts of surface water. Under such circumstances, any simple but effective water storage augmentation facility such as rainwater harvesting (RWH) structures gain vital importance for sustainability of water supply and survivals in arid and semi-arid regions. The objective of this study is to explore the possibility of RWH over a basin in the western province of Saudi Arabia called Wadi Al-Lith under climate change. Climatic data is obtained from the IPCC AR5 GCMs, which is further downscaled using a regional climate model RegCM4 for the Arabian Peninsula domain. The RegCM4 is driven to simulate climatic parameters including rainfall at 25 km grid resolution for the present climate (1971–2000), and future climate (2006–2099) with representative concentration pathways, RCP4.5 and RCP8.5. Results indicate that more durable and longer wet durations are expected with increasing surplus rainfall amounts in the far future because of climate change impacts. Consequently, future climate scenarios are expected to enhance floods and flash floods occurrences, which call for progressive measures to harness the RWH opportunity. [ABSTRACT FROM AUTHOR]

The relationship between the Mediterranean 500-hPa storm tracks and wet season (November-April) rainfall over Saudi Arabia is investigated. The analysis is based on the application of an objective tracking scheme to the 6-hourly 500-hPa geopotential height ERA-Interim dataset (0.75° × 0.75°) for the period 1979-2012. The resulting tracks are then associated with the ERA-Interim rainfall events over Saudi Arabia. The association procedure showed that 34 % of the tracks are related to about 70 % of the rainfall. These associated tracks are used to construct climatology. A climatology of these storm tracks revealed that the eastern Mediterranean region is the preferred location for cyclogenesis with a maximum in the southwest parts of the Black Sea. The study also examined the mean radius, average intensity and average depth of the storms. The number of tracks in winter (December-February) is about 60 % of the total number which confirms the major contribution of the Mediterranean storms to rainfall over Saudi Arabia. A significant negative trend was found for storm cyclogenesis over the central Mediterranean, and the Black sea. A significant trend decrease in track density is observed over most of the northern parts of Saudi Arabia. The peaks of storm activities are observed in December and January in 1996, 1997 and 2009. Storm activity generally declines after 2000, especially in the second half of the wet season months (February-April). [ABSTRACT FROM AUTHOR]

Yanbu, on the Red Sea, is an affluent Saudi Arabian industrial city of modest size. Substantial effort has been spent to balance environmental quality, especially air pollution, and industrial development. We have analyzed six years of observations of criteria pollutants O3, SO2, particles (PM2.5and PM10) and the known ozone precursors—volatile organic compounds (VOCs) and nitrogen oxides (NOx). The results suggest frequent VOC-limited conditions in which ozone concentrations increase with decreasing NOxand with increasing VOCs when NOxis plentiful. For the remaining circumstances ozone has a complex non-linear relationship with the VOCs. The interactions between these factors at Yanbu cause measurable impacts on air pollution including the weekend effect in which ozone concentrations stay the same or even increase despite significantly lower emissions of the precursors on the weekends. Air pollution was lower during the Eids (al-Fitr and al-Adha), Ramadan and the Hajj periods. During Ramadan, there were substantial night time emissions as the cycle everyday living is almost reversed between night and day. The exceedances of air pollution standards were evaluated using criteria from the U.S. Environmental Protection Agency (EPA), World Health Organization (WHO), the Saudi Presidency of Meteorology and Environment (PME) and the Royal Commission Environmental Regulations (RCER). The latter are stricter standards set just for Yanbu and Jubail. For the fine particles (PM2.5), an analysis of the winds showed a major impact from desert dust. This effect had to be taken into account but still left many occasions when standards were exceeded. Fewer exceedances were found for SO2, and fewer still for ozone. The paper presents a comprehensive view of air quality at this isolated desert urban environment. Implications: Frequent VOC-limited conditions are found at Yanbu in Saudi Arabia that increase ozone pollution if NOxis are reduced. In this desert environment, increased nightlife produces the highest levels of VOCs and NOxat night rather than the day. The effects increase during Ramadan. Fine particles peak twice a day—the morning peak is caused by traffic and increases with decreasing wind, potentially representing health concerns, but the larger afternoon peak is caused by the wind, and it increases with increasing wind speeds. These features suggest that exposure to pollutants must be redefined for such an environment. [ABSTRACT FROM PUBLISHER]

The climate of Saudi Arabia is arid-semiarid with infrequent but sometimes intense rainfall, which can cause flooding. Interannual and intraseasonal precipitation variability in the region is related to ENSO and MJO tropical convection. The predictability of these tropical signals gives some expectation of skillful extended-range rainfall forecasts in the region. Here, the extent to which this predictability is realizable in the Climate Forecast System (CFS), version 2, a state-of-the-art coupled global ocean-atmosphere model, is assessed. While there are deficiencies in the forecast climatology likely related to orography and resolution, as well as lead-dependent biases, CFS represents the climatology of the region reasonably well. Forecasts of the areal average of rainfall over Saudi Arabia show that the CFS captures some features of a spring 2013 heavy rainfall event up to 10 days in advance and a transition from dry to wet conditions up to 20 days in advance. Analysis of a 12-yr (1999-2010) reforecast dataset shows that the CFS can skillfully predict the rainfall amount, the number of days exceeding a threshold, and the probability of heavy rainfall occurrence for forecast windows ranging from 1 to 30 days. While the probability forecasts show good discrimination, they are overconfident. Logistic regression based on the ensemble mean value improves forecast skill and reliability. Forecast probabilities have a clear relation with the MJO phase in the wet season, providing a physical basis for the observed forecast skill. [ABSTRACT FROM AUTHOR]

This paper presents a one-year record of in situ air-quality data from nine sites throughout Saudi Arabia. The data set is composed of hourly measurements of ozone (O3), nitrogen dioxide (NO2), and carbon monoxide (CO) at six of the largest cities in Saudi Arabia (Riyadh, Jeddah, Makkah, Yanbu, Dammam, Hafouf) and two remote locations in the mountainous southwestern region of Alsodah for the year 2007. The authors found that international O3and CO standards were routinely exceeded throughout the year at many sites, and that exceedances increased during Ramadan (Sep. 12 – Oct. 13), the Islamic month of fasting when much of normal daily activity is shifted to nighttime hours. In general NO2and CO levels were higher in Saudi cities compared to U.S. cities of comparable population, while O3levels were lower. There was a general trend for O3and NO2to be negatively correlated in Saudi cities in contrast to U.S. cities where the correlation is positive, suggesting that ozone chemistry in Saudi Arabia is limited by volatile organic compound emissions. This may be caused by low biogenic emissions from vegetation. Pollutant levels were lower at most Saudi sites during the four day Hajj period (Dec. 18–21) but higher in Makkah which receives millions of visitors during Hajj. The authors also found that ozone levels were elevated during the weekend (Thursday & Friday) relative to weekday levels despite lower NO2, a phenomenon known as the “weekend effect.” As little air quality data is available from Saudi Arabia in the English-language literature, this data set fills a knowledge gap and improves understanding of air quality in an important but under-reported region of the world. Implications:Air quality measurements at nine sites in Saudi Arabia provide a detailed look at spatial and temporal patterns of ozone (O3), nitrogen dioxide (NO2), and carbon monoxide (CO). NO2 and CO levels increased in most cities during the fasting month of Ramadan, whereas O3 levels decreased. This led to an increased frequency of CO exceedances based on international standards. NO2 and CO also increased in Makkah during the Hajj pilgrimage. In general, NO2 and O3 levels were anticorrelated at most sites, suggesting that O3 chemistry is limited by volatile organic compound emissions throughout much of Saudi Arabia. [ABSTRACT FROM PUBLISHER]

ABSTRACT Long-term changes in seasonal temperature extremes based on daily data across Saudi Arabia for the period 1981-2010 are analysed by assessing the trends for the four conventional seasons. Surface observations of daily maximum and minimum temperatures from high-quality datasets at 27 stations are used as the input. The trend throughout each season is then derived by employing Sen's slope estimator to four extreme value indices, four relative indices and three mean value indices. Warming trends for extreme value indices are observed for the majority of stations, particularly significant (at 95% level) in spring and summer seasons, however, mixed increase/decrease trends are found for the cold temperature extremes in autumn and winter seasons. Relative indices show significant warming trends for the majority of stations in all seasons; however, strong warming (above 5 days decade−1) is witnessed in the spring, summer and autumn seasons. The rapid rise (fall) of the number of warm (cool) days compared to warm (cool) nights is observed in the winter, summer and autumn (winter and spring) seasons. Warming of cool/warm nights is insignificant for the majority of stations in winter. The national average of mean value index diurnal temperature range shows an increasing trend for all seasons; however, its mixed increase/decrease trends are observed for the majority of stations in summer and autumn seasons. Time series analysis reveals that irrespective of seasons, warming is clearly visible in Saudi Arabia after 1997. Variations of warming for different regions across the country are also noticed. [ABSTRACT FROM AUTHOR]

ABSTRACT In characterizing the patterns of climate change across Saudi Arabia, several extreme indices are calculated from station values daily maximum and minimum temperature data. The trend analyses are performed on 13 annual extreme indices for Saudi Arabia, using observations from 27 surface stations with high-quality data for the period 1981-2010. RClimDex is used to calculate the indices, and simple regression methods are employed for the trend analysis. The analyses of extreme temperature indices detected a significant increase in the majority of the stations, which further indicates that the country has experienced a warming trend. The findings show that 92/89% of the stations displayed a significant increase in the annual occurrence of warm days/nights and 96/93% revealed a significant decrease for the occurrence of cool days/nights. Time-series analysis has also shown an important feature of the climate change signal. When the dataset is divided into two sub-periods, the analysis reveals a distinctive long-term trend that clearly distinguishes the two periods. It was found that the temperature extremes (hot and cold) in Saudi Arabia have increased significantly with greater magnitude in the recent-past (1996-2010) compared to the previous period (1981-1995). The most telling evidence for this is the heat- and cold-waves, where indices of both have occurred more frequently in the second part of the two sub-periods. [ABSTRACT FROM AUTHOR]

We study the possible effects of urbanization on the rise of air temperature in Saudi Arabia for the period 1981-2010. The effects of variations in elevation and marine temperature on the air temperature trend are also investigated. Surface air temperature data are analyzed for 24 sites which are mostly located at the airports across the country. The population data for the current (2010) and earlier (2004 and 1992) censuses are used for the nearest cities where the observation sites are located. A national average is calculated using two different approaches (simple averaging and weighted according to area for 1985-2010 when all stations are available) which gives trends of 0.60 and 0.51 °C/decade respectively, both significant at the 99 % level. We find no link between the temperature increase and population increase nor with elevation at the 24 sites which are mostly located in the urban effected area but not at the city centers. This suggests that the rise in air temperature is not likely due to urbanization changes resulting from the population increases. [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]

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 paper investigates the effect of large-scale forcings on the variability of the mean air temperature of Saudi Arabia, using the observed data and the National Centers for Environmental Prediction (NCEP) reanalysis gridded datasets for the period 1978-2010. The analysis shows that the seasonal mean temperature variability is high in the northern and central regions compared to the southern. Moreover, the temperature variability is highest (~30%) in the winter season and lowest (~2 %) in the summer. Following global warming indications, the interannual variability of the mean air temperature of Saudi Arabia indicates a warming phase that started in the late 1990s. The analysis reveals that the strong variability in temperature over Saudi Arabia is closely associated with the North Atlantic Oscillation (NAO) index for all seasons except the autumn; however, the relationship is most prominent during the winter season. The study indicates that the winter season temperature is also influenced by the Arctic Oscillation (AO) index, whereas the spring season temperature is influenced by the El Niño Southern Oscillation (ENSO). This research concludes that the negative phases of ENSO, AO and NAO all play a major role in the temperature increase over most parts of Saudi Arabia. [ABSTRACT FROM AUTHOR]

The rainfall and temperature climatology over the Arabian Peninsula are analysed on an annual basis using various gridded datasets. For Saudi Arabia, the area of which represents almost 80% of the Peninsula, the climatic datasets from its 27 ground observations are analysed for the period 1978-2009, with additional gridded datasets used to describe the observed state and change of the present climate. The gridded datasets represent well the very dry (40-80 mm) area over the world's largest sand desert (Rub Al-Khali), the dry (80-150 mm) area over middle-to-north of Saudi Arabia, and the wettest (>150 mm) region in the southwest of the Peninsula. The annual temperature is relatively high (24-27 °C) in the middle-to-south of the Peninsula and low (<21 °C) in the northwest and southwest. The highest temperature (>27 °C) is obtained over the Rub Al-Khali. Over Saudi Arabia, the observed annual rainfall showed a significant decreasing trend (47.8 mm per decade) in the last half of the analysis period, with a relatively large interannual variability, while the maximum, mean and minimum temperatures have increased significantly at a rate of 0.71, 0.60, and 0.48 °C per decade, respectively. This information is invaluable to consider in any climate impact assessment studies in Saudi Arabia. Copyright © 2012 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

a step towards the adoption and use of the regional climate model (RegCM3) for the simulation of intense rainfall events over the Arabian Peninsula, this study examines its sensitivity to domain size, boundary location, forcing fields, and resolution. In the climatological results, RegCM3 performs well in reproducing the annual and the seasonal mean precipitation as well as the contrast between wet and dry years in terms of the amounts and locations of the rainbands. In addition, simulations are performed for two cases of intense rainfall events in the Jeddah area and surroundings using a combination of three domains and two boundary forcings at 50 km. The results show that different combinations of these parameters provide different skills for the regional model. However, RegCM3 performs relatively better when ERA40 (NNRP2) is used at the boundaries in the smaller domain (larger domain), indicating the importance of the stronger (relatively weaker) influence of boundary forcing needed to capture these intense rainfall events around Jeddah. This may be explained by the fact that around that region, RegCM3 produces, in the smaller domain, higher relative humidity and stronger wind vectors closer to the reanalyses when nested within the ERA40, while it shows its best performance with the larger domain when driven by NNRP2. It is also shown that the use of high resolution does not systematically improve the simulation of such events, although some encouraging results were produced. [ABSTRACT FROM AUTHOR]

Abstract: The short-term rainfall climatology regime over Saudi Arabia is obtained from the Tropical Rainfall Measuring Mission (TRMM) data for the period 1998–2009. The TRMM rainfall amounts are calibrated with respect to the rain-gauge data recorded at 29 stations across the country. Day-to-day rainfall comparisons show that the TRMM rainfall trends are very similar to the observed data trends, even if a general overestimation in the satellite products must be highlighted. Besides, especially during the wet season, some of the TRMM algorithm runs tend to underestimate the retrieved rainfalls. The TRMM rainfall data also closely follow the observed annual cycle on a monthly scale. The correlation coefficient for rainfall between the TRMM and the rain-gauge data is about 0.90, with a 99% level of significance on the monthly scale. The spatio-temporal distributions of rainfall over Saudi Arabia are analyzed. Besides the four conventional seasons, this analysis consider the wet (November–April) and dry (June–September) seasons, based on the rainfall amounts recorded. Spring is the highest and winter is the second highest rainfall-occurring season, resulting in large amounts of rainfall during the wet season over most of the country. Regional variations in the rainfall climatology over Saudi Arabia are studied through defining four regions. The false alarm ratio, probability of detection, threat score, and skill score are calculated to evaluate the TRMM performance. The country''s average annual rainfall measured by the TRMM is 89.42mm, whereas the observed data is 82.29mm. Thus, the rainfall in Saudi Arabia is suggested as being the TRMM value multiplied by 0.93 plus 0.04. After this calibration, the TRMM-measured rainfall is almost 100% of the observed data, thereby confirming that TRMM data may be used in a variety of water-related applications in Saudi Arabia. [Copyright &y& Elsevier]

The observed records of recent decades show increased economic damage associated with flash flooding in different regions of Saudi Arabia. An increase in extreme rainfall events may cause severe repercussions for the socio-economic sectors of the country. The present study investigated the observed rainfall trends and associated extremes over Saudi Arabia for the 42-year period of 1978–2019. It measured the contribution of extreme events to the total rainfall and calculated the changes to mean and extreme rainfall events over five different climate regions of Saudi Arabia. Rainfall indices were constructed by estimating the extreme characteristics associated with daily rainfall frequency and intensity. The analysis reveals that the annual rainfall is decreasing (5.89 mm decade−1, significant at the 90% level) over Saudi Arabia for the entire analysis period, while it increased in the most recent decade. On a monthly scale, the most significant increase (5.44 mm decade−1) is observed in November and the largest decrease (1.20 mm decade−1) in January. The frequency of intense rainfall events is increasing for the majority of stations over Saudi Arabia, while the frequency of weak events is decreasing. More extreme rainfall events are occurring in the northwest, east, and southwest regions of Saudi Arabia. A daily rainfall of ≥ 26 mm is identified as the threshold for an extreme event. It is found that the contribution of extreme events to the total rainfall amount varies from region to region and season to season. The most considerable contribution (up to 56%) is found in the southern region in June. Regionally, significant contribution comes from the coastal region, where extreme events contribute, on average, 47% of the total rainfall each month from October to February, with the largest (53%) in November. For the entire country, extreme rainfall contributes most (52%) in November and least (20%) in July, while contributions from different stations are in the 8–50% range of the total rainfall. [ABSTRACT FROM AUTHOR]

Extreme temperature events (ETEs) over Saudi Arabia have been receiving special attention in recent decades due to their impacts on water resources, the energy sector, human health, and crop yields. In this study, maximum temperature (Tmax) data for the summer season (June-Aug) obtained from 27 meteorological stations in Saudi Arabia have been analyzed for the period 1981–2017. Frequency analysis revealed that stations located in the Central, Northern, and Coastal regions have a relatively higher number of summer ETEs. A composite analysis has been performed to assess the association between global circulations and ETEs in Saudi Arabia using global reanalysis data. It is found that the summer ETEs in Saudi Arabia are associated with a mid-latitude circumglobal wave-like (CGT) pattern. The upper-level circulations associated with the ETEs in various regions of Saudi Arabia display a weak (e.g., Coastal region) to well-developed (e.g., Central region) CGT wave pattern in the mid-latitudes. The upper level anomalous high (low) pressure over Eurasia (Central Asia) coupled with the surface anomalous low (high) pressure anomalies assists the hot dry air from desert regions that favour the occurrence of ETEs in different regions of Saudi Arabia. A lead-lag relationship between 200 hPa geopotential height and ETEs in the Central region of Saudi Arabia reveals a strong association between mid-latitude circulation and ETEs. Moreover, an inverse relationship between Tmax over Saudi Arabia and the El-Niño Southern Oscillation (ENSO) is found. The ENSO modulates the regional Tmax anomalies over Saudi Arabia through the upper-level mid-latitude circulation. Unlabelled Image • Summer extreme temperature events are analyzed using observed data over Saudi Arabia. • Extreme temperature events are more frequent over central parts of Saudi Arabia. • Extreme temperature events over this region are associated with the mid-latitude wave train. • Mid-latitude wave train leads the extreme temperature events over central parts of Saudi Arabia. • Extreme temperature events over Saudi Arabia also show remarkable association with ENSO during summer season. [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]

This paper investigates the temperature and precipitation extremes over the Arabian Peninsula using data from the regional climate model RegCM4 forced by three Coupled Model Intercomparison Project Phase 5 (CMIP5) models and ERA–Interim reanalysis data. Indices of extremes are calculated using daily temperature and precipitation data at 27 meteorological stations located across Saudi Arabia in line with the suggested procedure from the Expert Team on Climate Change Detection and Indices (ETCCDI) for the present climate (1986–2005) using 1981–2000 as the reference period. The results show that RegCM4 accurately captures the main features of temperature extremes found in surface observations. The results also show that RegCM4 with the CLM land–surface scheme performs better in the simulation of precipitation and minimum temperature, while the BATS scheme is better than CLM in simulating maximum temperature. Among the three CMIP5 models, the two best performing models are found to accurately reproduce the observations in calculating the extreme indices, while the other is not so successful. The reason for the good performance by these two models is that they successfully capture the circulation patterns and the humidity fields, which in turn influence the temperature and precipitation patterns that determine the extremes over the study region. [ABSTRACT FROM AUTHOR]

Dengue is an important global arboviral disease with expanding geographical range. It is a major public health concern in Western Saudi Arabia since its first detection in the city of Jeddah in 1994. In this retrospective study, we examined dengue incidence among febrile patients suspected for acute dengue infection at King Abdulaziz University Hospital, Jeddah from 2010 to 2014 and we tried to determine the effect of climate factors on dengue incidence in the city. Acute dengue incidence rates among clinically suspected patients showed annual variation with a range from 29.3% to 57%. Male gender and 11–30 years age range were found to be risk factors for dengue infection in Jeddah. While dengue infections can be detected throughout the year, most cases occurred between March and July with peaks in May and June. Seasonality of dengue was found to be significantly associated with the decrease in relative humidity and increase in temperature within the range of ∼25 °C to ∼33 °C but not extremely hot temperatures. Moreover, we found that rainfall during winter (November to February) has a significant lag effect on dengue infection among febrile patients in the city. Jeddah is the second largest city in Saudi Arabia and a major hub for pilgrims because of its close proximity to the holy sites in the Kingdom. The observed high rates of acute dengue infections clearly show the endemicity of dengue in Jeddah. The observed higher incidence rates at young age are expected to cause an increase in severe dengue cases in the future especially that multiple dengue serotypes are co-circulating in the city. Furthermore, the significant association between the different climate factors and dengue and their impact on the disease seasonality should help in the effort to implement effective control and management measures to reduce dengue burden in the Kingdom. [ABSTRACT FROM AUTHOR]

Knowledge of aerosol size and composition is very important for investigating the radiative forcing impacts of aerosols, distinguishing aerosol sources, and identifying harmful particulate types in air quality monitoring. The ability to identify aerosol type synoptically would greatly contribute to the knowledge of aerosol type distribution at both regional and global scales, especially where there are no data on chemical composition. In this study, aerosol classification techniques were based on aerosol optical properties from remotely-observed data from the Ozone Monitoring Instrument (OMI) and Aerosol Robotic Network (AERONET) over Saudi Arabia for the period 2004–2016 and validated using data from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO). For this purpose, the OMI-based Aerosol Absorption Optical Depth (AAOD) and Ultra-Violet Aerosol Index (UVAI), and AERONET-based AAOD, Ångström Exponent (AE), Absorption Ångström Exponent (AAE), Fine Mode Fraction (FMF), and Single Scattering Albedo (SSA) were obtained. Spatial analysis of the satellite-based OMI-AAOD showed the dominance of absorbing aerosols over the study area, but with high seasonal variability. The study found significant underestimation by OMI AAOD suggesting that the OMAERUV product may need improvement over bright desert surfaces such as the study area. Aerosols were classified into (i) Dust, (ii) Black Carbon (BC), and (iii) Mixed (BC and Dust) based on the relationships technique, between the aerosol absorption properties (AAE, SSA, and UVAI) and size parameters (AE and FMF). Additionally, the AE vs. UVAI and FMF vs. UVAI relationships misclassified the aerosol types over the study area, and the FMF vs. AE, FMF vs. AAE and FMF vs. SSA relationships were found to be robust. As expected, the dust aerosol type was dominant both annually and seasonally due to frequent dust storm events. Also, fine particulates such as BC and Mixed (BC and Dust) were observed, likely due to industrial activities (cement, petrochemical, fertilizer), water desalination plants, and electric energy generation. This is the first study to classify aerosol types over Saudi Arabia using several different aerosol property relationships, as well as over more than one site, and using data over a much longer time-period than previous studies. This enables classification and recognition of specific aerosol types over the Arabian Peninsula and similar desert regions. Image 1 • AERONET, OMI, and CALIPSO datasets were used for classifying aerosols. • OMI AAOD shows the dominance of absorbing aerosols with high seasonal variability. • Dust, then mixed black carbon and dust dominated over the study area, Saudi Arabia. • Mixed aerosol types suggest increasing fossil fuel and biogenic emissions. • FMF vs. (AE, AAE, and SSA) are the best techniques for classifying aerosols. [ABSTRACT FROM AUTHOR]

Plastic pollution and its impact on marine ecosystems are major concerns globally, and the situation was exacerbated after the outbreak of COVID-19. Clean-up campaigns took place during the summer season (June-August 2020) in two coastal cities in Egypt (Alexandria and Hurghada) and Jeddah, Saudi Arabia to document the abundance of beach debris through public involvement, and then remove it. A total of 3673, 255, and 848 items were collected from Alexandria, Hurghada, and Jeddah daily, respectively. Gloves and face masks (personal protective equipment "PPE") represent represented 40-60% of the total plastic items collected from each of the three cities, while plastic bags represented 7-20% of the total plastics litter collected from the same cities. The results indicated the presence of 2.79, 0.29, and 0.86 PPE item m -2 in Alexandria, Hurghada and Jeddah, respectively. This short focus provides an assessment of the environmental impacts of single-use gloves and masks used for COVID-19 protection from June to August 2020. To the best of our knowledge, this study presents the first such information from the Middle East, specifically Egypt and Saudi Arabia. It highlights the need for further knowledge and action, such as safe, sustainable, and transparent waste management processes related to COVID-19 to reduce the negative impacts now, as well as in future events. Furthermore, this study helps in achieving key components of the United Nation's Sustainable Development Goals (SDGs). This short focus can serve as a multipurpose document, not only for scientists of different disciplines but for social media and citizens in general., Competing Interests: Declaration of competing interest We believe this subject is interesting and no data were published from Egypt or Saudi Arabia. We have the pleasure to submit this paper as a short communication. Having said that, I could not find a short communication option regarding the submission, so I have selected the nearest option. The authors declare no potential conflicts of interest concerning the research, authorship, and/or publication of this article., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Air pollution has been an increasing concern within the Kingdom of Saudi Arabia and other Middle Eastern countries. In this work the authors present an analysis of daily ozone (O3), nitrogen oxide (NO(x)), and particulate matter (< 10 miccrom aerodynamic diameter; PM10) concentrations for two years (2010 and 2011) at sites in and around the coastal city of Jeddah, as well as a remote background site for comparison. Monthly and weekly variations, along with their implications and consequences, were also examined. O3 within Jeddah was remarkably low, and exhibited the so-called weekend effect--elevated O3 levels on the weekends, despite reduced emissions of O3 precursors on those days. Weekend O3 increases averaged between 12% and 14% in the city, suggesting that NO(x)/volatile organic compound (VOC) ratios within cities such as Jeddah may be exceptionally high. Sites upwind or far removed from Jeddah did not display this weekend effect. Based on these results, emission control strategies in and around Jeddah must carefully address NO(x)/VOC ratios so as to reduce O3 at downwind locations without increasing it within urban locations themselves. PM10 concentrations within Jeddah were elevated compared with North American cites of similar climatology though comparable to other large cities within the Middle East. Implications: Daily concentrations of O3, PM10, and NO(x) in and around the city of Jeddah, Saudi Arabia, are analyzed and compared with those of other reference cities. Extremely low O3 levels, along with a significant urban weekend effect (higher weekend O3, despite reduced NO(x) concentrations), is apparent, along with high levels of PM10 within the city. Urban O3 in Jeddah was found to be lower than that of other comparable cities, but the strong weekend effect suggests that care must be taken to reduce downwind O3 levels without increasing them within the city itself. Further research into the emissions and chemistry contributing to the reduced O3 levels within the city is warranted.