The Effect Of Topographical And Monsoonal Factors On The Spatial-temporal Variations Of The Climate Extremes Over North China

North China is one of the most important agricultural areas and industrial production centers in China.This area is also strong affected by the impact of climate extremes.In recent years,an increase in the climate extremes has been found over this area,which resulted in considerable socio-economic loses.This study investigates the variations of the climate extremes over China through spatial and temporal approaches.The spatial variations of the climate extremes,including the mean climatological distribution and the climatic trends,are firstly discussed.We further investigate the correlation between spatial variations of the climate extremes and various topographical factors and use such correlation to perform a downscaling analysis of the climate extremes so as to provide scientific information for understanding the fine-scale distribution of local climate extremes.The result shows a general increase(decrease)in high-temperature(frozen)days over North China during 1961-2016.A general increase(decrease)is also found in the consecutive warm(cold)events.For precipitation extremes,dry days tend to decrease(increase)over the northern(southern)area,while heavy rain days tend to increase(decrease)over the northern(southern)area;Moreover,consecutive dry days tend to increase(decrease)over the northern(southern)area,while consecutive wet days tend to increase(decrease)over the northern(southern)area.Given the significant impact of the East Asian Monsoon,the variation of monsoonal intensity can lead to apparent differences in climate extremes and the associated large-scale circulation patterns.With intensified summer(winter)monsoon,an increase in the high(low)temperature extremes is found in June-August(December-February)over most of North China.A relatively strong winter monsoon can lead to significant decreases in dry days and consecutive dry days over the northeast of Inner Mongolia.A relatively strong summer monsoon can lead to minor increases in consecutive wet days in the mid of North China.The correlation between climate extremes and topographical factors is analyzed through the DEM(digital elevation model)downscaling analysis.A close correlation is found between latitude and the local extreme events.The climate extremes are also found to be strongly affected by various factors including longitude,slope and the meridional/zonal components of aspect.Furthermore,the DEM downscaling analysis of the extreme events are found to be able to resolve more details in the influences of geographical factors to the spatial characteristics of extreme events,which can provide useful information of the climate extreme distributions within county-scale for the local impact assessment of climate extremes.Overall,the climate extremes in North China are found to be closely associated with the physical fields of monsoonal systems as well as topography.The use of such associations is helpful to understand the physical mechanism of the variation in local climate extremes,which can provide important information for coping with regional climate change.