| The Qilian Mountain ranges provide nearly all the sources of water for the inland river basins(terminal lakes)in the arid northwest region of China,making it the "water tower" of the inland river basins.Since rainfall and evapotranspiration are important sources of water input and output in the hydrological cycle of the Qilian Mountains,respectively,accurate acquisition of rainfall and evapotranspiration data in the mountainous areas is of great significance for analyzing regional water resources changes,and ensuring the regional sustainable development.Current methods for obtaining rainfall and evapotranspiration data are mainly based on in-situ observations and satellite remote sensing.However,due to the complex natural environment and terrain conditions in the Qilian Mountains,the hydrological observation station is scarce,and the applicability of remote sensing products in the cold mountainous areas is limited.Therefore,obtaining rainfall and evapotranspiration data in mountainous areas is quite challenging,and it is urgent to develop a rainfall and evapotranspiration acquisition method suitable for cold mountainous areas.Research shows that rainfall and evapotranspiration information is contained in soil moisture observation data,and the method of estimating rainfall and evapotranspiration based on soil moisture has been widely used.At the same time,compared with meteorological observation,soil moisture observation is convenient and easy to install in mountainous areas with complex terrain.However,there is still insufficient research on assessing the applicability and the sources of errors of such methods of using soil moisture to estimate rainfall and evapotranspiration in cold mountainous areas.Meanwhile,the effects of different environmental factors on the performance of the methods have not been adequately analyzed.Therefore,based on the meteorological stations in the upstream of the Heihe River in the Qilian Mountains,such as Dayekou and Arou,this study evaluated the applicability of using soil moisture to estimate rainfall and evapotranspiration in the cold mountainous areas.Firstly,this study assessed the applicability of using the SM2RAIN(Soil Moisture to Rainfall)algorithm to estimate rainfall in cold mountainous areas based on the surface soil moisture data and rainfall data of nine meteorological stations such as Dayekou,Arou,and Dashalong.The study also analyzed the influence of different landcover types and elevations on the performance of the SM2 RAIN algorithm in estimating rainfall,and compared the estimated rainfall with the CMFD(the China Meteorological Forcing Dataset)rainfall data.Inaddition,based on the soil moisture profile and evapotranspiration data of Dayekou and Arou stations,the performance and error sources of using the improved soil water balance method(ISWB)to estimate evapotranspiration in cold mountainous areas were also analyzed,and compared with the conventional evapotranspiration estimation methods of FAO-56 Penman-Monteith(FAO-56 PM)and Hargreaves-Samani(HS).The main conclusions of this study are as follows:1.Rainfall estimation using the SM2 RAIN in cold mountainous areas(1)The SM2 RAIN algorithm behaves differently for different landscapes in high mountainous areas.In general,the performance of the SM2 RAIN in alpine meadows is better than in forest and farmland.Forestland has strong rainfall interception,and soil moisture responds only to heavy rainfall events,leading to the underestimation of rainfall by the SM2 RAIN algorithm.Irrigation events in farmland led to an increase in soil moisture,resulting in inaccurate estimation of rainfall by the SM2 RAIN algorithm.(2)In the cold mountainous areas,the performance of the SM2 RAIN decreases with rising elevation.The higher the altitude,the greater the rainfall,and the wetter the surface soil,surface runoff and deep infiltration are more likely to occur during rainfall,which leads to an underestimation of rainfall by the SM2 RAIN.(3)Rainfall products based on the SM2 RAIN algorithm have great potential for estimating large-scale rainfall in high-altitude mountain areas.Comparison of Rsim(estimated rainfall from in-situ soil moisture by the SM2 RAIN algorithm),SM2RAINASCAT(the Advanced SCATterometer)(estimated rainfall from ASCAT soil moisture by the SM2 RAIN algorithm)and CMFD rainfall data with in-situ observed rainfall shows that the Rsim has the best performance,and SM2RAIN-ASCAT and CMFD have similar performances in estimating rainfall in the study region2.Evapotranspiration estimation using the ISWB in cold mountainous areas(1)ISWB can accurately and reliably estimate evapotranspiration,and provide a new method for the quantitative study of evapotranspiration in mountainous areas.Comparisons of the estimated evapotranspiration using the ISWB,FAO-56 PM,and HS methods with the observed evapotranspiration indicate that the ISWB method performs better than the FAO-56 PM and HS methods.(2)The performance of evapotranspiration estimation using the ISWB method from surface(0-5 cm)soil moisture at the Dayekou and Arou observation stations is poor,indicating that the information on evapotranspiration contained in the surface soil moisture is limited.(3)The 0-25 cm soil moisture profile is the main source of evapotranspiration under grassland in the study area.The performance of the ISWB method for evapotranspiration estimation performs better in the soil layers below 25 cm compared to the surface layer(0-20 cm),and there is no significant difference in the performance of the ISWB between the soil layers below 25 cm.(4)The errors of the ISWB method mainly include:(1)the influence of canopy interception evaporation on ET estimation,(2)the uncertainty in the correlation between soil moisture loss(LSM)and observed ET,and(3)the uncertainty of the parameters of the ISWB.This study analyzed the performance of using soil moisture to estimate rainfall and evapotranspiration,respectively,in high altitude mountainous areas,and the results show that the SM2 RAIN and ISWB methods can estimate rainfall and evapotranspiration well in mountainous areas.The above research results provide a new,simple,and reliable method for obtaining rainfall and evapotranspiration data in datascarce high-altitude mountainous areas,supporting research on hydrological processes and analysis of regional water resource balance in mountainous areas. |
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