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We use high quality climate data from ground meteorological stations in the Iberian Peninsula (IP) and robust drought indices to confirm that drought severity has increased in the past five decades, as a consequence of greater atmospheric evaporative demand resulting from temperature rise. Increased drought severity is independent of the model used to quantify the reference evapotranspiration. We have also focused on drought impacts to droughtsensitive systems, such as river discharge, by analyzing streamflow data for 287 rivers in the IP, and found that hydrological drought frequency and severity have also increased in the past five decades in natural, regulated and highly regulated basins. Recent positive trend in the atmospheric water demand has had a direct influence on the temporal evolution of streamflows, clearly identified during the warm season, in which higher evapotranspiration rates are recorded. This pattern of increase in evaporative demand and greater drought severity is probably applicable to other semiarid regions of the world, including other Mediterranean areas, the Sahel, southern Australia and South Africa, and can be expected to increasingly compromise water supplies and cause political, social and economic tensions among regions in the near future. ; This work has been supported by research projects CGL201127574CO202, CGL201127536 and CGL2011–24185 financed by the Spanish Commission of Science and Technology and FEDER, 'Demonstration and validation of innovative methodology for regional climate change adaptation in the Mediterranean area (LIFE MEDACC)' financed by the LIFE programme of the European Commission, CTTP1/12, financed by the Comunidad de Trabajo de los Pirineos, and QSECA (PTDC/AAGGLO/ 4155/2012) funded by the Portuguese Foundation for Science and Technology (FCT). ASL was supported by a postdoctoral fellowship from the Catalan Government (2011 BPB 00078) and CAM was supported by a Juan de la Cierva fellowship by the Spanish Government.

9 Pags., 6 Figs. The Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the of the work, journal citation and DOI. ; We use high quality climate data from ground meteorological stations in the Iberian Peninsula (IP) and robust drought indices to confirm that drought severity has increased in the past five decades, as a consequence of greater atmospheric evaporative demand resulting from temperature rise. Increased drought severity is independent of the model used to quantify the reference evapotranspiration. We have also focused on drought impacts to drought-sensitive systems, such as river discharge, by analyzing streamflow data for 287 rivers in the IP, and found that hydrological drought frequency and severity have also increased in the past five decades in natural, regulated and highly regulated basins. Recent positive trend in the atmospheric water demand has had a direct influence on the temporal evolution of streamflows, clearly identified during the warm season, in which higher evapotranspiration rates are recorded. This pattern of increase in evaporative demand and greater drought severity is probably applicable to other semiarid regions of the world, including other Mediterranean areas, the Sahel, southern Australia and South Africa, and can be expected to increasingly compromise water supplies and cause political, social and economic tensions among regions in the near future. ; This work has been supported by research projects CGL2011-27574-CO2-02, CGL2011-27536 and CGL2011–24185 financed by the Spanish Commission of Science and Technology and FEDER, 'Demonstration and validation of innovative methodology for regional climate change adaptation in the Mediterranean area (LIFE MEDACC)' financed by the LIFE programme of the European Commission, CTTP1/12, financed by the Comunidad de Trabajo de los Pirineos, and QSECA (PTDC/AAG-GLO/4155/2012) funded by the Portuguese Foundation for Science and Technology (FCT). ASL was supported by a postdoctoral fellowship from the Catalan Government (2011 BP-B 00078) and CAM was supported by a Juan de la Cierva fellowship by the Spanish Government. ; Peer reviewed

Droughts are natural events that can cause water scarcity and can consequently have undesired political, social and environmental impacts. Since the end of 2013 the southeastern Brazil has suffered the worst drought in 55 years. This severe drought imposes water shortages for approximately 40 million people. Land use and land cover changes may drastically influence local climate, which increases the surface temperature. The aim of this work was to assess the negative impact of aforementioned drought on the vegetation health in a representative watershed in southeastern Brazil. The preliminary results showed the potential of satellite data in identify the drought periods and to classify the severity.

Droughts are natural events that can cause water scarcity and can consequently have undesired political, social and environmental impacts. Since the end of 2013 the southeastern Brazil has suffered the worst drought in 55 years. This severe drought imposes water shortages for approximately 40 million people. Land use and land cover changes may drastically influence local climate, which increases the surface temperature. The aim of this work was to assess the negative impact of aforementioned drought on the vegetation health in a representative watershed in southeastern Brazil. The preliminary results showed the potential of satellite data in identify the drought periods and to classify the severity.

This study developed a streamflow drought severity–duration–frequency (SDF) curve that is analogous to the well-known depth–duration–frequency (DDF) curve used for rainfall. Severity was defined as the total water deficit volume to target threshold for a given drought duration. Furthermore, this study compared the SDF curves of four threshold level methods: fixed, monthly, daily, and desired yield for water use. The fixed threshold level in this study is the 70th percentile value ( Q 70 ) of the flow duration curve (FDC), which is compiled using all available daily streamflows. The monthly threshold level is the monthly varying Q 70 values of the monthly FDC. The daily variable threshold is Q 70 of the FDC that was obtained from the antecedent 365 daily streamflows. The desired-yield threshold that was determined by the central government consists of domestic, industrial, and agricultural water uses and environmental in-stream flow. As a result, the durations and severities from the desired-yield threshold level were completely different from those for the fixed, monthly and daily levels. In other words, the desired-yield threshold can identify streamflow droughts using the total water deficit to the hydrological and socioeconomic targets, whereas the fixed, monthly, and daily streamflow thresholds derive the deficiencies or anomalies from the average of the historical streamflow. Based on individual frequency analyses, the SDF curves for four thresholds were developed to quantify the relation among the severities, durations, and frequencies. The SDF curves from the fixed, daily, and monthly thresholds have comparatively short durations because the annual maximum durations vary from 30 to 96 days, whereas those from the desired-yield threshold have much longer durations of up to 270 days. For the additional analysis, the return-period–duration curve was also derived to quantify the extent of the drought duration. These curves can be an effective tool to identify streamflow droughts using severities, durations, and frequencies.

This study developed a streamflow drought severity–duration–frequency (SDF) curve that is analogous to the well-known depth–duration–frequency (DDF) curve used for rainfall. Severity was defined as the total water deficit volume to target threshold for a given drought duration. Furthermore, this study compared the SDF curves of four threshold level methods: fixed, monthly, daily, and desired yield for water use. The fixed threshold level in this study is the 70th percentile value (Q70) of the flow duration curve (FDC), which is compiled using all available daily streamflows. The monthly threshold level is the monthly varying Q70 values of the monthly FDC. The daily variable threshold is Q70 of the FDC that was obtained from the antecedent 365 daily streamflows. The desired-yield threshold that was determined by the central government consists of domestic, industrial, and agricultural water uses and environmental in-stream flow. As a result, the durations and severities from the desired-yield threshold level were completely different from those for the fixed, monthly and daily levels. In other words, the desired-yield threshold can identify streamflow droughts using the total water deficit to the hydrological and socioeconomic targets, whereas the fixed, monthly, and daily streamflow thresholds derive the deficiencies or anomalies from the average of the historical streamflow. Based on individual frequency analyses, the SDF curves for four thresholds were developed to quantify the relation among the severities, durations, and frequencies. The SDF curves from the fixed, daily, and monthly thresholds have comparatively short durations because the annual maximum durations vary from 30 to 96 days, whereas those from the desired-yield threshold have much longer durations of up to 270 days. For the additional analysis, the return-period–duration curve was also derived to quantify the extent of the drought duration. These curves can be an effective tool to identify streamflow droughts using severities, durations, and frequencies.

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) ; Processo FAPESP: 2012/19821-1 ; Processo FAPESP: 2015/21586-9 ; Droughts are natural events that can cause water scarcity and can consequently have undesired environmental, social and political effects. Because droughts are related to land use and land cover modifications, satellite images are used to monitor and identify drought episodes through indices as Standardized Precipitation Index based on rainfall data and vegetation-based indices as Normalized Difference Vegetation Index (NDVI). Changes in vegetation cover have as impact the increasing of the land surface temperature (LST) that is a significant indicative of drought occurrence. This work explored the NDVI-LST relation through the Vegetation Health Index (VHI) in a tropical environment in Tiet River, State of So Paulo, Brazil, in order to assess changes in vegetation condition in two periods (2000 and 2014). Results showed that stressed areas are coincident with areas presenting high rate of modification in land cover; this areas presented low values of VHI and high values of LST. The worst conditions are verified in 2014, the same period of the most severe drought occurrence that reduced storage capacity in reservoirs in Tiet River.

Assessing the risk, the severity and the likely evolution of droughts are key tasks for improving preparedness of regions prone to drought conditions, and mitigation of drought consequences. The access to real-time and high-quality climatic information is essential for this purpose. Different climatic databases are being developed and made available on real time by climatic research institutions, but their capability for quantifying droughts characteristics including severity, or spatio-temporal variability, is uncertain given their low spatial resolution. In this study, we assessed the capability of three databases with contrasted spatial resolution for measuring spatial and temporal variability of drought occurrence. The standardized precipitation index, calculated for each database, showed that the low resolution datasets allow an acceptable measurement of the magnitude, intensity and duration of droughts, while failing mostly in detecting the spatial patterns of the specific drought episodes. Moreover, the capability of the datasets for assessing the impacts of droughts on surface hydrology and tree growth was examined. Results confirmed the usefulness of the drought index for assessing drought impacts on water resources and forest ecosystems even when low resolution databases are used. © 2012 Royal Meteorological Society. ; This work has been supported by the research projects CGL2008-01189/BTE, CGL2011-27574-CO2-02 and CGL2011-27536 financed by the Spanish Commission of Science and Technology and FEDER, EUROGEOSS (FP7-ENV-2008-1-226487) and ACQWA (FP7-ENV-2007-1-212250) financed by the VII Framework Programme of the European Commission, 'Efecto de los escenarios de cambio climático sobre la hidrología superficial y la gestión de embalses del Pirineo Aragonés' financed by 'Obra Social La Caixa' and the Aragón Government and Influencia del cambio climático en el turismo de nieve, CTTP01/10, Financed by the Comisión de Trabajo de los Pirineos. ; Peer Reviewed

Abstract
A decision framework is developed for quantifying the economic value of information (VOI) from the Gravity Recovery and Climate Experiment (GRACE) satellite mission for drought monitoring, with a focus on the potential contributions of groundwater storage and soil moisture measurements from the GRACE data assimilation (GRACE-DA) system. The study consists of (i) the development of a conceptual framework to evaluate the socioeconomic value of GRACE-DA as a contributing source of information to drought monitoring; (ii) structured listening sessions to understand the needs of stakeholders who are affected by drought monitoring; (iii) econometric analysis based on the conceptual framework that characterizes the contribution of GRACE-DA to the U.S. Drought Monitor (USDM) in capturing the effects of drought on the agricultural sector; and (iv) a demonstration of how the improved characterization of drought conditions may influence decisions made in a real-world drought disaster assistance program. Results show that GRACE-DA has the potential to lower the uncertainty associated with the understanding of drought and that this improved understanding has the potential to change policy decisions that lead to tangible societal benefits.

A monthly global dataset of a multiscalar drought index is presented and compared in terms of spatial and temporal variability with the existing continental and global drought datasets based on the Palmer drought severity index (PDSI). The presented dataset is based on the standardized precipitation evapotranspiration index (SPEI). The index was obtained using the CRU TS3.0 dataset at a spatial resolution of 0.5°. The advantages of the new dataset are that; i) it improves the spatial resolution of the unique global drought dataset at a global scale; ii) it is spatially and temporally comparable to other datasets, given the probabilistic nature of the SPEI, and, in particular; iii) it enables identification of various drought types, given the multiscalar character of the SPEI. The dataset is freely available on the web page of the Spanish National Research Council (CSIC) in three different formats (NetCDF, binary raster, and plain text). ; This work has been supported by the research projects CGL2008-01189/BTE and CGL2006-11619/HID financed by the Spanish Commission of Science and Technology and FEDER, EUROGEOSS (FP7-ENV- 2008-1-226487) and ACQWA (FP7-ENV-2007-1- 212250) financed by the VII Framework Programme of the European Commission, "Las sequías climáticas en la cuenca del Ebro y su respuesta hidrológica" and "La nieve en el Pirineo aragonés: Distribución espacial y su respuesta a las condiciones climática" Financed by "Obra Social La Caixa" and the Aragón Government ; Peer reviewed

9 Pag., 5 Fig. ; We discuss here shortcomings of the PDSI in adequately modeling the soil water balance, and its limited ability to quantify and monitor droughts of different types. Conversely, we describe the advantages of statistically based drought indices in analyzing the spatial and temporal variability of drought, identifying drought impacts in a variety of systems, and monitoring drought conditions in real time. ; This work has been supported by the research projects CGL2006‐11619/HID, CGL2008‐01189/BTE, CGL2011‐27574‐ CO2‐02 and CGL2011‐27536 financed by the Spanish Commission of Science and Technology and FEDER, EUROGEOSS (FP7‐ENV‐2008‐1‐ 226487) and ACQWA (FP7‐ENV‐2007‐1‐ 212250) financed by the VII Framework Programme of the European Commission, "Efecto de los escenarios de cambio climático sobre la hidrología superficial y la gestión de embalses del Pirineo Aragonés" financed by "Obra Social La Caixa" and the Aragón Government and "Influencia del cambio climático en el turismo de nieve", CTTP01/10, Financed by the Comisión de Trabajo de los Pirineos. ; Peer reviewed