Evaluation Of Evapotranspiration And Submarine Fresh Groundwater Discharge In Laizhou Bay Catchment Area

Submarine groundwater discharge(SGD)is an important part of water and material exchange between ocean and land.Driven by both terrestrial and marine forcing components,SGD comprises submarine fresh groundwater discharge(SFGD)and re-circulated submarine groundwater discharge(RSGD).SGD increases the amount and variety of dissolved substances in seawater.SFGD,a net water input from land to ocean increases the volume of seawater.Laizhou bay is one of the three bays in the Bohai Sea,China.It is a semi-enclosed bay and the coastline length is 319.06 km.The catchment of Laizhou bay comprises 11 river basins and covers an area of 33537.83 km~2.According to previous studies,the SFGD in Laizhou bay is very large.In order to verify this conclusion,this study takes the laizhou bay catchment area as the research object,and estimates the SFGD in Laizhou bay,based on analysis of the spatial and temporal variation of evapotranspiration in Laizhou Bay catchment area.Based on SEBS(Surface Energy Balance System)algorithm and Water balance principle,the evapotranspiration,NDVI and SFGD were estimated using ENVI software,AVHRR data,DEM data and meteorological data in the Laizhou bay catchment area from 2006 to 2015.Furthermore,the long-term variation and spatial distribution of evapotranspiration are studied.The results are was follows.(1)Evapotranspiration is affected not only by vegetation,air pressure,air temperature,wind speed,humidity,but also by rainfall and irrigation.Evapotranspiration is larger in coastal area than the inner land areas.Due to the large amount of farmland covering,the seasonal variations in evapotranspiration is large.(2)Annual NDVI variation with time in the Laizhou bay catchment area has double peaks since there are two harvests.(3)The annual SFGD of Laizhou bay catchment area is about 2.32×10~7m~3/d,The annual SFGD of the south coast region is about 1.94×10~7m~3/d,The annual SFGD of the west coast region is about 2.31×10~6m~3/d,The annual SFGD of the east coast region is about1.50×10~6m~3/d.