Incident Solar Radiation Research Articles

Contributions of Local Land‒Atmosphere Coupling and Mesoscale Atmospheric Circulation to the 2013 Extreme Flash Drought and Heatwave Compound Event Over Southwest China

AbstractThe flash drought and heat wave compound event of the 2013 summer in Southwest China was exceptional, with profound socio‒economic impacts. Existing studies have captured the signal of this compound event; however, its causes are still poorly understood. In this study, we utilized a high‐resolution index to examine the life cycle of this compound event from 1980 to 2020 and quantified the relative contributions of land‒atmosphere coupling and mesoscale atmospheric circulation using the air parcel backward tracking method. It was found that the dry soil caused by the precipitation deficit further inhibited precipitation and caused the soil to become even drier, which then led to the development of the flash drought. The dry soil induced a substantial increase in the land‒atmosphere sensible heat flux and a rise in the near‐surface air temperature. During this process, the strength of land‒atmosphere coupling was 2.5 standard deviations higher than the mean value of the climate, playing an integral role in the near‐surface air temperature increase, accounting for 55.9% of the maximum temperature changes. The mesoscale atmospheric circulation contributed 44.1%, of which horizontal advection accounted for 41.1%, while vertical advection only accounted for 3.0%. The western Pacific subtropical high expanded westward, accompanied by the northward‐moving westerly jet stream, which prevented cold air from accessing the Southwest China, and abnormal subsidence interfered with precipitation formation. Furthermore, the control of an abnormally high‐pressure system over the region led to a decrease in cloud cover, allowing more surface incident solar radiation and contributing to the increase in the near‐surface air temperature.

Headwater stream temperature response to forest harvesting: Do lower flows cause greater warming?

AbstractThis study addressed two hypotheses regarding the relationship between stream temperature response to shade removal and streamflow: (a) that temperature response increases as flow declines and (b) that the relationship can be complicated by shifts in dominant streamflow sources and pathways during low‐flow periods. The study was based on a paired‐catchment design in rain‐dominated headwater catchments in the southern Coast Mountains of British Columbia, Canada, and focused on the effect of a 50% thinning treatment on daily maximum temperature in June, July and August for three sites within the harvest treatment. At the two upstream sites, the treatment response exhibited a negative relationship with daily mean streamflow, especially for days with high incident solar radiation. This result suggests that the effectiveness of forest practice rules for protecting cold‐water habitat may be reduced under future climatic conditions characterized by more frequent extended drought. However, stream temperature response at the most downstream site exhibited a pronounced inverted‐U‐shaped relationship with streamflow measured at a weir. It is hypothesized that the response at the most downstream temperature logger was controlled by the existence of a stable, relatively cool inflow just upstream of the logger, which represented an increasing fraction of flow as streamflow generated higher up in the catchment declined through time. There was a lack of convergent surface topography upstream of the logger, and it is hypothesized that localized inflow may have been controlled by the topography of the soil‐till interface and/or originated as hyporheic discharge.

Irrigation increases on-farm soybean yields in water-limited environments without a trade-off in seed protein concentration

Context or problemA trade-off between seed protein concentration (SPC) and yield has been reported for soybean. Therefore, assessing management practices that can nullify this trade-off is relevant to avoid further declines in SPC in the future as yield continues to increase. While the positive effect of irrigation on yield is well documented, only a few studies have assessed the impact of irrigation on SPC, showing conflicting results. Objective or research questionThe objective was to determine if the trade-off between seed yield and SPC persists when irrigation is applied and how management, soil, and weather factors influence the trade-off. We hypothesized that yield increases induced by irrigation would likely decrease SPC. MethodsOur experimental approach involved the use of producer-reported data, in-situ seed collection, and crop modeling. Yield and management data were collected from 268 soybean fields in Nebraska (USA), along with data on SPC, seed oil concentration (SOC), and seed carbohydrate concentration (SCC) determined from samples collected in each field. Field-specific phenological data were derived from model simulations. The combined data were then used to assess the effect of irrigation on seed yield and constituents as influenced by management, soil, and weather factors. ResultsOn average, both seed yield (+0.86 Mg ha−1) and SPC (+3.2 g kg−1) were higher, but SOC (–2.0 g kg−1) was lower, and SCC was unaffected in irrigated versus rainfed field pairs. Yield and SPC increased simultaneously in response to irrigation in two-thirds of the fields, especially when environmental conditions did not favor seed oil synthesis (e.g., cooler temperature and less incident solar radiation). A trade-off of higher seed yield and lower SPC occurred with irrigation in the remaining fields wherein conditions were favorable for seed oil synthesis (e.g., warmer temperatures and greater radiation). ConclusionsDespite higher seed yield generated in irrigated versus rainfed fields, no concurrent reduction occurred in SPC in the majority of irrigated fields – a surprising finding that was not consistent with the general expectation that higher soybean yields typically result in yield-SPC trade-off. Implications or significanceThis study showed that irrigation-induced higher soybean yields are possible without an attendant SPC penalty when temperatures and radiation are conducive for its mitigation. We are unaware of any other yield-increasing practices – except nitrogen (N) fertilization - that do not result in a concomitant decline in SPC. A hypothesized higher N supply via soil N mineralization and/or biological N fixation in irrigated fields in this study may explain the absence of yield-protein trade-off.

An experimental study on parabolic trough solar cookers with materials collector of chrome stickers and glass mirrors

Cooking, a fundamental human necessity, frequently relies on environmentally harmful energy sources. Concentrated solar power offers a promising solution through solar cookers to address this issue. This study assesses a Parabolic Trough Collector (PTC) solar cooker's performance with two reflector materials: chrome stickers and glass mirrors. The PTC-type solar cooker comprises essential components, including an absorber tube, a flexible conduit, and a spiral-shaped cooking container holder that accommodates a diverse range of cooking vessels. In the configuration of the PTC collector, reflectors fabricated from chrome stickers and glass mirrors are strategically employed to harness and concentrate solar radiation effectively. The absorber tube, crafted from copper, is filled with a heat-transfer fluid consisting of soya oil. Experimental investigations were conducted in a two-stage process, encompassing trials without any applied load and subsequently with varying loads. In the no-load experiments, alterations were made to the PTC collector's inclination angle, spanning the ranges of 15º, 20º, 25º, and 30º. In contrast, the load-bearing tests encompassed the assessment of the PTC solar cooker's performance under a diverse array of cooking scenarios, including boiling water, heating oil, frying eggs, and crisping crackers. The evaluated parameters encompassed key metrics such as incident solar radiation (Ir), ambient temperature (Ta), receiver temperature (Tr), fluid temperature (Tf), spiral furnace temperature (Tsf), and load temperature (To). Subsequently, the outcomes of the experiments were employed to determine the efficiency of the solar cooker. Analysis of the no-load test results indicates that the most favorable performance, as observed in the parameters Tr, Tf, and Tsf, is achieved at a collector inclination angle of 15º for both chrome sticker and glass mirror reflector materials. The solar cooker demonstrated commendable proficiency in boiling water, heating oil, frying eggs, and crisping crackers, accomplishing these tasks within a time frame ranging from 5 to 20 minutes. Notably, the solar cooker featuring the glass mirror reflector exhibited a superior thermal efficiency of 33.7%, surpassing the efficiency of the counterpart with the chrome sticker reflector, which registered an efficiency of 30.9%. These findings underscore the efficacy of the glass mirror reflector in harnessing solar energy for enhanced cooking performance within this solar cooker configuration.

Anlık Güneş Işınımı ve Meteorolojik Parametrelere Bağlı Olarak Fotovoltaik Panel Güç Üretiminin Değerlendirilmesi

The solar radiation incident on the surface of photovoltaic (PV) panels, dependent on the inclination 
 angle, and the temperature of the panels are the most significant parameters affecting power 
 generation. These two parameters are necessary to accurately evaluate the electrical performance by 
 enabling the calculation of cell and module temperatures. In this study, the efficiencies and electrical 
 power behaviors of PV panels positioned towards the sun at a 37° inclination angle in Hakkari province 
 were examined under real solar radiation and ambient temperature values. In addition, the effect of 
 wind speed parameters was also considered, and the impact on panel efficiency and PV panel output 
 power was evaluated. When the results were evaluated, it was confirmed that the effect of wind 
 increases the efficiency of PV panels, resulting in an increasing in PV output power.

Enhanced surface temperature over India during 1980–2020 and future projections: causal links of the drivers and trends

The Earth’s surface temperatures have increased significantly since the beginning of industrialisation. The high emissions of greenhouse gases have contributed to global warming and climate change, which is expected to continue. Here, we investigate the long-term trends of surface temperature in India using surface, satellite and reanalysis data for the period of 1980–2020, and assess the influence of geophysical drivers on temperature change using the causal discovery. The highest mean surface temperatures are observed in the southern India and the lowest in Himalaya in accordance with the incidence of solar radiation. Causal discovery reveals the relative influence of atmospheric processes, aerosols and specific humidity on surface temperature. We observe a positive trend in temperature during pre-monsoon (0.1–0.3 °C dec−1) and post-monsoon (0.2–0.4 °C dec−1) seasons in the northwest, northeast and north-central India. The analysis exposes high annual (0.22 ± 0.14 °C dec−1) and monsoon (0.24 ± 0.08 °C dec−1) warming in the northeast India. Post-monsoon season shows a positive trend in the entire India, where the highest value is estimated for the western Himalaya (0.2–0.5 °C dec−1) and northeast India (0.1–0.4 °C dec−1). Analyses with the Coupled Model Intercomparison Project 6 (CMIP6) results show that temperature can increase up to 1.1–5.1 °C by year 2100 under the Shared Socioeconomic Pathways (SSP5)–8.5 scenario. The increasing trend of temperature in India is a big concern, which calls for adaption and mitigation measures to alleviate adverse effects of accelerated warming and regional climate change.

Cultivation of Polar Microalgae in a Rotating Flat-Panel Photobioreactor

With the increasing urbanisation of the polar regions, the demand for sustainable technologies that are able to transform waste materials into high-value products is growing. For the production of microalgal biomass, nutrients contained in wastewater or carbon dioxide in flue gas can be used. Microalgae strains that have adapted to the extreme climatic conditions of polar regions appear to be a suitable alternative to conventional industrially cultivated microalgae species. Nevertheless, technologies for the production of polar microalgae can also be applied in areas of central and eastern Europe where climatic conditions are not suitable for year-round cultivation of conventional microalgae. For isolated polar microalgae species, a photobioreactor able to rotate according to the current position of the sun has been designed. The rotating flat-panel photobioreactor is able to efficiently use the incident solar radiation, which is crucial for microalgae growth. The designed concept of the rotating photobioreactor has been successfully tested in extreme climatic conditions at the Czech Arctic Research Station in Svalbard.

Evaluation of the Performance of Polycrystalline and Monocrystalline PV Technologies in a Hot and Arid Region: An Experimental Analysis

In arid regions, the behavior of solar panels changes significantly compared to the datasheets provided by the manufacturer. Therefore, the objective of this study is to determine the performance of both polycrystalline and monocrystalline solar modules in an arid region characterized by a large potential for solar irradiation and high temperatures. The influence of environmental parameters, such as temperature and dust, on the output power of solar modules with different technologies (monocrystalline and polycrystalline) has been investigated. The Artificial Hummingbirds Algorithm (AHA) has been used to extract parameters for PV modules. As a result, it has been demonstrated that for high solar irradiation, the polycrystalline PV module experiences a smaller decrease in output power than the monocrystalline PV module as the module temperature increases. The percentage drop in output power is approximately 14% for the polycrystalline PV module and nearly 16% for the monocrystalline PV module. However, for low solar irradiation, it is advisable to use monocrystalline modules, as a 21% decrease in power was observed for polycrystalline modules compared to a 9% decrease for monocrystalline modules. Additionally, the monocrystalline PV module was more affected by dust than the polycrystalline PV module under high solar irradiation conditions, while under low incident solar radiation, the polycrystalline PV module was more affected by dust than the monocrystalline PV module. The power drop of the monocrystalline PV module was greater than that of the polycrystalline PV module for high solar radiation (>500 W/m2). Therefore, the advantage of this proposed work is to recommend the use of polycrystalline solar panels in regions characterized by high solar irradiation and high temperatures instead of monocrystalline solar panels, which are more efficient in regions worldwide characterized by low solar irradiation and low temperatures.

Using satellite multi-angle polarization measurements to characterize atmospheric aerosol above Bohai Bay

The paper analyzes data from the PARASOL optical multi-angle polarization radiometer over the waters of Bohai Bay under various atmospheric conditions and different seawater optical types. The study considered cases of clear atmosphere, haze, dust aerosol, and cloud coverage. The waters of Bohai Bay were categorized into areas heavily influenced by river inflows and relatively clear waters. By utilizing PARASOL data, the degree of polarization (DoP) values of optical radiation at scattering angles of about 90° between incident solar radiation and recorded radiation were determined. Appropriate scatterplots were created using measurements from the 490, 670, and 865 nm bands. Polarimetric pseudo-color maps were presented to classify various atmospheric states. The scatterplots successfully identified atmospheric dust, dust in clouds, haze, and water areas with high levels of suspended particles. The results obtained are consistent with the experience of using the Umov effect to study dust aerosol, which consists in the negative correlation between the maximum polarization of radiation and geometric albedo. The presence of suspended particles in water led to decrease in correlation coefficients between analyzed DoP at different wavelengths within the investigated sea area. The strong influence of river inflows on Bohai Bay in polarimetric data was observed only under clean atmospheric conditions.

Energy performance assessment of a solar-driven thermochemical cycle device for green hydrogen production

This paper presents a novel dynamic simulation model for assessing the energy performance of solar-driven systems employed in green hydrogen production. The system consists of a parabolic dish collector that focuses solar radiation on two cerium-based thermochemical reactors. The model is based on a transient finite-difference method to simulate the thermal behaviour of the system and it integrates a theoretical analysis of materials and operating principles. Different empirical data were considered for experimentally validating it: a good agreement between experimental and simulated results was obtained for the temperatures calculated inside the thermochemical reactor (R2 = 0.99, MAPE = 6.3%) and the hourly flow rates of hydrogen, oxygen, and carbon monoxide (R2 = 0.96, MAPE = 10%) inside the thermochemical reactor. The model was implemented in a MatLab tool for the system dynamic analysis under different boundary conditions. Subsequently, to explore the capability of this approach, the developed tool was used for analysing the examined device operating in twelve different weather zones. The obtained results comprise heat maps of specific crucial instants and hourly dynamic trends showing redox reaction cycles occurring into the thermochemical reactors. The yearly hydrogen production ranges from 1.19 m3/y to 1.64 m3/y according to the hourly incident solar radiations, outdoor air temperatures and wind speeds. New graphic tools for rapid feasibility studies are presented. The developed tools and the obtained results can be useful to the basic design of this technology and for the multi-objective optimization of its layout and main design/operating parameters.

Micrometeorological Analysis and Glacier Ablation Simulation in East Kunlun

Worldwide, there are great challenges for meteorological monitoring and glacier ablation monitoring in high-altitude mountain areas. It is often difficult to capture fine-scale climate and glacial changes in high-altitude mountainous areas due to the harsh natural environment and the extreme lack of observational sites. Based on high-altitude meteorological stations erected on the eastern shore of Aqikkule Lake (AQK) and at the terminus of Shenshechuan Glacier (SSG), as well as on mass balance data from SSG, the characteristics and correlation of temperature, solar radiation, relative humidity, precipitation, wind speed and direction of the two regions, and the mass balance in the ablation area of SSG from 30 May 2022 to 18 May 2023 were analyzed, and the average melting depth of SSG was simulated. The results indicate the following: (1) The average annual temperature of AQK and the terminus of SSG is −3.7 °C and −7.7 °C, respectively, and the vertical lapse rate of temperature in the summer half of the year is greater than that in the winter half of the year. Precipitation timing has a great influence on daily temperature differences. (2) Precipitation in both places is concentrated in summer; the glaciers in this area are of the summer recharge type, and precipitation has a significant reducing effect on the solar incident radiation and increases the relative humidity in this region. (3) AQK and SSG both have local circulation development, in the area of AQK all year round due to the lake effect, while the terminus of SSG only has the development of valley winds in the summer, being controlled in the winter by the westerly wind belt. (4) The average mass balance value of the ablation area of SSG was −1786 mm as measured by the range poles method. The average annual ablation depth of SSG simulated by using the empirical formula was 587–597 mm, which is not large compared with other glacier areas in the Tibetan Plateau, and it has the characteristics of typical continental-type glaciers.

The energy efficiency of a solar greenhouse for biomass drying

Solar energy is a renewable, inexhaustible and clean source, it is becoming the main target of several applications, both domestic or industrial, cutting costs on electrical and thermal demands when compared with conventional sources. In the case of solar chamber, which makes use of incident solar radiation, it creates a favorable microclimate for drying inputs for reducing humidity to prevent the spread of biodegradable agents, on agricultural, forestry, and other products. With the objective to verify the energy efficiency of a prototype of the Greenhouse model, a solar chamber was built, where energy data and environmental variables were daily monitored in the drying process. For the determination of energy efficiency the ratio between converted energy into heat by the received energy was used. It was found that the chamber presented a daily energy gain of 220141,7 kJ, a daily thermal efficiency of 13,96% and up to 3 pm in 24,19%. The percentage difference in this efficiency is attributed to the chamber structure, which transmits and absorbs a higher percentage of solar energy during the day, but at night due to its transmissibility, emissivity properties, in addition to small structural failures that favor greater energy losses.

Performance Analysis of Bus Voltage in Distribution Network with High Penetration of PV Controlled via Data-Driven Approach

Integration of large-scale distributed photovoltaic (PV) generation resources can lead to technical challenges, particularly voltage rise caused by PVs power injection at the time of high solar radiation profile and low load demand. Reactive power control of PV inverters can help mitigate the voltage rise, which arises just for a short duration due to high incident solar radiation. There is a possibility to control functions on these PV inverters based on the rating of the PV inverter. For one-second resolution, local data-driven voltage sensitivity estimation is applied to update the control functions such as volt-var and volt-watt on the PV inverters so as to regulate the bus voltage. Different forms of solar radiation profiles, transient varying, smooth varying, and worst operating scenario corresponding to the minimum load at the time of high PV generation, are included. The study is demonstrated for different PV penetration levels. The voltage analysis on buses is performed using power hardware (PV emulator) in the loop simulation, at one of the buses in the network, while the remaining PVs are being controlled using volt-var control (VVC)/volt-watt control (VWC) methods. The applied approach confirms to maintaining bus voltage within limits even against a very short transient time instant of solar radiation profile.

Experimental optimization of the heating element for a direct-coupled solar photovoltaic water heater

In the last few years, the price of photovoltaic (PV) modules has decreased significantly. As a result, solar PV has become an interesting option for water heating. In a direct-coupled PV water heater (DPVWH) system, the PV array is directly connected to the heating element. Therefore, the optimization of the heating element resistance value is an essential step to design a DPVWH system. This research aims to optimize the resistance value of the heating element for different climatic conditions (Montreal and Bagotville in Canada, and Fez in Morocco). Simulation models were developed using MATLAB/Simulink and TRNSYS software to evaluate the performance of a PV system directly connected with the heating element over a one-year period. This simulation model was validated with an experimental setup. The coefficient of determination (R2) ranges from 98.75% to 99.89%. The results of the experimental optimization indicate that in areas with high incident solar irradiation, the optimal resistance value is low, while the opposite is true for areas with lower solar irradiation. Furthermore, it is found that a direct-coupled PV water heater with a capacity of 3000 Wp achieves an average annual solar fraction of 41% in Montreal, and 73% in Fez. Additionally, the simulation results show that the use of an MPPT (Maximum Power Point Tracking) controller could increase the PV energy production by 29% in average. However, a direct-coupled PV solar water heater system is recommended for a remote and cold region, due to its robustness, its low operating cost, and its simplicity.

Reflectance and Color Tuning in TiO2-CuO Nanoparticle Composition Mixing

Energy consumption for building cooling is directly related to incident solar radiation. Therefore, solutions of high reflectivity, while keeping color comfort, are being actively researched. Here, finite-difference time-domain (FDTD) simulations were used to investigate the influence of nanoparticle and core–shell additives on coating reflection and color. Different TiO2 and CuO nanoparticle mixings were tested, with relative concentrations varying from 0 to 20% of each on acrylic. The same compounds were used to define core–shells with a varied inner radius (0–30 nm) for both TiO2 and CuO as the core and shell. The numerical simulations demonstrate that mixing CuO with TiO2 enables dark colors while maintaining the overall reflectance. The reflectance results for the core–shell structure are comparable with those of the nanoparticles when CuO is the core, while a more pronounced color change is originated when CuO is the shell.

Tanques de armazenamento cilindricos e atmosféricos: otimização de projeto considerando critérios ambientais

Atmospheric tank projects cover a wide range of technical characteristics, ranging from their purpose, according to the regulatory framework, the type of product stored, the technical aspects of the tank to serve this storage with structural safety, and finally, the devices and technical resources to make the equipment financially and economically viable and sustainable. As a basis for criteria for this assessment, the correct regulatory framework for each type of tank, based on its application, and the correct selection of material for its performance and life expectancy, were addressed. Performance improvement criteria were also evaluated, such as the proper sizing of the tank inlet, outlet, and vent nozzles, the use of sensors and devices, and equipment to avoid overpressure or vacuum, and the use of internal floating roofs. In addition, environmental criteria were also presented, such as the correct selection of tank colors and the assessment of their area of ​​incidence of solar radiation. The list of criteria and technical, performance, and environmental details can be further complemented and developed with other characteristics of the tanks, and the objective of this article was to evaluate the main parameters of analysis to guide the developer of the tank project to execute it seeking to optimize technical data with immediate execution and operating costs and the environmental impact of project decisions for welded vertical cylindrical atmospheric storage tanks.

Experimental investigation of a compound parabolic concentrator with aerogel and polycarbonate cover

This study experimentally investigates the performance of a novel compound parabolic concentrator integrated with aerogel and polycarbonate cover for process heat generation in low to medium temperature ranges. The experimental setup included a compound parabolic concentrator with a flat absorber surface at its focal plane, with an optically transparent and thermally insulating aerogel placed over it. The assembly was enclosed within a compound parabolic shape made of anodised aluminium sheets, with a concentration ratio of four, and protected by a transparent polycarbonate cover. The under-the-sun experiments were performed in Mumbai, India between March and June, 2022. A test set-up was developed to characterise the performance of this collector using the Indian Standard code 16648 (Part5, 2017). Four compound parabolic concentrator configurations were examined: only compound parabolic concentrator, compound parabolic concentrator with aerogel, compound parabolic concentrator with aerogel and polycarbonate cover, and compound parabolic concentrator with polycarbonate cover. The results indicate that while the addition of the polycarbonate cover offered protection to the reflector against environmental elements such as rain, wind, dust, snow, and bird droppings, it also led to a reduction in optical performance by about 16 %. It was also observed that using compound parabolic concentrator with aerogel results in a 30.6 % increase in the collector efficiency at the testing site with an inlet water temperature of 60°C, ambient temperature of 20°C, and an incident solar radiation of 700Wm-2. Thus, this research contributes to the advancement of stationary, non-imaging concentrating collectors, catering to the thermal energy requirements of various processes in the low to medium temperature range.

High vacuum flat plate photovoltaic-thermal (HV PV-T) collectors: Efficiency analysis

Through a numerical model developed in MATLAB, we investigate the performance of a novel hybrid flat plate photovoltaic-thermal collector under high-vacuum (HV PV-T) to optimize the solar-to-thermal energy conversion and efficiently meet the thermal loads of industrial processes up to 150 °C along with additional production of electrical energy. In the proposed design, the photovoltaic (PV) cell is positioned directly above the Selective Solar Absorber (SSA) in a multi-layered PV-SSA structure.The performance analysis of the system has been first carried out by considering the theoretical Shockley-Queisser limit of the electrical efficiency, different values of energy bandgap (0.66 eV ≤Eg≤3.00eV), emittance (0.1≤ɛ≤1), and working temperature (25°C ≤TPV≤175°C) of the PV layer, and secondly by focusing on a wide variety of actual semiconductive materials. We analyzed the specific case of high bandgap materials, such as CdTe, CdS, and GaAs reported in previous publications. The analysis performed shows that full exploitation of the incident solar radiation with HV-PVT collectors can produce about 12.2% of electrical efficiency while 76.4% of the incident power remains available for thermal conversion at 100 °C. Moreover, obtaining the same annual energy using stand-alone solutions (i.e., a combination of the best PV and solar thermal collectors commercially available) would require up to 50% of the collector area more than the proposed HV PV-T collector.

Global Sensitivity of Penman–Monteith Reference Evapotranspiration to Climatic Variables in Mato Grosso, Brazil

Understanding how climatic variables impact the reference evapotranspiration (ETo) is essential for water resource management, especially considering potential fluctuations due to climate change. Therefore, we used the Sobol’ method to analyze the spatiotemporal variations of Penman–Monteith ETo sensitivity to the climatic variables: downward solar radiation, relative humidity, maximum and minimum air temperature, and wind speed. The Sobol’ indices variances were estimated by Monte Carlo integration, with sample limits set to the 2.5th and 97.5th percentiles of the daily data of 33 automatic weather stations located in the state of Mato Grosso, Brazil. The results of the Sobol’ analysis indicate considerable spatiotemporal variations in the sensitivity of ETo to climatic variables and their interactions. The dominant climatic variable responsible for ETo fluctuations in Mato Grosso is incident solar radiation (53% to 93% of annual total sensitivity—Stot), which has a more significant impact in humid environments (70% to 90% of Stot), as observed in the areas of the Amazon biome in the state. Air relative humidity and wind speed have higher sensitivity indices during the dry season in the Cerrado biome (savanna) areas in Mato Grosso (20% and 30% of the Stot, respectively). Our findings show that changes in solar radiation, relative humidity, and wind speed are the main driving forces that impact the reference evapotranspiration.

URBAN ISLAND EFFECT & MITIGATION MEASURES

As the global rate of urbanization is increasing, the cumulative effect of all the negative impacts of urbanization leads to the modification of the physical and chemical properties of the atmosphere, the soil surface, and the air quality,etc. The experience of higher temperature in the Urban areas compared to the rural areas as a result of the heat stored in the built structures from incident solar radiation and also due to the heat released from human activities (alterations of surface area, improper urban planning, infrastructure by replacing open land and vegetation), emissions from vehicles, machinery and equipment ,this phenomena leads to the formation of heat pockets that are called as the “Urban Heat Island” (UHI), which are mostly the city centers. High temperature in the city centers (urban areas) than its surroundings (suburban areas) cause discomfort to the dwellers in the summer time is alarming and requires much attention around the globe to overcome the advances in technology and its effects. An attempt has been made to list the various measures to mitigate UHI effect and the processes by which the mentioned strategies work. Key Words: Urban Heat Island, microclimate, solar reflectance, thermal emissivity, absorbed energy.