| 1. |
- Arndt, D. S., et al.
(author)
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STATE OF THE CLIMATE IN 2017
- 2018
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In: Bulletin of The American Meteorological Society - (BAMS). - : American Meteorological Society. - 0003-0007 .- 1520-0477. ; 99:8, s. S1-S310
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Research review (peer-reviewed)
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| 2. |
- Azorin-Molina, Cesar, et al.
(author)
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Evaluating anemometer drift: A statistical approach to correct biases in wind speed measurement
- 2018
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In: Atmospheric research. - : Elsevier BV. - 0169-8095. ; 203, s. 175-188
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Journal article (peer-reviewed)abstract
- Recent studies on observed wind variability have revealed a decline (termed “stilling”) of near-surface wind speed during the last 30–50 years over many mid-latitude terrestrial regions, particularly in the Northern Hemisphere. The well-known impact of cup anemometer drift (i.e., wear on the bearings) on the observed weakening of wind speed has been mentioned as a potential contributor to the declining trend. However, to date, no research has quantified its contribution to stilling based on measurements, which is most likely due to lack of quantification of the ageing effect. In this study, a 3-year field experiment (2014–2016) with 10-minute paired wind speed measurements from one new and one malfunctioned (i.e., old bearings) SEAC SV5 cup anemometer which has been used by the Spanish Meteorological Agency in automatic weather stations since mid-1980s, was developed for assessing for the first time the role of anemometer drift on wind speed measurement. The results showed a statistical significant impact of anemometer drift on wind speed measurements, with the old anemometer measuring lower wind speeds than the new one. Biases show a marked temporal pattern and clear dependency on wind speed, with both weak and strong winds causing significant biases. This pioneering quantification of biases has allowed us to define two regression models that correct up to 37% of the artificial bias in wind speed due to measurement with an old anemometer.
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| 3. |
- Azorin-Molina, Cesar, et al.
(author)
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Recent trends in wind speed across Saudi Arabia, 1978-2013: a break in the stilling
- 2018
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In: International Journal of Climatology. - : Wiley. - 0899-8418. ; 38
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Journal article (peer-reviewed)abstract
- We analyse recent trends and variability of observed near-surface wind speed from 19 stations across Saudi Arabia (SA) for 1978-2013. The raw wind speed data set was subject to a robust homogenization protocol, and the stations were then classified under three categories: (1) coast, (2) inland and (3) mountain stations. The results reveal a statistically significant (p<0.05) reduction of wind speed of -0.058m s(-1) dec(-1) at annual scale across SA, with decreases in winter (-0.100m s(-1) dec(-1)) and spring (-0.066m s(-1) dec(-1)) also detected, being non-significant in summer and autumn. The coast, inland and mountain series showed similar magnitude and significance of the declining trends across all SA series, except for summer when a decoupled variability and opposite trends of wind speed between the coast and inland series (significant declines: -0.101m s(-1) dec(-1) and -0.065m s(-1) dec(-1), respectively) and the high-elevation mountain series (significant increase: +0.041m s(-1) dec(-1)) were observed. Even though wind speed declines dominated across much of the country throughout the year, only a small number of stations showed statistically significant negative trends in summer and autumn. Most interestingly, a break in the stilling was observed in the last 12-year (2002-2013) period (+0.057m s(-1) dec(-1); not significant) compared to the significant slowdown detected in the previous 24-year (1978-2001) period (-0.089m s(-1) dec(-1)). This break in the slowdown of winds, even followed by a non-significant recovery trend, occurred in all seasons (and months) except for some winter months. Atmospheric circulation plays a key role in explaining the variability of winds, with the North Atlantic Oscillation positively affecting the annual wind speed, the Southern Oscillation displaying a significant negative relationship with winds in winter, spring and autumn, and the Eastern Atlantic negatively modulating winds in summer.
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| 4. |
- Azorin-Molina, Cesar, et al.
(author)
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Wind speed variability over the Canary Islands, 1948–2014: focusing on trend differences at the land–ocean interface and below–above the trade-wind inversion layer
- 2018
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In: Climate Dynamics. - : Springer Science and Business Media LLC. - 0930-7575 .- 1432-0894. ; 50:11-12, s. 4061-4081
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Journal article (peer-reviewed)abstract
- This study simultaneously examines wind speed trends at the land–ocean interface, and below–above the trade-wind inversion layer in the Canary Islands and the surrounding Eastern North Atlantic Ocean: a key region for quantifying the variability of trade-winds and its response to large-scale atmospheric circulation changes. Two homogenized data sources are used: (1) observed wind speed from nine land-based stations (1981–2014), including one mountain weather station (Izaña) located above the trade-wind inversion layer; and (2) simulated wind speed from two atmospheric hindcasts over ocean (i.e., SeaWind I at 30 km for 1948–2014; and SeaWind II at 15 km for 1989–2014). The results revealed a widespread significant negative trend of trade-winds over ocean for 1948–2014, whereas no significant trends were detected for 1989–2014. For this recent period wind speed over land and ocean displayed the same multi-decadal variability and a distinct seasonal trend pattern with a strengthening (late spring and summer; significant in May and August) and weakening (winter–spring–autumn; significant in April and September) of trade-winds. Above the inversion layer at Izaña, we found a predominance of significant positive trends, indicating a decoupled variability and opposite wind speed trends when compared to those reported in boundary layer. The analysis of the Trade Wind Index (TWI), the North Atlantic Oscillation Index (NAOI) and the Eastern Atlantic Index (EAI) demonstrated significant correlations with the wind speed variability, revealing that the correlation patterns of the three indices showed a spatio-temporal complementarity in shaping wind speed trends across the Eastern North Atlantic.
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| 5. |
- Chen, Aifang, 1990, et al.
(author)
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Assessing reliability of precipitation data over the Mekong River Basin: A comparison of ground-based, satellite, and reanalysis datasets
- 2018
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In: International Journal of Climatology. - : Wiley. - 0899-8418. ; 38:11, s. 4314-4334
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Journal article (peer-reviewed)abstract
- Accurate precipitation data are the basis for hydro-climatological studies. As a highly populated river basin, with the biggest inland fishery in Southeast Asia, freshwater dynamics is extremely important for the Mekong River Basin (MB). This study focuses on evaluating the reliability of existing gridded precipitation datasets both from satellite and reanalysis, with a ground observations-based gridded precipitation dataset as the reference. Two satellite products (Tropical Rainfall Measuring Mission [TRMM] and the Precipitation Estimation from Remote Sensing Information using an Artificial Neural NetworkClimate Data Record [PERSIANN-CDR]), as well as three reanalysis products (Modern-Era Retrospective analysis for Research and Applications [MERRA2], the European Centre for Medium-Range Weather Forecasts interim reanalysis [ERA-Interim], and the Climate Forecast System Reanalysis [CFSR]) were compared with the Asian PrecipitationHighly Resolved Observational Data Integration Towards Evaluation of Water Resources (APHRODITE) over the MB. The APHRODITE was chosen as the reference for the comparison because it was developed based on ground observations and has also been selected as reference data in previous studies. Results show that most of the assessed datasets are able to capture the major climatological characteristics of precipitation in the MB for the 10-year study period (1998-2007). Generally, both satellite data (TRMM and PERSIANN-CDR) show higher reliability than reanalysis products at both spatial and temporal scales across the MB, with the TRMM outperforming when compared to the PERSIANN-CDR. For the reanalysis products, MERRA2 is more reliable in terms of temporal variability, but with some underestimation of precipitation. The other two reanalysis products CFSR and ERA-Interim are relatively unreliable due to large overestimations. CFSR is better positioned to capture the spatial variability of precipitation, while ERA-Interim shows inconsistent spatial patterns but more realistically resembles the daily precipitation probability. These findings have practical implications for future hydro-climatological studies.
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| 6. |
- Dominguez-Castro, F., et al.
(author)
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Mapping seasonal and annual extreme precipitation over the Peruvian Andes
- 2018
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In: International Journal of Climatology. - : Wiley. - 0899-8418. ; 38:15, s. 5459-5475
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Journal article (peer-reviewed)abstract
- Seasonal and annual extreme precipitation over the Peruvian Andes have been mapped for the first time. Maps were developed using the most complete, quality-controlled and homogenous daily precipitation records in Peru from 1973 to 2016. For each observed rain gauge series, we defined parameters as the de-clustered daily intensity, total precipitation duration, total magnitude and dry-spell length. Then, we fitted the seasonal and annual series of these variables to a Generalized-Pareto distribution using a peak-over-threshold approach. We estimated the distribution parameters and validated the performance of different thresholds to obtain the best estimation of precipitation probability. We also mapped the distribution parameters obtained for the different meteorological stations using the universal kriging algorithm, accounting for elevation and the distance to the Pacific Ocean as co-variables. The accuracy of the extreme precipitation maps for a period of 25 and 50 years were validated using a jack-knife approach. Some of the maps show strong uncertainty given the random spatial distribution of the variables as a consequence of the complex topography and climate of the region. Nevertheless, the maps show a useful general assessment of the spatial distribution of the precipitation hazard probability over the region, providing a good agreement with the estimations obtained in the meteorological stations for some variables and time periods analysed. Extreme precipitation maps over this high-complex terrain of Peru are of key importance for flood risk assessment, water resources management, crop yield, soil conservation and human settlements.
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| 7. |
- Khorchani, M., et al.
(author)
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Average annual and seasonal Land Surface Temperature, Spanish Peninsular
- 2018
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In: Journal of Maps. - : Informa UK Limited. - 1744-5647. ; 14:2, s. 465-475
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Journal article (peer-reviewed)abstract
- The first long-term Land Surface Temperature (LST) maps for the Peninsular Spain at annual and seasonal time scales for 1981-2015 is presented in this work. A robust protocol for correcting and calibrating NOAA-AVHRR images and computing LST datasets at the spatial resolution of 1.1km has been used. Simultaneously, maximum air temperature (Tmax) maps at the same spatial resolution have been produced using data from meteorological stations. The comparison between the two datasets resulted in statistically significant spatial correlations at annual and seasonal scales. Finally, the Normalized Difference Vegetation Index (NDVI) data were also compared with the obtained LST datasets and the results showed significant negative correlations between the two variables, especially in summer.
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| 8. |
- Khorchani, M., et al.
(author)
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Trends in LST over the peninsular Spain as derived from the AVHRR imagery data
- 2018
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In: Global and Planetary Change. - : Elsevier BV. - 0921-8181. ; 166, s. 75-93
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Journal article (peer-reviewed)abstract
- This study analyzes the spatio-temporal variability and trends of land surface temperature (LST) over peninsular Spain, considering all the available historical satellite imagery data from the NOAA-AVHRR product from July 1981 to June 2015 and explores whether changes in LST are related to the observed changes in air temperature, solar radiation and land cover. We found that LST showed a significant increase between 1982 and 2014, with an average increase on the order of 0.71 °C decade−1, being stronger during summertime (1.53 °C decade−1). The results also indicate a strong spatial coherence between LST and NDVI changes. The areas that experienced an increase in the LST were spatially consistent with those areas with no changes or even a dominant decrease in vegetation coverage. In addition, the strong increase of LST is coherent with observations of the recent radiative forcing affecting Spain, particularly during summertime. The confidence of the obtained LST trends during summer is also reinforced by the spatial differences recorded in trends, in addition to the differences found between land cover types. Specifically, the magnitude of this increase was much higher in the dryland non-permanent agricultural areas, which are usually harvested during summer, when soil is dominantly nude. In contrast, in well-developed forests, the magnitude of LST was much lower. Our results on the observed LST trends and their spatial patterns can contribute to better understanding of the recent eco-hydrological processes in peninsular Spain. © 2018 Elsevier B.V.
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| 9. |
- Navarro-Serrano, F., et al.
(author)
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Estimation of near-surface air temperature lapse rates over continental Spain and its mountain areas
- 2018
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In: International Journal of Climatology. - : Wiley. - 0899-8418. ; 38:8, s. 3233-3249
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Journal article (peer-reviewed)abstract
- Although the mean environmental lapse rate (MELR) value (a linear decrease of -6.5 degrees 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 degrees C/km; Cantabrian range -5.22 degrees C/km; Central range -5.78 degrees C/km; Baetic range -4.83 degrees C/km; Iberian range -5.79 degrees C/km) and for the entire continental Spain (-5.28 degrees C/km). For the entire continental Spain the steepest NSLR values were found in April (-5.80 degrees C/km), May (-5.58 degrees C/km), and October (-5.54 degrees C/km) because of the dominance of northerly and westerly advections of cold air. The weakest NSLR values were found in July (-4.67 degrees C/km) and August (-4.78 degrees 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.
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| 10. |
- Vicente-Serrano, S. M., et al.
(author)
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A comparison of temporal variability of observed and model-based pan evaporation over Uruguay (1973-2014)
- 2018
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In: International Journal of Climatology. - : Wiley. - 0899-8418. ; 38:1, s. 337-350
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Journal article (peer-reviewed)abstract
- This study analyses variability and trends of atmospheric evaporative demand (AED) across Uruguay in the past four decades. Changes were assessed using pan evaporation measurements from 10 meteorological stations and compared to PenPan model calculations, which is a physically based model that employs meteorological data as input. Results demonstrate a high agreement between the observed AED and those estimated from the PenPan model. Both observations and model estimations agree on a high interannual variability in AED, though being statistically insignificant (p>0.05) at seasonal and annual scales. Given that AED shows high sensitivity to changes in relative humidity and sunshine duration, as a surrogate of solar radiation, the lack of significant trends in the AED observations and estimations over Uruguay can be linked to the insignificant trend found for these climate variables for the period from 1973 to 2014. This is the first study that reports Pan evaporation trends for this part of the world, helping to infill gaps for mid-latitude Southern Hemisphere areas, which are poorly represented in Pan evaporation trends.
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