Drought is a common hydrometeorological phenomenon and a pervasive global hazard. As our climate changes, it is likely that drought events will become more intense and frequent. Effective drought ...monitoring is therefore critical, both to the research community in developing an understanding of drought, and to those responsible for drought management and mitigation. Over the past 50 years remote sensing has shifted the field away from reliance on traditional site-based measurements and enabled observations and estimates of key drought-related variables over larger spatial and temporal scales than was previously possible. This has proven especially important in data poor regions with limited in-situ monitoring stations. Available remotely sensed data products now represent almost all aspects of drought propagation and have contributed to our understanding of the phenomena. In this review we chart the rise of remote sensing for drought monitoring, examining key milestones and technologies for assessing meteorological, agricultural and hydrological drought events. We reflect on challenges the research community has faced to date, such as limitations associated with data record length and spatial, temporal and spectral resolution. This review then looks ahead to the future in terms of new technologies, such as the ESA Sentinel satellites, analytical platforms and approaches, such as Google EarthEngine, and the utility of existing data in new drought monitoring applications. We look forward to the continuation of 50 years of progress to provide effective, innovative and efficient drought monitoring solutions utilising remote sensing technology.
•RS has led to a paradigm shift in drought monitoring approaches.•RS allows for observations of drought at high resolution.•Data is now available to quantify most relevant drought variable.•RS allows for effective, innovative and efficient drought management.
Droughts are known as the world's costliest natural disasters impacting a variety of sectors. Despite their wide range of impacts, no universal drought definition has been defined. The goal of this ...study is to define a universal drought index that considers drought impacts on meteorological, agricultural, hydrological, and stream health categories. Additionally, predictive drought models are developed to capture both categorical (meteorological, hydrological, and agricultural) and overall impacts of drought. In order to achieve these goals, thirteen commonly used drought indices were aggregated to develop a universal drought index named MASH. The thirteen drought indices consist of four drought indices from each meteorological, hydrological, and agricultural categories, and one from the stream health category. Cluster analysis was performed to find the three closest indices in each category. Then the closest drought indices were averaged in each category to create the categorical drought score. Finally, the categorical drought scores were simply averaged to develop the MASH drought index. In order to develop predictive drought models for each category and MASH, the ReliefF algorithm was used to rank 90 variables and select the best variable set. Using the best variable set, the adaptive neuro-fuzzy inference system (ANFIS) was used to develop drought predictive models and their accuracy was examined using the 10-fold cross validation technique. The models' predictabilities ranged from R2 = 0.75 for MASH to R2 = 0.98 for the hydrological drought model. The results of this study can help managers to better position resources to cope with drought by reducing drought impacts on different sectors.
•This study introduces a new universal drought index named MASH.•Thirteen drought indices were calculated for 145 subbasins over 30 years.•Meteorological, agricultural, hydrological, & stream heath drought categories were considered.•Cluster analysis was performed to create the categorical drought score.•Predictive models were developed for categorical drought indices and MASH.
Drought stress is one of the main factors limiting horticultural crops, especially in environments like the Mediterranean basin, which is often characterized by sub-optimal water availability. The ...global change will determine the increase in semi-arid conditions, so all horticultural crops will have to cope with the water scarcity. Appropriate plant selection and new cultivation methods, especially methods of deficit irrigation, are crucial in improving the crop cultivation performances.Horticultural plants can have specific adaptive mechanisms to overcome the negative effects of drought stress. Drought-tolerant plants show different adjustment mechanisms to overcome this stress, including morphological, physiological, and biochemical modifications. The plant responses include increasing the root/shoot ratio, growth reduction, leaf anatomy change, reduction of leaf size, and reduction of total leaf area to limit the water loss and guarantee the photosynthesis process. Furthermore, drought stress influences gas exchange and other physiological parameters. Recent acquisitions on the mechanism of signal transduction and the development of drought tolerance in plants are useful to understand the action mechanisms. Dr. Stefania Toscano Dr. Giulia Franzoni Dr. Sara Álvarez Guest Editors
Drought monitoring and declaration in India are challenging due to the requirement of multiple drought indices representing meteorological, hydrological, and agricultural droughts that are often not ...available in near real‐time. In addition, the current drought monitoring efforts do not consider groundwater storage variability. To overcome this, we develop an Integrated Drought Index (IDI) that combines the response of meteorological, hydrological, and agricultural droughts and accounts for groundwater storage. We use the Gaussian copula to integrate the 12‐month Standardized Precipitation Index (SPI), 4‐month Standardized Runoff Index (SRI), 1‐month Standardized Soil moisture Index (SSI), and 1‐month Standardized Groundwater Index (SGI) to develop IDI. Hydrologic variables (total runoff, soil moisture, and groundwater) required in IDI were simulated using the Variable Infiltration Capacity (VIC) with SIMple Groundwater Model (VIC‐SIMGM). We evaluated IDI against the Drought Severity Index (DSI), terrestrial and groundwater storage anomalies from the Gravity Recovery and Climate Experiment (GRACE) satellites, groundwater well, and streamflow anomalies. Moreover, we identify the three major droughts with the highest severity (based on IDI) that occurred in 1965, 1987, and 2002 in the Sabarmati river basin. The three most severe droughts occurred in 1966, 1979, and 2010 in the Brahmani basin. Notwithstanding the large intermodel uncertainty, which arises primarily from precipitation projections, the drought frequency based on IDI is projected to decline in Sabarmati while it increases in Brahmani basin under the warming climate. Our results show that IDI can be effectively used for drought monitoring and assessment under retrospective and future climate in India.
Key Points
Developed an Integrated Drought Index based on meteorological, hydrological, and agricultural droughts
IDI uses SPI, SRI, SSI, and SGI by incorporating the response of precipitation, runoff, soil moisture, and groundwater
IDI performs well against the Drought Severity Index (DSI) and groundwater well and streamflow observations
Drought is a costly natural hazard with far-reaching impacts on agriculture, ecosystem, water supply, and socio-economy. While propagating through the water cycle, drought evolves into different ...types and affects the natural system and human society. Despite much progress made in recent decades, a synthesis of the characteristics, approaches, processes, and controlling factors of drought propagation is still lacking. We bridge this gap by reviewing the recent progress of drought propagation and discussing challenges and future directions. We first introduce drought propagation characteristics (e.g., response time scale, lag time), followed by different approaches, including statistical analysis and hydrological modeling. The recent progress in the propagation from meteorological drought to different types of drought (agricultural drought, hydrological drought, and ecological drought) is then synthesized, including the basic process, commonly used indicators, data sources, and main findings of drought propagation characteristics. Different controlling factors of drought propagations, including climate (e.g., aridity, seasonality, and anomalies of meteorological variables), catchment properties (e.g., slope, elevation, land cover, aquifer, baseflow), and human activities (e.g., reservoir operation and water diversion, irrigation, and groundwater abstraction), are then summarized. Challenges in drought propagation include the discrepancy in drought indicators (and approaches) and difficulty in characterizing the full propagation process and isolating influencing factors. Future analysis of drought propagation should shift from single indicators to multiple indicators, from individual drivers to combined drivers, from uni-directional analysis to feedbacks, from hazards to impacts, and from stationary to nonstationary assumptions. This review is expected to be useful for drought prediction and management across different regions under global warming.
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•Drought propagation characteristics include response time scale, lag time, propagation rate, and spatial propagation•Correlation analysis, run theory, and response functions are statistical approaches for drought propagation analysis•Impacts of climate, catchments, and human activities on drought propagation were synthesized•Difficulties in modeling full propagation processes and isolating influences factors are prevailing challenges•Future directions of drought propagation analysis were discussed
•A drought risk atlas was created housing over 3000 stations with a 70year average period of record.•Over 1billion drought indices records have been generated up through 2012 and are freely ...available.•When fully completed, will house a cache of more than 500,000 gridded drought indices maps.•A robust web interface allows for multiple data and display queries at: droughtatlas.unl.edu.•The concept of using the DRA as a decision-support tool for drought planning is discussed.
Decision makers have continuously asked for better tools and resources to help them assess their risks related to climate variability and extremes. Drought is one of the risks they face, and the need for better drought risk tools and resources has also been expressed. With drought continuing to be one of the most problematic and costly natural disasters within the United States, and building on the work of the original National Drought Atlas (NDA) (1996), an updated and expanded Drought Risk Atlas (DRA) decision support tool for the United States was developed and is housed at the National Drought Mitigation Center. The DRA (1) provides weekly calculations of multiple indices/indicators, with more than a billion records made freely available, including the SPI, SPEI, PDSI, scPDSI, Deciles and U.S. Drought Monitor; (2) houses more than 3000 stations with data through 2012, nearly tripling the station count of the original NDA; (3) utilizes a much longer period of record, nearly double that of the NDA in most cases; (4) when fully completed, will house a cache of more than 500,000 gridded drought index maps; (5) will allow us to analyze and assess trends and various characteristics of drought, including frequency, intensity, duration and magnitude; (6) will become a resource for the National Weather Service (NWS) personnel around the country by transferring the application into the field through integration within the NWS’s newly developed Local Climate Analysis Tool (LCAT); and (7) work directly with the National Integrated Drought Information System (NIDIS) program office to include the information contained in the DRA into NIDIS’s regional drought early warning system pilot basins and the U.S. Drought Portal for broad dissemination to the user community and general public.
Recent prolonged dry periods in summer 2018 and spring 2020 have reawakened interest in drought in Ireland, prompting questions regarding historical drought occurrence and potential long‐term risks. ...Employing 250 years of monthly precipitation and flow reconstructions, we investigate historical drought in Irish catchments evaluating the characteristics (number of events, duration, and deficits) of moderate, severe, and extreme droughts as well as the propagation of meteorological to hydrological drought. Using standardized indices, we identify three distinct catchment types. Cluster 1 catchments, located in the wetter northwest are characterized by small areas, low groundwater storage, and the highest frequency of hydrological drought relative to other catchments. Cluster 3 catchments, located in the drier east and southeast have larger areas, greater groundwater storage, the highest frequency of meteorological drought but the least hydrological droughts. However, once established, droughts in Cluster 3 tend to be more persistent with large accumulated deficits. Cluster 2 catchments, located in the southwest and west, are intermediate to Clusters 1 and 3, with hydrological droughts typically of shorter durations, reduced accumulated deficits but greater mean deficits. The most extreme droughts based on accumulated deficits across all catchments occurred in 1803–1806, 1854–1859, 1933–1935, 1944–1945, 1953–1954, and 1975–1977. Although not as severe, droughts in 1887–1888, 1891–1894, and 1971–1974 also appear as significant extremes. Changes in drought characteristics reveal a complex picture with the direction, magnitude, and significance of trends dependent on the accumulation period used to define drought, the period of record analysed, and the reference period used to standardize indices. Of particular note is a tendency towards shorter, more intense meteorological and hydrological droughts. Our findings offer important insight for drought and water management in Ireland given the paucity of extreme droughts in short observed river flow records.
We evaluate historical meteorological and hydrological drought for 51 catchments in Ireland over the 1767–2016 period by applying standardized drought indices to monthly reconstructions of precipitation and streamflow. We identify extreme droughts from our records and examine trends in the characteristics of moderate and severe events. We find that shorter droughts show evidence of increasing frequency and mean deficits despite decreasing duration, indicating a tendency towards shorter, more intense meteorological and hydrological droughts.
Satellite based remote sensing offers one of the few approaches able to monitor the spatial and temporal development of regional to continental scale droughts. A unique element of remote sensing ...platforms is their multi-sensor capability, which enhances the capacity for characterizing drought from a variety of perspectives. Such aspects include monitoring drought influences on vegetation and hydrological responses, as well as assessing sectoral impacts (e.g., agriculture). With advances in remote sensing systems along with an increasing range of platforms available for analysis, this contribution provides a timely and systematic review of multi-sensor remote sensing drought studies, with a particular focus on drought related datasets, drought related phenomena and mechanisms, and drought modeling. To explore this topic, we first present a comprehensive summary of large-scale remote sensing datasets that can be used for multi-sensor drought studies. We then review the role of multi-sensor remote sensing for exploring key drought related phenomena and mechanisms, including vegetation responses to drought, land-atmospheric feedbacks during drought, drought-induced tree mortality, drought-related ecosystem fires, post-drought recovery and legacy effects, flash drought, as well as drought trends under climate change. A summary of recent modeling advances towards developing integrated multi-sensor remote sensing drought indices is also provided. We conclude that leveraging multi-sensor remote sensing provides unique benefits for regional to global drought studies, particularly in: 1) revealing the complex drought impact mechanisms on ecosystem components; 2) providing continuous long-term drought related information at large scales; 3) presenting real-time drought information with high spatiotemporal resolution; 4) providing multiple lines of evidence of drought monitoring to improve modeling and prediction robustness; and 5) improving the accuracy of drought monitoring and assessment efforts. We specifically highlight that more mechanism-oriented drought studies that leverage a combination of sensors and techniques (e.g., optical, microwave, hyperspectral, LiDAR, and constellations) across a range of spatiotemporal scales are needed in order to progress and advance our understanding, characterization and description of drought in the future.
•Multi-sensor observations provide advantages in addressing knowledge gaps.•Drought related remote sensing datasets are identified for multi-sensor studies.•Key drought phenomena and mechanisms benefiting from multi-sensors are highlighted.•Recent advances for multi-sensor drought monitoring models are synthesized.•Challenges and opportunities using multi-sensors for drought studies are provided.
•This paper presents a comprehensive review of multivariate drought indices.•Discussions of different development methods are provided.•Suggestions are made for implementing different multivariate ...drought indices.
Drought is a recurring natural phenomenon that has plagued the civilization throughout its history. Due to the complex nature and widespread impacts of drought, there is a lack of universally accepted definition of drought, which also affects the development of drought indices to characterize drought conditions. Because an individual drought indicator is generally not sufficient for characterizing complex drought conditions and impacts, multiple drought-related variables and indices are required to capture different aspects of complicated drought conditions. To address this issue, a variety of multivariate drought indices have been developed recently to combine multiple drought-related variables and indices for integrated drought characterizations. This paper presents a comprehensive review of major multivariate drought indices developed recently. Different development methods of multivariate drought indices are introduced along with their strengths and limitations. This paper provides useful information for operational drought characterization with current multivariate drought indices and for the development of new multivariate drought indices.
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