Research On The Impact Of Climate Change On The Marsh Distribution And Its Risk Assessment In The Sanjiang Plain

Climate change has seriously threatened water safety and ecological safety in our country, and also lead to wetland facing a series of risk, such as water shortage, wetland shrinkage, and functional degradation. Distribution and area is considered the most obvious and direct indicator to represent the impact of climate change on the marsh. The Sanjiang Plain, where is the concentrated distribution area of freshwater marshes in our country was chosen as the study area in this paper. We analyzed the spatial and temporal variation characteristics of climate change and the distribution of marsh over the past 60 years, simulated the potential distribution of marsh in different periods by maximum entropy model with present distribution data of marsh and environment variables, quantitatively analyzed climate factors affecting wetland potential distribution, and predicted the distribution and area of marsh under the future climate scenarios. Also, we established methods of wetland risk assessment under the background of climate change, and explored the risk and its grading division of marsh in the future. All the researcher above was to provide a theoretical basis for the corresponding adaptive management strategies to deal with the wetland risk in the future. Main results were presented as follows:(1) Characteristics of climate change and its future trends in the Sanjiang plainUnder the background of global climate warming, annual average temperature(AAT) and growing season average temperature(GSAT) both presented warming trend, with the rates of 0.30℃/10 a and 0.20℃/10 a in the Sanjiang plain over the past 60 year, which were significantly higher than the warming rate in the country. Annual precipitation(AP) and growth season precipitation(GSP) both showed slight downward trends, with the rates of 10.22 mm/10 a and 11.41mm/10a; warmth index(WI) and coldness index(CI) showed linear increase trends with the rates of 1.29℃/10 a and 2.34℃/10 a, humidity index(HI) showed extremely weak declining trend, with the rate of 0.35 mm/℃10a and dryness index(DI) showed weak increasing trend with the rate of 0.02 mm/℃10a.Under the scenarios of RCP 2.6, RCP 4.5, RCP 6.0 and RCP 8.5, AAT and GSAT in the Sanjiang Plain also showed linear upward trends, and the warming rates were higher than that in the past. AP and GSP showed slightly upward trends and the rainfall concentration degree decreased in plant growth season. WI and CI showed linear increasing trends and the rates were higher than that in the past. HI showed a weak downward trend and variation tendency of DI was not obvious and the mean was lower than that in the past.(2) Spatial variation of marsh in the Sanjiang Plain over the past 60 yearsIn recent 60 years(1954-2010), the area proportion of land utilization types in the Sanjiang Plain has changed. The area of marsh sharply declined and the distribution tended to fragment. The area loss proportion of marsh was up to 80.35%, and the percentage of marsh accounts for all the land use types decreased by 25.85%. Conversion proportions of marsh during the period from 1954 to 1986 and 1986 to 2010 were 74.82% and 18.55%, respectively.(3) Effect of climate change on the distribution of marsh in the Sanjiang PlainDuring the period from 1954 to 2010, area proportions of unsuitable, low suitable, medium suitable and high suitable marsh in the Sanjiang Plain increased by 2.67%、2.53% 、-3.80% and-1.42%, respectively. Climate change expanded the area of unsuitable and low suitable marsh, shrunk that of medium suitable and high suitable and suppressed marsh distribution. Despite the impact of climate change on marsh is negative during the whole period, but the effect of promoting the distribution of marsh gradually appeared. In the last 60 years, the main meteorological factors affecting distribution of marsh in the Sanjiang Plain and their percent contribution were: CI > GSAT > WI > HI > AAT > DI > AP > GSP. Suitable habitat conditions of distribution of marsh in the Sanjiang Plain were as follows: Al 30 ~ 350 m, Sl 0 ~ 0.3°, AAT 0.5 ~ 4.0℃, GSAT 16.0 ~ 18.2℃, AP 525 ~ 780 mm, GSP 425 ~ 575 mm, WI > 52℃, CI-IX X 112 ~-80℃, DI 0.85 ~ 1.16 mm/℃ and HI 4.8 ~ 6.9 mm/℃.(4) Prediction and risk assessment on the distribution of marsh under future climate change scenariosCompared with 2010, under the two scenarios of RCP 2.6 and RCP 8.5, potential distribution of marsh in the Sanjiang Plain in 2050 both showed phenomena of area reducing of unsuitable, low suitable and high suitable, and increasing of medium suitable. However, under the two scenarios of RCP 4.5 and RCP 6.0, phenomena of area reducing of unsuitable, and increasing of low, medium and high suitable appeared. Climate change promoted the distribution of marsh, and had positive effect on marsh.Under the climate change scenarios of RCP 2.6, RCP 4.5、RCP 6.0 and RCP 8.5, the marsh areas of climatic expanding zone in the Sanjiang Plain in 2050 were all greater than those of shrinking region suffered from adverse effects of climate change. Compared with the reference period, the marsh area suffered from adverse effects of climate change under the four scenarios were all less than 50% of the original distribution. Risk grading division of marsh in the Sanjiang Plain was zero risk level, which showed the characteristics of moderate adaptability. Moderate adaptability is not very suitable for climate change. That means distribution of marsh nearly hasn’t changed under the influence of climate change, but the probability of marsh existence decreases and is greater than critical value of suitable existence probability.(5) Wetland adaptive management strategies under the background of climate changeWetland adaptive management strategies should be taken in our country under the background of climate change, including strengthening wetland conservation, reduce disturbance, strengthening wetland restoration and taking priority to adapt.