Impact Of Vegetation Parameters On Regional Climate Simulation In China

The land surface process is an essential component of the climate system as it interacts with the atmosphere through hydrometeorological,biophysical and biogeochemical processes.Therefore,the regional climate model simulation performance strongly depends on the accuracy of land surface boundary conditions.In particular,the use of vegetation parameters with higher accuracy and spatial resolution is necessary to improve the land surface process parameterization so that the land-atmosphere interaction can be realistically represented and the regional climate model performance can be enhanced.In this paper,the MODIS LAI data with interannual variations from 2000 to 2015 are used in the regional climate model CWRF,replacing its default AVHRR LAI data with only the annual cycle,to evaluate their effects on China's climate simulation,focusing on the annual cycle,interannual variation,extreme precipitation and climatic trend.The main conclusions are as follows:(1)MODIS and AVHRR LAI data show large differences in China,with obvious seasonal variations.The largest differences occur during summer in Inner Mongolia,the Central China,and the Northeast.Numerious studies have concluded that MODIS LAI makes many improvements and corrections to AVHRR LAI,and hence better reflects observed land vegetation conditions.This study compares the experiments between CWRF 2000-2015 simulations using MODIS LAI(EXP)and AVHRR LAI(CTL)and demonstrates that EXP improves over CTL China's climate simulation,especially the annual cycles of temperature and precipitation over regions with large LAI differences.(2)MODIS LAI improves over AVHRR LAI also in the CWRF simulation of China's climate interannual variations.In all seasons,the interannual correlations with observed surface air temperature,precipitation,relative humidity,and surface wind speed anomalies are systematically higher by EXP and than CTL.These climate variables simulated by EXP are more consistent with the observed evolutions,especially in the Northeast,where MODIS and AVHRR LAI values differ most.EXP using MODIS LAI with interannual variations corrects CTL using AVHRR LAI with only the annual cycle in spatiotemporal biases from observations,and hence enables CWRF to more accurately represent the land surface and atmospheric interaction processes,both of which improves the regional climate simulation.(3)MODIS LAI improves over AVHRR LAI futher in the CWRF simulation of China's extreme precipitation in spring,summer,and autumn,especially over the Northeast.From the climatological mean perspective,higher LAI values from MODIS than AVHRR increases evapotranspiration and hence precipitation through their positive feedback over the region,causing CWRF to simulate more extreme precipitation in EXP closer to observations than CTL.In addition,EXP including interannual variations of MODIS LAI more accurately represents the trend of observed vegetation,and thus improves the simulation of the climatic trends of precipitation and surface air temperature.