Urbanization effects on the air temperature rise in Saudi Arabia

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.     

Detecting climate change signals in Saudi Arabia using mean annual surface air temperatures

Climate change signals in Saudi Arabia are investigated using the surface air temperature (SAT) data of 19 meteorological stations, well distributed across the country. Analyses are performed using cumulative sum, cumulative annual mean, and the Mann–Kendall rank statistical test for the period of 1978–2010. A notable change in SAT for the majority of stations is found around 1997. The results show a negative temperature trend (cooling) for all stations during the first period (1978–1997), followed by a positive trend (warming) in the second period (1998–2010) with reference to the entire period of analysis. The Mann–Kendall test confirms that there is no abrupt cooling at any station during the analysis period, reflecting the warming trend across the country. The warming trend is found to be 0.06 °C/year, while the cooling trend is 0.03 °C/year, which are statistically significant.     

A mass flux closure function in a GCM based on the Richardson number

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.     

A climatological analysis of Saharan cyclones

In this study, the climatology of Saharan cyclones is presented in order to understand the Saharan climate, its variability and its changes. This climatology includes an analysis of seasonal and interannual variations, the identification and classification of cyclone tracks, and a presentation of their chief characteristics. The data used are drawn from the 1980–2009, 2.5° × 2.5°, NCEP/NCAR reanalysis (NNRP I) dataset. It is found that cyclone numbers increase in September–October–November (SON) at 4.9 cyclones per decade, while they decrease in June–July–August at 12.3 cyclones per decade. The identification algorithm constructed 562 tracks, which are categorized into 12 distinct clusters. Around 75 % of the Saharan cyclones originate south of the Atlas Mountains. The percentage of tracks that move over the Sahara is around 48 %. The eastern Mediterranean receives 27 % of the Saharan tracks, while the western basin receives only 17 and 8 % of all the Saharan cyclones decay over the Arabian Peninsula. The maximum cyclonic activity occurs in April. There is a general decrease in the number of tracks in all categories between 1993 and 2009, compared with the period between 1980 and 1992. About 72 % of the Saharan cyclones do not live more than 3 days, and about 80 % of the cyclones in the tracks never reach central pressures 1,000 hPa during their lifetimes. The maximum deepening in the tracks occurs over the western Mediterranean and over northern Algeria.     

Calibration of TRMM rainfall climatology over Saudi Arabia during 1998–2009

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 89.42 mm, whereas the observed data is 82.29 mm. 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.     

Siberian high variability and its teleconnections with tropical circulations and surface air temperature over Saudi Arabia

Based on a generated time series for the central pressure of the Siberian High, and on defining a robust Siberian High Index (SHI), the behavior of this atmospheric center of action is examined from 1949 to 2010 with regard to inter-annual variations, persistence, trends, abrupt changes, spectral analysis and interactions. The interannual variability in the central pressure of the Siberian High is considerable. The mean downward linear and non-linear trend over the entire period (1949–2010) is estimated and is found to be statistically significant at the 95 % confidence level. Low frequency variation and linearity within the SHI time series are found from the persistence analysis. Using spectral analysis, the center of action of the Siberian High is characterized by non-periodic behavior; the peaks occur only at the lowest frequency and may be related to the Sea Surface Temperature (SST) over the El Niño region. The Siberian High is affected by the Hadley circulation cell; there is no detectable connection between the Walker circulation cell and the Siberian High. SSTs over the El Niño region may affect the Siberian High. Interactions between the Siberian High and the SSTs over the tropical Atlantic Ocean are absent. The SHI is positively correlated to surface air temperatures over Saudi Arabia, and this is statistically significant in the western and north-western regions.     

Direct effects and feedback of desert dust on the climate of the Arabian Peninsula during the wet season: a regional climate model study

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.     

A quantitative assessment of changes in seasonal potential predictability for the twentieth century

Changes over the twentieth century in seasonal mean potential predictability (PP) of global precipitation, 200 hPa height and land surface temperature are examined by using 100-member ensemble. The ensemble simulations have been conducted by using an intermediate complexity atmospheric general circulation model of the International Center for Theoretical Physics, Italy. Using the Hadley Centre sea surface temperature (SST) dataset on a 1° grid, two 31 year periods of 1920–1950 and 1970–2000 are separated to distinguish the periods of low and high SST variability, respectively. The standard deviation values averaged for the (“Niño-3.4”; 5°S–5°N, 170°W–120°W) region are 0.71 and 1.15 °C, for the periods of low and high SST variability, respectively, with a percentage change of 62 % during December–January–February (DJF). The leading eigenvector and the associated principal component time series, also indicate that the amplitude of SST variations have positive trend since 1920s to recent years, particularly over the El Niño Southern Oscillation (ENSO) region. Our hypothesis states that the increase in SST variability has increased the PP for precipitation, 200 hPa height and land surface temperature during the DJF. The analysis of signal and noise shows that the signal-to-noise (S/N) ratio is much increased over most of the globe, particularly over the tropics and subtropics for DJF precipitation. This occurs because of a larger increase in the signal and at the same time a reduction in the noise, over most of the tropical areas. For 200 hPa height, the S/N ratio over the Pacific North American (PNA) region is increasing more than that for the other extratropical regions, because of a larger percentage increase in the signal and only a small increase in noise. It is also found that the increase in seasonal mean transient signal over the PNA region is 50 %, while increase in the noise is only 12 %, during the high SST variability period, which indicates that the increase in signal is more than the noise. For DJF land surface temperature, the perfect model notion is utilized to confirm the changes in PP during the low and high SST variability periods. The correlation between the perfect model and the other members clearly reveal that the seasonal mean PP changed. In particular, the PP for the 31 years period of 1970–2000 is higher than that for the 31 years period of 1920–1950. The land surface temperature PP is increased in northern and southern Africa, central Europe, southern South America, eastern United States and over Canada. The increase of the signal and hence the seasonal mean PP is coincides with an increase in tropical Pacific SST variability, particularly in the ENSO region.     

Intensification of future heat waves in Pakistan: a study using CORDEX regional climate models ensemble

Future trends in the occurrence of heat waves (HW) over Pakistan have been presented using three regional climate models (RCMs), forced by three different global climate models (GCMs) runs under RCP8.5 scenarios. The results of RCMs are obtained from CORDEX (Coordinated Regional climate Downscaling EXperiment) database. Two different approaches for the assessment of HWs are defined, namely Fixed and Relative approaches. Fixed approach is defined for a life-threatening extreme event in which the temperature can reach more than 45 °C for a continuous stretch of several days; however, Relative approach events may not be directly life-threatening, but may cause snow/ice melt flooding and impact on food security of the country in summer and winter seasons, respectively. The results indicate a consistent increase in the occurrence of HWs for both approaches. For the Fixed approach, the increase is evident in the eastern areas of Pakistan, particularly plains of Punjab and Sindh provinces which host many big cities of the country. It is argued that the effect of HWs may also be exacerbated in future due to urban heat island effect. Moreover, summer time HWs for Relative approach is most likely to increase over northern areas of the country which hosts reservoirs of snow and glacier, which may result in events like glacial lake outburst flood and snow/ice melt flooding. Furthermore, the increase in winter time HWs for Relative approach may affect negatively on the wheat production, which in turn can distress the overall food productivity and livelihoods of the country. It is concluded that this study may be a useful document for future planning in order to better adapt to these threats due to climate change.     

Engineering risk assessment on water structures under climate change effects

The increase in the average temperature in the lower atmosphere caused by climate change triggers changes in various elements of the hydrological cycle at different scales depending on location in the world. Although numerous published studies are concerned with the effect of climate change on hydrological elements such as temperature, precipitation, evaporation, wind, and runoff, unfortunately, the performance of water engineering structures is not taken into consideration. Nevertheless, as an integral part of the whole water resources systems, engineering structures such as dams, canals, culverts, and wells are also subject to climate change impacts. This examines the performance of engineering structures by taking into account how climate change impacts on the risk assessment formulation. For this purpose, the risk concept is redefined and the climate change impact is taken into account by a factor dependent on the positive or negative slope of the trend from the historical record. The risk levels are revised for 10-year, 50-year, and 100-year return periods. The application of the proposed methodology is given for precipitation records for three different meteorological stations in the southeastern European province of Turkey and for the same number of stations from central east-west belt over Saudi Arabia. It is observed that including the climate change factor in the risk calculation formulation generally leads to an increase in the return period and in the risk compared to conventional calculations. Therefore, it is recommended that rather than using the standard risk formulation, the simple, effective climate change risk approach, as suggested in this paper, be applied to future water engineering structure designs.