Evaporation Trends Research Articles

Analysis of Characteristic of Meteorological Variables in Golmud, China during 1955-2015 and Prediction of its Future Change

Global warming and its impact on socio-economic and eco-environment in the more drought-prone regions have attracted great attention. Arid regions account for about 30% of the total China’s land area, which are quite sensitive and vulnerable to climate change. The annual trends of three meteorological variables were analyzed in Golmud City during 1955-2015. The linear regression, cumulative anomaly and R/S methods were used to determine the characteristics of the meteorological variables. The Morlet wavelet transforms method was employed to detect the dynamic periodic features of the meteorological variables. The results were obtained as follows: 1) the significant increasing trends were indicated in both temperatures (0.5°C/10a, p<0.01) and precipitation (3.3mm/10a, p<0.05), the decreasing trend in evaporation (118.4mm/10a, p>0.05). This states that the climate of Golmud City was turned from cold-dry to warm-wet. 2) The Hurst indexes of each annual variable were all greater than 0.5, it suggested that there would be obvious Hurst phenomenon in the future. 3) The wavelet analysis revealed that the temperature, precipitation, evaporation, had the periods of 12-14a, 7-9a, 11-12a oscillations, respectively. 4) According to the analysis results by synthesis we can predict that there will still keep the warming and increasing trend of temperature and precipitation in the future. In general, the results of using the Mann-Kendall and R/S proved the good consistency in detection of the trend for temperature and precipitation. This study can be used as a reference for further analysis of climate as well as the impacts of climate change. More importantly it can provide theoretical support for context-specific plan for water resources development and agricultural and animal husbandry production in Golmud City.

Trend characteristics of rainy days and evaporation at a tropical rainforest region in East Malaysia, Borneo

Impact of climate change over the hydrological system in a region can be identified through statistical characterization of hydrometerological parameters such as rainfall, temperature, humidity and evaporation. In order to understand the influence of climate change, statistical trend characteristics of rainy days, non-rainy days and evaporation rate in the Limbang River Basin (LRB) in Sarawak, Malaysia, Northern Borneo was assessed in the present research. Annual rainfall and monthly evaporation data, over a period of 46 years, (1970 - 2015) corresponding to three rain gauging stations, the Limbang DID, Ukong and Long Napir were used in the research. Linear regression model, Mann Kendall and Sen’s slope estimator techniques were applied to detect the statistical trends in rainy days and evaporation. A statistically significant increasing trend in annual rainy days was found at all the stations. Non-rainy days showed a statistically significant decreasing trend at Limbang DID and Ukong. Monthly evaporation rates showed an overall increasing trend and the greatest increasing trend in evaporation was observed in September (2.55 mm/year) for the Limbang DID and in December (2.61 mm/year) for Ukong. Evaporation measured at the Ukong station also showed a non-significant decrease during June and September. A comparison of the evaporation controlling meteorological variables such as rainfall, temperature and relative humidity indicates inter-influence at various strengths. Along with local precipitation characteristics, wind and fluctuation of atmospheric temperature over the region plays a vital role in increased rate of evaporation from the region. Overall, the analysis identified a statistically significant increasing trend in rainy days and evaporation in the LRB. The results of the present research can be used as critical planning data for micro and macro hydroelectric projects in the river basin.

Australian Precipitation Recycling and Evaporative Source Regions

AbstractThe relative importance of atmospheric advection and local land–atmosphere coupling to Australian precipitation is uncertain. Identifying the evaporative source regions and level of precipitation recycling can help quantify the importance of local and remote marine and terrestrial moisture to precipitation within the different hydroclimates across Australia. Using a three-dimensional Lagrangian back-trajectory approach, moisture from precipitation events across Australia during 1979–2013 was tracked to determine the source of moisture (the evaporative origin) and level of precipitation recycling. We show that source regions vary markedly for precipitation falling in different regions. Advected marine moisture was relatively more important than terrestrial contributions for precipitation in all regions and seasons. For Australia as a whole, contributions from precipitation recycling varied from ~11% in winter up to ~21% in summer. The strongest land–atmosphere coupling was in the northwest and southeast where recycled local land evapotranspiration accounted for an average of 9% of warm-season precipitation. Marine contributions to precipitation in the northwest of Australia increased in spring and, coupled with positive evaporation trends in the key source regions, suggest that the observed precipitation increase is the result of intensified evaporation in the Maritime Continent and Indian and Pacific Oceans. Less clear were the processes behind an observed shift in moisture contribution from winter to summer in southeastern Australia. Establishing the climatological source regions and the magnitude of moisture recycling enables future investigation of anomalous precipitation during extreme periods and provides further insight into the processes driving Australia’s variable precipitation.

Inconsistencies between chemistry–climate models and observed lower stratospheric ozone trends since 1998

Abstract. The stratospheric ozone layer shields surface life from harmful ultraviolet radiation. Following the Montreal Protocol ban on long-lived ozone-depleting substances (ODSs), rapid depletion of total column ozone (TCO) ceased in the late 1990s, and ozone above 32 km is now clearly recovering. However, there is still no confirmation of TCO recovery, and evidence has emerged that ongoing quasi-global (60∘ S–60∘ N) lower stratospheric ozone decreases may be responsible, dominated by low latitudes (30∘ S–30∘ N). Chemistry–climate models (CCMs) used to project future changes predict that lower stratospheric ozone will decrease in the tropics by 2100 but not at mid-latitudes (30–60∘). Here, we show that CCMs display an ozone decline similar to that observed in the tropics over 1998–2016, likely driven by an increase in tropical upwelling. On the other hand, mid-latitude lower stratospheric ozone is observed to decrease, while CCMs that specify real-world historical meteorological fields instead show an increase up to present day. However, these cannot be used to simulate future changes; we demonstrate here that free-running CCMs used for projections also show increases. Despite opposing lower stratospheric ozone changes, which should induce opposite temperature trends, CCMs and observed temperature trends agree; we demonstrate that opposing model–observation stratospheric water vapour (SWV) trends, and their associated radiative effects, explain why temperature changes agree in spite of opposing ozone trends. We provide new evidence that the observed mid-latitude trends can be explained by enhanced mixing between the tropics and extratropics. We further show that the temperature trends are consistent with the observed mid-latitude ozone decrease. Together, our results suggest that large-scale circulation changes expected in the future from increased greenhouse gases (GHGs) may now already be underway but that most CCMs do not simulate mid-latitude ozone layer changes well. However, it is important to emphasise that the periods considered here are short, and internal variability that is both intrinsic to each CCM and different to observed historical variability is not well-characterised and can influence trend estimates. Nevertheless, the reason CCMs do not exhibit the observed changes needs to be identified to allow models to be improved in order to build confidence in future projections of the ozone layer.

A Raman lidar tropospheric water vapour climatology and height-resolved trend analysis over Payerne, Switzerland

Abstract. Water vapour is the strongest greenhouse gas in our atmosphere, and its strength and its dependence on temperature lead to a strong feedback mechanism in both the troposphere and the stratosphere. Raman water vapour lidars can be used to make high-vertical-resolution measurements on the order of tens of metres, making height-resolved trend analyses possible. Raman water vapour lidars have not typically been used for trend analyses, primarily due to the lack of long-enough time series. However, the Raman Lidar for Meteorological Observations (RALMO), located in Payerne, Switzerland, is capable of making operational water vapour measurements and has one of the longest ground-based and well-characterized data sets available. We have calculated an 11.5-year water vapour climatology using RALMO measurements in the troposphere. Our study uses nighttime measurements during mostly clear conditions, which creates a natural selection bias. The climatology shows that the highest water vapour specific-humidity concentrations are in the summer months and the lowest in the winter months. We have also calculated the geophysical variability of water vapour. The percentage of variability of water vapour in the free troposphere is larger than in the boundary layer. We have also determined water vapour trends from 2009 to 2019. We first calculate precipitable water vapour (PWV) trends for comparison with the majority of water vapour trend studies. We detect a nighttime precipitable water vapour trend of 1.3 mm per decade using RALMO measurements, which is significant at the 90 % level. The trend is consistent with a 1.38 ∘C per decade surface temperature trend detected by coincident radiosonde measurements under the assumption that relative humidity remains constant; however, it is larger than previous water vapour trend values. We compare the nighttime RALMO PWV trend to daytime and nighttime PWV trends using operational radiosonde measurements and find them to agree with each other. We cannot detect a bias between the daytime and nighttime trends due to the large uncertainties in the trends. For the first time, we show height-resolved increases in water vapour through the troposphere. We detect positive tropospheric water vapour trends ranging from a 5 % change in specific humidity per decade to 15 % specific humidity per decade depending on the altitude. The water vapour trends at five layers are statistically significant at or above the 90 % level.

Analysis on the Variation Trend of Evaporation and Precipitation in Xiaolangdi Reservoir

Based on the monthly evaporation and precipitation data from 1982 to 2013 of 13 meteorological stations in and around the Xiaolangdi Reservoir, the linear tendency estimation method, cumulative anomaly, M-K mutation detection method and ARIMA model are used to study and predict the changing characteristics of evaporation and precipitation. The results show that the annual evaporation and precipitation in the reservoir area both show a downward trend. The evaporation has an abrupt decline in 2001, and the precipitation decreases suddenly in 2003 and 2011. After impoundment, the annual evaporation volume changed from the upward trend to a weak downward trend, and the downward trend of annual precipitation is weakened. The impact of impoundment on evaporation and precipitation is limited, and the impact intensity decreases with increasing distance from the reservoir. The reservoir area’s evaporation and precipitation have significant seasonal variation characteristics, and the future evaporation will show a slight downward trend, while the precipitation will show a slight upward trend.

Trends in pan evaporation and climate variables in Iran

Contrary to expectations that global warming will be accompanied by an increase in terrestrial evaporation, pan evaporation (PE) has decreased in several parts of the world during the last decades. This opposing relationship is known as the pan evaporation paradox phenomenon that can be affected by climate change. For this purpose, this study identifies spatial and temporal trends in PE and its associated climate variables (Cvars) in Iran at seasonal and annual time scales. Hence, PE and Cvars data from 68 meteorological stations distributed over Iran during the period 1987–2016 were selected. The analyses of the temporal and spatial trends in PE, Cvars, and relationships among them were examined using the statistical techniques to identify the causes of PE trends. Results indicated that stations located in the subtropical region (latitude below 32°), which is mostly located in the southern half of Iran, showed significant negative PE trends (about 20–30% of stations) in spite of an increasing trend in temperatures indicating the “pan paradox” phenomenon. However, stations with significant positive PE trends (about 40% of stations), which are mostly located in the northern half of Iran, are placed at latitudes above 32°. Trend analysis of other Cvars indicated significant increases in temperatures, sunshine duration, and wind speed in more than half of the stations on all time scales. In addition, minimum, maximum, and mean temperatures, and sunshine duration were the most dominant variables affecting PE in annual, spring, autumn, and summer, respectively, in Iran.

Horizontal Moisture Transport Dominates the Regional Moistening Patterns in the Arctic

AbstractAlong with the amplified warming and dramatic sea ice decline, the Arctic has experienced regionally and seasonally variable moistening of the atmosphere. Based on reanalysis data, this study demonstrates that the regional moistening patterns during the last four decades, 1979–2018, were predominantly shaped by the strong trends in horizontal moisture transport. Our results suggest that the trends in moisture transport were largely driven by changes in atmospheric circulation. Trends in evaporation in the Arctic had a smaller role in shaping the moistening patterns. Both horizontal moisture transport and local evaporation have been affected by the diminishing sea ice cover during the cold seasons from autumn to spring. Increases in evaporation have been restricted to the vicinity of the sea ice margin over a limited period during the local sea ice decline. For the first time we demonstrate that, after the sea ice has disappeared from a region, evaporation over the open sea has had negative trends due to the effect of horizontal moisture transport to suppress evaporation. Near the sea ice margin, the trends in moisture transport and evaporation and the cloud response to those have been circulation dependent. The future moisture and cloud distributions in the Arctic are expected to respond to changes in atmospheric pressure patterns; circulation and moisture transport will also control where and when efficient surface evaporation can occur.

Evaporation from a large lowland reservoir – (dis)agreement between evaporation models from hourly to decadal timescales

Abstract. Accurate monitoring and prediction of surface evaporation become more crucial for adequate water management in a changing climate. Given the distinct differences between characteristics of a land surface and a water body, evaporation from water bodies requires a different parameterization in hydrological models. Here we compare six commonly used evaporation methods that are sensitive to different drivers of evaporation, brought about by a different choice of parameterization. We characterize the (dis)agreement between the methods at various temporal scales ranging from hourly to 10-yearly periods, and we evaluate how this reflects in differences in simulated water losses through evaporation of Lake IJssel in the Netherlands. At smaller timescales the methods correlate less (r=0.72) than at larger timescales (r=0.97). The disagreement at the hourly timescale results in distinct diurnal cycles of simulated evaporation for each method. Although the methods agree more at larger timescales (i.e. yearly and 10-yearly), there are still large differences in the projected evaporation trends, showing a positive trend to a more (i.e. Penman, De Bruin–Keijman, Makkink, and Hargreaves) or lesser extent (i.e. Granger–Hedstrom and FLake). The resulting discrepancy between the methods in simulated water losses of the Lake IJssel region due to evaporation ranges from −4 mm (Granger–Hedstrom) to −94 mm (Penman) between the methods. This difference emphasizes the importance and consequence of the evaporation method selection for water managers in their decision making.

Long-term surface water trends and relationship with open water evaporation losses in the Namoi catchment, Australia

Economic pressures on natural resources have led to a modification of natural surface water patterns. This has affected the hydrologic cycle at a global scale with multiple environmental and socioeconomic implications. This study evaluates long-term trends in surface water occurrence and related climate variables in a large agricultural catchment of Australia to understand trends in evaporative water losses from open water bodies. Surface water detection was based on a supervised classification of Landsat images between 1988 and 2018 to obtain inundation and surface water frequencies across the catchment, which were compared with other surface water products. Climate trends were based on monthly SILO gridded datasets. Open water evaporation was estimated using the FAO56 methodology and compared with the Penman-Monteith-Leuning Evapotranspiration V2 (PML_V2) product. Evaporation trends were analysed using the Mann Kendall (MK) test and the Sen’s slope (SS). Generally, open water frequencies showed significant negative trends, though these varied spatially. The number of dams, on the other hand, had an increasing trend. Temperatures are increasing in the catchment, while rainfall and relative humidity are decreasing, resulting in an overall positive trend for reference evapotranspiration (ETr) across 90% of the catchment. Even though ETr and evaporation per unit area of water show positive trends, lumped open water evaporation showed a negative trend, possibly associated with an average decrease in surface water frequencies. Annual evaporative losses averaged 201.9 GL, exceeding annual total account usage of surface water in the catchment. All the studied changes imply a loss of blue and green water in the catchment, and provide evidence of an overall intensification of the hydrologic cycle as predicted under climate change.

Trend Analyses of Meteorological Variables and Lake Levels for Two Shallow Lakes in Central Turkey

Trend analyses of meteorological variables play an important role in assessing the long-term changes in water levels for sustainable management of shallow lakes that are extremely vulnerable to climatic variations. Lake Mogan and Lake Eymir are shallow lakes offering aesthetic, recreational, and ecological resources. Trend analyses of monthly water levels and meteorological variables affecting lake levels were done by the Mann-Kendall (MK), Modified Mann-Kendall (MMK), Sen Trend (ST), and Linear trend (LT) methods. Trend analyses of monthly lake levels for both lakes revealed an increasing trend with the Mann-Kendall, Linear, and Sen Trend tests. The Modified Mann-Kendall test results were statistically significant with an increasing trend for Eymir lake levels, but they were insignificant for Mogan lake due to the presence of autocorrelation. While trend analyses of meteorological variables by Sen Test were significant at all tested variables and confidence levels, Mann-Kendall, Modified Mann-Kendall, and Linear trend provided significant trends for only humidity and wind speed. The trend analyses of Sen Test gave increasing trends for temperature, wind speed, cloud cover, and precipitation; and decreasing trends for humidity, sunshine duration, and pan evaporation. These results show that increasing precipitation and decreasing pan evaporation resulted in increasing lake levels. The results further demonstrated an inverse relationship between the trends of air temperature and pan evaporation, pointing to an apparent “Evaporation Paradox”, also observed in other locations. However, the increased cloud cover happens to offset the effects of increased temperature and decreased humidity on pan evaporation. Thus, all relevant factors affecting pan evaporation should be considered to explain seemingly paradoxical observations.

Quantitative Analysis of Impact of Climate Variability and Human Activities on Water Resources Change in Suzhou City

Assessing the contribution of climate variability and human activities to Suzhou’s water resources change is important to the design of water resources and provide technical support for the overall planning of Suzhou sponge city. Based on Suzhou hydrology history data, Mann-Kendall method and linear regression method is used to study the change trend of more than 50 years of Suzhou rainfall runoff evaporation, coupled with Mann-Kendall method to validate the abrupt change point of the annual runoff series. The elasticity method is used to analysis the contribution of climate variability and human activities, to explore the main cause of the change of the runoff. The results show that the overall trend of rainfall over the years is increasing, the overall trend of runoff over the years is significantly increasing, and the overall trend of evaporation over the years is decreasing, and a sudden change occurred in 1991. climate variability in Suzhou is the main factor of runoff change, contributing 58.52% and contributing 41.48% to human activities.

Recent trends in the UTLS temperature and tropical tropopause parameters over tropical South Indian region

The Upper Troposphere and Lower Stratosphere (UTLS) region plays an important role in the climate system. Quantifying the processes that control UTLS represents a crucial task. We assess UTLS trends and associated tropopause parameters (Cold Point Tropopause temperature/altitude (CPT/CPH), Lapse Rate Tropopause temperature/altitude (LRT/LRH), Convective outflow level temperature/altitude (COT/COH) and Tropical Tropopause Layer (TTL) thickness). This study is based on high-resolution daily radiosonde data from 2006 to 2018 over a tropical station Gadanki in south India supported by satellite measurements. The results show an increase of CPH (LRH) of ~0.06 km (~0.10 km), decrease of CPT (LRT) of ~1.09 K (1.16 K), increase of COH of ~0.29 km and decrease of TTL thickness of ~0.23 km in the recent decade. The vertical temperature trends show a strong cooling trend at lower stratosphere (17–19 km) with a maximum cooling rate of 1.3 ± 0.86 K per decade at 19.4 km altitude unlike reported recently using global radiosonde network. A warming trend is observed in the entire troposphere (0–15 km) with maximum warming rate of 0.44 ± 0.55 K at 11.6 km during the last decade. Distinct variability in the temperature is noticed below and above the tropopause with the strong seasonal change above the tropical tropopause (18 and 19 km) compared to the below the tropopause (15–17 km). The observed trends are explained in relation to the ozone (O3) and water vapor (WV) trends over Gadanki. Compare to the ozone changes, the WV increasing trend was found strongly influencing the LS cooling trend in the recent decade over Indian monsoon region.

Cantilever-Droplet-Based Sensing of Magnetic Particle Concentrations in Liquids.

Cantilever-based sensors have attracted considerable attention in the recent past due to their enormous and endless potential and possibilities coupled with their dynamic and unprecedented sensitivity in sensing applications. In this paper, we present a technique that involves depositing and vaporizing (at ambient conditions) a particle-laden water droplet onto a defined sensing area on in-house fabricated and commercial-based silicon microcantilever sensors. This process entailed the optimization of dispensing pressure and time to generate and realize a small water droplet volume (Vd = 49.7 ± 1.9 pL). Moreover, we monitored the water evaporation trends on the sensing surface and observed total evaporation time per droplet of 39.0 ± 1.8 s against a theoretically determined value of about 37.14 s. By using monodispersed particles in water, i.e., magnetic polystyrene particles (MPS) and polymethyl methacrylate (PMMA), and adsorbing them on a dynamic cantilever sensor, the mass and number of these particles were measured and determined comparatively using resonant frequency response measurements and SEM particle count analysis, respectively. As a result, we observed and reported monolayer particles assembled on the sensor with the lowest MPS particles count of about 19 ± 2.

Hydrology of Mountain Blocks in Arizona and New Mexico as Revealed by Isotopes in Groundwater and Precipitation

Mountain-block groundwater in the Southern Basin-and-Range Province shows a variety of patterns of δ18O and δ2H that indicate multiple recharge mechanisms. At 2420 m above sea level (masl) in Tucson Basin, seasonal amount-weighted means of δ18O and δ2H for summer are −8.3, −53‰, and for winter, −10.8 and −70‰, respectively. Elevation-effect coefficients for δ18O and δ2H are as follows: summer, −1.6 and −7.7 ‰ per km and winter, −1.1 and −8.9 ‰ per km. Little altitude effect exists in 25% of seasons studied. At 2420 masl, amount-weighted monthly averages of δ18O and δ2H decrease in summer but increase in winter as precipitation intensity increases. In snow-banks, δ18O and δ2H commonly plots close to the winter local meteoric water line (LMWL). Four principal patterns of (δ18O, δ2H) data have been identified: (1) data plotting along LMWLs for all precipitation at &gt;1800 masl; (2) data plotting along modified LMWLs for the wettest 30% of months at &lt;1700 masl; (3) evaporation trends at all elevations; (4) other patterns, including those affected by ancient groundwater. Young, tritiated groundwater predominates in studied mountain blocks. Ancient groundwater forms separate systems and mixes with young groundwater. Recharge mechanisms reflect a complex interplay of precipitation season, altitude, precipitation intensity, groundwater age and geology. Tucson Basin alluvium receives mountain-front recharge containing 50%–90% winter precipitation.

Trends in surface radiation and cloud radiative effect at four Swiss sites for the 1996–2015 period

Abstract. The trends of meteorological parameters and surface downward shortwave radiation (DSR) and downward longwave radiation (DLR) were analysed at four stations (between 370 and 3580 m a.s.l.) in Switzerland for the 1996–2015 period. Ground temperature, specific humidity, and atmospheric integrated water vapour (IWV) trends were positive during all-sky and cloud-free conditions. All-sky DSR and DLR trends were in the ranges of 0.6–4.3 W m−2 decade−1 and 0.9–4.3 W m−2 decade−1, respectively, while corresponding cloud-free trends were −2.9–3.3 W m−2 decade−1 and 2.9–5.4 W m−2 decade−1. Most trends were significant at the 90 % and 95 % confidence levels. The cloud radiative effect (CRE) was determined using radiative-transfer calculations for cloud-free DSR and an empirical scheme for cloud-free DLR. The CRE decreased in magnitude by 0.9–3.1 W m−2 decade−1 (only one trend significant at 90 % confidence level), which implies a change in macrophysical and/or microphysical cloud properties. Between 10 % and 70 % of the increase in DLR is explained by factors other than ground temperature and IWV. A more detailed, long-term quantification of cloud changes is crucial and will be possible in the future, as cloud cameras have been measuring reliably at two of the four stations since 2013.

Evaluating Evaporation Methods for Estimating Small Reservoir Water Surface Evaporation in the Brazilian Savannah

Small reservoirs play a key role in the Brazilian savannah (Cerrado), making irrigation feasible and contributing to the economic development and social well-being of the population. A lack of information on factors, such as evaporative water loss, has an impact on the design and management of these reservoirs, as well as on regional water safety. Acquiring this information is crucial for hydrologists to develop more effective water resource management strategies and policies. This study assesses the performance of a diverse number of methods that are used to estimate evaporation and provides evaporation probability curves on a fortnightly period for small reservoirs in the Brazilian savannah region. Evaporation data were collected for a small water reservoir located in the Buriti Vermelho watershed, a typical dam of the Brazilian savannah region. Among the assessed methods, those of Kohler et al. (1955) and Linacre (1993) presented the best performances on both the daily and monthly scales for evaporation estimates. By simulating the evaporation rates for a timeseries, an increasing trend in evaporation was observed for the transition between the dry and wet seasons, jeopardizing double cropping in the region. The developed probability curves are an important tool for improving water resource planning and increasing the local water availability.

Satellite based trend analysis of few atmospheric parameters over the Indian region

The present work has been carried to analyze the changes in trend of temperature, water vapor and ozone profiles at different atmospheric layers, total column integrated methane (TCH4) and total column integrated carbon-monoxide (TCO) over the Indian region. The atmospheric column was divided into few atmospheric layers: surface-850 hPa, 850–500 hPa, 500–100 hPa, 100–50 hPa and 50–1 hPa. Monthly averages of these parameters were calculated from AIRS Level 2 Standard Products for a decade from 2003 to 2012. A non-parametric statistical test with seasonal modification was applied to check the trends of various parameters. Monthly means were used to examine the seasonal dependency in the trend, and allowing more information from the data to be used. The layer average temperature in surface-850 hPa layer has shown significant increase in overall annual trend over eastern part, southern part and averaged over whole India with an increase of 0.041 K/year, 0.034 K/year and 0.034 K/year, respectively. The overall trend was decreasing over all but southern parts in 100–50 hPa layer at the rate of 0.079 K/year over whole India. For water vapor trends, it has been found that layer integrated water vapor (LIWV) in surface-850 hPa layer has significant overall increasing trend over western part, southern part and averaged over whole India with the rate of increase of 0.555%/year, 0.598%/year and 0.486%/year respectively. For LIWV (850–500 hPa), only western part has significant increasing trend at a rate of 0.879%/year. However, LIWV in 500–100 hPa layer does not show any significant trend. Total water vapor (TWV) has shown significant annual increasing trend over all the parts except over the central part. The increasing trend has been estimated as 0.962%/year over whole India. The layer integrated ozone (LIOZ) in surface-850 hPa has significant increasing trend over western part (0.062%/year) and southern part (0.071%/year). In 500–100 hPa layer, the LIOZ has statistically significant decreasing trend over whole India at a rate of 0.112%/year. For LIOZ averaged over whole India in 100–50 hPa, there is significant decreasing trend with a rate of 0.273%/year. Overall, the ozone concentration is increasing near surface, whereas it is decreasing in lower stratosphere. The total column ozone (TOZ) has not shown any significant trend. The column integrated methane has shown an increasing trend (0.366%/year) over all parts of the country, whereas, TCO has not shown any significant trend.

Establishing a time series trend structure model to mine potential hydrological information from hydrometeorological time series data

This paper addresses the problem of missing latent time series information caused by the differences in the analysis of time series data and non-time series data. A time series trend structure model (TSTM) was established using the analysis of time series patterns and rules, the trends of patterns and rules, and trends in confidence and support. Shandong Province was selected as the study area. Rainfall and evaporation time series data from this area were input into the TSTM. The results show that: (1) the structure of multi-year precipitation and evaporation trends of the meteorological stations in the study area have continuously increasing or decreasing characteristics. The TSTM can excavate the different trend structure characteristics of different meteorological elements and enables diversity in time series data analysis; (2) the evaporation trend structure tends to change synchronously with increases and decreases in precipitation and evaporation. The synchronous change frequency is essentially the same as that of the rainfall trend structure. This indicates that the TSTM has spatial and temporal characteristics for time series data analysis; and (3) from the maximal non-descending and non-ascending subsequence in the TSTM, it can be concluded that there exists continuity in the years when the trend structure of precipitation and evaporation increases and decreases synchronously. In addition, the degree of similarity in the model is well reflected in the spatial distribution characteristics of time series data, and the model provides clustering characteristics for time series data analysis. The TSTM proposed in this paper can effectively obtain the potential hydrological information contained in time series data, and provides a scientific and reliable basis for rules for the spatial optimization of watershed data and for the calibration of hydrological models.

Trends of Vertically Integrated Water Vapor over the Arctic during 1979–2016: Consistent Moistening All Over?

Abstract Arctic trends of integrated water vapor were analyzed based on four reanalyses and radiosonde data over 1979–2016. Averaged over the region north of 70°N, the Arctic experiences a robust moistening trend that is smallest in March (0.07 ± 0.06 mm decade−1) and largest in August (0.33 ± 0.18 mm decade−1), according to the reanalyses’ median and over the 38 years. While the absolute trends are largest in summer, the relative ones are largest in winter. Superimposed on the trend is a pronounced interannual variability. Analyzing overlapping 30-yr subsets of the entire period, the maximum trend has shifted toward autumn (September–October), which is related to an accelerated trend over the Barents and Kara Seas. The spatial trend patterns suggest that the Arctic has become wetter overall, but the trends and their statistical significance vary depending on the region and season, and drying even occurs over a few regions. Although the reanalyses are consistent in their spatiotemporal trend patterns, they substantially disagree on the trend magnitudes. The summer and the Nordic and Barents Seas, the central Arctic Ocean, and north-central Siberia are the season and regions of greatest differences among the reanalyses. We discussed various factors that contribute to the differences, in particular, varying sea level pressure trends, which lead to regional differences in moisture transport, evaporation trends, and differences in data assimilation. The trends from the reanalyses show a close agreement with the radiosonde data in terms of spatiotemporal patterns. However, the scarce and nonuniform distribution of the stations hampers the assessment of central Arctic trends.