Tuesday, December 05, 2023

 

Real-time assessments of regional weather and human comfort index on 10-meter-resolution were provided over Tiananmen area, Beijing


Peer-Reviewed Publication

SCIENCE CHINA PRESS

Simulated human comfort index over Tiananmen area, Beijing 

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HORIZONTAL DISTRIBUTION OF UNIVERSAL THERMAL CLIMATE INDEX IN ℃ AT 2-METER-OFF GROUND AT 10 A.M. JULY 1ST 2021, HIGHER VALUE INDICATES MORE HEAT STRESS.

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CREDIT: ©SCIENCE CHINA PRESS




This study is led by Dr. Xiaoran Guo and Dr. Chao Yan (both from Institute of Urban Meteorology, China Meteorological Administration). A fast urban micro-meteorology model was developed and applied over the central Beijing region in summer during a large outdoor event. In comparison with conventional weather forecast methods, the main feature of this model lies in the fine spacial structures of wind, air temperature, humidity and human comfort index revealed by the simulation, which is adequate to capture the shapes of local green belts, water surfaces and 3-D buildings. With these urban morphology resolved, their blockage effects on wind fields and sun lights are calculated as well as the evaporations over certain land type. To realize fast simulation, the wind fields around building cluster were constructed according to statistical relationships and empiracal parameterizations, which largely improve the computational efficiency comparing with traditional CFD methods. To quantify the comprehensive influences of weather and environment on human physiological process, universal thermal climate index was calculated and visualized as a main product for the weather service.

Taking the simulated horizontal distribution of human comfort index as an example, at 10 a.m. july 1st 2021, there were cool areas at the west sides of each building hidden in their shadows, while the east sides were generally under higher heat stress, partly due to the weak wind within building’s lee-side cavity zone. In contrast, through the evaporation processes, the hot stresses were considerably reduced by water surface while effectiveness of vegetation were limited. Through model verification, their results were generally in good agreement with measurements.

See the article:

Guo X, Yan C, Miao S. 2023. A rapid modeling method for urban microscale meteorology and its applications. Science China Earth Sciences, 66(10): 2224‒2238

JOURNAL

DOI

Satellite observations reveal latitudinal variability and asymmetry in local temperature responses to actual land cover changes


Peer-Reviewed Publication

SCIENCE CHINA PRESS

The temperature responses to all actual land cover changes (LCC). 

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(A) LATITUDINAL VARIABILITY IN THE TEMPERATURE RESPONSES TO LCCS (ΔTLCC) AND IN THE RATIOS OF ΔTLCC TO THE OVERALL TEMPERATURE VARIATION (ΔT) AT THE SAME LOCATION OVER THE SAME PERIOD; (B) SEASONAL ΔTLCC PATTERNS IN FOUR LATITUDE ZONES.

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CREDIT: ©SCIENCE CHINA PRESS




Land cover changes (LCCs) affect surface temperatures at local scale through biophysical processes. However, limited by the coarse spatial resolution of available data, past observation-based studies mainly focused on the potential effects of virtual afforestation/deforestation using the space-for-time assumption. Prof. Li and his team firstly generated a high-resolution temperature dataset, and then explored the actual effects of all types of realistic LCCs by adopting the space-and-time scheme and utilizing extensive satellite observations.

They identified a total of 529,128 1-km pixels experienced LCC from 2006 to 2015. The widely studied afforestations/deforestations accounted for 46.28%, whereas previously underexplored transitions within non-forest vegetation types and almost unnoticed changes involving non-vegetation types occurred with proportions of 18.62% and 35.10%, respectively, illustrating the necessity to explore the comprehensive influences of all LCC types instead of considering only the influences of forest changes, as has been done in previous research.

The average temperature in the areas with LCCs increased by 0.08 K globally, but varied significantly across latitudes, ranging from -0.05 K to 0.18 K. These effects accounted for up to 44.6% of overall concurrent warming, emphasizing the importance of LCC biophysical influences. By comparing the importance of different LCC processes within a unified framework, the researchers found that cropland expansions dominated cooling effects in the northern mid-latitudes, whereas forest-related LCCs caused warming effects elsewhere.

Unlike the symmetric assumption of potential effects, the researchers revealed obvious asymmetries in the actual effects: LCCs with warming effects occurred more frequently, with stronger intensities, than LCCs with cooling effects. Even for the mutual changes between two covers in the same region, warming LCCs generally had larger magnitudes than their cooling counterparts. Attribution analysis indicated that the asymmetric temperature effects was caused by a combination of asymmetric changes in transition fractions and driving variables. These findings demonstrated that the increase in temperature resulting from a specific LCC cannot be counteracted by simply performing its reverse LCC of the same area during the same period, providing a new perspective on the land management and climate adaptation policies.

https://doi.org/10.1016/j.scib.2023.09.046

(a) Area weight of each type of LCC in global LCCs and (b) the influence of each type of LCC on temperature.

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©Science China Pres

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