Flash drought: definition, dynamics, detection, and prediction 

Flash droughts (FDs) are distinguished from slower-developing droughts by their rapid rate of intensification. They may occur during the initial stage of a long-term drought, represent a period of rapid intensification within a longer-term drought, or terminate after a relatively short, yet impactful, event. Due to their rapid development, FDs are difficult to manage and can be particularly devastating for agriculture. They can occur with little or no warning due to limitations in monitoring capabilities, prediction skill of relevant environmental variables, and understanding of key physical mechanisms. Efforts to create working definitions of FD have been hindered by these limitations and a lack of data to quantify the many impacts associated with FD. This session welcomes abstracts relating to:
1) proposed FD definitions,
2) regionality and seasonality of FD physical mechanisms,
3) advances in FD detection and monitoring,
4) predictability and prediction of FDs,
5) quantification of impacts of FD, and
6) the changes in FD frequency and intensity in response to human-induced climate change.
We also encourage contributions that benefit from multivariate analysis, model-observation comparison, uncertainty quantification, or machine-learning predictions.

Convener: Mike Hobbins | Co-conveners: Celine Bonfils, Andrew Hoell, David HoffmannECSECS, Matthew Wheeler
vPICO presentations
| Thu, 29 Apr, 15:30–17:00 (CEST)

Session assets

Session materials

vPICO presentations: Thu, 29 Apr

Chairperson: Mike Hobbins
Flash drought (FD) introduction and definition(s)
Joel Lisonbee, Molly Woloszyn, and Marina Skumanich

The topic of “Flash Drought” has rapidly gained attention within the research and drought management communities within the last decade. In preparation for a recent workshop on Flash Drought, the National Integrated Drought Information System (NIDIS) prepared a literature review to synthesize the research to-date (as of August 2020) and to provide a basis for future research on the topic. Specifically, this review is focused on documenting the range of definitions of "flash drought" that have been proposed by the research community. The term first appeared in the peer-reviewed literature in 2002, and by 2020, has become an area of active research. Within that 18-year span, 19 papers have provided measurable, defining criteria used to distinguish a flash drought from other drought. Of these papers, 11 distinguish flash drought as a rapid-onset or rapid-intensification drought event while seven distinguish flash drought as a short-term or short-lived, yet severe, drought event, and one paper considers flash drought as both a short-lived and rapid-onset event. Currently, there is no universally accepted definition or criteria for “flash drought,” despite recent research that has called for the research community to adopt the principle of rapid-intensification of drought conditions. This topic was further explored at the NIDIS-sponsored Flash Drought Workshop on 1-3 December 2020, where additional perspectives were shared about the key characteristics of flash drought that should inform its definition.  We will provide a review of the literature-derived definitions as well as a brief overview of this additional discussion.

How to cite: Lisonbee, J., Woloszyn, M., and Skumanich, M.: Making sense of flash drought: definitions, indicators, and where we go from here, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6423, https://doi.org/10.5194/egusphere-egu21-6423, 2021.

Akif Rahim and Yannis Markonis

Over the past decades, the evolution of the “flash drought” concept has offered new insights in the analysis of extreme climate. Rapid development and devastating effects on the ecosystem have made flash droughts different from the traditional drought. For example, the flash drought event of 2012 across the Great Plains in the USA caused an agricultural loss of $30 billion. In this study, we reviewed the progress and determined the growth rate of flash drought research over the past decades. Furthermore, we compiled the challenges addressed by the researchers and then presented the future perspectives to cope with these challenges. We used the Scopus database as a search engine to track articles published from 2000 to 2020. The association technique of clustering s applied to the author’s keywords and research titles to identify the hot spots of flash drought research. The results show that the literature on flash droughts has grown rapidly over the past decade. The main identified challenges are the appropriate definition and identification of flash drought, the development of an effective early warning system, the determination of the ecosystem response time to flash droughts, and the data scarcity in both spatial and temporal scales. Future research should establish a detailed framework to integrate each of the challenges and provide mitigation suggestions to the effects of flash drought.


How to cite: Rahim, A. and Markonis, Y.: Flash Drought Research: Growth, Challenges and Future Perspectives , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14105, https://doi.org/10.5194/egusphere-egu21-14105, 2021.

Tonya Haigh, Joel Lisonbee, Marina Skumanich, and Molly Woloszyn

Defining flash drought is important not only for the development of the science but also for ensuring clear and useful early warning information to end users. In preparation for a December 2020 U.S-based workshop on flash drought, the National Integrated Drought Information System (NIDIS) and National Drought Mitigation Center (NDMC) undertook a survey of NIDIS contacts to explore how flash drought is understood within and outside of the research community. End users represented in the survey include researchers (outside of flash drought specialty), policy-makers, decision-makers, communicators, and educators and public engagement specialists, largely working within universities or federal agencies across the U.S. Flash drought researchers were asked to describe how they intend for the term “flash drought” to be interpreted when they use it. End users (whether they had heard/used the term before or not) were asked to describe what they think of when they hear the term “flash drought”. Their answers emerged into themes, including: onset/intensification, duration, drivers, impacts, seasonality, predictability, intensity, spatial scale, and uncertainty about its meaning. In this presentation, we will elaborate upon these themes, and discuss similarities and differences in how flash drought researchers and end users conceptualize flash drought.

How to cite: Haigh, T., Lisonbee, J., Skumanich, M., and Woloszyn, M.: Perceptions of Flash Drought in the U.S.: How do End-Users and Researchers Compare?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3441, https://doi.org/10.5194/egusphere-egu21-3441, 2021.

Jason Otkin, Yafang Zhong, Eric Hunt, Jordan Christian, Jeff Basara, Hanh Nguyen, Matthew Wheeler, Trent Ford, Andrew Hoell, Mark Svoboda, and Martha Anderson

Flash droughts are characterized by a period of unusually rapid drought intensification over sub-seasonal time scales that often take vulnerable stakeholders by surprise given their rapid onset. Various studies have shown that flash drought is more likely to develop when extreme weather conditions persist over the same region for several weeks or longer. Though precipitation deficits over some period of time are a prerequisite for drought, their presence alone is unlikely to lead to flash drought because a lack of precipitation is only one of several factors that contribute to rapid drought development. When below normal precipitation occurs alongside other extreme weather anomalies such as intense heat that enhance atmospheric evaporative demand, their co-occurrence can lead to a rapid depletion of root zone soil moisture content due to increased evapotranspiration. This in turn can lead to a rapid increase in vegetation moisture stress and the onset of flash drought conditions.

Several recent studies have used quantitative definitions based on rapid changes in a given drought monitoring dataset to identify flash droughts in the climatological record. Here, we build upon these recent studies by developing a new flash drought intensity index that accounts not only for their rapid rate of intensification, but also for how severe the drought conditions become during and after the period of rapid intensification. The method includes two components that together capture the suddenness of flash drought development (faster intensification corresponds to a more severe flash drought) and the actual drought severity after the rapid intensification period ends (severe drought conditions lasting for a longer period correspond to a more severe flash drought). The motivation behind this method is the desire to account for both the “flash” and “drought” aspects of flash drought because both of these characteristics influence how people view flash droughts. Thus, a metric that considers both of these aspects provides a more comprehensive assessment of flash drought intensity and its impacts on the environment. In this talk, we will present the proposed flash drought intensity index methodology, along with results from individual case studies and a 40-year climatology to illustrate its use.

How to cite: Otkin, J., Zhong, Y., Hunt, E., Christian, J., Basara, J., Nguyen, H., Wheeler, M., Ford, T., Hoell, A., Svoboda, M., and Anderson, M.: Development of a flash drought intensity index, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1418, https://doi.org/10.5194/egusphere-egu21-1418, 2021.

Jordan Christian, Eric Hunt, Jeffrey Basara, and Jason Otkin

Flash drought is a critical subseasonal phenomenon that leads to significant environmental and socioeconomic impacts. Given the short timeframe in which these events development (a few weeks to a couple of months), detection and monitoring of rapid drought intensification remains a challenging task. As such, it is essential to have an environmental variable or a set of environmental variables that effectively evaluate flash drought development. This presentation provides an overview of the standardized evaporative stress ratio (SESR) and its utility in 1) detecting flash drought events, 2) monitoring the evolution of flash drought development, 3) quantifying the intensity (rate of intensification) of flash drought, and 4) representing impact (evaporative stress) on the environment. While the calculation of SESR is relatively simple (the ratio of evapotranspiration and potential evapotranspiration), approaches using evaporative stress can provide a wealth of information with respect to flash drought characteristics (e.g., timing, intensity (rate of change towards drought), severity (magnitude of evaporative stress), length, and shape/evolution). The diverse utility of SESR is presented with known flash drought case studies, such as the 2012 flash drought in the central United States and the 2010 flash drought in western Russia. Additional applications of SESR are also discussed, including climatological analysis and real-time flash drought monitoring.

How to cite: Christian, J., Hunt, E., Basara, J., and Otkin, J.: The Utility of the Standardized Evaporative Stress Ratio in Flash Drought Detection, Monitoring, and Evaluation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8049, https://doi.org/10.5194/egusphere-egu21-8049, 2021.

Jeffrey Basara, Stuart Edris, Jordan Christian, Bradley Illston, Eric Hunt, Jason Otkin, and Scott Salesky

Flash droughts occur rapidly (~1 month timescale) and have produced significant ecological, agricultural, and socioeconomical impacts. Recent advances in our understanding of flash droughts have resulted in methods to identify and quantify flash drought events and overall occurrence. However, while it is generally understood that flash drought consists of two critical components including (1) anomalous, rapid intensification and (2) the subsequent occurrence of drought, little work has been done to quantify the spatial and temporal occurrence of the individual components, their frequency of covariability, and null events. Thus, this study utilized the standardized evaporative stress ratio (SESR) method of flash drought identification applied to the North American Regional Reanalysis NARR) to quantify individual components of flash drought from 1979 – 2019. Individual case studies were examined and the the drought component was assessed using the United States Drought Monitor for 2010 – 2019.   Additionally, the flash component was assessed using results of previous flash drought studies. Further, the correlation coefficient and composite mean difference was calculated between the flash component and flash droughts identified to determine what regions, if any, experienced rapid intensification but did not fall into flash drought. The results yielded that SESR was able to represent the spatial coverage of drought well for regions east of the Rocky Mountains, with mixed success regarding the intensity of the drought events. The flash component tended to agree well with other flash drought studies though some differences existed especially for areas west of the Rocky Mountains which experience rapid intensification at high frequencies but did not achieve drought designations due to hyper-aridity.

How to cite: Basara, J., Edris, S., Christian, J., Illston, B., Hunt, E., Otkin, J., and Salesky, S.: Decomposing the Critical Components of Flash Drought Using the Standardized Evaporative Stress Ratio, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13683, https://doi.org/10.5194/egusphere-egu21-13683, 2021.

FD studies using reanalysis data on case studies
Pedro Henrique Lima Alencar, José Carlos de Araújo, and Eva Nora Paton

Flash droughts recently started to draw a larger curiosity to its occurrence and, therefore, its features. Differently from the slow development of droughts (months to years), flash droughts evolve over a short time (weeks) of a rapid intensification. Over the last few years, multiple methods for flash drought identification were proposed. Those methods, although sharing some characteristics, as tracking of soil water content and/or evapotranspiration (actual and potential), end up not flagging the same periods under flash drought events. We compared six well-known flash drought identification methods from the literature and used two different datasets. The datasets are: (1) the FluxNET15 dataset (Pastorello et al, 2020), a collection of worldwide, quality-controlled measurements of several hydroclimatic variables, such as soil water content, precipitation, temperature, and wind speed; and (2) the ECMWF Reanalysis 5 (ERA5 – Hersbach et al., 2019) provides over three hundred different data including soil water content in multiple levels, evapotranspiration, precipitation, and temperature. Ten stations from FluxNET15 were selected and the data from the ERA5 on the respective pixels was acquired. The aim of this work is to compare the event identification of different methods using different datasets as input (direct measures and reanalysis based).

How to cite: Lima Alencar, P. H., de Araújo, J. C., and Paton, E. N.: Flash Drought identification – a comparison of definitions across different datasets., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16383, https://doi.org/10.5194/egusphere-egu21-16383, 2021.

Miguel A. Lovino, Ernesto H. Berbery, Gabriela V. Müller, and M. Josefina Pierrestegui

This study investigates the frequency of occurrence of two types of flash droughts in southern South America: heatwave flash droughts (HWFD) and precipitation deficit flash droughts (PDFD). To this end, we employ ERA5 products at 0.25° horizontal resolution under the assumption that they add valuable information in regions of scarce observations. The analysis is based on 1979-2019 ERA5 pentad data of precipitation (P), 2-m air mean temperature (T), evapotranspiration (ET), and root-zone soil moisture (SM). HWFD and PDFD exhibit different functional mechanisms related to surface moisture and surface energy fluxes. In HWFD, high T causes ET to increase and lead to decreases of SM. When combined with negative P anomalies before a drought's onset, there is a significant increase in the magnitude of negative SM anomalies. The mechanism of PDFD formation starts with a precipitation deficit prior to the drought onset. The lack of precipitation causes a reduction in SM and ET, which results in increased T (the Bowen ratio and T increase in response to the decreased ET). 

HWFDs at each grid point and each pentad are identified as those that meet the following conditions: (a) T anomalies are larger than one standard deviation (SD) computed from the 1979-2019 period for that pentad, (b) ET anomalies are positive, (c) P anomalies are negative, and (d) the SM is below the 40th percentile. PDFDs are identified when (a) P is below the 40th percentile, (b) SM% < 40, (c) ET anomalies are negative, and (d) T anomalies > 1 SD. The frequency of occurrence (FOC) of HWFD or PDFD is defined as the percentage of pentads exceeding those thresholds. Composites of all variables for pentads under HWFD or PDFD were prepared to determine such droughts' spatial structure.

Our results indicate that cases of HWFD are more common than those of PDFD. HWFDs are more likely to occur over the arid western region and central-eastern Brazil. HWFDs are more common in both areas in spring (SON) and summer (DJF), reaching FOC values of 14-16% over each season. On the other hand, PDFDs can occur almost everywhere but less frequently. The maximum annual FOC for PDFD (4 - 6%) is located towards Brazil's center. Composite maps show that the most frequent HWFDs occur in regions of highest T and ET anomalies, with a SM decrease to the 10-20th percentile range.

In contrast, the most frequent PDFDs do not occur in regions of highest P deficit, i.e., northeastern Argentina and southern Brazil. However, the precipitation deficit towards the center of Brazil, the area with the highest frequency of PDFD, is significant ( -3 mm / day). This P deficit leads to decreased soil moisture to the 20-30th percentile range and mean ET anomalies between -0.2 and -0.5 mm/day.

How to cite: Lovino, M. A., Berbery, E. H., Müller, G. V., and Pierrestegui, M. J.: Flash droughts in southern South America as captured by ERA5 reanalysis data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3241, https://doi.org/10.5194/egusphere-egu21-3241, 2021.

Mike Hobbins, Tess Parker, Ailie Gallant, and David Hoffmann

Until the scientific community coalesces around a consensus definition of flash drought, we might usefully distinguish them from “ordinary” droughts by applying a criterion of a rapid intensification from near-normal soil moisture to drought conditions over a period of a few weeks. Here, we use such a definition to generate the first spatially distributed, long-term climatology of flash droughts across Australia, which we derive using a suite of indices that capture both the supply and the demand perspectives of drought: evaporative demand describes the atmospheric demand for moisture from the surface; precipitation, the supply of moisture from the atmosphere to the surface; and evaporative stress, the supply of moisture from the surface relative to evaporative demand.

Regardless of metric-based definition, flash droughts are observed across all seasons. They can terminate as rapidly as they start, but in some cases can eventuate in a seasonal-scale drought. We show that flash-drought variability and its prevalence can be related to ENSO phases, which suggests an opportunity for enhanced seasonal-scale prediction. We examine a case study in the Wimmera Region of southeast Australia (around the South Australia / Victoria border), we show that monitoring precipitation is less useful for capturing the onset of flash drought. Instead, indices that capture the demand perspective of drought--such as the Evaporative Demand Drought Index (EDDI) and Evaporative Stress Index (ESI)--are more useful for monitoring flash-drought development.

How to cite: Hobbins, M., Parker, T., Gallant, A., and Hoffmann, D.: Flash drought in Australia: deriving a long-term climatology from drought metrics based on precipitation, evapotranspiration, and evaporative demand., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16380, https://doi.org/10.5194/egusphere-egu21-16380, 2021.

Taylor Grace, Jordan Christian, and Jeffery Basara

Flash droughts and heat waves have substantial impacts on agriculture, socioeconomics, and human health. The combined influence of these two events exacerbate the damage to several sectors. The positive feedback between drought and heat waves has been previously studied, but the connection between flash drought and heat waves (or record temperatures) has only been investigated to occur roughly at the same temporal period. Further understanding the compound and cascading impacts of flash droughts and heat waves could potentially enhance monitoring and/or predictability of flash drought events benefiting subseasonal-to-seasonal forecasts, minimize human mortality, and prevent agricultural yield loss. We present a novel approach to analyzing compound and cascading impacts from the flash drought-heat wave relationship by investigating multiple case studies (e.g., 1950s drought event, 2011-2012 U.S. flash drought, and 2019 U.S. flash drought). Several reanalysis datasets were utilized to examine the intensity, temporal duration, and spatial extent relationships between flash drought and heat wave conditions during the case study events. We define heat waves using the following framework which incorporates classifications employed in previous studies; one classification is dependent on a relative threshold (i.e., 95th percentile) applied to daily maximum and minimum temperatures, whereas the second part of the definition utilizes heat index under the same relative threshold. In order for a heat wave event to begin, this definition must hold true for three or more consecutive days for a specified spatial method. Our flash drought analysis incorporated a percentile methodology based on standardized evapotranspiration stress ratio (SESR). Comparison between intensity, spatial extent, and temporal duration relationships for compound and cascading events were of particular focus for this study. A mixture of compound and cascading events were found within one flash drought study (i.e., 2011-2012 flash drought). As such, we further hypothesize that the intensity and temporal duration will differ between compound and cascading events. Yet, we expect the spatial extent to remain positively correlated as shown from previous studies.

How to cite: Grace, T., Christian, J., and Basara, J.: Flash Drought and Heat Waves: An Overview of Cascading and Compound Events, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6614, https://doi.org/10.5194/egusphere-egu21-6614, 2021.

Nadeem Tariq, Akif Rahim, Farhan Aziz, and Muhammad Yousaf

Drought is a complex and less understandable natural phenomenon. Historical characteristics of droughts helps to understand the dynamics of the regional drought patterns. Numerous studies have predicted that the Chitral-Kabul River Basin (CKRB) is prone poses to serious threat due to global warming. This may endanger 10 million in habitants. The aim of this study is to revisit the characteristics of droughts in Kabul watershed, shared by Pakistan and Afghanistan. The monthly Standardized Precipitation-Evapotranspiration Index (SPEI) grided data (0.5o 0.5o) generated by climate research unit (CRU)version 4 has been used for study during the period 1901–2018. The four characteristics features i.e.  Areal extend, Frequency, Duration and Severity has been studied on spatial and temporal scale. The results show that the Kabul Basin has experienced an increasing extent of severe drought between 1940 and 1960, which increased further after the year 2000. The frequency of drought events in the northern part of the basin is much higher than in the southern part of the basin. Whereas the duration of the drought shows a declining trend in the northern part of the basin. The southern and western parts of the basin experienced a growing trend in the severity drought. At the same time, the incidence of consecutive droughts in the Kabul River basin has also increased. This study suggests that dry conditions in Kabul river basin have been enhanced in recent years. Overall, this study confirms the importance of SPEI for assessing the effects of regional drought.

Keywords: Drought analysis, Frequency, Severity, Duration, Kabul river basin

How to cite: Tariq, N., Rahim, A., Aziz, F., and Yousaf, M.: Space and Time Characteristics of Droughts in Kabul River Basin., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-392, https://doi.org/10.5194/egusphere-egu21-392, 2021.

FD studies using weather/hydrological model data
Li xu

As one key innovation in the NOAA hydrological modeling, the National Water Model (NWM) was recently upgraded to v2.0 in June 2019. The NWM could provide not only the streamflow prediction for hydrological guidance, but also the real-time high-resolution land state analysis and assimilation.  Based on the NWM v2.0 retrospective analysis from 1993 to 2018, we evaluated NWM soil moisture (SM) and evapotranspiration(ET) for the drought monitor application.  The Soil Moisture Percentile (SMP) from NWM is compared with the official US drought monitor (USDM) map in major drought events. The drought categories (D0-D4) based on NWM, is quantitively compared with similar drought monitor from the NLDAS2 multi-model ensemble.  A long time-series soil moisture monitor from CPC leaky bucket model is also compared against NWM, to distinguish the importance of the long temporal record vs high spatial resolution for drought monitor. The rapid intensification or rapid onset drought, i.e. flush drought, is also investigated by the temporal change of the SMP. The preliminary results indicated the NWM could well capture the major droughts during 2000 to 2018. In particular, the flash droughts indicated by the NWM could provide one to three weeks early warning than the USDM map, show great potential in the future application for flash drought detection, monitor and prediction.


How to cite: xu, L.: Early detection of the flash drought: a preliminary study by the National Water Model, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1315, https://doi.org/10.5194/egusphere-egu21-1315, 2021.

Noemi Vergopolan, Julio E. Herrera-Estrada, Justin Sheffield, Lyndon Estes, and Eric F. Wood

Drought is the most threatening natural hazard for agriculture. Between 1983 and 2003, drought led to a cumulative agriculture production loss of 166 billion U.S. dollars globally, thus monitoring and forecasting capabilities are essential for adaptation and preparedness. Soil moisture simulations play an indispensable role in reconstructing historic drought conditions and predicting future scenarios. However, there is a spatial scale gap between the resolution of soil moisture-based drought indices (10–25 km) and typical farm field sizes (1–2 ha). This spatial-scale gap hampers drought indices’ applicability for capturing and monitoring flash and local-scale agricultural droughts, particularly over heterogeneous landscapes and smallholder farming. 

This work presents a novel approach that uses hyper-resolution modeling and machine learning to identify droughts, characterize their topologies, and evaluate detection rates. We present a case-study for Zambia, where we simulated the root zone soil moisture at a daily 30-m resolution between 1981–2018 using the HydroBlocks land surface model. Using these simulations, we computed a weekly percentile-based drought index, defining it as in drought when the index dropped below the 20th percentile. Given the space and time location of the drought conditions, we applied a Hierarchical Density-Based Spatial Clustering of Applications with Noise (HDBSCAN) algorithm to determine space- and time-connected clusters/events. We analyzed the topology of 7712 drought events, with a minimum 10-km2 coverage and two weeks duration. Our results showed that 88% were flash droughts (lasting less than one month), 82% were local events (less than 1,000 km2), and 62% were local flash droughts happening during the growing season (October–May). We performed a synthetic spatial scaling analysis to compute the change in detection rate across spatial resolutions. When considering drought conditions over at least 1,000-km2, our results showed that 10–50 km spatial resolution data missed 19 to 44 % of drought conditions captured with 30-m resolution data. This work demonstrates how current capabilities are likely underestimating droughts, and it highlights the urgent need to monitor and forecast droughts at a high spatial resolution. Such refined data can critically benefit local-scale drought mitigation and food security policy design.

How to cite: Vergopolan, N., Herrera-Estrada, J. E., Sheffield, J., Estes, L., and Wood, E. F.: Improved detection of flash droughts using hyper-resolution hydrological modeling, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6972, https://doi.org/10.5194/egusphere-egu21-6972, 2021.

Future FD perspectives and challenges
Brandi Gamelin, Jiali Wang, and V. Rao Kotamarthi

Flash droughts are the rapid intensification of drought conditions generally associated with increased temperatures and decreased precipitation on short time scales.  Consequently, flash droughts are responsible for reduced soil moisture which contributes to diminished agricultural yields and lower groundwater levels. Drought management, especially flash drought in the United States is vital to address the human and economic impact of crop loss, diminished water resources and increased wildfire risk. In previous research, climate change scenarios show increased growing season (i.e. frost-free days) and drying in soil moisture over most of the United States by 2100. Understanding projected flash drought is important to assess regional variability, frequency and intensity of flash droughts under future climate change scenarios. Data for this work was produced with the Weather Research and Forecasting (WRF) model. Initial and boundary conditions for the model were supplied by CCSM4, GFDL-ESM2G, and HadGEM2-ES and based on the 8.5 Representative Concentration Pathway (RCP8.5). The WRF model was downscaled to a 12 km spatial resolution for three climate time frames: 1995-2004 (Historical), 2045-2054 (Mid), and 2085-2094 (Late).  A key characteristic of flash drought is the rapid onset and intensification of dry conditions. For this, we identify onset with vapor pressure deficit during each time frame. Known flash drought cases during the Historical run are identified and compared to flash droughts in the Mid and Late 21st century.

How to cite: Gamelin, B., Wang, J., and Kotamarthi, V. R.: Assess 21st century Flash Drought in the United States using high resolution regional climate models, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13102, https://doi.org/10.5194/egusphere-egu21-13102, 2021.

Xing Yuan, Yumiao Wang, and Miao Zhang

Conventional droughts are creeping climate anomalies that take months or years to fully develop, causing devastating impact silently. In contrast, flash droughts have been considered as a type of drought with more rapid onset, develop and terminate at a shorter time scale. There has been a hot debate on the definition of flash drought, and whether it is necessary to investigate the impact of flash drought given the duration is usually shorter than conventional drought. We clarify that flash drought is not a monster, while it has complete onset and recovery processes as conventional drought. Flash drought expands the conventional drought from seasonal-to-decadal scales to sub-seasonal scale, where synoptic land-atmospheric coupling might become critical for its onset. Focusing on a once-in-a-century flash drought in late summer of 2019, we analyze the latest Coupled Model Intercomparison Project Phase 6 (CMIP6) climate model data and show that climate change caused by anthropogenic activities (e.g., emissions of greenhouse gases and aerosols, land use change, etc) has increased the likelihood of such drought onset speed by 42±19%. A further analysis based on CMIP6 multi-model ensemble simulations over the global land areas shows that there was no significant trend in frequency during 1850-1970, but flash drought became more frequency in the recent 40 years. All these results suggest that climate change accelerates the drought development speed, and flash drought might become as a new normal in a warming climate. The eco-hydrological impact of this “new normal” will also be discussed by investigating FLUXNET in-situ observations and MODIS satellite retrievals.

How to cite: Yuan, X., Wang, Y., and Zhang, M.: Flash drought as a new normal in a warming climate, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8555, https://doi.org/10.5194/egusphere-egu21-8555, 2021.