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Lanzhou University (2018)

The Changes and Characteristics of Temperature and Precipitation in the Global Dry Land during 1948-2008


Titre : The Changes and Characteristics of Temperature and Precipitation in the Global Dry Land during 1948-2008

Auteur : 杨子凡;

Grade : Master’s Theses 2018

Université : Lanzhou University

Dry land covers about 40 % of the land in the earth where about one third of the people live here.Therefore,it is particularly important to study the characteristics of climate change in global dry lands.This paper divides dry lands into hyper-arid land,arid land,semi-arid land and dry sub humid land.Besides,according to the northern and southern hemispheres and winter and summer seasons and based on the data from CPC(Climate Prediction Center),GLDAS(Global Land Data Assistance System)and NCEP(National Centers Environmental Prediction),the paper analyzes the distribution and characteristics of the change in global dry lands’ temperature and precipitation and the characteristics and differences of circulation fields before and after climate catastrophe by using the methods of Mann-Kendall test,wavelet analysis,curve fitting,EOF decomposition and correlation coefficient.The main conclusions are as follows :(1)In the globe,the drier the place is,the higher the annual average temperature and the less the precipitation is.However,the distribution of arid areas is not always strictly consistent with that of high temperature and rare precipitation areas.The occurrence of drought is the result of the comprehensive action and complementarities of temperature and precipitation.The temperature change periods of different dry land types are different.The trends of global land and dry land temperature change with latitude are basically the same as most regions,but there are great differences in performance near the equator.The reasons may be caused by less distribution of dry areas and fewer reference points in the equatorial region.(2)As a whole,the time variation of the first mode of AI(arid index)is an increasing trend,which indicates that the total drought area has a tendency to gradually expansion.The eigenvector of the first mode of temperature is basically positive.The time variation of the first mode of precipitation is opposite to that of temperature,and it is mostly negative.Through the correlation comparison of EOF decomposition of AI,temperature and precipitation,it is found that the first mode of AI is mainly determined by the precipitation in the second mode,and the second mode of AI is determined by the temperature in the first mode.While AI’s second mode is mainly determined by the first mode of precipitation.It shows that AI is obviously more influenced by precipitation than by temperature.(3)The research results show that the average temperature change rates of different dry land types in the northern and southern hemispheres are quite different : extremely drought areas are the areas with the largest average temperature change rates in winter in the southern hemisphere,while other areas are all with obvious changes in the northern hemisphere than in the southern hemisphere.The temperature and its abrupt changes in the northern and southern hemispheres are also quite different.Compared with the northern hemisphere,the average summer temperature in the southern hemisphere has larger periodic fluctuation and more small periods,but the obvious large periods are less than those in the northern hemisphere,and the period is generally shorter than that in the northern hemisphere.(4)The contribution rate of warming dry land in the winter northern hemisphere is higher than that in summer,especially in semi-arid land and dry sub humid land,which is more obvious.Among the dry lands in the southern hemisphere in winter,the increase of temperature in the hyper-arid land is the most obvious,and the temperature change in winter is obviously higher than that in summer.This phenomenon is more obvious than the regional coverage rate in the northern hemisphere.(5)The precipitation decreases fastest in dry sub humid land,followed by semi-arid land.The average precipitation in the northern and southern hemispheres is also quite different : in the summer northern hemisphere,the area where the average precipitation decreases more obviously than other areas where it increases.In summer,the southern hemisphere is opposite to the northern hemisphere,and the areas where the average precipitation increases are more than those where it decreases.In global dry land,the contribution rate of precipitation change in winter is lower than that in summer,and the change rate of average precipitation in southern hemisphere in winter presents a decreasing trend in winter and an increasing trend in summer.(6)In recent 60 years,the high-value areas of average perceptible water in the whole atmosphere are concentrated in the low-latitude areas,and there are four high-value centers,decreasing from the low-latitude to the high-latitude areas.Precipitation in north-central Africa,northwest China and equatorial region of the middle east and Pacific ocean has decreased in the past 60 years,especially in northwest China and north-central Africa where the decrease is deeper,which also means that the degree of drought has deepened

Mots clés : Dry land; Temperature; Precipitation; Aarid index; EOF;

Présentation (CNKI)

Page publiée le 2 octobre 2018