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This study analyzes the long‐term observed changes of mean (Tmean), maximum (Tmax) and minimum (Tmin) air temperatures, relative humidity (RH) and vapour pressure deficit (VPD) at different elevation ranges across Bolivia from 1950 to 2019. The linear trends in air temperature series present a significant increase, with no substantial seasonal or spatial differences. On an annual basis, RH exhibited a non‐significant decrease (−0.08% decade−1), while VPD showed a significant increase (0.01 hPa decade−1) (p < 0.05). Although prior research has suggested that highland elevations experience faster warming than the global average, we have not identified a distinct correlation between elevation gradients and differential warming rates in Bolivia. Future research could investigate elevation‐dependent climate trends by examining seasonal and monthly patterns of climatic variables in relation to topographical gradients in various highland regions. [ABSTRACT FROM AUTHOR]

The near‐surface wind speed over land has declined in recent decades, a trend known as terrestrial stilling (TS). However, recent studies have indicated a reversal of the TS during the last decade, triggering renovated interest in the future wind speed changes. This study examines the TS over the Northern Hemisphere (NH) land areas and explores its future changes under Model Inter‐comparison Projection Phase 6 Shared Socioeconomic Pathways (SSP) scenarios. The results show that the NH mid‐latitude TS will likely continue during the whole 21st century under mid‐to‐high greenhouse warmings (SSPs‐245, 370, and 585). Nevertheless, if the world reduces carbon emissions substantially (SSP‐126), the TS will be interrupted and likely reversed after the mid‐21st century. The projected TS shows seasonal differences, with the largest (smallest) decreasing trends of wind speed in boreal summer (winter). Moreover, the TS reversal during the last decade is suggested as a multi‐decadal fluctuation related to the Pacific and Atlantic multi‐decadal oscillations. In addition, this study proposes that increased upper‐air warming in the future climate could play a key role in reducing the NH mid‐latitude surface wind speed. The continuing TS provides strong implications for the near‐surface environment and wind energy development, particularly for countries in the NH mid‐latitudes. Plain Language Summary: The 10‐m wind speed (NWS) is a key parameter in meteorology and climate science, whose changes could affect the natural environment and human society. Previous studies reported that the 10 m wind speed over land had weakened over the past several decades, a phenomenon termed terrestrial stilling (TS). However, recent studies based on observation and reanalyzes showed that the TS started to recover during the last decade, which had caused renewed interest in wind speed changes in the future. This study indicates that the NWS in the Northern Hemisphere (NH) mid‐latitudes will likely continue to weaken during the 21st century forced by increased greenhouse gases. However, if the world cuts carbon emissions substantially, the decline of NWS will be interrupted and reversed after the mid‐21st century. Future changes in NWS show seasonal differences, with the largest (smallest) decreasing trends of NWS in summer (winter). In this study, we propose that elevated upper‐air warmings over the mid‐latitudes could also play a key role in reducing the NWS. This study is useful for understanding the changes in hydrological cycles, air pollution, and wind energy development, particularly for countries in the NH mid‐latitudes. Key Points: Terrestrial stilling (TS) is projected to continue in the Northern Hemisphere mid‐latitudesThe stilling‐reversal could be related to the Pacific and Atlantic multi‐decadal oscillationsIncreased upper‐air warming may favor the TS [ABSTRACT FROM AUTHOR]

This study provides a long-term (1891–2014) global assessment of precipitation trends using data from two station-based gridded datasets and climate model outputs evolved through the fifth and sixth phases of the Coupled Model Intercomparison Project (CMIP5 and CMIP6, respectively). Our analysis employs a variety of modeling groups that incorporate low- and high-top level members, with the aim of assessing the possible effects of including a well-resolved stratosphere on the model's ability to reproduce long-term observed annual precipitation trends. Results demonstrate that only a few regions show statistically significant differences in precipitation trends between observations and models. Nevertheless, this pattern is mostly caused by the strong interannual variability of precipitation in most of the world regions. Thus, statistically significant model-observation differences on trends (1891–2014) are found at the zonal mean scale. The different model groups clearly fail to reproduce the spatial patterns of annual precipitation trends and the regions where stronger increases or decreases are recorded. This study also stresses that there are no significant differences between low- and high-top models in capturing observed precipitation trends, indicating that having a well-resolved stratosphere has a low impact on the accuracy of precipitation projections. [ABSTRACT FROM AUTHOR]

The dynamics of blue and green water partitioning under vegetation and climate change, as well as their different interactions during wet and dry periods, are poorly understood in the literature. We analyzed the impact of vegetation changes on blue water generation in a central Spanish Pyrenees basin undergoing intense afforestation. We found that vegetation change is a key driver of large decreases in blue water availability. The effect of vegetation increase is amplified during dry years, and mainly during the dry season, with streamflow reductions of more than 50%. This pattern can be attributed primarily to increased plant water consumption. Our findings highlight the importance of vegetation changes in reinforcing the decrease in water resource availability. With aridity expected to rise in southern Europe over the next few decades, interactions between climate and land management practices appear to be amplifying future hydrological drought risk in the region. Plain Language Summary: Forest recovery, due to human land abandonment, has been observed in several regions worldwide. To improve integrated land and water management, it is crucial to explore how these changes affect resource availability in water‐stressed areas. Forest regeneration has resulted in a large decrease in streamflow in a natural catchment in southwestern Europe, which cannot be explained by climate change. During the dry season, forest regeneration amplifies the impact of drought and water availability, with less impacts in the wet season. Therefore, the effects of vegetation recovery on water resources differ based on water availability, with the most serious implications for water resources occurring during dry periods. Key Points: Forest secondary succession is the main driver of streamflow trends in mountain Mediterranean areasThe effects of vegetation changes on water availability strongly differ between dry and humid periodsTrends in streamflow in response to vegetation changes are mostly recorded during the dry and warm season [ABSTRACT FROM AUTHOR]

The ERA5 reanalysis product has been compared with hourly near-surface wind speed and gust observations across Sweden for 2013–2017. ERA5 shows closer agreement than the previous ERA-Interim reanalysis with regard to both mean wind speed and gust measurements, although significant discrepancies are still found for inland and mountainous regions. Therefore, attempts have been made to improve formulations of the gust parametrization used in ERA5 by adding an elevation-dependency and by adjusting the convective gust contribution. Major improvements, especially over mountain regions, are achieved when the elevation differences among the stations are considered. Closer agreement between the observed and parametrized gusts is reached when the convective gust contribution is also tuned. The newly designed gust parametrization was also tested for Norway, which is characterized by more complex topography. Wind gusts from the selected Norwegian stations are more realistically simulated when both the elevation-dependency and the tuned convective contribution are implemented, although the parametrized gusts are still negatively biased. Such biases are not explained by the different in gust duration in recorded wind gusts between Sweden and Norway. [ABSTRACT FROM AUTHOR]

Although the mean environmental lapse rate (MELR) value (a linear decrease of −6.5 °C/km) is the most widely used, near‐surface (i.e., non‐free atmosphere) air temperature lapse rates (NSLRs; measured at ~1.5 m height) are variable in space and time because of their dependence on topography and meteorological conditions. In this study we conducted the first analysis of the spatial and temporal variability of NSLRs for continental Spain and their relationship to synoptic atmospheric circulation (circulation weather types [CWTs]), focusing on major mountain areas including the Pyrenees, Cantabrian, Central, Baetic, and Iberian ranges. The results showed that the NSLR varied markedly at spatial and seasonal scales and depended on the dominant atmospheric conditions. The median NSLR values were weaker (less negative) than the MELR for the mountain areas (Pyrenees −5.17 °C/km; Cantabrian range −5.22 °C/km; Central range −5.78 °C/km; Baetic range −4.83 °C/km; Iberian range −5.79 °C/km) and for the entire continental Spain (−5.28 °C/km). For the entire continental Spain the steepest NSLR values were found in April (−5.80 °C/km), May (−5.58 °C/km), and October (−5.54 °C/km) because of the dominance of northerly and westerly advections of cold air. The weakest NSLR values were found in July (−4.67 °C/km) and August (−4.78 °C/km) because of the inland heating, and in winter because of the occurrence of thermal inversions. As the use of the MELR involves the assumption of large errors, we propose 1 zonal, 12 monthly, 11 CWTs, and 132 hybrid monthly–CWTs NSLRs for each of the mountain ranges and for the entire continental Spain. More regional studies are urgently needed to accurately assess the NSLR as a function of atmospheric circulation conditions. [ABSTRACT FROM AUTHOR]

In this study, we analyzed the influence of El Niño-Southern Oscillation (ENSO) on the spatio-temporal variability of droughts in Ecuador for a 48-year period (1965-2012). Droughts were quantified from 22 high-quality and homogenized time series of precipitation and air temperature by means of the Standardized Precipitation Evapotranspiration Index. In addition, the propagation of two different ENSO indices (El Niño 3.4 and El Niño 1 + 2 indices) and other atmospheric circulation processes (e.g., vertical velocity) on different time-scales of drought severity were investigated. The results showed a very complex influence of ENSO on drought behavior across Ecuador, with two regional patterns in the evolution of droughts: (1) the Andean chain with no changes in drought severity, and (2) the Western plains with less severe and frequent droughts. We also detected that drought variability in the Andes mountains is explained by the El Niño 3.4 index [sea surface temperature (SST) anomalies in the central Pacific], whereas the Western plains are much more driven by El Niño 1 + 2 index (SST anomalies in the eastern Pacific). Moreover, it was also observed that El Niño and La Niña phases enhance droughts in the Andes and Western plains regions, respectively. The results of this work could be crucial for predicting and monitoring drought variability and intensity in Ecuador. [ABSTRACT FROM AUTHOR]

ABSTRACT This work analysed the changes in air temperature in 25 meteorological stations in the Altiplano and the surrounding Andean slopes of Bolivia and Peru, and their relationship with El Niño-Southern Oscillation ( SO) and the Pacific Decadal Oscillation ( PDO). The analysis focused on annual, warm season ( DJF) and cold season ( JJA) maximum and minimum temperatures. All analyses were undertaken during 1965-2012, but some analyses were also from 1945 and 1955 when data were available. Principal component analysis was applied to the annual and seasonal series to identify spatial differences of changes in maximum and minimum air temperature. There was an overall increase of temperatures since the mid-20th century. The most intense and spatially coherent warming was observed for annual and warm season maximum temperature, with warming rates from 0.15 to 0.25 °C decade−1. Changes in the cold season maximum temperature were more heterogeneous, and statistically significant trends were mostly in the Bolivian Altiplano. Minimum temperatures increased, but there was higher spatial variability and lower rates of warming. Maximum temperature was negatively correlated with the Southern Oscillation index ( SO) in the warm season, and positively correlated with the SO in the cold season; there were less statistically significant correlations with the PDO, that exhibited inverse sign than those for SO. The strongest correlations were in the region near Lake Titicaca. The negative correlation of minimum temperatures with SO and the positive correlation of minimum temperatures with PDO were lower than the observed for maximum temperature. The changes in temperature and correlations with SO and PDO were highly dependent on the selected period, with stronger trends in the last 30-40 years. This suggests reinforcement of warming rates that cannot be only explained by SO and PDO variability. [ABSTRACT FROM AUTHOR]

This study presents monthly and annual climate maps for relevant hydroclimatic variables in Bolivia. We used the most complete network of precipitation and temperature stations available in Bolivia, which passed a careful quality control and temporal homogenization procedure. Monthly average maps at the spatial resolution of 1 km were modeled by means of a regression-based approach using topographic and geographic variables as predictors. The monthly average maximum and minimum temperatures, precipitation and potential exoatmospheric solar radiation under clear sky conditions are used to estimate the monthly average atmospheric evaporative demand by means of the Hargreaves model. Finally, the average water balance is estimated on a monthly and annual scale for each 1 km cell by means of the difference between precipitation and atmospheric evaporative demand. The digital layers used to create the maps are available in the digital repository of the Spanish National Research Council. [ABSTRACT FROM PUBLISHER]

We analysed recent evolution and meteorological drivers of the atmospheric evaporative demand (AED) in the Canary Islands for the period 1961-2013. We employed long and high quality time series of meteorological variables to analyze current AED changes in this region and found that AED has increased during the investigated period. Overall, the annual ETo increased significantly by 18.2 mm decade-1 on average, with a stronger trend in summer (6.7 mm decade-1). The radiative component showed much lower temporal variability than the aerodynamic component did. Thus, more than 90% of the observed ETo variability at the seasonal and annual scales can be associated with the variability of the aerodynamic component. The variable that recorded more significant changes in the Canary Islands was relative humidity, and among the different meteorological factors used to calculate ETo, relative humidity was the main driver of the observed ETo trends. The observed trend could have negative consequences in a number of water-depending sectors if it continues in the future. [ABSTRACT FROM AUTHOR]

Road and railway infrastructure increased in the Mediterranean region during the last three decades. This included the building of embankments, which are assumed to be a~large source of sediments and runoff. However, little is known about soil erosion rates, the factors that control them, and the processes that contribute to detachment, transport and deposition of sediments from road and railway embankments. The objective of this study was therefore to assess the impacts of road and railway embankments as a source of sediment and water, and compare them to other land use types (citrus plantations and shrublands) representative of the Cànyoles watershed to evaluate the importance of road embankments as a~source of water and sediment under high magnitude low frequency rainfall events. Sixty rainfall experiments (1 m² plots; 60 min duration; 78 mm h-1 rainfall intensity) were carried out on these land use types: 20 on two railway embankments (10 + 10), 20 on two road embankments (10 + 10), and 10 on citrus and 10 on shrubland. Road and railway embankments were characterized by bare soils with low organic matter and high bulk density. Erosion processes were more active in road, railway and citrus plots, and null in the shrublands. The non-sustainable soil erosion rates of 3 Mg ha-1 y-1 measured on the road embankments were due to the efficient runoff connectivity plus low infiltration rates within the plot as the runoff took less than one minute to reach the runoff outlet. Road and railway embankments are both an active source of sediments and runoff, and soil erosion control strategies must be applied. The citrus plantations also act as a~source of water and sediments (1.5 Mg ha-1 y-1), while shrublands are sediment sinks, as no overland flow was observed due to the high infiltration rates. [ABSTRACT FROM AUTHOR]

ABSTRACT In this study, the spatio-temporal variability and trends of droughts across Bolivia between 1955 and 2012 were investigated using two climate drought indices: the Standardized Precipitation Index ( SPI), which is based on precipitation data, and the Standardized Precipitation Evapotranspiration Index ( SPEI), which is based on the difference between the precipitation and the reference evapotranspiration ( ETo). We found that the average drought conditions across the country showed a temporal behaviour mainly characterized by decadal variations. The spatial pattern of drought evolution showed marked differences between the Amazonian region and the Bolivian Altiplano. Both regions showed different drought periods, a lower frequency of drought variability in the Amazon region and trends towards drier conditions in the Altiplano, mainly due to a higher atmospheric water demand as a consequence of increased ETo. We also showed that inclusion of ETo, obtained from maximum and minimum temperature records, increased the spatial heterogeneity of the drought evolution in relation to the evolution observed when only precipitation droughts were considered. The SPEI, the calculation of which includes precipitation and ETo, indicated intensification in drought severity in the last years analysed relative to the pattern found when precipitation droughts alone were considered, and also indicated an increase in the magnitude and duration of drought events. The potential for increasing drought conditions under various climate change scenarios is discussed. [ABSTRACT FROM AUTHOR]

In this study, we analyzed the effects of the forest canopy and trunks of a pine stand in the central Spanish Pyrenees on the snow depth (SD) distribution. Using LiDAR technology with a terrestrial laser scanner (TLS), high-resolution data on the SD distribution were acquired during the 2011-2012 and 2012-2013 snow seasons, which were 2 years having very contrasting climatic and snow accumulation conditions. Average SD evolution in open and canopy areas was characterized. Principal component analysis was applied to identify days having similar spatial patterns of SD distribution. There was a clear contrast in the temporal variability of the snowpack in different areas of the forest stand, corresponding generally to beneath the canopy, and in open sites. The canopy and openings showed markedly different accumulation and melting, with higher snow accumulation found in openings. Differences ranged from 14 to 80% reduction (average 49%) in the SD beneath the canopy relative to open sites. The difference in SD between open and canopy areas increased throughout the snow season. The surveyed days were classified in terms of SD distribution, and included days associated with: high SD, low SD, intense melting conditions and periods when the SD distribution was driven by wind conditions. The SD increased with distance from the trunks to a distance of 3.5-4.5 m, coinciding with the average size of the crown of individual trees. [ABSTRACT FROM AUTHOR]

This paper presents the methodology used to develop snow depth distribution maps for a small catchment in the Central Spanish Pyrenees covering 55 ha in a 1:10,000 scale. The Main Map was obtained using LiDAR (light detection and ranging) technology from a long-range Terrestrial Laser Scanner (TLS) in six field surveys undertaken during the 2012 winter–spring period. This technique enabled the acquisition of information at a very high resolution concerning the spatial variability of snow cover, providing snow depth information for remote areas where data acquisition is complex and hazardous. We describe the methodological steps and the quality assessment applied in developing the maps. Comparison with manual measurements confirmed the reliability of the snow depth maps, including areas located at large distances from the scanner (800 m). This method provides a promising tool for future investigations of snow dynamics in mountainous environments. [ABSTRACT FROM AUTHOR]

The article discusses the development and relevance of the Campbell-Stokes surface solar radiation recorder. It notes that the sunshine data recorder invented by John Francis Campbell and modified by George Gabriel Stokes has become the standard instrument in meteorological stations across Great Britain. The sunshine recorder has proven its usefulness in understanding the variability and climatic change with periodic increase or decrease data in solar radiation.

The article offers information on high surface wind speeds revealed by observational datasets in 2015. Topics mentioned include the global average anomaly from the climatology between 1981-2010, the negative long-term trends of wind speed observed in land surface between 1979-2015, and the use of the global HadlSD and Australian datasets and the ERA-Interim reanalysis to examine the spatial and temporal variability of winds.

The focus of this study is on sea breeze (SB) characteristics during May and August in the Bay of Alicante (south-eastern coast of the Iberian Peninsula, IP, Spain) for the period 2000–2005 in relation to dominating synoptic-scale winds. A dataset containing 292 SB events was objectively constructed to study the impact of the daily synoptic winds at 850 hPa on the main characteristics of SBs. The winds were used to designate three major synoptic-scale regimes: offshore, onshore, and coast-parallel flows. The SB features examined include mean lag of the SB passage, wind speed and direction at the time of onset, mean lag of SB cessation, mean duration of SB, mean maximum velocity, and inland propagation of SB. Some of the characteristics had not been previously considered in the literature. It is found that in comparison with onshore synoptic flows, offshore favors the delayed arrival and termination of SBs, resulting in a longer mean duration. Further, they produce the most intense passages, cause a more frequent southeasterly component, and result in a higher SB gust speed and shorter mean inland penetration. Results from coast-parallel flows are also presented. The strength of the large-scale flows plays a major role upon SB parameters, which essentially support other numerical modeling results. [ABSTRACT FROM AUTHOR]