Altitude Effects of Climatic Variation on Tibetan Plateau and Its Vicinities

High topographies, such as the Tibetan plateau （TP） in China, have been considered as the sensitive areas in response to global climate change. By analyzing the relationship between warming structure and altitude （1 000-5 000 m） in the TP and its vicinities using the 46-year January mean observed temperature data, we found that there was a significant altitude effect of temperature warming onset time （mutation time） on the plateau and the neighboring regions： the higher the altitude, the later the climate warming happens, and vice versa. There also seems a slight altitude effect on warming magnitude： the higher the altitude, the less the warming magnitude. Therefore, the temperature warming in the high altitude area of the TP （below 5 000 m） responds to global warming less sensitively than the low-altitude neighboring areas both in onset time and magnitude, which may be mainly caused by high albedo and large thermal capacity of the ice/snow cover on the higher part of the plateau and possible heat island effect in the lower part of the plateau.

Climate response and radial growth of Pinus tabulaeformis at different altitudes in Qilian Mountains

In order to test whether the relationship between climate and the radial growth of trees is affected by altitude,altitude variability and time stability of climate-influenced radial growth of a dominant conifer,Chinese pine(Pinus tabulaeformis),in the eastern Qilian Mountains were studied against the background of climate change using dendrochronology.Results show that 1)droughts at the end of the growing season of last year and during the early and middle growing season of the current year were the main limiting factors for the radial growth of Chinese pine at two altitude gradients;this was determined by analyzing the relationship between tree-ring width chronologies and climate factors.2)The sensitivity of the radial growth of trees to climate change gradually decreased and was affected more by drought stress at a lower altitude.3)An unstable divergence response was observed in the radial growth at the two altitudes,in response to controlling climatic factors;this observation was based on the moving correlation analysis of growth/climate relationships,and the aggravation of drought stress caused by increasing temperature was the main reason.4)The growth rate of Chinese pine at the two altitudes increased at first and then decreased,as measured by basal area increment(BAI)modeling.Future temperature rises may have significant effects on mountain forest ecosystems in arid and semi-arid regions.Effective management and protection measures should be taken,according to the response patterns of trees to climate change at different altitude gradients.

Oxygen-18 in different waters in Urumqi River Basin

The variations of the stable oxygen isotope in different water mediums in Urumqi River Basin, China, are analyzed. The stable oxygen isotope in precipitation has marked temperature effect either under synoptic or seasonal scale at the head of Urumqi River. The linear regression equations of δ18O against temperature are δ18O=0.94T-12.38 and δ18O=1.29T-13.05 under the two time scales, respectively. The relatively large δ18O/temperature slopes show the strong sensitivity of δI8O in precipitation to temperature variation at the head of Urumqi River. According to the analyses on the δ18O in precipitation sampled at three stations with different altitudes along Urumqi River, altitude effect is notable in the drainage basin. The δ18O/altitude gradients have distinct differences: the gradient from Urumqi to Yuejinqiao is merely -0.054%c/hm, but -0.192%e/hm from Yuejinqiao to Daxigou, almost increasing by 2.6 times over the former. No altitude effect is found in surface firn in the east branch of Glacier No. 1 at the head of Urumqi River, showing that precipitation in the glacier is from the cloud cluster with the same condensation level. Influenced by strong ablation and evaporation, the δ18O in surface firn increases with increasing altitude sometimes. Survey has found that the δ18O in meltwater at the terminus of Glacier No. 1 and in stream water at Total Control have the similar change trend with the former all smaller than the latter, which displays the different runoff recharges, and all mirror the regime of temperature in the same term basically.

Assessment of Erythemal UV Level in Nepal Based on Solar UV Estimates from Total Ozone Mapping Spectrometer

Nepal lies on the southern slope of Himalaya in Asia. In a width ranging between 150 and 250 km, the altitude varies greatly from about 100 m at its southern border to a maximum of 8848 min the northern part. Like the variation in altitude, climatic condition varies quite a lot. Long-term monthly mean erythemal UV daily dose values for Nepal are evaluated using Total Ozone Mapping Spectrometer （TOMS） estimation from the time of its overpass between 1996 and 2003. The results are presented as summer and winter maps of mean UV levels in each satellite grid. The mean winter erythemal UV daily dose ranges between 2.1 and 3.6 kJ m-2 whereas summer values are found to lie between 4.6 and 9.7 kJ m-2. The altitude variation increases the UV levels by about 0.2 kJ km-1 in winter months, and 0.9 kJ km-1 in summer. A multiyear monthly average erythemal daily dose in most of the areas shows that the summer value is about three times higher than that in winter. Although year-to-year variation is not pronounced in high- and mid-elevation regions, UV levels seemed to decrease from 1997 to 2002 in the southern part of the country in the low elevation region by about 5.35%. Due to the combined effects of the altitude, low ozone concentration in the troposphere, and thin air, surface UV radiation at higher altitudes is found to be higher than in the surrounding regions.

Variation in Short-term Temperature Fluctuations Across China During the Past 60 Years

Short-term temperature fluctuations(STFs),including amplitude and frequency fluctuations,are one of the main features of weather and play vital roles in determining the type of ecosystem present.Although temperature fluctuations at different time scales have been extensively discussed,the research on week-scale STFs is lacking.In this study,we developed a method,that can quantify the amplitude and frequency of STFs by the thresholds from all years.We used this method to quantify the amplitude and frequency of the 7-d STFs from 1951 to 2019 across China.Our results indicate that the amplitude of the STF was much higher in the eastern part of China than in the western part,while the frequency of the STF was higher in the middle part than in the southern and northern parts;further-more,the STF was highly dependent on internal factors such as topography.The long-term STF mainly showed a decreasing trend before 1990,which implies that temperature became increasingly stable from the 1950s to the 1990s.The main influencing factors were related to topography since the trends were relatively consistent in space.A case study in Taihu Lake showed that an unstable STF in winter and summer resulted in a smaller bloom area in the following spring and autumn.Our method could eliminate seasonal effects and is capable of analyzing STFs at scales ranging from days to years.Quantifications of the amplitude and frequency also make the STF indicators more comprehensive.Furthermore,the STF increased significantly across most of China after 1990,which implies that temperature is becoming increasingly unstable.The drivers of these STFs are related to human impacts since the trends are different in space.

Estimation of evaporation losses based on stable isotopes of stream water in a mountain watershed

Water stable isotopes(δ^(2) H andδ^(18)O)can record surface water evaporation,which is an important hydrological process for understanding watershed structure and function evolution.However,the isotopic estimation of water evaporation losses in the mountain watersheds remains poorly explored,which hinders understanding spatial variations of hydrological processes and their relationships with the temperature and vegetation.Here we investigatedδ^(2) H,δ^(18)O,and d-excess values of stream water along an altitude gradient of 2130 to 3380 m in Guan’egou mountain watershed at the east edge of the Qinghai-Tibet Plateau in China.The meanδ^(2) H(-69.6‰±2.6‰),δ^(18)O(-10.7‰±0.3‰),and dexcess values(16.0‰±1.4‰)of stream water indicate the inland moisture as the major source of precipitation in study area.Water stable isotopes increase linearly with decreasing altitudes,based on which we estimated the fractions of water evaporation losses along with the altitude and their variations in different vegetations.This study provides an isotopic evaluation method of water evaporation status in mountain watersheds,the results are useful for further understanding the relationship between hydrological processes and ecosystem function under the changing climate surrounding the Qinghai-Tibet Plateau.

Patterns of Multiscale Temperature Variability over the Eastern and Central Tibetan Plateau During 1960-2008

Climate variability is an important inherent characteristic of climate and it varies on all timescales. Through examination of temperature variability on multiple temporal scales at 63 stations over the eastern and central Tibetan Plateau （TP） during 1960-2008, we find decreasing trends in daily and intraannual temperature, especially in cold seasons （autumn and winter）. These changes are more sensitive than those in the eastern China coastal region at the same latitude and indicate an asymmetric change of temperature, with hourly, daily, and monthly trends in cold periods stronger than those in warm periods during the recent years. The variation of interannual temperature is complex, showing an increasing trend in autumn and winter and decreasing trend in spring and summer, which is similar to those in the northern polar region. The changes of multiscale variability of temperature are mainly related to changes of atmospheric water vapor, cloudiness, anthropogenic aerosols, monsoon-driven climate, and some local factors. To find the influences of local conditions on temperature variability, we analyze the effects of altitude, topography, and urbanization. The results show that elevation is strongly and positively related to diurnal temperature range （DTR） and slightly positively related to interannual temperature variability （IVT）, but intraannual temperature variability shows no clear elevation dependency. Topography and urbanization also play important roles in multiscale temperature variability. Finally, strong relationships are observed between temperature variability on each scale and different extreme indices.