Impact of Sea-Level-Rise and Human Activities in Coastal Regions:An Overview

Coastal regions are becoming increasingly vulnerable to flooding because of accelerating sea-level-rise(SLR),local ground subsidence,and the changes in topography and morphology.Moreover,coastal areas are usually highly urbanized and increased human activities have an effect on the stability and preservation of the environment.For instance,the growing demand for new lands to accommodate the population and the industrial facilities in China has required the design and the deployment of land-reclamation projects from the ocean,with a marked impact on fragile coastal eco-systems.Specifically,the Yangtze River and Pearl River Estuary,two major estuaries of the world,have long been subject to intensive human activities over the past decades.Long-term ground subsidence evolution,topographic changes,and morphological variation of the coastal regions have drawn great attention.This paper provides an overview of well-established Earth Observation(EO)remote sensing(RS)technologies that are employed to continuously monitor the changes of urbanized regions.The combined use of EO-based DInSAR analyses along with the knowledge of the geomorphology of the coastal regions allows a more precise picture of the SLR risk in the investigated coastal regions.In this paper,we will concentrate on remote sensing technologies that allow the gathering of heterogeneous information,such as those based on the use of synthetic aperture radar(SAR),satellite altimeters and tide gauge data.We will underline how human activities trigger changes in the living environment of coastal zones and the associated risks for the population.Observed coastline changes,coastal regions terrain subsidence,and offshore bathymetry have a pronounced effect on the increasing risk of flooding.Accordingly,we also present insights into some inundation model projections employed for evaluating the potential flooding risk in coastal regions.

Remote sensing observations of phytoplankton increases triggered by successive typhoons

Phytoplankton blooms in the Western North Pacific, triggered by two successive typhoons with different intensities and translation speeds under different pre-existing oceanic conditions, were observed and analyzed using remotely sensed chlorophyll-a （Chl-a）, sea surface temperature （SST）, and sea surface height anomaly （SSHA） data, as well as typhoon parameters and CTD （conductivity, temperature, and depth） profiles. Typhoon Sinlaku, with relatively weaker intensity and slower translation speed, induced a stronger phytoplankton bloom than Jangrni with stronger intensity and faster translation speed （Chl-a〉0.18 mg-m-3 versus Chl- a〈 0.15 mg.m-3） east of Taiwan Island. Translation speed may be one of the important mechanisms that affect phytoplankton blooms in the study area. Pre-existing cyclonic circulations provided a relatively unstable thermodynamic structure for Sinlaku, and therefore cold water with rich nutrients could be brought up easily. The mixed-layer deepening caused by Typhoon Sinlaku, which occurred first, could have triggered an unfavorable condition for the phytoplankton bloom induced by Typhoon Jangmi which followed afterwards. The sea surface temperature cooling by Jangmi was suppressed due to the presence of the thick upper-ocean mixed-layer, which prevented the deeper cold water from being entrained into the upper-ocean mixed layer, leading to a weaker phytoplankton augment. The present study sug- gests that both wind （including typhoon translation speed and intensity） and pre-existing conditions （e.g., mixed- layer depths, eddies, and nutrients） play important roles in the strong phytoplankton bloom, and are responsible for the stronger phytoplankton bloom after Sinlaku＇s passage than that after Jangmi＇s passage. A new typhoon- influencing parameter is introduced that combines the effects of the typhoon forcing （including the typhoon intensity and translation speed） and the oceanic pre- condition. This parameter shows that the forcing effect of Sinlaku was stronger than that of Jangmi.

An ultraviolet to visible scheme to estimate chromophoric dissolved organic matter absorption in a Case-2 water from remote sensing reflectance

In a typical Case-2 coastal water environment(here,the Pearl River Estuary(PRE),China),chromophoric dissolved organic matter(CDOM)and suspended particulates dominate the water optical properties,and CDOM fluorescence contributes considerably to surface water reflectance.In this paper,an ultraviolet(UV)to visible scheme to retrieve CDOM absorption(ag)is developed based on a set of in situ observations.First,the CDOM UV absorption and spectral slope(Sg)are derived directly from the visible remote sensing reflectance;then the Sg is extrapolated to obtain the spectrum from UV to visible spectral range.This algorithm performs well,with an overall mean absolute percent difference(MAPD)of^30%,~5%and^6%for the estimation of ag in 250–450 nm,Sg over 250–400 nm,and 250–700 nm,respectively.The effectiveness and stability of the algorithm is further demonstrated in capturing the distribution pattern of CDOM absorption in the PRE from satellite ocean color imagery with multiple spatial and spectral resolution,namely:the Visible Infrared Imaging Radiometer Suite(VIIRS)(750 m/Multispectral),the Ocean and Land Color Instrument(OLCI)(300 m/Multispectral),the Hyperspectral Imager for the Coastal Ocean(HICO)(100 m/Hyperspectral),and the Landsat 8 Operational Land Imager(OLI)(30 m/Multispectral).The UV to visible scheme can benefit the CDOM absorption estimation in two aspects:1)it is free from the disturbance of suspended matter;2)it avoids uncertainties caused by the low signalto-noise ratio(SNR)of ag measurements in the visible range.The algorithm is effective in revealing multiple scales of variation of CDOM absorption from ocean color observations.