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Monthly and daily gridded precipitation datasets are one of the most demanded products in climatology and hydrology. These datasets describe the high spatial and temporal variability of precipitation as a continuous surface and for defined periods. However, due to the complex characteristics of precipitation, it is difficult to obtain accurate estimations. Thus, the creation of a gridded dataset from observations requires the comprehensive and precise application of quality control, reconstruction, and gridding procedures. Yet, despite multiple advances, most of the gridded datasets created and published since the mid-1990s to the present use a wide variety of techniques, methods, and outputs, which can completely change the final representativity of the data. It is, therefore, critical to provide general guidelines for the development of future and more robust gridded datasets based on the data characteristics, geographical factors, and advanced statistical techniques. We identified gaps and challenges for near-future perspectives and provide guidelines for implementing improved approaches based on the performance of 48 products. Finally, we concluded that, despite better spatial and temporal resolutions, data access, and data processing capabilities, observational coverage remains a challenge. Moreover, scientists should adopt tailored strategies to improve the representativity and uncertainty of the estimates. This article is categorized under: Science of Water > Hydrological Processes Science of Water > Water Extremes Science of Water > Methods ; This work was supported by the Government of Aragón through the "Program of research groups" (group H09_20R, "Climate, Water, Global Change, and Natural Systems"). Ernesto Tejedor is partially funded by the NSF-PIRE (OISE- 1743738)

15 Pags. - 3 Figs. The definitive version, with Appendix and Supplementary Data, is available at: http://www.sciencedirect.com/science/journal/13648152 ; Daily precipitation datasets are usually large, bulky and hard to handle, but they are of key importance in many environmental studies. We developed a tool to create custom datasets from observed daily precipitation records. Reference values (RV) are computed for each day and location using multivariate logistic regression with altitude, latitude and longitude as covariates. The operations were compiled in an Open Source R package called reddPrec. The reddPrec package consists of a set of functions used to: i) apply a comprehensive quality control over original daily precipitation datasets, flagging suspect data based on five predefined criteria; ii) fill missing values in original data series by estimating precipitation values using the 10 nearest observations for each day; and iii) create new series and gridded datasets in locations where no data were recorded. ; This study was supported by research projects CGL2012-31668, CGL2015-69985-R, CGL2011-24185 and CGL2014-52135-C3-1-R, financed by the Spanish Ministerio de Economía y Competitividad (MINECO) and FEDER-ERDF funds. We were financially supported by the Government of Aragón through the 'Programme of research groups' (groups 'H38, Clima, Cambio Global y Sistemas Naturales' and 'E68, Geomorfología y Cambio Global'). ; Peer reviewed

51 Pags.- 12 Figs.- 3 Tabls. The definitive version is available at: http://www.int-res.com/journals/cr/cr-home/ ; This work presents a method for the reconstruction of fragmentary daily precipitation datasets. The method aims to preserve the local and temporal variability characteristic of high-frequency precipitation data, and does not use the time-structure of the data. Based on the precipitation values recorded at closest neighbours during a target day, 2 reference values (RVs) are computed: a binomial prediction (BP) expressing the probability of occurrence of a wet day; and a magnitude prediction (MP), referring to the amount of precipitation. Generalised linear models (GLMs) are used to compute the RVs using the precipitation data (occurrence and magnitude) of the 10 nearest neighbours as the dependent variable, and the geographic information of each station (latitude, longitude, and altitude) as the independent variables. The RVs are then used to (1) apply quality control to the data, flagging suspect records according to 5 predefined criteria; (2) obtain serially complete time series by imputing RVs to missing observations in the original dataset; and (3) create new time series at locations where there were no observations or gridded datasets with even spatial coverage over the study area. The routines used were compiled into an R-package called 'reddPrec' (reconstruction of daily data - Precipitation) available to any user. We applied these methods to the complete daily precipitation dataset of the island of Majorca in Spain, spanning the period from 1971-2014. ; This study was supported by research projects CGL2012-31668, CGL2015-69985-R, CGL2011-24185 and CGL2014-52135-C3-1-R, financed by the Spanish Ministerio de Economía y Competitividad (MINECO) and FEDER-ERDF funds. The researchers were supported by the Government of Aragón through the 'Programme of research groups' (groups H38, 'Clima, Cambio Global y Sistemas Naturales' and 'E68, Geomorfología y Cambio Global'). ; Peer reviewed

The increase in the number of tropical nights (TN; minimum temperature ‡20°C) constitutes important evidence of the global warming process throughout the Mediterranean region. A significant increase in the number of these events has been recorded since the second half of the 20th century. From the meteorological observations in the period 1950-2014 in the regions of Valencia and Murcia, in the central sector of the Spanish Mediterranean coast, we analyse the evolution of the number of tropical nights, the length of the episodes and their frequency. Our results indicate that the study regions experienced a significant increase in tropical nights within the last 3 decades due to climate change and the increase in sea surface temperatures (SST) in the central Western Mediterranean. We also discuss the relationship of the number of tropical nights with the increase in the Mediterranean Sea surface temperatures in the neighbouring sectors, as well as the possible implications of the combined effects of this with the urban heat island effect. Tropical nights are a cause of thermal discomfort, and thus there is a need to adapt buildings and manage urban planning to ameliorate this, and to be prepared for more frequent events in the future. ; R.S.N. was funded by a 'Juan de la Cierva' postdoctoral grant FJCI-2017-31595. J.M. thanks the Spanish Ministerio de Economía y Competitividad and the European Regional Development Fund (FEDER) through the project CGL2015-64268-R (MINECO/FEDER, UE). O.M.R. thanks the Climatology Group (2017SGR1362, Catalan Government) and the CLICES Project (CGL2017-83866-C3-2-R).

20 Pags.- 5 Tabls.- 8 Figs. Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) ; Floods modify the natural dynamics of river environments and greatly affect urban areas, especially in mountain regions where flooding is frequent because of the precipitation characteristics and orographic configuration. In this study the vulnerability of the central sector of the Pyrenees to flood events was investigated using frequency analysis of daily flow and precipitation data for the period from 1940 to 2012 for the headwaters of the Aragón and Ésera rivers. The land use evolution over the past 60 years was also analyzed. The return periods showed that floods have not been exceptional, and the high flow frequency has been large and closely related to precipitation events. This, combined with a large increase in human occupation, particularly since the 1990s, of fluvial areas associated with the land use evolution since 1956, has increased exposure to flood risks. ; This study was supported by the Spanish Ministry of Economy and Competitiveness through the projects CGL2015-69985-R, and by the Government of Aragon through the 'programme of research groups' (group Clima, Cambio Global y Sistemas Naturales, BOA 147, 18-12-2002) and ERDF funds. ; Peer reviewed

35 Pags.- 7 Figs.- 4 Tabls. The definitive version is available at: https://rmets.onlinelibrary.wiley.com/journal/10970088 ; The long‐term hydroclimatic variability in Santiago (Chile) was analysed by means of a new 481‐year (1536–2016 CE) tree‐ring reconstruction of the Standardized Precipitation Evapotranspiration Index (SPEI) of August, integrating the hydroclimatic conditions during the preceding 14 months. Results show a high frequency of extreme drought events in the late 20th and early 21st centuries, while the frequency of extreme wet events was higher in the 17th–18th centuries. The mid‐20th century represents a breaking point for the hydroclimatic history in the region, including some significant changes: (a) the interannual variability increased; (b) the wet events became less intense; (c) the extreme dry events became more frequent; and (d) the most intense dry event of the entire period was identified, coinciding with the so‐called Megadrought (2006–2016). A correlation analysis between the reconstructed SPEI and three climate indices (PDO, SOI and Niño3.4) was performed at monthly scale, considering different multi‐annual aggregations. The analysis shows diverse impacts on the hydroclimatic variability, with positive correlations between SPEI and PDO as well as Niño3.4, and negative correlations between SPEI and SOI. The most significant correlations were, overall, found at multi‐annual time scales (>7 years). Results help to better understand the current hydroclimatic changes (Megadrought) in a long‐term context. ; R.S.N. is funded by a "Juan de la Cierva" postdoctoral grant FJCI-2017-31595. This work was developed under the project CAS/1900020 funded by the Spanish Ministry of Science and the Fulbright Foundation. O.M.R., P.S. and R.S.N. thank the Climatology Group (2017SGR1362, Catalan Government) and the CLICES Project (CGL2017-83866-C3-2-R). R.S.N. and M.D.L. are supported by the Government of Aragón through the "Programme of research groups" (group H38, "Clima, Agua, Cambio Global y Sistemas Naturales") and thank the project CGL2015-69985-R. E.T. and M.V. were partially supported by NSF-PIRE (OISE-1743738) and NSF-P2C2 (AGS-1702439). M.F. is funded by a postdoctoral grant CONICYT PIA AFB170008 of the Institute of Ecology and Biodiversity (IEB). ; Peer reviewed

The long-term hydroclimatic variability in Santiago (Chile) was analysed by means of a new 481-year (1536-2016 CE) tree-ring reconstruction of the Standardized Precipitation Evapotranspiration Index (SPEI) of August, integrating the hydroclimatic conditions during the preceding 14 months. Results show a high frequency of extreme drought events in the late 20th and early 21st centuries, while the frequency of extreme wet events was higher in the 17th-18th centuries. The mid-20th century represents a breaking point for the hydroclimatic history in the region, including some significant changes: (a) the interannual variability increased; (b) the wet events became less intense; (c) the extreme dry events became more frequent; and (d) the most intense dry event of the entire period was identified, coinciding with the so-called Megadrought (2006-2016). A correlation analysis between the reconstructed SPEI and three climate indices (PDO, SOI and Nino3.4) was performed at monthly scale, considering different multi-annual aggregations. The analysis shows diverse impacts on the hydroclimatic variability, with positive correlations between SPEI and PDO as well as Nino3.4, and negative correlations between SPEI and SOI. The most significant correlations were, overall, found at multi-annual time scales (>7 years). Results help to better understand the current hydroclimatic changes (Megadrought) in a long-term context. ; "Juan de la Cierva" postdoctoral grant FJCI-2017-31595 Spanish Government CAS/1900020 Fulbright Foundation CAS/1900020 Climatology Group (Catalan Government) 2017SGR1362 CLICES Project CGL2017-83866-C3-2-R Government of Aragon through the "Programme of research groups" H38 National Science Foundation (NSF) NSF - Office of the Director (OD) OISE-1743738 National Science Foundation (NSF) NSF - Directorate for Geosciences (GEO) AGS-1702439 CONICYT PIA of the Institute of Ecology and Biodiversity (IEB) AFB170008 CGL2015-69985-R

Wildfires are gaining importance in the Mediterranean regions owing to climatechange and landscape changes due to the increasing closeness between urban areas and forests prone to wildfires. We analysed the dry season wildfire occurrences in the Mediterranean region of Central Chile (32 degrees S-39 degrees 30'S) between 2000 and 2017, using satellite images to detect burned areas, their landscape metrics and the land use and covers (vegetal) pre-wildfire, in order to determine the population living in areas that may be affected by wildfires. The existing regulations in western Mediterranean countries (Portugal, Spain, France, and Italy) were used to identify and define the wildland-urban interface (WUI) areas, quantifying the people inhabiting them and estimating the population affected by burned areas from 2001 to 2017. We used the Google Earth Engine to process MODIS products and extract both burned areas and land covers. We detected that 25% of the urban population inhabits WUI areas (i.e. Biobio, Araucania and Valparaiso regions) where the urban population exposed to burned areas exceeds 40%. Must of the land use and land covers affected by wildfires are anthropogenic land covers, classified as savannas, croplands, evergreen broadleaf forests and woody savannas, representing >70% of the burned areas. Urban areas show only 0.6% of the burned surface from 2001 to 2017. We estimate that 55,680 people are potentially affected by wildfires, and 50% of them are in just one administrative region. These results show the imperative need for public policies as a regulating force for establishing WU1 areas with the purpose of identifying wildfire risk in urban areas, such as establishing prevention methods as firewalls and prescribed fires. ; Climatology Group (Catalan Government) "Juan de la Cierva" postdoctoral grant CLICES Project Comisión Nacional de Investigación Científica y Tecnológica (CONICYT) CONICYT FONDAP

Northern Chile is a region characterised by an extremely dry climate; however, there is a brief rainy season from December to March (austral summer), mainly above 3000 m a.s.l. It is interesting to consider where the humid air masses that generate such rain come from. For this purpose, daily precipitation data from 161 meteorological stations located in this area (18° S–19° S) were considered, and four clusters formed by k-means clustering. For each cluster, days of extreme precipitation (above 90th percentile) were selected to obtain flow strength (F), direction (D), and vorticity (Z) for each event according to the Jenkinson and Collison (JC) method. The back trajectory, for the previous 72 h, of air masses affecting the centroid of each cluster was determined by means of the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model. The analyses were carried out at sea level (1013 hPa) and in the middle (500 hPa) and upper (250 hPa) troposphere. Surface circulation was not a determining factor in the occurrence of extreme events, but it did influence circulation at 500 and 250 hPa. For stations located in the northern Altiplano, moisture advection from the Amazon basin is evident due to the configuration of the Bolivian high—an upper level anticyclone that develops over the Bolivian Altiplano during austral summer. For stations located in the southern part of the study area, the main source of moisture is the Pacific Ocean, and the weather is related to the arrival of frontal systems and to the configuration of cut-off low pressure systems in the mid-troposphere. ; The authors want to thank the FONDECYT Project 11160059 of the Chilean Government, the Climatology Group (2017SGR1362, Catalan Government) and the CLICES Project (CGL2017-83866-C3-2-R) for the institutional support. R.S.N. is funded by the Spanish Ministry of Science and Innovation (grant no. FJCI-2017-31595).

2 .pdf files: File 1. Author's article final version, Post-Print (19 Pags.- 4 Figs.- 2 Tabls.). File 2. Supplementary Materials (3 Figs.- 2 Tabls.- 1 Model Equation). ; Aim Previous work demonstrated the global variability of synchrony in tree growth within populations, that is, the covariance of the year‐to‐year variability in growth of individual neighbouring trees. However, there is a lack of knowledge about the causes of this variability and its trajectories through time. Here, we examine whether climate can explain variation in within‐population synchrony (WPS) across space but also through time and we develop models capable of explaining this variation. These models can be applied to the global tree cover under current and future climate change scenarios. Location Global. Time period 1901–2012. Major taxa studied Trees. Methods We estimated WPS values from a global tree‐ring width database consisting of annual growth increment measurements from multiple trees at 3,579 sites. We used generalized linear mixed effects models to infer the drivers of WPS variability and temporal trends of global WPS. We then predicted WPS values across the global extent of tree cover. Finally, we applied our model to predict future WPS based on the RCP 8.5 (2045–2065 period) emission scenario. Results Areas with the highest WPS are characterized by a combination of environments with both high mean annual temperature (>10°C) and low precipitation (<300 mm). Average WPS across all temperate forests has decreased historically and will continue to decrease. Potential implications of these patterns include changes in forest dynamics, such as higher tree growth and productivity and an increase in carbon sequestration. In contrast, the WPS of tropical forests of Central and South America will increase in the near future owing to reduced annual precipitation. Main conclusions Climate explains WPS variability in space and time. We suggest that WPS might have value as an integrative ecological measure of the level of environmental stress to which forests are subjected and therefore holds potential for diagnosing effects of global climate change on tree growth. ; E.T. and M.V. were partially supported by National Science Foundation ‐ Partnership in International Research and Education (OISE‐1743738) and National Science Foundation ‐ Paleo Perspectives on Climate Change (AGS‐1702439). R.S.‐N. is funded by a "Juan de la Cierva" postdoctoral grant FJCI‐2017‐31595. E.T., M.S., R.S.‐N. and M.D.L. are supported by the Government of Aragón through the "Program of research groups" (group H38, "Clima, Agua, Cambio Global y Sistemas Naturales"). A.L. was supported by grant EVA4.0, No. CZ.02.1.01/0.0/0.0/16_019/0000803, financed by OP RDE and by the U.S. Department of Agriculture Forest Service. ; Peer reviewed

Mountain systems within the Mediterranean region, e.g., the Pyrenees, are very sensitive to climate change. In the present study, we quantified the magnitude of extreme precipitation events and the number of days with torrential precipitation (daily precipitation ≥ 100 mm) in all the rain gauges available in the Pyrenees for the 1981-2015 period, analyzing the contribution of the synoptic scale in this type of event. The easternmost (under Mediterranean influence) and north-westernmost (under Atlantic influence) areas of the Pyrenees registered the highest number of torrential events. The heaviest events are expected in the eastern part, i.e., 400 mm day−1 for a return period of 200 years. Northerly advections over the Iberian Peninsula, which present a low zonal index, i.e., implying a stronger meridional component, give rise to torrential events over the western Pyrenees; and easterly advections favour extreme precipitation over the eastern Pyrenees. The air mass travels a long way, from the east coast of North America, bringing heavy rainfall to the western Pyrenees. In the case of the torrential events over the eastern Pyrenees, the trajectory of the air mass causing the events in these areas is very short and originates in the Mediterranean Basin. The North Atlantic Oscillation (NAO) index has no influence upon the occurrence of torrential events in the Pyrenees, but these events are closely related to certain Mediterranean teleconnections such as the Western Mediterranean Oscillation (WeMO) ; The present study was conducted within the framework of the Climatology Group of the University of Barcelona (2017 SGR 1362, Catalan Government) and the Spanish CLICES project (CGL2017-83866-C3-2-R, AEI/FEDER, UE). M.L.-C. was awarded a pre-doctoral FPU Grant (FPU2017/02166) from the Spanish Ministry of Science, Innovation and Universities. R.S.-N. and J.M.C. are partially supported by the Government of Aragón through the "Program of research groups" (group H38, "Clima, Agua, Cambio Global, y Sistemas Naturales")

19 Pags.- 5 Figs.- 5 Tabls. © 2018 The Authors. Published by Elsevier B.V. Under a Creative Commons license Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0). ; National accounting either ignores or fails to give due values to the ecosystem services, products, incomes and environmental assets of a country. To overcome these shortcomings, we apply spatially-explicit extended accounts that incorporate a novel environmental income indicator, which we test in the forests of Andalusia (Spain). Extended accounts incorporate nine farmer activities (timber, cork, firewood, nuts, livestock grazing, conservation forestry, hunting, residential services and private amenity) and seven government activities (fire services, free access recreation, free access mushroom, carbon, landscape conservation, threatened biodiversity and water yield). To make sure the valuation remains consistent with standard accounts, we simulate exchange values for non-market final forest product consumption in order to measure individual ecosystem services and environmental income indicators. Manufactured capital and environmental assets are also integrated. When comparing extended to standard accounts, our results are 3.6 times higher for gross value added. These differences are explained primarily by the omission in the standard accounts of carbon activities and undervaluation of private amenity, free access recreation, landscape and threatened biodiversity ecosystem services. Extended accounts measure a value of Andalusian forest ecosystem services 5.4 times higher than that measured using the valuation criteria of standard accounts. ; This RECAMAN project research has received financial support from Agency of Environment and Water (AMAYA); Department of Environment and Territory Planning (CMAYOT) (contract No NET165602). ; Peer reviewed