Impact Of Climate Change And Human Activity On The Dynamic Geomorphcialevolution Of The Estuary Of Wulong River (Dingzi Bay) In Jiaodong Peninsula

River runoff and sediment is one of the most important source of the terrestrial material inthe estuarine and coastal area, the variation of which will inevitably lead to profound changesin the hydrodynamics, water environment, sedimentary, landform, resources and ecologicalenvironment. Studies have shown that in the last decades, the runoff and sediment loaddischarged into the sea from many rivers of the world were tested varying degrees of decline,mainly due to the climate change and human activities (such as Reservoir dam construction inthe River Basin, land cover change and water diversion). Since the1950s, the climate changeworldwide is very significant, especially for the coastal zone, where there exists twounderlying surfaces of ocean and land which have totally different thermal properties, as wellas the significant impact of human activities. Thus it will have a significant impact on the totalrunoff, sediment load into the sea from coastal mountain rivers, which will lead to theevolution of the dynamic geomorphology of the estuaries finally. The climate change, and theimpact of climate change and human activities on the runoff and sediment load into the seaduring the last60years are analyzed in this study, taking Wulong river basin located inSouthern Jiaodong Peninsula, which is the largest peninsula in China as an example. And thenumerical simulation method is used to simulate the hydrological conditions in the estuary ofWulong River (Dingzi Bay), the effect of the river hydrology process evolution, as well as thehuman activities, like tidal flat reclamation, on the sediment dynamic topography over thepast60years in Dingzi Bay are analyzed subsequently.First of all, the climate change in Jiaodong Peninsula was analyzed in this paper by thenon-parametric Mann–Kendall test, Accumulated Difference Curve and Order ClusterAnalysis methods, based upon the datas of annual mean, maximum and minimum temperatureand annual precipitation, precipitation from June to September over the past60years. Resultsobtained showed a number of observations: The coastal climate change of Jiaodong Peninsulawas characterized by a remarkable warming trend around1990, after an abrupt drier conditionaround1980over the past60years. In which, the annual mean temperature of JiaodongPeninsula showed a significant increasing trend, with a distinct abrupt change point detectedaround1990, during the past6decades. The warming of the Peninsula over the last60yearswas due mainly to the significant increase of annual minimum temperature. The annual maximum temperature demonstrated a mixed trend of decreasing and increasing, but wasstatistically insignificant, and no abrupt change was detected. The annual precipitationexhibited a decreasing trend during the past6decades, with an abrupt change detected around1980at most stations; but there was an earlier transition point at1966, at a few stations. Thereduction in precipitation, from June to September, was responsible mainly for the decrease ofannual precipitation. Besides, the proportion of the June-September precipitation in the yeardeclined slightly over the last60years. Within the Peninsula, the abrupt change oftemperature and precipitation in the Southeast was earlier than that in the Northwest; as wellas a larger reduction of precipitation was in the Southeast. In comparison, the temperatureevolution in Jiaodong Peninsula was basically consistent with most parts of China over thesame period; but the decreasing trend of precipitation was more significant.The non-parametric Mann–Kendall Test, Accumulated Difference Curve, Order ClusterAnalysis and Linear-Regression Analysis methods were used next in this paper to reveal theeffect of the climate change and human activities on the variation of the annual runoff andsediment load in the Wulong river over the past60years. Results obtained showed that theannual runoff and sediment load into the sea of Wulong River Basin showed a periodicaldecreasing process since1950s. The annual runoff and sediment load of Wulong River mostlyconcentrated from June to September over the last60years; The annual runoff showed asignificant reduction after1980, due mainly to the decrease of precipitation, but there was anobvious fluctuation at about1966; The sediment load showed a periodical decreasing processaffected mostly by the annual precipitation and annual runoff, with the abrupt change detectedaround1966and1980; In comparison, the decreasing trend of sediment load was moresignificant than that of the annual runoff. In addition, the human activities, such as a largearea of terracedfield transformed from the sloping farmland, as well as the forest and orchardland construction since1966, also made a great contribution to the decrease of runoff andsediment load in the basin. Overall, the total water and sediment discharge into the sea ofWulong River reduced by about70-80%and20-30%owing to the climate change and humanfactors respectively over the last60years.Finally,3S technology was used to determine the landform type and its variation of theWulong River estuary (Dingzi Bay) in the past60years, based on the large-scale nautical charts and topographic maps of Dingzi Bay in1961,1981,1995and2010. Moreover,boundary conditions of Dingzi Bay has changed affected mainly by the hydrology processvariation of the river and tidal flat reclamation in the Dingzi Bay, thus the numericalsimulation method was used to simulate the the tidal dynamic characteristics under differentboundary conditions. The results show that the coastal landforms transformed notably in thelast50years, mainly natural landforms, such as the tidal area reduced significantly, theartificial landforms, such as shrimp pond and saltern increased significantly, while tidal inletsilted up, and shrinking. The coastal landform transformation and erosion and depositioncondition evolution in Dingzi Bay were stagely different: Dingzi Bay sustained the slowaccretion state since the Gulf formed and was not deeply affected by human activities from1961to1981, thus the net conversion was from water to tidal flat. Dingzi Bay was in floodasymmetry state in this period. From the late1970s to the early1980s, with thegeomorphological structure and boundary conditions of the Gulf were changed dramaticallyby human activities, such as the dam construction and large area of tidal flats were turned intoshrimp ponds. The net conversion of water to tidal flataccelerated in Dingzi Bay. At the sametime, degree of flood asymmetry increased, which means it entered into a rapid sedimentationperiod in Dingzi Bay. As the human exploitation and reclamation to the tidal flat were almostover after1995, the conversion between water and tidal flat was diminished, but former netconversion from water to tidal flat was turned into the net conversion from tidal flat to water.The constantly enhanced flood asymmetry suddenly reversed to the ebb asymmetry in DingziBay. Therefore, it showed an erosion trend in Dingzi Bay after a sedimentation-dominatedperiod until1995, and speculated that this trend may be increased for some time in the future.This shows that human activities has profoundly changed the original dynamic geomorphicevolution in the gulf. Meanwhile, the other typical tidal inlet gulfs located in SouthernJiaodong Peninsula showed similar characteristics.Also, as the boundary conditions significantly changes during the recently50years, theaverage high, and low bit are has fell, while the average tidal range has increased in DingziBay; The flood duration behaved a monotonic declining trend, while the ebb durationincreased, and this change was more obvious near Bay top; But the change process of theflood/ebb tide duration was more complex, the velocity of the flood/ebb current showed an opposite trend correspondingly. At the same time, the suspended sediment concentrationincreased significantly until1995, due to the large amount of man-made sand in Dingzi Bay,even if the sediment load into the sea from Wulong River was significantly reduced after1981,but the suspended sediment concentration is significantly reduced after1995.In short, as a whole, the dynamic geomorphological evolution Dingzi Bay of JiaodongPeninsula attributed to the combination of human activities and hydrological elementschanges of Wulong River for the last50years. But different to the climate change, especiallythe precipitation reduction around1980, was the dominant influence factor to the variation ofthe hydrological factors in Wulong River basin, the large-scaleexploitation and reclamation tothe intertidal flat from1980played a more significant impact on the landform typeconversion,the erosion and deposition conditions and the dynamic evolution characteristics inDingzi Bay. The landform type and boundary conditions were significantly changed over tenyears, and the dynamic geomorphological features reached new balance again under the newboundary conditions, produced a far-reaching effect on the dynamic geomorphologicalevolution Dingzi Bay.