Trend In Relative Humidity Research Articles

西北旱区近50年气候变化分析

气候变化对干旱半干旱地区的影响更加显著，为此，需要明确其气候变化趋势，从而为可持续发展提供管理依据。基于152个气象站点1961~2011年降水、温度、风速、湿度和日照时数等气象资料，分析了西北旱区气候的空间分布和变化趋势。近50年，各气象要素的空间分布具有明显的梯度变化特征，最高、最低及平均温度由东南–西北方向表现出增加的趋势，而降水和相对湿度则表现出递减的趋势；在旱区西部南北条带上，日照时数和风速较高，而降水和相对湿度较低。不同要素随时间变化趋势不同，降水和温度多呈上升趋势，而日照时数、相对湿度和风速则多呈下降趋势；变化趋势的显著站点数不同，92%以上站点温度和降水的上升趋势明显，69%站点的风速下降趋势显著，约40%站点的相对湿度和日照时数下降趋势显著；各气象要素基本上都在1980s发生了突变。 A more significant impact on arid and semi-arid area from climate change has long been certified. Therefore, it is necessary to be clear about the trend of climate change in arid area of Northwest China, so as to provide management basis for sustainable development. Based on the data from 152 meteorological stations of precipitation, temperature, wind speed, humidity and sunshine hours during 1961 to 2011, the spatial distribution and temporal trends in the arid region of northwest China were analyzed using different methods. In resent 50 years, these meteorological elements on the Arid Northwest spatially distributed with an obvious gradient. Maximum, minimum and mean temperature showed an increasing trend, while precipitation and relative humidity exhibited the trend of decrease from the southeast to the northwest; data showed that, sunshine hours and wind speed were high, while precipitation and relative humidity were low on the north and south strip. Different elements represent different changing trends over time, overall, in investigating years on researching area, precipitation and temperature were mostly on the rise, while sunshine hours, relative humidity and wind speed mostly decreased. The numbers of stations with significant trends for different meteorological elements were quite different. About 92% of stations had significant upward trends in precipitation and temperature, 69% of stations had significantly downward trends in wind speed, and about 40% of stations had significant downward trends in relative humidity and sunshine hours. The meteorological elements basically present abrupt change in the 1980s.

Climate change trends in some of the rubber growing regions of North-East India

<div><table cellspacing="0" cellpadding="0" align="center"><tbody><tr><td align="left" valign="top"><p>Climate change analysis has been conducted using daily surface meteorological datasets in respect of nine parameters from five rubber growing locations in the East and North-East India. Monthly, seasonal and annual variability in meteorological parameters showed decreasing trends in relative humidity, sunshine hours and pan evaporation rates coupled with increasing temperature extremes. Rise in mean temperature was seen to be highest (0.34 0C per decade) for Dhenkanal which experiences dry sub-humid type of climate. The data on relative humidity and temperature also revealed the fact that warm surface temperatures, along with limited moisture availability, may lead to lower relative humidity in the future, since all the stations are away from the moist coastal belts. Decreasing trends in sunshine hours were mainly observed during winter and post monsoon seasons with decreasing number of days even with the optimum required daily sunshine hours. The fact that there were no significant changes in the amount of rainfall or the number of rainy days was in conformity with several earlier reports in the northeast. Mean monthly decadal variations have also been tested with earlier and recent sets. With long term trends in most of the weather parameters, being lesser when compared to that of the traditional rubber growing regions in India, it is imperative that for rubber cultivation to thrive in this non-traditional belt, future policy inputs will have to be based depending on the magnitude of climate change effects.</p></td></tr></tbody></table></div>

Trends in reference evapotranspiration in Turkey: 1975-2006

This study examines the trends in reference evapotranspiration (ETo) in Turkey by analysing data from 77 weather stations for a 32-year period (1975–2006). ETo values were calculated using the Penman–Monteith method using air temperature, wind speed, relative humidity, and sunshine hours data. Trends in annual and monthly ETo were determined using the Mann–Kendall trend test with the trend-free prewhitening procedure. The magnitude of trends was estimated by calculating the Sen's slope. The collective or field significance of the trends was evaluated using Walker test. The possible causes of changes in ETo were discussed by analysing the trends in air temperature, wind speed, relative humidity, and solar radiation data collected at the same stations. The implications of ETo trends for crop water requirements were evaluated. The analyses showed that the majority of stations (88%) in Turkey had annual ETo between 750 and 1200 mm during the 32-year period and ETo decreased gradually from south to north. From 1975 to 2006, 58% of stations had upward trends in annual ETo. Upward trends were statistically significant at the 0.05 level for 32% of stations. The rates of changes in annual ETo were on average 1.20 mm year−2. The trends detected in monthly ETo were mostly upward with an average magnitude between −0.01 and 0.14 mm month year−1. Trends detected at the annual timescale and for the majority of the months provided the field significance at the 0.05 level. Analysis of other climatic data showed that upward trends in air temperatures, downward trends in wind speeds, and downward trends in relative humidity were widespread over Turkey for the same time period. Changes in these three parameters could explain the majority of the changes in ETo rates. The ETo changes affect crop water requirements and increase the demand for irrigation.

Reactivity of Perovskites with Water: Role of Hydroxylation in Wetting and Implications for Oxygen Electrocatalysis

Oxides are instrumental to applications such as catalysis, sensing, and wetting, where the reactivity with water can greatly influence their functionalities. We find that the coverage of hydroxyls (*OH) measured at fixed relative humidity trends with the electron-donor (basic) character of wetted perovskite oxide surfaces. Using ambient pressure X-ray photoelectron spectroscopy, we report that the affinity toward hydroxylation, coincident with strong adsorption energies calculated for dissociated water and hydroxyl groups, leads to strong H bonding that is favorable for wetting while detrimental to catalysis of the oxygen reduction reaction (ORR). Our findings provide novel insights into the coupling between wetting and catalytic activity and suggest that catalyst hydrophobicity should be considered in aqueous oxygen electrocatalysis.

(Corrosion Division Morris Cohen Student Award) Impact of Salt Deliquescence on the Humidity-Dependence of Atmospheric Corrosion

In atmospheric environments, corrosion is often approximated as a discontinuous process reliant on the availability of electrolyte to provide ionic conduction between cathodic and anodic sites. A critical question in atmospheric corrosion is when can a surface be considered wet enough for corrosion to occur at a considerable rate? For surfaces contaminated with hygroscopic salts, such as those which comprise atmospheric sea salt particles, the relative humidity (RH) associated with the deliquescence of these salts is often assumed to serve as the wet/dry threshold in this regard. Deliquescence is the bulk phase transformation whereby solid salt spontaneously absorbs water to form an aqueous electrolyte at and above a specific RH, the deliquescence RH (DRH). In this work, we examined the relationship between the hygroscopic phase transitions of NaCl, MgCl2 and ASTM artificial seawater (ASW) and the response of mild steel contaminated with these sea salt simulants at the initial stage of corrosion. The hygroscopic behavior of salt microparticles of each composition, similar in size to natural atmospheric aerosol, was characterized by impedance measurements across an interdigitated electrode sensor. The corrosion behavior of mild steel loaded these microparticles was investigated as a function of RH under isohumidity, room temperature conditions. Both the attack morphology and volume loss rates were quantified using optical profilometry. Ex-situ characterization of the dried salts on the corroded steel and sensor were carried out using SEM/EDS and Raman spectroscopy. Trends in corrosion loss versus RH were not directly reflective of the deliquescence phase transitions observed or predicted for the salts examined. Considerable corrosion was observed below the DRH of the salts and attributed to (1) the presence of non-equilibrium electrolyte due to kinetic limitations during drying, (2) alteration of the deliquescence behavior by the corrosion chemistry and (3) adsorbed electrolyte at the solid salt/metal interface. For NaCl, sustained corrosion was observed down to 33% RH for up to 300 days. At 53% RH and above, attack proceeded at rates comparable to that observed above the DRH (76%) due to the development of hygroscopic corrosion chemistry. There was no significant difference in attack depth and volume loss trends between samples that were originally loaded with droplets and those loaded with NaCl crystals prior to isohumidity exposure. The initiation of corrosion under NaCl deposits well below the DRH can be explained in terms of the presence of adsorbed water associated with the salt crystals in contact with the steel. For MgCl2 and ASW, sustained corrosion was detectable down to 11% and 23% RH, respectively, for up to 30 days. This is well below the DRH of MgCl2 (33%), which is often considered the active component of sea salt mixtures at low humidity levels. Significant admittance was measured across ASW and MgCl2 deposits on the electrode sensors at < 2% RH after 24 hours, likely due to trapping of supersaturated MgCl2 fluid under solid salt crusts. Trends in attack morphology and volume loss above 33% RH of ASW-loaded samples were similar to those loaded with NaCl alone. This may be explained by the similar corrosion chemistry that developed on the NaCl and ASW samples. Together, these results show that DRH of an individual salt contaminant for the systems under study did not serve as the delineation between a wet and a dry surface, nor as the boundary between significant and insignificant corrosion attack. The impact of these findings on humidity-dependent atmospheric corrosion models along with translation to understanding atmospheric corrosion of other alloy systems will be discussed.

Observed climatology and trend in relative humidity in the central and eastern Tibetan Plateau

AbstractMonthly surface relative humidity (RH) data for 71 stations in the Tibetan Plateau (TP) provided by the National Meteorological Information Center/China Meteorological Administration are compared with corresponding grid points from the National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR hereafter) reanalysis. Mean climatologies, interannual variabilities, and trends calculated by the Mann‐Kendal method are analyzed during 1961–2013. The annual regional long‐term mean surface RH is 55.3%, with a clear maximum in summer (66.4%) and minimum in winter (44.9%). Compared with observations, NCEP/NCAR overestimates RH in all seasons, especially in spring (18.2%) and winter (17.8%). Mean annual regional surface RH has decreased by −0.23% decade−1 and even more rapidly in summer (−0.60% decade−1) and autumn (−0.39% decade−1). The reduction of surface RH is also captured by the NCEP/NCAR reanalysis at the surface, 400, 500, and 600 hPa. A particularly sharp reduction of RH since the mid‐1990s is evident in both data sets, in line with rapid warming over the plateau. This suggests that moisture supply to the plateau from the Arabian Sea and the Bay of Bengal is limited and that variability and trends of surface RH over the TP are not uniquely driven by the Clausius‐Clapeyron relationship.

Diurnal and seasonal changes in near‐surface humidity in a complex orography

AbstractChanges in near‐surface humidity are evaluated in relation to changes in other meteorological variables such as air temperature, precipitation, and sunshine duration for a 31 year period (1981–2011) using hourly time series recorded in Switzerland. Trends in meteorological variables are analyzed at the seasonal and subdaily scale, and changes in water vapor are tested for Clausius‐Clapeyron scaling. Results show a marked seasonality of climatic changes with a trend toward warmer, clearer, and drier near‐surface atmosphere strengthening from January to June. During this period considerable negative trends in relative humidity are detected. An abrupt shift in climatic trends occurs during the month of July, after which warming trends are considerably smaller and relative humidity remains constant or increases. An evaluation of reanalysis products demonstrates strong consistency with station observations and when combined with teleconnection indices supports the hypothesis that shifts in the general circulation patterns rather than local feedbacks are the principal drivers of observed seasonality of climate change. However, local feedbacks can play a role in enhancing summer humidity and convective activity (lightning and evening precipitation). Subdaily changes are significant with more pronounced daytime trends of temperature and humidity during spring and the opposite during summer. The strong seasonality and diurnal variability of changes in near‐surface meteorology over the last three decades in Switzerland warns against climate change impact assessments at local scale that consider uniform changes in air temperature and assume Clausius‐Clapeyron scaling for near‐surface humidity.

Temporal Dynamics of Trend in Relative Humidity with RH-SARIMA Model

The relative humidity (RH) of 13 stations all over the peninsular Malaysia for the period of 1968 to 2009 is examined in this study. In understanding the trend flow, the Mann–Kendall (MK) trend test of RH of selected 13 stations all over Malaysia reported a decreasing trend over all parts excluding one station. RH prediction is an important problem in the climate change study; it determines future trend based on past values. The main goal of this paper is to create a model and make future trend predictions using RH data. Among the most effective and prominent approaches for analysing time series data is the methods introduced by Box and Jenkins. In this study we applied the Box-Jenkins methodology to build an RH-Seasonal Autoregressive Integrated Moving Average model (SARIMA) for monthly RH data. The RH-SARIMA model for each station was developed. These models were used to forecast 30 months upcoming RH data. The result will help decision makers to establish priorities in terms of climate change impact over peninsular Malaysia.

Focus on relative humidity trend in Iran and its relationship with temperature changes during 1960–2005

In this research, the mean relative humidity (RH) trend was investigated in the monthly, seasonal and annual timescales during 1960–2005 in 32 synoptic meteorological stations. The Mann–Kendall test after the removal of the significant lag-1 serial correlation effect from the RH time series by pre-whitening was used to determine significant trends. Sen’s slope estimator was used to determine the median slope of positive or negative RH trends in seasonal and annual timescales. Also, in order to facilitate trend analysis and exploring in datasets, 10-year moving average low-pass filter was applied on mean annual normalized RH. Furthermore, smoothed time series by the mentioned filter were classified in four clusters and then they were mapped to show the spatial distribution of trend patterns in Iran. Results showed both significant downward and upward trends, but the number of negative trends was more than positive ones. In general, the stations located in arid central and eastern parts of country had more negative trends. Results of the Sen’s slope estimator showed that in annual timescale, Gorgan synoptic station had the most increasing slope by (+) 2 % per decade, while the most negative slope was detected in Bam by (−) 2.79 % per decade. Also, the analysis of smoothed time series of RH and their relationship with smoothed temperatures showed a strong inverse relationship particularly after 1995. It can be concluded that alongside the increasing of temperature in many parts of Iran, lack of sufficient water vapor has led to decreasing trend of RH in the country.

Recent Trends in Temperature and Relative Humidity in Bawku East, Northern Ghana

Extensive analyses of trends in mean annual and mean seasonal minimum and maximum temperatures and relative humidity were examined for Bawku East, northern Ghana, for the period 1961 to 2012. Mean monthly maximum and minimum temperatures were used to analyse and establish recent temperature trends on an annual and seasonal basis. The year was divided into rainy and dry seasons for the seasonal trends. Mean monthly relative humidity at 6 am and 3 pm from 1961 to 2012 were considered to show recent trends in humidity since temperature and humidity interact to determine the heat exposure for outdoor workers. Regression analysis was used to illustrate trends and calculate mean yearly and seasonal rate of change. A Durbin-Watson statistical test was employed to verify autocorrelation of the residuals of the trend models and none was detected. Results showed a gradual and statistically significant rise in both mean minimum and mean maximum temperatures at two stations (Manga and Garu). There was an inconsistent pattern of trend observed at the third station (Binduri). Declining trends in relative humidity were observed at 6 am and 3 pm at seasonal and annual levels at Binduri and Garu, while there was a rising trend in relative humidity at Manga. The importance of this study hinges on the linkage between heat exposure (temperature and air humidity) and human health in the wake of climate change on outdoor farmers in developing countries who spend many hours doing manual work in the heat. On the whole, the rising temperature has impacted on ecosystem services in the study area.

Climate change and corrosion damage risks for reinforced concrete infrastructure in China

A changing climate which leads to increases in atmospheric CO2 concentration, and changes in temperature and relative humidity (RH), especially in the longer term, will accelerate the deterioration processes and consequently decline the safety, serviceability and durability of reinforced concrete (RC) infrastructure. This paper presents an investigation of carbonation-induced deterioration in three typical Chinese cities (Kunming, Xiamen and Jinan) under a changing climate. The changing trends of atmospheric CO2, local temperature and RH of typical Chinese cities are projected based on the latest CO2 emission scenarios. The time-dependent analysis is based on Monte Carlo simulation, and includes the uncertainty of climate projections, deterioration processes, material properties, dimensions and accuracy of predictive models. Deterioration of RC structures is represented by the probabilities of reinforcement corrosion initiation and damage. It was found that the mean carbonation depths by 2100 may increase by up to 45% for RC structures in China due to a changing climate. It was also found that climate change can cause an additional 7–20% of carbonation-induced damage by 2100 for RC buildings in temperate or cold climate areas in China. The findings provide a basis for the development of climate adaptation strategies through the improved design of concrete structures.

Evaluation of temporal and spatial trends in relative humidity and dew point temperature in Bangladesh

Trend analysis of climatic variables on different spatial and temporal scales has been of great concern during the past century because of the attention given to global climate change by the scientific community. In this study, trends of the annual and seasonal relative humidity and dew point temperature time series have been investigated for 15 stations all over Bangladesh during 1961–2010. The magnitude of the climatic trends was derived from the slopes of the Sen’s estimator. The statistical significance of the trends was determined by means of the Mann–Kendall test. Pre-whitening was used to eliminate the influence of serial correlation on the Mann–Kendall test. The percentage of stations showing a significant trend is moderate in the case of relative humidity, but is a lot higher in dew point temperature series at the 95 % confidence limit. On average, relative humidity is increasing at 0.53, 0.86, and 1.18 % per decade on annual, winter, and pre-monsoon (summer) scales, respectively, in the western part of the country. Significant negative trends of relative humidity series are apparent in monsoon season. On the other hand, there is no significant decreasing trend in both annual and seasonal dew point temperature time series at any station. Again, a higher magnitude of the significant trends is observed in the western part of the country. The majority of the slopes are above zero, indicating an increasing nature in annual and seasonal dew point temperatures over Bangladesh. This warming of dew point temperature in Bangladesh is analogous to the global trend.

Influence of Urbanization on Haze

Defense Meteorological Satellite-Operational Linescan System night-time emission data was applied as a proxy approach to assess urbanization level. Using this approach, it was found the spatial distribution of annual haze days was consistent with that of night-time light intensity in Zhejiang. The intensities of haze and night-time light in Northeastern Zhejiang were greater than those in Southwestern Zhejiang, and the same intensities were higher in coastal areas (than inland areas). The distributions of haze and night-time light both presented the features of regional clusters and boundary crossing between urban and rural areas. From 1960 to 2010, the annual haze days exhibited three change phases separated by two change jumps around 1979 and 2000. The first and second change jumps corresponded to the reform and opening-up and to the intensified urbanization, respectively. A close relationship between haze and total night-time light was found, and the correlation coefficients were higher than 0.9. In the long term, a negative correlation between relative humidity and visibility was observed, but the synchronous delaying trends of relative humidity and visibility reveal that the visibility delay was induced by increased pollutants. A comparison of the change trends of relative humidity, particle concentration, and visibility in Hangzhou and Linan indicates that an atmosphere with drier and heavier air pollution surrounds urban areas. Therefore, urbanization has a significant impact on haze.

Forty years increase of the air ambient temperature in Greece: The impact on buildings

Air temperatures in urban areas continue to increase because of the heat island phenomenon (UHI) and the undeniable warming of the lower atmosphere during the past few decades. The observed high ambient air temperatures intensify the energy demand in cities, deteriorate urban comfort conditions, endanger the vulnerable population and amplify pollution problems especially in regions with hot climatic conditions. The present paper analyses 40years of hourly data series from nine meteorological stations in Greece in order to understand the impact of air temperature and relative humidity trends on the energy consumption of buildings. Using a typical office building, the analysis showed that for the period in question the heating load in the Greek building sector has decreased by about 1kWh/m2 per decade, while the cooling load increased by about 5kWh/m2 per decade. This phenomenon has major environmental, economic and social consequences, which will be amplified in the upcoming decades in view of the expected man-made climatic changes in this geographic area.

Future humidity trends over the western United States in the CMIP5 global climate models and variable infiltration capacity hydrological modeling system

Abstract. Global climate models predict relative humidity (RH) in the western US will decrease at a rate of about 0.1–0.6 percentage points per decade, albeit with seasonal differences (most drying in spring and summer), geographical variability (greater declines in the interior), stronger reductions for greater anthropogenic radiative forcing, and notable spread among the models. Although atmospheric moisture content increases, this is more than compensated for by higher air temperatures, leading to declining RH. Fine-scale hydrological simulations driven by the global model results should reproduce these trends. It is shown that the MT-CLIM meteorological algorithms used by the Variable Infiltration Capacity (VIC) hydrological model, when driven by daily Tmin, Tmax, and precipitation (a configuration used in numerous published studies), do not preserve the original global model's humidity trends. Trends are biased positive in the interior western US, so that strong RH decreases are changed to weak decreases, and weak decreases are changed to increases. This happens because the MT-CLIM algorithms VIC incorporates infer an overly large positive trend in atmospheric moisture content in this region, likely due to an underestimate of the effect of increasing aridity on RH. The result could downplay the effects of decreasing RH on plants and wildfire. RH trends along the coast have a weak negative bias due to neglect of the ocean's moderating influence. A numerical experiment where the values of Tdew are altered to compensate for the RH error suggests that eliminating the atmospheric moisture bias could, in and of itself, decrease runoff up to 14% in high-altitude regions east of the Sierra Nevada and Cascades, and reduce estimated Colorado River runoff at Lees Ferry up to 4% by the end of the century. It could also increase the probability of large fires in the northern and central US Rocky Mountains by 13 to 60%.

Effects of tillage and weed management on the vertical distribution of microclimate and grain yield in a winter wheat field

This paper presents results of a field study of the influence of tillage and weed on the vertical distribution of microclimate in the upper, middle, and deeper layers of a winter wheat population and grain yield during the 2008&amp;ndash;2009 and 2009&amp;ndash;2010 winter wheat growing seasons. The results showed that the microclimate of the winter wheat canopy was different among the upper, middle, and deeper layers. Illumination was higher in the upper layer of the canopy than in the middle and deeper layers; under no-tillage + weed-reserving, a greater difference was found among the 3 layers. In the upper layer, illumination was the highest and lowest under no-tillage + weed-control and conventional tillage + weed-control, respectively. In the upper layer, air temperature was higher under no-tillage + weed-control than under conventional tillage + weed-control. The effects of air temperature in the middle and deeper layers were relatively low with tillage and considerably higher with weeds. Relative humidity was the highest and lowest under no-tillage + weed-reserving and conventional tillage + weed-control, respectively. During the winter wheat growing seasons, illumination and air temperature were lower at the heading stage and increased to a maximum at the filling stage, whereas the trend for relative humidity was the opposite. With weed-control, grain yield was significantly (LSD, P &amp;lt; 0.05) higher under conventional tillage than under no-tillage; with weed-reserving, no significant (LSD, P &amp;lt; 0.05) differences in grain yield were found between conventional tillage and no-tillage. The results showed that tillage and weed influenced microclimate vertical distribution in the winter wheat canopy and grain yield of winter wheat.

Spatio-temporal variation of actual evapotranspiration in the Haihe River Basin of the past 50 years

In this paper, the spatio-temporal variation and trend of daily actual evapotranspiration (ETa) are calculated for the Haihe River Basin from 1961 to 2010. The methodology is based on the complementary relationship approach, i.e. the advection–aridity (AA) model with parameter validation from 1961 to 2010, which allows the determination of ETa that cannot be instrumentally measured. Daily data on mean/maximum/minimum temperature, air pressure, actual water vapor pressure, sunshine hours, wind speed, sunshine duration and cloud cover from 31 meteorological stations from 1961 to 2010 are used in order to identify the main drivers of changes in evapotranspiration. The trend tests applied in this study are the linear regression method and the nonparametric Mann–Kendall test (MKtest). The results show: 1) the Haihe River Basin has an annual ETa at about 484 mm/yr. The highest ETa occurs in summer, followed by autumn. From 1961 to 2010, the annual ETa, the ETa in summer and the ETa in autumn show a significant negative trend in the Haihe River Basin. The ETa varies insignificantly in spring and winter; 2) the ETa shows distinct spatial variability in the Haihe River Basin. It closely follows the topography and increases with greater distance from the sea, but varies significantly during the seasons; 3) the central plain area of the Basin around the capital city of Beijing shows the highest occurrence of negative trends of ETa with a decrease of ETa of 40 mm for the time series. 4) negative trends of ETa in summer are related to multiple factors: decreasing relative humidity and decreasing reduced sunshine duration under increasing surface temperatures in summer. Increases in surface temperature include the mean, maximum and minimum daily temperature. The decline of ETa in autumn can be explained by a negative trend of relative humidity. The decreasing ETa suggests a reduction in water availability and cycle in seasons with highest water demand.

Trends in U.S. Surface Humidity, 1930–2010

AbstractU.S. hourly surface observations are examined at 145 stations to identify annual and seasonal changes in temperature, dewpoint, relative humidity, and specific humidity since 1930. Because of numerous systematic instrument changes that have occurred, a homogeneity assessment was performed on temperatures and dewpoints. Dewpoints contained higher breakpoint detection rates associated with instrumentation changes than did temperatures. Temperature trends were tempered by adjusting the data, whereas dewpoints were unaffected. The effects were the same whether the adjustments were based on statistically detected or fixed-year breakpoints. Average long-term trends (1930–2010) indicate that temperature has warmed but that little change has occurred in dewpoint and specific humidity. Warming is strongest in spring. There is evidence of inhomogeneity in the relative humidity record that primarily affects data from prior to 1950. Therefore, long-term decreases in relative humidity, which are strongest in winter, need to be viewed with caution. Trends since 1947 indicate that the warming of temperatures has coincided with increases in dewpoints and a moistening of specific humidity. This moistening is especially pronounced during the summer in the Midwest. For the nation, trends in relative humidity show little change for the period 1947–2010, during which these data are more homogeneous. Moistening has occurred throughout the central United States while other regions have experienced drying. Urban-related warming and drying trends are present in the data, but their effect is minimal. Regional changes in land use and moisture availability are likely influencing trends in atmospheric moisture.

A study of surface humidity changes in china during the recent 50 years

This paper analyzes in detail the characteristics of surface humidity changes in China under the background of global warming in the recent 50 years by using the observation data compiled by the National Meteorological Information Center of China. The results reveal that (1) with the increase of temperature, surface saturation specific humidity (q s) shows basically an exponential growth, according to the Clausius-Clapeyron equation. The nationwide average moistening rate in winter is obviously less than the annual average rate and the summer rate. There are some regional differences in q s trends in different regions of China. For example, q s in central and eastern parts of China exhibits a reducing trend in summer, consistent with the weakening trend of temperature in these areas; (2) except parts of South China and Jianghuai Region in eastern China, unanimously increasing trends of annual and winter specific humidity (q) are found in most of China, especially in western China. In summer, except parts of Northeast China, Northwest China, and some areas over the Qinghai-Tibetan Plateau, the decreasing and drying trends are significant in most of China, which is not consistent with the global mean situation; (3) the surface relative humidity (RH) in most of China shows a reducing trend. One of the major reasons for the reduction of RH is that the increasing rates of q are smaller than those of q s. Nonetheless, upward trends of RH in central and eastern China mainly due to the cooling temperature and rising q in these regions are observed in summer, leading to more precipitation. From about 2003 or so, q s has remarkably increased while q has sharply decreased in most parts of China; therefore, RH has reduced to a great extent. This may be closely related to the persistent growth of drought areas in China in the recent 10 years.

Trends in Tropospheric Humidity from 1970 to 2008 over China from a Homogenized Radiosonde Dataset

Abstract Radiosonde humidity data provide the longest record for assessing changes in atmospheric water vapor, but they often contain large discontinuities because of changes in instrumentation and observational practices. In this study, the variations and trends in tropospheric humidity (up to 300 hPa) over China are analyzed using a newly homogenized radiosonde dataset. It is shown that the homogenization removes the large shifts in the original records of dewpoint depression (DPD) resulting from sonde changes in recent years in China, and it improves the DPD’s correlation with precipitation and the spatial coherence of the DPD trend from 1970 to 2008. The homogenized DPD data, together with homogenized temperature, are used to compute the precipitable water (PW), whose correlation with the PW from ground-based global positioning system (GPS) measurements at three collocated stations is also improved after the homogenization. During 1970–2008 when the record is relatively complete, tropospheric specific humidity after the homogenization shows upward trends, with surface–300-hPa PW increasing by about 2%–5% decade−1 over most of China and by more than 5% decade−1 over northern China in winter. The PW variations and changes are highly correlated with those in lower–midtropospheric mean temperature (r = 0.83), with a dPW/dT slope of ~7.6% K−1, which is slightly higher than the 7% K−1 implied by Clausius–Clapeyron equation with a constant relative humidity (RH). The radiosonde data show only small variations and weak trends in tropospheric RH over China. An empirical orthogonal function (EOF) analysis of the PW reveals several types of variability over China, with the first EOF (31.4% variance) representing an upward PW trend over most of China (mainly since 1987). The second EOF (12.0% variance) shows a dipole pattern between Southeast and Northwest China and it is associated with a similar dipole pattern in atmospheric vertical motion. This mode exhibits mostly multiyear variations that are significantly correlated with Pacific decadal oscillation (PDO) and ENSO indices.