| Climate change in arid regions has always been a very important scientific issue.Human activities,large terrain uplift,land-atmosphere interaction,air-sea interaction and other factors will have new characteristics and their effects,which will further increase the uncertainty of future climate change in arid regions,with further global warming and further expansion of the arid zone.Therefore,it is still necessary to study the characteristics of climate change in arid areas.Based on the latest 0.5°· 0.5°grid point monthly average data set of the clinical research unit(CRU)from January 1901 to December 2018,the variation characteristics of precipitation,temperature and AI index in the Pan-Central-Asia arid region in recent 70 years(1949-2018)were discussed,used the methods of statistical analysis,EOF decomposition,power spectrum analysis and wavelet analysis etc.Furthermore,the power spectrum and wavelet analysis of the main modes obtained by the EOF decomposition were carried out,and the periodic changes and the characteristics of some interdecadal transitional climate changes were revealed.In addition,arid regions in North Africa and North America are respectively selected as representative regions of low-latitude and mid-high latitude seaside arid regions,and the climate change characteristics of Pan-Central-Asia arid region in the hinterland of the mainland are compared with those of the two regions.The main results are as follows:(1)The trends of dryness and wetness are quite different in each region in the Pan-Central Asia arid zone.Compared with the traditional monsoon region,the warm season in the Pan-Central-Asia arid region did not show obvious warming and rainy.On the contrary,the increase of temperature and precipitation is more obvious in cold season.The precipitation showed an increasing trend in most parts of Northwest China,North Central Tajikistan,Eastern Kyrgyzstan,and between the Caspian Sea and the Aral Sea,while showed a negative growth in the rest of the country.The temperature in the Pan-Central Asia arid zone showed an increasing trend.Among them,the increase in the Hexi Corridor and the northeastern slope of the Qinghai-Tibet Plateau was relatively slow,while the rate of increase was the fastest in northwestern Mongolia.The trend of drought is obvious in central Kazakhstan,Turkmenistan and most of Mongolia.In contrast,the eastern and western sides of Kazakhstan,the northern part of Xinjiang Province of China and parts of the Pamirs show a significant trend of humidification,and most areas of Northwest China are generally showing a weak humidification trend.(2)The modes of precipitation and temperature anomaly field in the Pan-Central-Asia arid region have significant periodic changes.The precipitation anomaly field in the Pan-Central-Asia arid region can be decomposed into three modes: the first mode reflecting the overall consistency of the precipitation change trend in the whole region,but the precipitation change near Kyrgyzstan is more obvious than other regions,with significant quasi 3 a,5-7 a and quasi 12 a change cycles.The second mode reflecting the reverse characteristics of precipitation from southwest to northeast of the study area,with a significant quasi 3 a change period.The third mode reflecting the “+-+” alternating distribution of precipitation from west to East in the study area,with significant quasi 3 a and quasi 7 a change cycle.The temperature anomaly field in the Pan-Central-Asia arid region can be decomposed into two modes: the first mode reflecting the overall consistency of the temperature change trend in the whole region,but the temperature change in the Hexi Corridor and the northeastern slope of the Qinghai-Tibet Plateau in China is more gradual than other areas,with significant quasi 2 a and quasi 8-10 a change cycle.The second mode reflecting the reverse change characteristics from east to west of the study area,with obvious change period of 2-4 a and quasi 5 a.(3)The variation trend of temperature and precipitation is distinct in different arid areas.The precipitation in the Pan-Central-Asia arid region increased at a rate of1.393 mm/10 a.The precipitation in North Africa arid region showed a significant decreasing trend from 1949 to the end of the 1980 s,and then began to increased,but the precipitation was still decreasing at a rate of 2.812 mm/10 a generally.The precipitation in North America arid regions has been in a positive trend since 1949,and then slightly decreased until around 2000,and the overall increase was at a rate of3.881 mm/10 a in the past 70 years.The temperature changes in the three arid areas are all rising trends.The Pan-Central-Asia arid zone has the fastest rate of temperature increase,it has increased by more than 2? in the past 70 years,followed by the arid area of North Africa,with a temperature increase rate of about 0.2 ?/10 a,and the slowest increase in the arid area of North America,about 0.177 ?/10 a.The precipitation in the arid regions of North America and North Africa has obvious anti-phase phenomena,but the specific mechanism still needs to be further studied.(4)The arid zone of Pan-Central-Asian and North America have shown a trend of humidification as a whole in the past 70 years,especially since 2000.On the contrary,the arid zone of North Africa has shown a trend of drought.Since the beginning of the 21 st century,precipitation in the Pan-Central-Asia arid regions and North America arid regions has increased sharply compared with before.Correspondingly,the humidification trend of the latter is accelerating,while the former is slowing down,although the precipitation increment is significant and the temperature increment is small.Since the 1980 s,although the arid area of North Africa has turned into a humidification trend,but this change is minimal and has not significantly improved the local ecological environment and residents' living conditions.This kind of influence deserves more vigilance.In the study of the above-mentioned arid areas,the change of PDO should be considered first in the future,followed by SOI.(5)The climate in arid areas has different trends in cold and warm seasons.The precipitation in Northwest China is increasing both in warm season and cold season,while the trend in most parts of Central Asia is that the cold season is increasing and the warm season is decreasing.The situation in North America is similar.The arid region of North Africa has the characteristics of "drought in the north and flood in the South" in the cold season and "flood in the north and drought in the South" in the warm season,but there is no obvious precipitation increment on the whole,and the trend of aridity is not optimistic.The arid region of North Africa has the characteristics of "drought in the north and flood in the South" in the cold season and "flood in the north and drought in the South" in the warm season,but there is no obvious precipitation increment on the whole,and the trend of aridity is not optimistic.Most of the mid-to-high latitudes have a higher temperature trend than the low latitudes,including the North American arid zone and the Pan-Central Asia arid zone.The trend of temperature change in cold season is quite different from that in warm season.The strongest warming occurs in the middle and high latitudes of the northern hemisphere in the cold season.On the contrary,there are no strong warming in these regions in the warm season.The contribution of cold season to global warming is greater than that of warm season.In the northern hemisphere,the warming rate in the cold season is higher than that in the warm season in most regions,except for the arid regions of North Africa and West Asia in low latitudes.The reason why the temperature changes in low-latitude arid regions are opposite to those in other regions is worthy of further study in the future. |
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