土地利用类型影响四川盆地一次高温过程的模拟研究

Simulation Study on the Effect of Land Use Type on a High Temperature Process in Sichuan Basin

土地利用变化可通过影响地气间能量交换影响数值模式的预报效果。本文利用WRF模式对四川盆地2021年8月1—4日高温过程进行数值模拟,探究土地利用类型变化对模式高温天气预报能力的影响。结果表明:(1)GLC_FCS30-2020资料反映的近期土地利用类型相比WRF模式默认土地利用类型有明显差异,主要表现为农田、混交林急剧减少,城市与建筑、多树草原、稀树草原和农田/天然植被镶嵌类型明显增加。(2)土地利用类型更新后,WRF模式对高温天气,尤其是对最高气温的预报能力有明显提升,主要表现为气温冷偏差减小、暖偏差增加,即日间、最高温度、四川盆地中部地区的预报能力有明显提升,而夜间、最低温度、盆地东部和西部局部地区的预报能力有所下降。(3)土地利用类型变化使地表反照率增加使地表净辐射减少,但地表水热输送方式的变化是影响地表温度变化的主要原因。更新土地利用类型后,日间潜热通量输送减少,感热通量和地表热通量输送代偿性增加且变化幅度相当,从而导致地表气温升高。下垫面土地类型未改变的站点温度变化,可能是由于周边高温的水平运动导致的。(4)天空状况越晴朗,温度模拟与观测的偏差越大,温度预报能力越低。此外,更新土地利用类型可以间接引起云量变化。

Land use(LU)change can affect the forecasting performance of numerical models by influencing the energy exchange between land and atmosphere.In this study,the WRF model was used to simulate the high temperature process in the Sichuan Basin from August 1 to August 4,2021,and the impact of LU types change on the high temperature weather forecast ability of the model was discussed.The results show that:(1)There are significant differences between the recent LU types reflected by the GLC_FCS30-2020 data and the default LU types of WRF model,mainly manifested as sharp decreases in croplands and mixed forests,and significant increases in urban and built-up,savannas,woody savannas,and cropland/natural vegetation mosaic.(2)Updating the LU types significantly improves the temperature forecasting ability for high temperature weather,especially the maximum temperature.This is mainly manifested as a decrease in the cold bias and an increase in the warm bias,that is,the ability to forecast daytime,maximum temperature,and the central area of Sichuan Basin is significantly improved,while the forecst ability of nighttime,minimum temperature,and some areas in the eastern and western parts of the Basin is slightly decreased.(3)LU changes increase surface albedo and reduce net radiation,but the changes of surface water and heat transport are the main cause of surface temperature changes.After updating the LU types,the daytime latent heat flux transport decreases,while the sensible heat flux and surface heat flux transport compensatory increase,resulting in an increase in surface temperature.The temperature changes of stations without changing the LU type may be caused by the horizontal movement of surrounding high temperatures.(4)The clearer the sky condition is,the greater the deviation between the temperature simulation and observation is,and the lower the temperature forecasting ability is.In addition,updating LU types can indirectly cause changes in cloud cover.