Dust Module Research Articles

Performance assessment of CHIMERE and EURAD-IM’ dust modules

The purpose of this study is to investigate how two different atmospheric 3D modelling systems, with different dust modules, simulate a Saharan dust episode, using satellite data and in-situ observations to validate their performances. The episode occurred during 19–23 February 2016 and impacted the Iberian Peninsula. The two numerical modelling systems applied are the CHIMERE and the EURAD-IM chemistry transport models with different dust modules, both forced by the same WRF meteorological input. A common domain and resolution (27 × 27 km2) was adopted for the modelling setup. The comparison and evaluation of the two modelling results have shown that both models are able to capture the occurrence of the natural event, which was initiated by a cut-off low above the coast of Morocco, inducing a strong meridional transport of dust loaded air from Algeria straight towards eastern parts of the Iberian Peninsula. The most notable differences between the two model outputs concern the emission strengths and the emission source regions. In fact, different emission patterns and strengths are simulated by each model despite they use the same soil database, identical clay/silt/sand contribution for each soil type, and the same meteorological simulation. In general, CHIMERE simulates higher PM10, PM2.5, and dust concentrations than EURAD-IM for this event. In the South of Portugal, CHIMERE shows better agreement with observations, while in Central Portugal, EURAD-IM is closer to particle related measurements.

Modelling transportation of desert dust to the South Caucasus using WRF Chem model

The problem of the ongoing climate change resulting from natural and growing anthropogenic factors acquires a particular importance for the territory of the Caucasus. Dust aerosol represent one of the main pollutants on the territory of Georgia and impact on regional climate. In this study, the WRF Chemistry model with dust module is used to study transportation of dust to the territory of the South Caucasus from the Sahara and Sahel in Africa, Arabian and ar-Rub’ al-Khali deserts located in the Middle East, Kyzylkum, Karakum in the Central Asia. The results of calculations have shown the WRF model was able to simulate dust aerosols transportation to the Caucasus reliably in conditions of the complex topography and that dust aerosol is an important factor in the climate system of the South Caucasus.

WRF 1960-2014 Winter Season Simulations of Particulate Matter in the Sahel: Implications for Air Quality and Respiratory Health.

We use the Weather Research and Forecast model using the Goddard Global Ozone Chemistry Aerosol Radiation and Transport (GOCART) dust module (WRF‐CHEM) to simulate the particulate matter (PM) variations in the Sahel during the winter seasons (January–March) of 1960–2014. Two simulations are undertaken where the direct aerosol feedback is turned off, and only transport is considered and where the direct aerosol feedback is turned on. We find that simulated Sahelian PM10 and PM2.5 concentrations were lower in the 1960s and after 2003 and higher during the period between 1988 and 2002. Higher Sahelian PM10 concentrations are due to stronger winds between the surface and 925 hPa over the Sahara, which transport dust into the Sahel. Negative PM10 concentration anomalies are found over the Bodele Depression and associated with weaker 925 wind anomalies after 1997 through 2014. Further west, positive PM10 concentration anomalies are found across the Adrar Plateau in the Sahara and responsible for dust transport to the Western Sahel. The North Atlantic Oscillation (NAO) is positively correlated to Sahelian dust concentrations especially during the periods of 1960–1970 and 1988–2002. The temporal/spatial patterns of PM10 concentrations have significant respiratory health implications for inhabitants of the Sahel.

Modeling natural dust emissions in the central Middle East: Parameterizations and sensitivity

Middle East Area and especially the central part is a dust dominated domain and therefore estimation of natural dust emissions is critical. Aim of this study is to assess the sensitivity of state-of-the art dust modules, utilized in multiple modelling schemes, and especially of their three main components; namely the horizontal mass flux, the drag partition and the sandblasting efficiency. To accomplish this, several simulations with the Natural Emission MOdel (NEMO), driven by the Weather Research and Forecasting (WRF) model, were made for the period April–June 2015 focusing in the central Middle East (CME). First, the meteorological model was evaluated over the study period, as well as during a Shamal event, showing a satisfactory performance on wind speed which is the most important meteorological variable inserted in the dust modules. Second, dust emissions were found to be a few tenths of μg/m2s on average, while the daily amount exceeds 1000 mg/m2day. Over the studied period, the fluxes range from 15 to 750 g/m2. The total emissions in CME were estimated with the NEMO's basic configuration at 139 Tg. The most active areas are associated with clay content ranging between 17 and 25%, highlighting the importance of soil texture on the definition of the dust sources. During a Shamal event in the second half of June 2015, the mean dust emission fluxes reached up to several hundreds of μg/m2s, contributing 21 Tg in CME. Few such events could cover a large portion of the dust emissions. Finally, concerning the sensitivity of the total emissions, the drag partition scheme has the largest effect, followed by sandblasting efficiency and horizontal mass flux. The total dust emissions budget, among the 16 simulations was found to be in the range of 21–139 Tg, with the choice of the drag partition scheme to be mandatory for the narrowing of the total emissions in CME.

The use of ALADIN model and MERRA-2 reanalysis to represent dust seasonal dry deposition from 2006 to 2010 in Senegal, West Africa

The objective of this work is to study the seasonal distribution of dust dry deposition in West Africa particularly in Senegal. This initiative is part of the efforts to improve the performance of photovoltaic panels (PV) in dusty environments such as Sahel region. It will help to evaluate the impact of dust dry deposition on these PV. Two climate models including dust modules during 2006–2010, were used: MERRA-2 (Modern-Era Retrospective Analysis for Research and Applications, version 2) reanalysis and ALADIN (Aire Limitee Adaptation dynamique Developpement InterNational) model. In Mbour (Senegal), the aerosol optical depth (AOD) from these two products has been validated by in situ data. Indeed, MERRA-2 and ALADIN fairly simulate the AOD with a maximum in March and June. However, these products tend to overestimate measurements, especially for ALADIN. The correlation coefficient between in situ AOD and products is evaluate almost 0.83 for MERRA-2 and 0.72 for ALADIN. From 2007 to 2009, dust deposition measurement campaign was conducted in Mbour. The comparison between these seasonal data and simulations show a right coherence even if MERRA-2 underestimates measurement and ALADIN overestimates it. The correlation compared to in situ measurements is estimate to 0.71 for MERRA-2 and 0.72 for ALADIN. However, the results showed that ALADIN better describes the seasonal dry deposition during dry season which lasts 9 months despite a strong overestimation in winter. Finally, long-term simulation with ALADIN show that dry deposition maximum occurs from December to May in Senegal and throughout the West Africa region.

English

This study was carried out at the International Center for Training and Research in Solar Energy (CIFRES) and its main purpose was to study the performance of a solar module cleaning system. To handle this work, a measuring platform consisting of two polycrystalline (pc-Si) PV modules was designed. The modules were connected to a waterless cleaning system on the surface of the solar panels. The platform also contained a temperature sensor on the surface of the module, a pyranometer, shunt resistors (for current measurement), and an acquisition unit. This platform was exposed under real conditions and measurements of the parameters were taken in increments of ten seconds. Only one of the two modules was cleaned daily, and an evaluation of the degradation rate of the short-circuit current (Isc) of the dust module with respect to the cleaned module was carried out. After one month of exposure, the analysis of the results showed a degradation rate of 17.13% of the short circuit current (Isc) of the dirty module compared to the clean module. Compared to the initial conditions under the standard test conditions, a degradation of 10.16 and 24.09%, respectively for the clean module and the dirty module was obtained. This work also showed that a polynomial relation exists between the degradation rate and the dust deposition density with a coefficient of determination of 0.9933. Key words: Photovoltaic modules, dust, short-circuit current, impact, automatic cleaning without water, degradation.

Soiling Effect on Crystalline and Thin-film Technology PV Modules for Composite Climate Zone of India

Effect of soiling on thin film and crystalline technology for composite climate has been reported here. Three test setup structures with dual axis manual tracking have been installed at outdoors for exposure of modules at different tilt angles 130, 280 & 430. In the same structure with different inclination clean and dust module of each technology is installed to study the effect of variation in current, spectrum and temperature. The manual cleaning of non-dusty modules is done on daily basis in the early morning. The short circuit current of all modules are measured through a programmable digital multi-meter on continuous basis. There is a drop in Isc current for the dust module with the increase of dust accumulation. A change in spectrum is also observed for each day and drop in average photon energy was observed due to change in transmissivity.

Development and evaluation of a physics-based windblown dust emission scheme implemented in the CMAQ modeling system.

A new windblown dust emission treatment was incorporated in the Community Multiscale Air Quality (CMAQ) modeling system. This new model treatment has been built upon previously developed physics-based parameterization schemes from the literature. A distinct and novel feature of this scheme, however, is the incorporation of a newly developed dynamic relation for the surface roughness length relevant to small-scale dust generation processes. Through this implementation, the effect of nonerodible elements on the local flow acceleration, drag partitioning, and surface coverage protection is modeled in a physically based and consistent manner. Careful attention is paid in integrating the new windblown dust treatment in the CMAQ model to ensure that the required input parameters are correctly configured. To test the performance of the new dust module in CMAQ, the entire year 2011 is simulated for the continental United States, with particular emphasis on the southwestern United States (SWUS) where windblown dust concentrations are relatively large. Overall, the model shows good performance with the daily mean bias of soil concentrations fluctuating in the range of ±1 μg m−3 for the entire year. Springtime soil concentrations are in quite good agreement (normalized mean bias of 8.3%) with observations, while moderate to high underestimation of soil concentration is seen in the summertime. The latter is attributed to the issue of representing the convective dust storms in summertime. Evaluations against observations for seven elevated dust events in the SWUS indicate that the new windblown dust treatment is capable of capturing spatial and temporal characteristics of dust outbreaks.

Developing a Dust Emission Procedure for Central Asia

Airborne mineral dust is thought to have a significant influence on the climate through absorbing and scattering both shortwave and longwave radiations and affecting cloud microphysical processes. However, a knowledge of long-term dust emissions is limited from both temporal and spatial perspectives. Here, we have developed a quantitative climatology: the column-integrated mass of the dust aerosol loading in Central Asia by incorporating the dust module (DuMo) into the Weather Research and Forecasting coupled with Chemistry (WRF-Chem) model and accounting for regional climate and Land-Cover and Land-Use Changes for the 1950-2010 period in April. This data set is lowly to moderately correlated (0.22-0.48) with the satellite Aerosol Optical Depth in April of the 2000s and lowly correlated (0.02-0.11) with the Absorbing Aerosol Index in April of the 1980s, 1990s, and 2000s. The total dust loading is approximately 207.85 Mton per month in April during the recent decade (2000-2014) over dust source regions. Although only the month of April was simulated, results suggest that trends and magnitudes are captured well, using the WRF-Chem-DuMo.

Model development of dust emission and heterogeneous chemistry within the Community Multiscale Air Quality modeling system and its application over East Asia

Abstract. The Community Multiscale Air Quality (CMAQ) model has been further developed in terms of simulating natural wind-blown dust in this study, with a series of modifications aimed at improving the model's capability to predict the emission, transport, and chemical reactions of dust. The default parameterization of initial threshold friction velocity constants are revised to correct the double counting of the impact of soil moisture in CMAQ by the reanalysis of field experiment data; source-dependent speciation profiles for dust emission are derived based on local measurements for the Gobi and Taklamakan deserts in East Asia; and dust heterogeneous chemistry is also implemented. The improved dust module in the CMAQ is applied over East Asia for March and April from 2006 to 2010. The model evaluation result shows that the simulation bias of PM10 and aerosol optical depth (AOD) is reduced, respectively, from −55.42 and −31.97 % by the original CMAQ to −16.05 and −22.1 % by the revised CMAQ. Comparison with observations at the nearby Gobi stations of Duolun and Yulin indicates that applying a source-dependent profile helps reduce simulation bias for trace metals. Implementing heterogeneous chemistry also results in better agreement with observations for sulfur dioxide (SO2), sulfate (SO42−), nitric acid (HNO3), nitrous oxides (NOx), and nitrate (NO3−). The investigation of a severe dust storm episode from 19 to 21 March 2010 suggests that the revised CMAQ is capable of capturing the spatial distribution and temporal variation of dust. The model evaluation also indicates potential uncertainty within the excessive soil moisture used by meteorological simulation. The mass contribution of fine-mode particles in dust emission may be underestimated by 50 %. The revised CMAQ model provides a useful tool for future studies to investigate the emission, transport, and impact of wind-blown dust over East Asia and elsewhere.

Numerical Modeling of Topography-Modulated Dust Aerosol Distribution and Its Influence on the Onset of East Asian Summer Monsoon

A regional climate model coupled with a dust module was used to simulate dust aerosol distribution and its effects on the atmospheric heat source over the TP, East Asian summer monsoon onset, and precipitation in East Asia modulated by the uplift of the northern TP. We carried out four experiments, including a modern (i.e., high-mountain) experiment with (HMD) and without (HM) the major deserts in Northwest China and a low-mountain experiment with (LMD) and without (LM) the deserts. The results show that dust greatly increases in the Taklamakan Desert accompanied with the uplift of the northern TP, and the increase exceeds 150 µg kg−1in spring. A strong cyclone in the Tarim Basin produced by the uplifted northern TP enhances dust emissions in the Taklamakan Desert in summer. Meanwhile, the dust loading over the TP also increases induced by the uplift of the northern TP, causing the heat source over the TP decreased. Under the condition of the northern TP uplift to present altitude, dust delays the East Asia summer monsoon onset by two pentads and one pentad, respectively, in the southern and northern monsoon regions and greatly suppresses precipitation in East Asia compared with results in the low terrain experiments.

Can a coupled meteorology–chemistry model reproduce the historical trend in aerosol direct radiative effects over the Northern Hemisphere?

Abstract. The ability of a coupled meteorology–chemistry model, i.e., Weather Research and Forecast and Community Multiscale Air Quality (WRF-CMAQ), to reproduce the historical trend in aerosol optical depth (AOD) and clear-sky shortwave radiation (SWR) over the Northern Hemisphere has been evaluated through a comparison of 21-year simulated results with observation-derived records from 1990 to 2010. Six satellite-retrieved AOD products including AVHRR, TOMS, SeaWiFS, MISR, MODIS-Terra and MODIS-Aqua as well as long-term historical records from 11 AERONET sites were used for the comparison of AOD trends. Clear-sky SWR products derived by CERES at both the top of atmosphere (TOA) and surface as well as surface SWR data derived from seven SURFRAD sites were used for the comparison of trends in SWR. The model successfully captured increasing AOD trends along with the corresponding increased TOA SWR (upwelling) and decreased surface SWR (downwelling) in both eastern China and the northern Pacific. The model also captured declining AOD trends along with the corresponding decreased TOA SWR (upwelling) and increased surface SWR (downwelling) in the eastern US, Europe and the northern Atlantic for the period of 2000–2010. However, the model underestimated the AOD over regions with substantial natural dust aerosol contributions, such as the Sahara Desert, Arabian Desert, central Atlantic and northern Indian Ocean. Estimates of the aerosol direct radiative effect (DRE) at TOA are comparable with those derived by measurements. Compared to global climate models (GCMs), the model exhibits better estimates of surface-aerosol direct radiative efficiency (Eτ). However, surface-DRE tends to be underestimated due to the underestimated AOD in land and dust regions. Further investigation of TOA-Eτ estimations as well as the dust module used for estimates of windblown-dust emissions is needed.

Modelling ripples in Orion with coupled dust dynamics and radiative transfer

In light of the recent detection of direct evidence for the formation of Kelvin-Helmholtz instabilities in the Orion nebula, we expand upon previous modelling efforts by numerically simulating the shear-flow driven gas and dust dynamics in locations where the H$_{II}$ region and the molecular cloud interact. We aim to directly confront the simulation results with the infrared observations. Methods: To numerically model the onset and full nonlinear development of the Kelvin-Helmholtz instability we take the setup proposed to interpret the observations, and adjust it to a full 3D hydrodynamical simulation that includes the dynamics of gas as well as dust. A dust grain distribution with sizes between 5-250 nm is used, exploiting the gas+dust module of the MPI-AMRVAC code, in which the dust species are represented by several pressureless dust fluids. The evolution of the model is followed well into the nonlinear phase. The output of these simulations is then used as input for the SKIRT dust radiative transfer code to obtain infrared images at several stages of the evolution, which can be compared to the observations. Results: We confirm that a 3D Kelvin-Helmholtz instability is able to develop in the proposed setup, and that the formation of the instability is not inhibited by the addition of dust. Kelvin-Helmholtz billows form at the end of the linear phase, and synthetic observations of the billows show striking similarities to the infrared observations. It is pointed out that the high density dust regions preferentially collect on the flanks of the billows. To get agreement with the observed Kelvin-Helmholtz ripples, the assumed geometry between the background radiation, the billows and the observer is seen to be of critical importance.

Improved dust representation in the Community Atmosphere Model

AbstractAerosol‐climate interactions constitute one of the major sources of uncertainty in assessing changes in aerosol forcing in the anthropocene as well as understanding glacial‐interglacial cycles. Here we focus on improving the representation of mineral dust in the Community Atmosphere Model and assessing the impacts of the improvements in terms of direct effects on the radiative balance of the atmosphere. We simulated the dust cycle using different parameterization sets for dust emission, size distribution, and optical properties. Comparing the results of these simulations with observations of concentration, deposition, and aerosol optical depth allows us to refine the representation of the dust cycle and its climate impacts. We propose a tuning method for dust parameterizations to allow the dust module to work across the wide variety of parameter settings which can be used within the Community Atmosphere Model. Our results include a better representation of the dust cycle, most notably for the improved size distribution. The estimated net top of atmosphere direct dust radiative forcing is −0.23 ± 0.14 W/m2 for present day and −0.32 ± 0.20 W/m2 at the Last Glacial Maximum. From our study and sensitivity tests, we also derive some general relevant findings, supporting the concept that the magnitude of the modeled dust cycle is sensitive to the observational data sets and size distribution chosen to constrain the model as well as the meteorological forcing data, even within the same modeling framework, and that the direct radiative forcing of dust is strongly sensitive to the optical properties and size distribution used.

Dust storm simulation over Iran using HYSPLIT

Particulate matters have detrimental effects on human health, environment and economic. This pollutant may emit from anthropogenic or natural sources. On global scale, main proportion of natural particulate matter release to the atmosphere because of wind erosion from arid and semi-arid regions. Recently, the amount of dust coming from Arabian countries has dramatically increased, especially dust storms that are affecting western and even central parts of Iran. This phenomenon has caused a lot of environmental problems. Dust source identification and trajectory simulation using numerical techniques are the main aims of this study. HYSPLIT (Hybrid Single Particle Lagrangian Integrated Trajectory) model dust module and trajectory simulation are utilized in this research and two case studies are investigated (in May and June 2010). The base of the HYSPLIT dust module is the PM10 dust storm emission algorithm for desert land use. This methodology is applied to estimate hotspots and trajectories. Due to the results, dust storms started on May 17th and June 7th because of high wind shear (>8.5 m/s) from the western Syrian Desert. The source region limited to 32.50 °N to 33.80 °N and 38.00 °E to 38.80 °E coordinates. Dust plumes lifted and dispersed towards the east and southeast of the sources and reached Ahvaz on May 18th and June 8th. The average of PM10 concentration in these dates reached 625 and 494 on Ahvaz monitoring stations, respectively. Moreover, the results gained from the model for dust motion simulation are similar to the MODIS satellite images.

The importance of the diurnal cycle of Aerosol Optical Depth in West Africa

High resolution atmospheric simulations with the AROME model coupled with a dust module over West Africa for the whole of June 2006 were used to calculate aerosol optical thickness (AOT). Simulations showed a significant diurnal cycle of 0.2 in the dust AOT that could not be inferred from the MODIS Deep Blue retrievals due to their timings. Dust sources are mainly driven by the breakdown of the early morning low‐level jet and by moist convection in the afternoon, leading to opposite diurnal cycles. Also, simulations show that cloud cover significantly prevents the observation of AOT. The under‐sampling of the diurnal cycle by satellites plus the impact of cloud masks on the space‐borne AOT retrievals induce an underestimation of 0.28 (~40%) over the convective regions and an overestimation of 0.1 (17%) over morning source areas like Bodélé. A combination of observations and high‐resolution models could constrain bias and give a more realistic AOT climatology.

Simulation on the spatio-temporal distribution and emission flux of dust aerosol over East Asia in 2000-2009

A regional climate model (RegCM3), coupled with an online dust module, is used to simulate the spatio-temporal distribution and emission flux of dust aerosol (smaller than 20 μm in diameter) over East Asia in the period from 2000 to 2009. The model performance is firstly evaluated against available observations. Simulation results show that the model can capture the characteristics of spatio-temporal distribution of dust aerosol very well over East Asia. There always exist two extremes of dust aerosol optical depth (AOD) and column burden (CB), one is in the Taklimakan Desert of Xinjiang Uygur Autonomous Region, China, and the other is in the Badain Jaran Desert of Inner Mongolian Autonomous Region, China. The maximum value of CB appears in spring, secondary maximum in winter and minimum in autumn. To the east of 110°E, dust is transported eastward from a maximum center at a height of 700 hPa over the East Asian continent. Dust emission sources are mainly located in the Taklimakan Desert, Badain Jaran Desert, North Qinghai-Tibetan Plateau and Southwest Mongolia. There is also an obvious seasonal variation of dust emission flux (EF). Annual mean dust EF is 1,015.34 mg/(m 2 ·d), of which 62.4% and 2.3% are re-deposited onto the East Asian continent through a dry and wet deposition process, respectively, and the remaining 35.3% is injected into the atmosphere or subject to long-range transport.

Numerical Simulations of Asian Dust-Aerosols and Regional Impact on Weather and Climate- Part II: PRCM-Dust Model Simulation

ABSTRACTThe Purdue Regional Climate Model (PRCM)-Dust, an on-line coupled regional climate-dust model, has been developed to study the dust life cycle and radiative effect of dust on regional weather and climate in Asia in April 1998. The dust model is built on the PRCM discussed in Part I. The dust module includes the major phases of the mineral dust cycle, such as emission, advection, diffusion, and deposition. Furthermore, the optical properties of the dust aerosols are included in the radiation calculation of the PRCM, so that the feedback of radiative forcing of dust-aerosols can be considered in the PRCM modeling. The PRCM-Dust successfully simulated the uplifted dusts to reached around 500–800 hPa over the source regions and remained at 3–5 km or higher to be transported further eastward. The spatial and temporal distributions of the dust aerosols were consistent with the satellite images, the TOMS Aerosol Index maps, lidar observations, and the surface network reports. The regional climatic impacts due to radiative effect of dust aerosols include warming over the high concentration regions in North Asia and cooling in dust-free South Asia. Since there is no nudging, restart, or other artificial forcing in the PRCM-Dust model, the simulated dust concentrations, size distribution, as well as meteorological and soil environments follow the conservation laws of physics. They are suitable to study the interactions among dusts, soil, and regional weather/climate.

Numerical simulation of spatial‐temporal distribution of dust aerosol and its direct radiative effects on East Asian climate

The latest regional climate model version 4 (RegCM4) coupled with a dust module developed at the International Center for Theoretical Physics (ICTP, Italy) is used to simulate the spatial‐temporal distribution of dust aerosol and its climatic impact through direct radiative forcing over East Asia. Dust coupled and uncoupled experiments are carried out for the past decade (2000–2009). Comparison with satellite observed aerosol optical depth (AOD) shows that the coupled RegCM4 better reproduces spatial distribution of Asian dust loading that has been poorly resolved by general circulation models (GCM), capturing three surface dust concentration (SDC) centers in the Taklimakan desert, western Inner Mongolia, and northern Xinjiang respectively, with maximum values greater than 1000μg m−3 in spring. The negative surface shortwave (SW) irradiance is strongest in spring over East Asia. Its −20 W m−2 forcing near dust source centers results in surface temperature cooling by 0.8°C from spring through summer. SW irradiance at the top of the atmosphere (TOA) is also negative with a minimum value of up to −8 W m−2in North China. Dust aerosol induced cooling leads to the formation of a cyclonic circulation in the lower troposphere in Northwest China that further excites downstream an anticyclonic circulation (the Yellow River Loop) and a cyclonic circulation (East China Sea, ECS). The northeasterly flow in southern China straddled by the anticyclone and cyclone acts to weaken the southwest monsoon in southeastern China and the surrounding sea. Supported by the dust‐induced circulations, precipitation increases in cyclonic regions in Northwest China and ECS and decreases in the anticyclonic north‐central China.

Modeling the Summertime Climate of Southwest Asia: The Role of Land Surface Processes in Shaping the Climate of Semiarid Regions

Abstract Presented is a study on the role of land surface processes in determining the summertime climate over the semiarid region of southwest Asia. In this region, a warm surface air temperature bias of 3.5°C is simulated in the summer by using the standard configuration of Regional Climate Model version 3 (RegCM3). Biases are also simulated in surface albedo (underestimation), shortwave incident radiation (overestimation), and vapor pressure (underestimation). Based on satellite measurements documented in NASA’s surface radiation budget (SRB) dataset, a correction in surface albedo by 4% is introduced in RegCM3 to match the observed SRB data. Increasing albedo values results in a nearly 1°C cooling over the region. In addition, by incorporating RegCM3’s dust module and including subgrid variability for surface wind, shortwave incident radiation bias originally of about 45 W m−2 is reduced by 30 W m−2. As a result, the reduction of shortwave incident radiation cools the surface by 0.6°C. Finally, including a representation for the irrigation and marshlands of Mesopotamia produces surface relative humidity values closer to observations, thus eliminating a nearly 5-mb vapor pressure dry bias over some of the region. Consequently, the representation of irrigation and marshlands results in cooling of nearly 1°C in areas downwind of the actual land-cover change. Along with identified biases in observational datasets, these combined processes explain the 3.5°C warm bias in RegCM3 simulations. Therefore, it is found that accurate representations of surface albedo, dust emissions, and irrigation are important in correctly modeling summertime climates of semiarid regions.