Evaluation And Analysis Of The Extreme Climate Characteristics And Their Impact On Flood In Jinsha River Basin Based On Fusion Datasets

In recent years,extreme climate events have occurred frequently in China.Since July 2020,the Yangtze River basin has experienced several rounds of heavy rainfall that exceeded historical levels,and the rainfall amounts have been among the largest of the season since 1961.As a result,the Yangtze River basin has continuously experienced historically large floods,which directly affect its sustainable development and ecological environment.Studying the heavy rainfall in the basin,especially the extreme variations in precipitation and temperature,and their effects on runoff,is of profound significance for flood control and sustainable development.Currently,research on extreme climates focuses on simple analysis of precipitation and temperature data based on data collected at meteorological sites,while studies on re-analysis fusion data are rare.With the continuous development of satellite remote sensing,data fusion,and other advanced technologies,atmospheric data-fusion products have been widely used in areas with no or scarce data.At present,a number of comparative studies on atmospheric driven hydrological models for atmospheric fusion products are available,while few studies on extreme climates using multiple types re-analysis fusion data exist,especially on the upper reaches of the Yangtze River,where traditional meteorological observation stations are few.In this study,multiple types of internationally popular re-analysis fusion data were used to study the extreme climates of Jinsha River basin in the upper reaches of the Yangtze River.First,the spatial distribution,cycle,and sudden-change characteristics of the extreme precipitation and extreme temperature indexes in Jinsha River basin were analyzed using the precipitation and temperature observation data of meteorological stations in the basin.Second,the precipitation products(CMPA-H,CMADS,GPM(IMERG),and TRMM(TMPA))and temperature products(CMADS,and a 0.5°-resolution gridded temperature dataset)of various re-analysis fusion datasets were compared to analyze the applicability of the products in the study of extreme climates in the basin.Finally,based on the analysis results,the characteristics of extreme hourly precipitation and the variation in precipitation characteristics calculated using different timescales,s well as their influence on runoff of the Jinsha River basin,were analyzed.In summary,the main research contributions of this paper are the following:Based on the precipitation and temperature data of 31 meteorological stations in the Jinsha River basin in recent 57 years(1960–2016),the variation trend,cycle,sudden-change points,and spatial distributions of extreme climates’ feature thresholds and indexes were comprehensively analyzed.The results showed that 1)the spatial distribution of the extreme precipitation threshold showed an overall trend of low in the northwest,high in the southeast,and increasing from northwest to southeast;2)there was no obvious overall upward or downward trend in the number of extreme precipitation days in each representative station,The station-averaged,annual mean index of extreme precipitation events in the basin generally exhibited an obvious temporal cycle of about 2.5 years.Most of the extreme precipitation indices did not exhibit an obvious abrupt change.3)the extreme high-temperature threshold in downstream sub-basins was greater than that in upstream sub-basins,yet the extreme low-temperature threshold was the opposite;and 4)the number of days of extreme high temperature in the basin increased and the number of days of extreme low temperature decreased.The time series of extreme temperature indices generally exhibited an increasing trend.As far as daily temperature indices were concerned,the warm spell duration index(WSDI)exhibited an increasing trend,while the number of days of frost,the number of days in which ice occurred,and the cold spell duration index(CSDI)all exhibited a decreasing trend.The majority of the extreme temperature indices and the WSDI exhibited abrupt increases,while the CSDI exhibited an abrupt decrease.Moreover,the extreme temperature indices exhibited a relatively obvious trend to exceed the critical line,with their values showing dramatic increases or decreases.(2)The applicability of the merged precipitation datasets CMPA-H,CMADS,TRMM(TMPA),and GPM(IMERG)and merged temperature datasets to the extreme climate indices in the Jinsha River Basin was verified.Extreme precipitation thresholds were computed using the merged datasets versus the meteorological station observations.The results showed that extreme precipitation thresholds computed using CMADS and GPM(IMERG),especially CMADS,had a high congruence with those computed using the meteorological station observations.Most of the extreme precipitation indices computed using the merged data had high accuracy,with the indices derived from CMPA-H,CMADS,and GPM(IMERG)being slightly better than those derived from TRMM(TMPA).The extreme temperature indices TXx and TNn derived from the merged datasets,especially CMADS,had a high congruence with those derived from the meteorological station observations,indicating an acceptable applicability of merged data to the computation of the two indices above.The merged dataset-derived extreme precipitation indices generally showed a small deviation within 3% from meteorological observation-derived extreme precipitation indices.The maximum values of CMADS-derived extreme temperature indices were generally distributed at the same set of stations as the maximum values of meteorological observation-derived extreme temperature indices,and the deviations of the CMADS-derived indices from the meteorological observation-derived indices were as low as 0.15%,indicating the high accuracy of the CMADS temperature data.Considering the observation accuracy of ground stations corresponding to reanalysis fusion products and their recognition ability in spatial distribution characteristics,this study shows that it is feasible to calculate extreme climate indices of the Jinsha River basin using reanalysis fusion data products,especially in the upper reaches of the Yangtze River,where there are few meteorological stations.(3)To explore the characteristics of extreme precipitation processes,in this study the extreme precipitation characteristic index on an hourly scale,as well as the temporal and spatial variation characteristics of the extreme precipitation threshold and extreme precipitation feature index of Jinsha River basin,were analyzed.At hourly scales,the extreme precipitation thresholds were high throughout the basin in the flood seasons,as indicated by the dark colors of the contour lines.Moreover,the temporal change patterns of extreme precipitation indices and heavy precipitation indices at 3-hour,1-hour,and half-hour scales were significantly different in the dry seasons than in the flood seasons,which was observed not only at the basin scale but also in the upstream sub-basin and the downstream sub-basin.The thresholds of 3-hour extreme precipitation in the basin were more than 50% of the thresholds of daily extreme precipitation,while the thresholds of half-hour extreme precipitation were only 2% to 5% of the daily thresholds.The ability of extreme precipitation indices to describe extreme precipitation characteristics did not increase as the temporal scales became finer,and at least a 3-hour scale was required in order for the indices to describe an average of 40–60% of the spatial characteristics of daily extreme precipitation.The heavy precipitation indices increased in intensity with decreasing hourly scales.(4)Based on multiple types of reanalysis fusion data,the response of flood events to both extreme precipitation and temperature was evaluated.Quantitative analysis shows that the two typical flood events were mainly affected by extreme precipitation and the lag of flood propagation,with the extreme discontinuous precipitation near the exit contributing to floods.The maximum daily temperature of the entire basin was high and the temperature of each station closed to the threshold of extreme high temperature.The extreme precipitation,extreme temperature,and their spatial distribution characteristics in the basin area had an indicative effect on the occurrence of flood events.In this study,the extreme climate indices of the Jinsha River basin in the upper reaches of the Yangtze River were calculated systematically from four aspects,and the spatial distribution,cycle,and sudden change of the extreme climate indices in the long-term sequence of large-scale terrain complex basins revealed.The applicability of the dataset of various precipitation and temperature fusion data in calculating the extreme climate indices of the Jinsha River basin was verified from multiple perspectives.The spatial distribution of the extreme precipitation index at different timescales was discussed.The response of extreme runoff(flood)of the Jinsha River to strong and extreme precipitation events in the river basin was analyzed.The results can provide an important scientific basis for studies on extreme climatic characteristics in large-scale,no-data,or low-data-availability areas.