Vertical Variation Characteristics Of Precipitation And Its Influencing Factors In Qilian Mountains

Atmospheric precipitation,as an important link in the global water cycle,maintains the stability of global ecosystems,and too much or too little precipitation is prone to natural disasters such as floods and droughts.Research on regional water resources management,hydrological modeling,industrial and agricultural production and natural disaster prediction depends on accurate precipitation monitoring and forecasting.This paper first evaluated the applicability of five sets of precipitation products,TRMM,GPM,PERSIANN,MERRA2 and GLDAS,in the Qilian Mountains region based on measured precipitation data from 35 stations in the Qilian Mountains region,and further used two data fusion methods,Bayesian model averaging(BMA)and integrated model output statistics(EMOS),to derive a set of high-precision precipitation products applicable to the Qilian Mountains region,based on which the spatial and temporal distribution and elevation gradients of precipitation in the Qilian Mountains region from2001 to 2018 were analyzed.Secondly,based on the data of total water vapor,elevated condensation height and convective effective potential energy from ERA5 reanalysis data,the reasons for the different gradient characteristics of precipitation in the Qilian Mountains were explored,and the linear relationship between precipitation and each influencing factor was fitted.Finally,the relationship between the maximum precipitation height zone and glacier equilibrium line and forest line in the Qilian Mountains was analyzed by the second glacier inventory data and land use data.The following conclusions were mainly drawn.(1)The five sets of precipitation products showed different advantages at annual and different seasons,but no set of products showed advantages at annual and all seasonal scales at the same time.The correlation between the two sets of fused data and the measured precipitation was higher than that of the five sets of precipitation products;the root mean square error was lower than that of the five sets of precipitation products,and the correlation coefficient between the two sets of fused data and the measured precipitation was close to 0.9 except in winter,which indicated that the two sets of fused data were highly correlated with the measured precipitation with small errors and can be used for the analysis of the maximum precipitation height zone in the Qilian Mountains.Comparing the ratio of the standard deviation of the two sets with the measured precipitation,it was found that the BMA fusion data is better than the EMOS fusion data.(2)In terms of time,the multi-year average precipitation in the Qilian Mountains region was 207.1 mm,with the maximum annual precipitation occurring in 2018(276.3mm)and the minimum annual precipitation occurring in 1991(156.6 mm).The corrected multi-year average precipitation is 283.7 mm.Over the past 39 years,the annual precipitation showed a significant fluctuating upward trend with an average annual increase of 1.1 mm(P<0.05).The annual seasonal precipitation in the Qilian Mountains decreases with the rise in altitude,with a maximum precipitation height around 2900 m and a secondary precipitation height around 3500 m.The annual precipitation in the Qilian Mountains decreased with the rise in altitude,with a maximum precipitation height around 2900 m and a secondary precipitation height around 3500 m.The annual precipitation in the Qilian Mountains decreased with the rise in altitude.There was a maximum precipitation height around 2900 m and a secondary precipitation height around 3500 m.(3)The partial correlation coefficients of precipitation with total water vapor,lifting condensation height and convective effective potential energy in the Qilian Mountains region showed that precipitation in the Qilian Mountains region was significantly positively correlated with total water vapor and convective effective potential energy and negatively correlated with lifting condensation height,indicating that precipitation in the Qilian Mountains region was influenced by all three factors together.Based on the topographic factors and meteorological conditions,a hierarchical regression analysis was applied to analyze the factors influencing precipitation in the Qilian Mountains and the eastern,middle and western sections,and it was found that total water vapor was the most important factor influencing precipitation in the Qilian Mountains and the middle section,and convective effective potential energy was the most important factor influencing precipitation in the eastern and western sections.(4)The maximum precipitation height and the maximum precipitation amount in the eastern section of Qilian Mountains had shown a weak upward trend over the years,with an average annual increase of 20.9 m and 1.5 mm respectively,and both upward trends were not significant;the maximum precipitation height in the middle section showed a non-significant downward trend,with an average annual decrease of 8.9 m,and the maximum precipitation amount showed a significant upward trend,with an average annual increase of 6.8 mm;the maximum precipitation height in the western section showed a significant upward The maximum precipitation height in the western section showed a significant upward trend,rising by 46.9 m per year on average,and the maximum precipitation volume showed a non-significant upward trend,rising by3.2 mm per year on average.The average elevation of glacier equilibrium line in Qilian Mountain area was 4900 m;the average elevation of forest line is 3100 m;the average elevation of maximum precipitation height was 3600 m.The forest line,maximum precipitation height line and glacier equilibrium line were distributed from low elevation to high elevation in order.