Research On The Distribution Of Global Surface Soil Moisture And Growth And Decline Based On SMOS And SMAP Data

As an important boundary condition for land-air interaction,soil moisture plays a key role in the global water cycle and energy cycle,directly affecting the hydrological cycle processes such as precipitation,runoff,infiltration and evapotranspiration.The rapidly developing satellite remote sensing technology provides a way to obtain soil moisture on a large spatial scale and in a long time series.Among them,passive microwave remote sensing has become the main means of obtaining large-scale soil moisture due to its outstanding characteristics such as short revisit period,long time series,wide coverage,and little influence by the shape and structure of ground objects.The spatiotemporal pattern of soil moisture is affected by meteorological,non-meteorological and other factors.Since the 21 st century,global climate changes have changed the distribution and storage of global water resources by affecting the availability of surface water.To a certain extent,it reflects the degree and scope of climate change.Therefore,to find out the distribution and changes of global soil moisture can theoretically help optimize hydrological model parameters and improve its prediction accuracy,and help understand climate change and regional water cycle processes;in practice,it not only helps to formulate scientific agricultural production At the same time,it has played a key role in crop yield estimation,flood warning,and drought monitoring.Therefore,this study is based on the representative SMOS and SMAP passive microwave soil moisture data,combined with land type information,using statistical indicators,soil moisture and time-related variables and other indicators to analyze the global surface soil moisture distribution and fluctuations.The changes are gradually analyzed,and the partial correlation coefficient is used to preliminarily explore the dominant factors of soil moisture changes in different regions.The main research results of the paper are as follows:(1)The temporal change of the global annual average soil moisture is stable,and the spatial distribution is obviously different.From 2011 to 2020,soil moisture showed fluctuating changes,and the overall changes were not obvious.Spatially,areas with higher soil moisture were distributed in eastern North America and northern South America;areas with relatively low soil moisture were mainly distributed in northern Africa,Oceania,and parts of Asia and Europe.The regions with persistently low values of soil moisture for many years mainly include northern Africa and western Oceania;the regions with persistently high values of soil moisture for many years include eastern North America and northern South America;the regions with multi-year changes are widely distributed in most regions of all continents.The spatial and temporal distributions of soil moisture captured by SMOS and SMAP were consistent.(2)The global soil moisture is on the rise as a whole,with a significant decline in some areas.The obvious rising areas of soil moisture are distributed in eastern North America,most of northern Africa and parts of southwestern Eurasia;the areas of soil moisture decline are distributed in central and western Europe,Oceania and most of South America.The soil moisture in the continuous high-value area for many years decreased significantly;the soil moisture in the continuous low-value area for many years increased to varying degrees;the soil moisture in the multi-year change area showed an overall upward trend.The soil moisture captured by SMOS and SMAP varied in different land types.Globally,the ebb and flow of soil moisture captured by SMOS and SMAP in cropland,grassland and other land types has opposite changes.In the relative change area,SMOS reflects that soil moisture increases in forests and farmland,and decreases in other land types and grasslands;SMAP reflects that soil moisture decreases in farmland and increases in other types of land.(3)The global soil moisture is affected by both precipitation and evapotranspiration,but the responses of soil moisture to precipitation and evapotranspiration are different in some regions.In areas where farmland and grassland are widely distributed and soil moisture is relatively high,such as southeastern North America,northwestern Europe,and the Arabian Peninsula in Asia,soil moisture changes are greatly affected by the decline in evapotranspiration.In Oceania,the Great Plains of North America and other regions where other land types and forests are widely distributed,changes in soil moisture are the result of a combination of precipitation and evapotranspiration.The change of soil moisture in the central and western typical regions is closely related to the decrease of precipitation,and grassland and scattered farmland are widely distributed in this region;the change of soil moisture in most of the eastern part is mainly caused by the increase of precipitation and the decrease of evapotranspiration,and the widely distributed and Forest.