土地利用资料的更新对四川盆地高温天气数值模拟的影响

Influences of updated land-use datasets on WRF simulations for high-temperature weather in Sichuan Basin

土地利用情况影响区域天气和气候,采用与实况更为接近的下垫面资料能够为数值预报提供有力支撑。使用中尺度数值模式WRF对2019年8月四川盆地高温过程进行数值模拟试验,对比基于2019年更新的MODIS土地利用数据与WRF自带土地利用资料的差异,分析下垫面资料的更新对数值模拟效果的影响。结果表明:两组土地利用资料存在明显差异,更新后的MODIS资料刻画更为精细,模拟区域的土地利用类型更加丰富。2 m气温对土地利用资料十分敏感,更新土地利用资料后两次个例平均的2 m气温2℃以内的模拟准确率提高6.2%,日最高气温模拟准确率提高31.3%;而日最低气温模拟准确率下降2.1%。土地利用资料变化明显的四川盆地内部较更新前增温明显,局部增温超过4℃,最高气温模拟偏低的状况明显改善。选取四川盆地内部地表类型由农田转为城市和建筑的合川站作为典型站点进行分析,发现土地利用类型更新后发射率减小,植被气孔阻抗增大,粗糙度增大,陆面参数的变化导致地表对边界层大气向上的感热输送增加,地表蒸发及大气水分供应减少,气温升高,边界层高度升高。模拟初期土地利用资料的更新造成模拟差异的局地性较强,随着模拟时间增加,逐渐影响中高层及周边大气。土地利用资料的改变通过影响陆面参数的选择,导致模拟结果的差异。更新土地利用资料后可有效改善2 m气温及最高气温的模拟效果。

Land use affects regional weather and climate.The use of land-use data that is updated and closer to the observation can provide strong support for numerical prediction.The high-temperature processes in August 2019 in Sichuan Basin are simulated by using the mesoscale numerical model WRF.Updated land-use datasets extracted from MODIS data are compared with original WRF datasets,and the influences of updated land-use data on WRF simulation are analyzed.The results show that there are significant differences between two sets of land use data,the updated data is more detailed,and the land use types of the simulated area are more abundant.The2 m temperature is very sensitive to land use data,with update of land-use data,the accuracy ratio(absolute errors less than 2 ℃) of simulated 2 m temperature increased by 6.2%,and that of daily maximum temperature increased by 31.3%;the accuracy of simulated daily minimum temperature decreased by 2.1 %.Simulated temperature increases significantly in the Sichuan Basin where the land-use changed obviously,the increase in some areas is more than 4 ℃,and the negative bias in simulated daily maximum temperature by using original land-use datasets significantly reduces.The Hechuan station is selected as a typical station in the Sichuan Basin for analysis,where land-use type is changed from croplands to urban and built-up.It is found that after the change of land use type,the emissivity decreases,the roughness increases,and the stomata resistance of vegetation increases,and as a result,the upward sensible heat flux increases,surface evaporation and atmospheric water supply reduces,2 m temperature increases,and planet boundary layer height increases.Updated land-use data results in strong locality of the simulation difference in the initial stage,as the lead time increases it gradually affects the upper atmosphere and surrounding areas.Land-use data lead to differences of simulations by affecting the selection of landsurface parameters.The accuracy of simulated 2 m temperature and maximum temperature are improved with update of land-use data.