Characteristics and East Downscaling Forecast Model of Summer Precipitation in Northwest China

Abstract

Based on the precipitation data provided by China Meteorological Administration and NCEP/NCAR reanalysis data（data comes from a joint project between the National Centers for Environmental Prediction （NCEP） and the National Center for Atmospheric Research （NCAR））， this paper analyzed the climatic characteristics of precipitation in northwest China from 1961 to 2018， and constructed a statistical downscaling forecast model for short-term prediction of precipitation in eastern northwest China.The results demonstrate that the precipitation in northwest China showed an increasing trend from 1961 to 2018， especially after 2000.The precipitation in northwest China is characterized by less in the west and more in the east， while the precipitation in the western part of northwest China increases obviously， while there is no obvious trend change in the eastern part of northwest China.According to the attribution analysis of summer precipitation in the eastern part of Northwest China， four key factors were found， that is affecting the precipitation in the eastern part of Northwest China in the same period： geopotential height field of 200 hPa isobaric surface in Central Asia， meridional wind field of 850 hPa isobaric surface in North Pacific， zonal wind field of 850 hPa isobaric surface in North Atlantic and sea level pressure in South Indian Ocean.These four factors respectively reflect the characteristics of westerly jet， the "minus and plus" structure of sea level pressure in North Pacific， the characteristics of the North Atlantic Oscillation and the intensity of Mascarene High.When the intensity of westerly jet is stronger and the position of westerly jet is further north， the "minus and plus" structure of sea level pressure in the North Pacific Ocean is weaker， the North Atlantic Oscillation is stronger or the Mascarene High is weaker， it is beneficial to the precipitation in the eastern part of Northwest China.In the establishment stage of downscaling model， the average deviation between the downscaling model results and the summer precipitation in the eastern part of northwest China is 17.5 mm， and the average deviation rate is 10.3%.In the downscaling model test stage， the average deviation between the downscaling model results and the summer precipitation in the east of northwest China is 26.2 mm， with an average deviation rate of 16.4%.The statistical downscaling model can generally predict the precipitation in the eastern part of Northwest China， which can provide a new idea for the short-term climate prediction of precipitation in northwest China.

Keywords

• northwest china
• summer precipitation
• statistical downscaling
• precipitation forecast