| The three northeastern provinces are located in the high latitudes of China and have an abundance of water resources.As a result of global climate change,the total amount of water resources is also changing,which can affect crop growth,soil texture and ecological balance,thus having an impact on the economic development of food in the three northeastern provinces.Water storage is one of the most important indicators of water resources.The study of the spatial and temporal variability of water storage and its influencing factors has become a hot issue that needs to be addressed.This paper monitors the variation of terrestrial water storage in three northeastern provinces from2002 to 2017 based on GRACE gravity satellite data,and estimates the variation of groundwater storage in the study area using the water balance principle in connection with the GLDAS hydrological model,and compares the storage variation calculated based on the measured groundwater level data.To explore the effects of natural and human-induced factors on groundwater storage variations.Exploring drought conditions in the study area using GRACE data.The results of the study show that:(1)The GRACE monitoring of changes in terrestrial water reserves in the three northeastern provinces is generally consistent with the estimated changes in groundwater reserves.Modelled groundwater storage variations correlated well with measured groundwater storage variations,with a correlation coefficient of 0.72.Groundwater storage fluctuates throughout the year.the average growth rate was2.23mm/a.Maximum surpluses were generated in 2013 due to the severe flooding that affected the three northeastern provinces in that year,and maximum losses were generated in 2008 due to severe drought events in the three northeastern provinces.Groundwater storage had the largest surplus at the end of 2013,and the largest deficit at the beginning of 2008.The loss was obvious in winter and autumn,and gradually picked up in spring,and there was surplus in summer.The sudden variation points in groundwater storage between years,in spring,autumn and winter,all occurred around2012.The amount of change in groundwater storage basically follows a gradual upward trend after the abrupt variation had occurred.This is mainly due to the most severe soil drought and a significant decrease in soil moisture in spring,strong rainfall caused by several typhoons landing in autumn and widespread snowstorms in winter.The spatial distribution of terrestrial water storage had obvious differences.Groundwater reserves in the three northeastern provinces were less in the northeast and more in the southwest from 2002 to 2012,and more in the northeast and less in the southwest from 2013 to2017.The Daxing’an mountains of Heilongjiang Province has a stable groundwater storage capacity due to its strong soil water-holding capacity,while the spatial distribution of the other regions varies more markedly.Groundwater Storage in Liaoning Province and southern Jilin Province,which have been stable year-round,have been severely affected by droughts,and groundwater storage began to be in deficit and had difficulty recovering to normal levels over the long term,with the trend of deficit gradually spreading to Heilongjiang Province.The area around the Changbai Mountains was less affected by the floods and had the smallest increase in land water storage and groundwater storage in 2013.(2)The correlation between the groundwater reserves and the measured groundwater reserves in the black soil area of the Songnen Plain was high using GRACE simulations,with a correlation coefficient of 0.61.The average growth rate of groundwater reserve change over the study period was 4.09 mm/a,which was significantly higher than the measured groundwater reserve change.As its combined area is smaller than that of the three northeastern provinces,the magnitude of groundwater storage change is higher than that of the three northeastern provinces.There is also some temporal variability in the amount of groundwater storage change.The groundwater storage variation reached a maximum of 105.36 mm in October 2013 and a minimum of-139.94 mm in early 2008,which also affected by floods and drought disasters.Groundwater storage showed abrupt inter-annual,spring,summer and winter change points all around the second half of 2012,and also showed significant increases after the abrupt changes occurred,mainly due to increased precipitation in summer and autumn and widespread snowfall in most areas in winter,leading to a sustained rise in terrestrial water storage,which caused an increase in groundwater storage.The spatial distribution of groundwater storage in the black soil area of the Songnen Plain has significant seasonal differences.Some areas have significant surpluses in groundwater storage in summer and winter.There is also a surplus to some extent in spring due to the longer snowmelt in Heilongjiang Province.The largest surplus of groundwater reserves in summer and winter was located in Wudalianchi,where due to the local geological and environmental conditions,the surface water resource content is abundant,precipitation is abundant and the winter season is influenced by snowfall,groundwater reserves have been on an increasing trend for 16 consecutive years and total water resources are abundant.(3)Changes in precipitation were highly significantly correlated with groundwater storage changes in the three northeastern provinces,and the correlation coefficient was0.33.Agricultural water use is also highly significantly correlated with groundwater storage changes,and the correlation coefficient was 0.59.The pattern of temporal changes in groundwater storage is generally consistent with the pattern of changes in precipitation,but there is some delay in peak and trough values.In terms of spatial distribution,the Daxing’an mountains of Heilongjiang Province had a strong capacity to contain soil water,and during periods of decreasing precipitation,land water storage and groundwater storage also had an increasing trend.The Liaohe Plain and the Changbai Mountains were affected to some extent by potential evapotranspiration in addition to precipitation.During periods of increased precipitation,there is a significant deficit in terrestrial water reserves,while groundwater reserves remain stable and unchanged.Groundwater storage variations were also influenced by potential evapotranspiration in north-western Heilongjiang Province.Potential evapotranspiration and surface runoff can influence groundwater storage changes with other factors.Potential evapotranspiration was most significantly correlated with precipitation,and the correlation coefficient was 0.8,first showing a positive correlation and then a negative correlation as precipitation increased to a certain level.Surface runoff had the most significant response relationship with soil moisture,and the correlation coefficient was 0.68,showing a significant positive correlation in the later stages of increasing soil moisture.Agricultural water use fits well with the amount of groundwater storage change,with high correlation coefficients.For different stages of agricultural water use change,the amount of groundwater storage change will respond.For the black soil area of the Songnen Plain,the main influencing factors on groundwater storage changes are potential evapotranspiration and precipitation.(4)The standardized water storage deficit index(WSDI)was more accurate for monitoring drought events in the three northeastern provinces and the black soil region of the Songnen Plain.The 2006 drought event was characterised by spring drought with summer drought in both Heilongjiang and Liaoning Provinces,and spring-summer drought with severe autumn hanging in Jilin Province.Large-scale severe drought events began to occur in the study area in 2007,with drought phenomena of long duration and intensity.The drought led to a dramatic reduction in the production value of farmland in the three northeastern provinces and the black soil area of the Songnen Plain.Severe spring droughts occurred in Heilongjiang and Jilin provinces in 2008.There was also a severe drought event in the three northeastern provinces region between 2011-2012,with the greatest drought intensity between 2002-2017.In addition,WSDI can also accurately monitor potential drought events that had less impact on the climate environment.The WSDI drought index was more consistent with the SPI-12,SPEI-6,SPEI-12 and sc PDSI drought indices,and the WSDI correlation with the sc PDSI is the most obvious,and the correlation coefficient was 0.75.The severity of drought events in the Black Soil Region of the Songnen Plain was significantly higher than that of the three northeastern provinces,mainly due to the long duration of the drought events.The drought events that were commonly monitored by the drought index could be monitored by the WSDI,indicating that the WSDI was more applicable in the Songnen Plain region.2006-2009 was the longest and most severe drought period in the black soil area of the Songnen Plain,with a medium drought rating.2007 saw a rare summer drought in the eastern part of the Songnen Plain.All WSDI indices in the study area show an increasing trend,with drought conditions alleviated after 2013.To explore the spatial and temporal changes in terrestrial water reserves and their influencing factors in the three northeastern provinces and the black soil areas of the Songnen Plain,and to analyze the characteristics of their drought events,provides a scientific and theoretical basis for studying the changing characteristics of water resources in cold regions and improving the development and use of groundwater in cold regions.It played an important role in implementing efficient agricultural irrigation technology and optimizing the allocation of agricultural water in cold regions.This study further laid the theoretical foundation for regulating crop water demand during drought periods in cold regions and reducing the risk of food production.The importance of analyzing the monitoring,assessment and drought forecasting of large regional hydrological droughts was emphasized.The results of the study had important reference value for the economic development of the northeast region,the optimal allocation of water resources across basins and the sustainable development of the ecological environment in China and globally. |
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