Spatio-temporal Evolution Of Net Primary Productivity And Its Response To Extreme Climate In Songhua River Basin

Net Primary Productivity(NPP)constitutes a key metric for evaluating terrestrial ecosystems’caliber and carbon sequestration aptitude,assuming an integral function in carbon capture and climate change abatement.Contrasting with climatic averages,extreme meteorological occurrences are typified by pronounced abruptness and devastating potential,exerting a more significant influence on vegetation development within terrestrial ecosystems.Due to the Songhua River basin’s status as an essential hub for forestry and agricultural yield in China,extreme weather events inevitably substantially impact the basin’s terrestrial ecosystem.Despite this,the effects of extreme climatic incidents on the spatial variability of NPP within the Songhua River Basin’s terrestrial ecosystems and their interrelated impacts remain uncharted.Consequently,this investigation leveraged the MOD17A3HGF remote sensing dataset and meteorological station data,employing trend analysis,correlation analysis,M-K significance testing,spatial autocorrelation,Hurst index,and geographic probing to probe the spatiotemporal dynamics of NPP in the Songhua River Basin.The findings of this study illuminate a comprehensive examination of the spatiotemporal progression of NPP in the Songhua River Basin and its response mechanism to extreme climatic phenomena.The results show that:(1)The annual average NPP(Net Primary Productivity)value for the Songhua River basin is407.45 g/m~2/a(measured in terms of carbon,the same as below),and it exhibits a significant upward trend at a rate of 4.82 g/m~2/a(p<0.01).The forest ecosystem has the highest annual average NPP value,at 521.73 g/m~2/a,while the wetland ecosystem has the lowest annual average NPP value,at308.75 g/m~2/a.The average annual NPP values of all ecosystems are significantly increasing(p<0.01)at rates of 5.64 g/m~2/a(grassland ecosystem),5.61 g/m~2/a(forest ecosystem),4.01 g/m~2/a(farmland ecosystem),3.81 g/m~2/a(settlement ecosystem),and 3.44 g/m~2/a(wetland ecosystem)respectively.Spatially,the annual average NPP is low in the central plains and high in the surrounding mountainous areas,with spatial changes showing a rising trend in the north and a declining trend in the southeast.The annual average NPP has a distinct spatial clustering that weakens over time.The local autocorrelation mostly shows a high-high and low-low clustering trend in most years,with high-high clustering primarily in forest ecosystems and low-low clustering primarily in farmland and grassland ecosystems.Looking at the altitude range,the NPP is mainly distributed at altitudes below 255 m,with the annual average NPP predominantly ranging from 200-350 g/m~2/a.The farmland ecosystem predominates Within the R1 and R2(29-440 m),while within the R3-R5(440-2580 m)range,the forest ecosystem prevails.The future change in NPP shows a persistent downward trend,with the proportion of all ecosystems transitioning from an upward to a downward trend exceeding 50%.Sustained protection is essential and enhances ecosystems’carbon sequestration capacity.(2)The indices of extreme precipitation mostly show a significant upward trend(p<0.01),while the interannual trends of extreme temperature indices are mostly not significant.Spatially,extreme precipitation indices are consistent,while extreme temperature indices show distinct variations.The extreme climate of the basin is primarily characterized by warming,with the trend of increasing warm night days and annual average minimum temperature being significant and the trend of cooling nights gradually declining.The future changes in the extreme climate indices are persistent,mainly exhibiting weak anti-persistence characteristics.The annual mean values of extreme climate indices significantly correlate with altitude(p<0.05).Among them,R10mm,CWD,PRCPTOT,FD0,and TN90p show a significant positive correlation with altitude,while CDD,SDII,R95p,RX1day,RX5day,SU25,TN10p,TX10p,TX90p,TNn,TXx,TMAX,and TMIN show a significant negative correlation with altitude.Spatially,the NPP mostly has a significant positive correlation with extreme precipitation indices,with the tremendous significance of extreme precipitation events on the grassland ecosystem and the most negligible impact on the wetland ecosystem.In different altitude ranges,low-altitude areas are most affected by extreme precipitation effect impact of extreme temperature events on NPP is relatively small and mostly negatively correlated.The correlation between the extreme temperature indices and NPP has a lower dependency on altitude,and there is no apparent regularity in the correlation degree within different altitude ranges.(3)Extreme precipitation events significantly influence the spatial differentiation of NPP.Among these,the extreme precipitation index CWD has the most excellent significant power for the spatial differentiation of NPP,reaching 0.469.In each ecosystem,extreme precipitation events are the dominant factor in the spatial differentiation of NPP,with explanatory powers of 0.531(grassland ecosystem,CWD),0.480(farmland ecosystem,R10mm),0.470(settlement ecosystem,R10mm),0.425(wetland ecosystem,PRCPTOT),and 0.326(forest ecosystem,R95p)respectively.In different altitude ranges,the spatial differentiation of NPP at R1 altitude is mainly influenced by extreme temperature.In contrast,while at other altitudes,the spatial differentiation is primarily influenced by extreme precipitation events.(4)The interactive effects of different extreme climate events on NPP’s spatial differentiation are more significant than that of a single extreme climate event.This phenomenon is reflected across the entire Songhua River Basin,in different ecosystems,and at different altitude ranges.The interaction of two extreme precipitation events significantly impacts the spatial differentiation of NPP in farmland,grassland,and settlement ecosystems.In contrast,the interaction of extreme precipitation and extreme temperature events affects the spatial differentiation of NPP in forest and wetland ecosystems.At different altitude ranges,the spatial differentiation of NPP in low and medium-altitude areas is influenced by the interaction of extreme precipitation and extreme temperature indices.On the contrary,high-altitude altitude areas are influenced by the interaction of two extreme precipitation indices.