| The strengtrenth and frequency of extreme climate events have increasedobviously with global warming, which brings tremendous impacts to society,economy, agriculture and human life, so it is very important to investigate the changesand impacting mechanism in extreme climate. Based on daily maximum andminimum temperature as well as daily precipitation at115meteorological stationsover the Yangtze River basin from1962to2011, sixteen indices of extremetemperature and eleven indices of extreme precipitation are selected. The results areas follows:(1) The occurrences of cold days, cold nights, ice days, frost days and cold spellduration days have significantly decreased by-0.84,-2.78,-0.48,-3.29and-0.67daysper decade, respectively. While the occurrences of warm days, warm nights, summerdays, tropical nights, warm spell duration days and growing season length showstatistically significant increasing trends at rates of2.24,2.86,2.93,1.80,0.83and2.30days per decade, respectively. The tendency rates of monthly minimum value ofdaily maximum (minimum) temperature, monthly maximum value of daily maximum(minimum) and diurnal temperature range are0.33,0.47,0.16,0.19and-0.07℃perdecade, respectively. The trend magnitudes of maximum1-day precipitation,maximum5-day precipitation, very wet day precipitation, extremely wet dayprecipitation and annual total wet day precipitation (also summarized as amountindices) are0.21,-0.68,2.18,1.51and-11.96mm per decade, respectively. Theoccurrences of number of heavy/heavier/heaviest precipitation days, consecutive drydays and consecutive wet days (days indices) have decreased by-0.31,-0.25,-0.24,-0.15and-0.19days per decade, respectively. While the occurrence of simple dailyintensity index shows weakly increasing trend at a rate of0.07mm/day per decade.(2) Obvious spatial difference can be found for each temperature indices. For therelative indices, the annual averages for diffenrent subregions are mainly similar,ranging between17.0ane17.3days. For other indices, the regionally averaged valuesof cold indices in upper reaches of the Yantze River basin are larger than those in themiddle and lower reaches. However, the regionally averaged values of warm indicesand growing seasons except warm spell duration indicator are larger in middle and lower reaches than in upper reaches. The extreme precipitation indices also showobviously spatial differences, and change patterns of theses indices are not spatiallyclustered.(3) The magnitudes of changes in cold indices (cold nights, monthly minimumvalue of daily maximum, monthly minimum value of daily minimum) are obviouslygreater than those of warm indices (warm nights, monthly maximum value of dailymaximum and monthly maximum value of daily minimum), and the change ranges ofnight indices (warm nights and cold nights) are larger than those of day indices (warmdays and cold days), which indicates that the change of cold/warm and day/nighttemperature is asymmetrical.(4) The principal component analysis shows that the cumulative contribution of5principal components reaches84.2%of extreme temperature indices. The correlationanalysis indicates that there are significant correlations among of the extremetemperature indices except the diurnal temperature range, especially for the relativeindices.(5) Generally, the averages of most precipitation indices except consecutive drydays decrease as altitude rises. The main order of regional averages of precipitationindices for different topographical types is peak> plain> intermountain> valley.Extreme precipitation events during the following year of El Ni o years are generallymore frequently than those during El Ni o years, and precipitation extremes duringthe following year of La Ni a years are mainly lower than those during El Ni o years.The precipitation extremes are lagged after the ENSO events. The precipitationindices have high correlations with each other except consecutive dry days. |
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