Tree-ring based temperature reconstructions have successfully inferred the past inter-annual to millennium scales summer temperature variability. A clear relationship between annual and summer temperatures can provide...Tree-ring based temperature reconstructions have successfully inferred the past inter-annual to millennium scales summer temperature variability. A clear relationship between annual and summer temperatures can provide insights into the variability of past annual mean temperature from the reconstructed summer temperature. However, how similar are summer and annual temperatures is to a large extent still unknown. This study aims at investigating the relationship between annual and summer temperatures at different timescales in central Sweden during the last millennium. The temperature variability in central Sweden can represent large parts of Scandinavia which has been a key region for dendroclimatological research. The observed annual and summer temperatures during 1901-2005 were firstly decomposed into different frequency bands using ensemble empirical mode decomposition(EEMD) method, and then the scale-dependent relationship was quantified using Pearson correlation coefficients. The relationship between the observed annual and summer temperatures determined by the instrumental data was subsequently used to evaluate 7 climate models. The model with the best performance was used to infer the relationship for the last millennium. The results show that the relationship between the observed annual and summer temperatures becomes stronger as the timescale increases, except for the 4-16 years timescales at which it does not show any relationship. The summer temperature variability at short timescales(2-4 years) shows much higher variance than the annual variability, while the annual temperature variability at long timescales(>32years) has a much higher variance than the summer one. During the last millennium, the simulated summer temperature also shows higher variance at the short timescales(2-4 years) and lower variance at the long timescales(>1024 years) than those of the annual temperature. The relationship between the two temperatures is generally close at the long timescales, and weak at the short timescales. Overall the summer temperature variability cannot well reflect the annual mean temperature variability for the study region during both the 20 th century and the last millennium. Furthermore, all the climate models examined overestimate the annual mean temperature variance at the 2-4 years timescales,which indicates that the overestimate could be one of reasons why the volcanic eruption induced cooling is larger in climate models than in proxy data.展开更多
Highland barley(Hordeum vulgare Linn.cv.nudum Hook.f.)is the principal cereal crop over the Tibetan Plateau(TP).The response of highland barely to climate change in the past decades,especially in terms of yields still...Highland barley(Hordeum vulgare Linn.cv.nudum Hook.f.)is the principal cereal crop over the Tibetan Plateau(TP).The response of highland barely to climate change in the past decades,especially in terms of yields still remains uncertain.In this study,its responses to climate change were investigated using daily weather data and agriculture data during 1961–2018.The results showed that the annual mean air temperature over the TP increased at 0.33°C per decade during 1961–2018,and the rate of warming increased with altitude,reaching 0.41°C per decade at altitudes of 4500–4700 m.The growing degree days(GDDs)increased by 9.6%during 2011–2018 compared with the 1960s,whereas low temperature degree days(LDDs)decreased by 40.3%over the same period,indicating that the thermal conditions for highland barley cultivation have improved.A strong relationship was observed between the yield of highland barley and LDDs(−0.76,p<0.001)than GDDs(0.58,p<0.001)in Xizang,where sufficient irrigation water is available from the melting of snow cover or glaciers.In Sichuan,with abundant precipitation,significant correlations were noticed between county-level barley yield and GDDs and LDDs(0.60,p<0.001;−0.65,p<0.001).In Qinghai,the dry regions,county-level yields were influenced significantly by temperature and precipitation.These results indicated that climate warming was beneficial to highland barley yield in most region of the TP,mainly due to decreased LDDs.The potential altitude at which highland barley cultivation is feasible increased by approximately 280–484 m during 2016–2018,compared with 1981–1983.In Xizang,highland barley could be cultivated up to an altitude of 4507 m a.s.l.between 2016 and 2018,and it increased to 4179 m a.s.l.in Qinghai.These results could help local government to take actions to adapt to global warming and improve food security.展开更多
文摘Tree-ring based temperature reconstructions have successfully inferred the past inter-annual to millennium scales summer temperature variability. A clear relationship between annual and summer temperatures can provide insights into the variability of past annual mean temperature from the reconstructed summer temperature. However, how similar are summer and annual temperatures is to a large extent still unknown. This study aims at investigating the relationship between annual and summer temperatures at different timescales in central Sweden during the last millennium. The temperature variability in central Sweden can represent large parts of Scandinavia which has been a key region for dendroclimatological research. The observed annual and summer temperatures during 1901-2005 were firstly decomposed into different frequency bands using ensemble empirical mode decomposition(EEMD) method, and then the scale-dependent relationship was quantified using Pearson correlation coefficients. The relationship between the observed annual and summer temperatures determined by the instrumental data was subsequently used to evaluate 7 climate models. The model with the best performance was used to infer the relationship for the last millennium. The results show that the relationship between the observed annual and summer temperatures becomes stronger as the timescale increases, except for the 4-16 years timescales at which it does not show any relationship. The summer temperature variability at short timescales(2-4 years) shows much higher variance than the annual variability, while the annual temperature variability at long timescales(>32years) has a much higher variance than the summer one. During the last millennium, the simulated summer temperature also shows higher variance at the short timescales(2-4 years) and lower variance at the long timescales(>1024 years) than those of the annual temperature. The relationship between the two temperatures is generally close at the long timescales, and weak at the short timescales. Overall the summer temperature variability cannot well reflect the annual mean temperature variability for the study region during both the 20 th century and the last millennium. Furthermore, all the climate models examined overestimate the annual mean temperature variance at the 2-4 years timescales,which indicates that the overestimate could be one of reasons why the volcanic eruption induced cooling is larger in climate models than in proxy data.
基金supported by National Key Technology R&D Program of China(2019YFD1002204)and S&T Development Fund of CAMS.
文摘Highland barley(Hordeum vulgare Linn.cv.nudum Hook.f.)is the principal cereal crop over the Tibetan Plateau(TP).The response of highland barely to climate change in the past decades,especially in terms of yields still remains uncertain.In this study,its responses to climate change were investigated using daily weather data and agriculture data during 1961–2018.The results showed that the annual mean air temperature over the TP increased at 0.33°C per decade during 1961–2018,and the rate of warming increased with altitude,reaching 0.41°C per decade at altitudes of 4500–4700 m.The growing degree days(GDDs)increased by 9.6%during 2011–2018 compared with the 1960s,whereas low temperature degree days(LDDs)decreased by 40.3%over the same period,indicating that the thermal conditions for highland barley cultivation have improved.A strong relationship was observed between the yield of highland barley and LDDs(−0.76,p<0.001)than GDDs(0.58,p<0.001)in Xizang,where sufficient irrigation water is available from the melting of snow cover or glaciers.In Sichuan,with abundant precipitation,significant correlations were noticed between county-level barley yield and GDDs and LDDs(0.60,p<0.001;−0.65,p<0.001).In Qinghai,the dry regions,county-level yields were influenced significantly by temperature and precipitation.These results indicated that climate warming was beneficial to highland barley yield in most region of the TP,mainly due to decreased LDDs.The potential altitude at which highland barley cultivation is feasible increased by approximately 280–484 m during 2016–2018,compared with 1981–1983.In Xizang,highland barley could be cultivated up to an altitude of 4507 m a.s.l.between 2016 and 2018,and it increased to 4179 m a.s.l.in Qinghai.These results could help local government to take actions to adapt to global warming and improve food security.
