Recent Drought Events Research Articles

Large tree mortality leads to major aboveground biomass decline in a tropical forest reserve.

Humans are transforming the ecology of the Earth through rapid changes in land use and climate. These changes can affect tropical forest structure, dynamics and diversity. While numerous studies have focused on diversity metrics, other aspects of forest function, such as long-term biomass dynamics, are often less considered. We evaluated plant community structure change (i.e., abundance, diversity, composition, and aboveground biomass) in a 2.25ha forest dynamics plot located within a ~ 365ha reserve in southern Costa Rica. We censused, mapped and identified to species all plants ≥ 5cm diameter at breast height (DBH) in three surveys spanning 2010-2020. While there were no changes in late-successional species diversity, there were marked changes in overall species composition and biomass. Abundance of large (≥ 40cm DBH) old-growth dense-wooded trees (e.g., Lauraceae, Rosaceae) decreased dramatically (27%), leading to major biomass decline over time, possibly driven by recent and recurrent drought events. Gaps created by large trees were colonized by early-successional species, but these recruits did not make up for the biomass lost. Finally, stem abundance increased by 20%, driven by increasing dominance of Hampea appendiculata. While results suggest this reserve may effectively conserve overall plant diversity, this may mask other key shifts such as large aboveground biomass loss. If this pattern is pervasive across tropical forest reserves, it could hamper efforts to preserve forest structure and ecosystem services (e.g., carbon storage). Monitoring programs could better assess carbon trends in reserves over time simply by tracking large tree dynamics.

A multi-century July-August streamflow reconstruction of Metro Vancouver's water supply contribution from the Capilano and Seymour watersheds in southwestern British Columbia, Canada

Recent summer water shortages in Metro Vancouver are the result of unanticipated changes in the timing of regional snowmelt and rising summer temperatures. Continuing shortfalls over the next century would pose a significant challenge for water supply management decisions. To understand the magnitude of recent drought events in the context of those that happened in the past, we developed a tree-ring reconstruction of regionalised July–August streamflow to 1711 for Metro Vancouver’s Capilano and Seymour watersheds. We used the annual tree-ring widths of mountain hemlock (Tsuga mertensiana (Bong.) Carr.) and Pacific silver fir (Abies amabilis Douglas ex J. Forbes) trees exhibiting a relationship to the seasonal snowpack as proxies for the nival component of streamflow in a regression model. The model indicates that more multi-year, below-average, streamflow departures occurred during the instrumental record than over the 1711–1992 reconstruction period. The El Niño-Southern Oscillation was significantly (p < 0.05) associated with both reconstructed and measured streamflow for the study region. Similarly, seasonal Pacific Decadal Oscillation demonstrated strong statistical relationships (p < 0.05) with measured streamflow. Over the duration of the reconstruction, significant decadal and multi-decadal periodicities were also observed. The research places the Metro Vancouver water supply in a longer-term context than was previously possible and offers a basis for advancing water supply planning decisions in the context of a rapidly changing climate.

The variable climate response of Rocky Mountain bristlecone pine (Pinus aristata Engelm.)

Recent increases in temperature over the semi-arid western United States have been shown to exacerbate drought, reducing streamflow, and increasing stress on ecosystems. Our understanding of the role temperature played during drought in the more distant past is far from complete. While numerous tree-ring proxy records of moisture provide evidence for past extreme droughts in this region, few contemporaneous tree-ring proxy records of temperatures exist. This limits our ability to evaluate the variable influence of temperature on drought over past centuries and to contextualize the present interplay of moisture and temperature during more recent drought events. It is also important to understand the complexity of climatic interactions that produced drought under natural variability prior to evaluating the potential impacts of future climate change. In response to this knowledge gap, we undertook the first extensive evaluation of climate sensitivity in Rocky Mountain bristlecone pine (Pinus aristata Engelm.), focusing on the potential for developing new multi-century proxy records of both temperature and precipitation. We isolated dominant patterns of growth variability among trees from ten ring-width datasets across the Southern Rocky Mountains of Colorado and New Mexico and assessed their response to climate. We utilized both an empirical orthogonal function (EOF) analysis and a modified form of hierarchical cluster analysis to produce time series representing growth patterns in P. aristata. The results indicate a widespread June drought stress signal with a high potential for multi-millennial reconstruction. We also found a positive minimum temperature response during late summer, evident only at lower frequency and co-occurring at locations with the June drought stress signal. The potential for temperature reconstruction will require further investigation into the physiological linkages between P. aristata and climate variability. The presence of multiple climate responses within P. aristata sampling sites highlights the need for particular care when including P. aristata in regional climate reconstructions.

Application of Signal Processing in Tracking Meteorological Drought in a Mountainous Region

This study addresses the application of signal processing in the evaluation of meteorological drought associated with monthly precipitation time series. Several drought indices and a Haar wavelet decomposition (WD) with ten components are implemented in the evaluation of the monthly precipitation of a mountainous region called Mount Uludag in Turkey. Monthly precipitation time series in three meteorological stations at the summit and foothills are used. The Standardized Precipitation Index (SPI) is used at monthly, annual, and 12- and 48-month moving average time frames as the benchmark to investigate the drought patterns. The results obtained by the WD and SPI are then confirmed using the Z-score index (ZSI) at monthly and annual scales, together with the modified China Z-index (MCZI) and rainfall anomaly index (RAI) at a monthly scale. Changes in the moments of the distribution, correlation analysis, mutual information, and power spectrum are applied to investigate the nature of the relationship between the sequences of precipitation events in time and space. The temporal correlation analysis, together with the mutual information, showed that the system has a short-term memory with strong seasonality. Similarly, the power spectra depicted major seasonality at 1, 3, 5, 6, 12, 22, and 60 months in the precipitation time series. It is concluded that the recent drought events have an infrequent nature, which altered the sinusoidal patterns of the large-scale events. The SPI-48 and the WD showed that declines are strongly related to the large-scale cycles, but the decline patterns are more related to the station located at the mountain summit.

Past megadroughts in central Europe were longer, more severe and less warm than modern droughts

Megadroughts are notable manifestations of the American Southwest, but not so much of the European climate. By using long-term hydrological and meteorological observations, as well as paleoclimate reconstructions, here we show that central Europe has experienced much longer and severe droughts during the Spörer Minimum (~AD 1400–1480) and Dalton Minimum (~AD 1770–1840), than the ones observed during the 21st century. These two megadroughts appear to be linked with a cold state of the North Atlantic Ocean and enhanced winter atmospheric blocking activity over the British Isles and western part of Europe, concurrent with reduced solar forcing and explosive volcanism. Moreover, we show that the recent drought events (e.g., 2003, 2015, and 2018), are within the range of natural variability and they are not unprecedented over the last millennium.

A High‐Resolution Land Data Assimilation System Optimized for the Western United States

AbstractThe Western Land Data Assimilation System (WLDAS) is a custom instance of the NASA Land Information System that combines land surface parameters, meteorological forcing data, and satellite products within a land surface model to produce daily estimates of the water and energy budget variables for the western United States. WLDAS was configured through discussions with partners, with the goal of groundwater sustainability planning for the state of California in mind. The publicly available output dataset has a 1‐km grid resolution and spans 1979–present, which makes it suitable for water resources assessments. The data are also able to contextualize the recent drought events in California. Assimilation of Leaf Area Index, which is demonstrated herein to improve simulation over agricultural areas in California, specifically in terms of evapotranspiration in irrigation regions, will be included along with other data assimilation in subsequent releases of WLDAS.

Sub‐Seasonal Tree‐Ring Reconstructions for More Comprehensive Climate Records in U.S. West Coast Watersheds

AbstractTree‐ring records of preinstrumental hydroclimate, which contribute needed context for understanding recent drought and flood events, typically provide one value per year that represents the entire year or one particular season. This may introduce a seasonal bias to the records or omit seasonally variable moisture. Here, I use tree‐ring records to reconstruct precipitation and runoff in 28 U.S. West Coast watersheds for running 1, 3, 6, and 12‐month intervals. When compared on a yearly basis, the Monthly and Four‐Season models have higher overall skill and better extreme capture in most basins than the Cool‐Warm and Annual models. The Monthly and Four‐Season versions also decrease model error in years with more intense precipitation and retain more variability in the preinstrumental period. Improved capture of year‐round moisture can provide a more complete representation of the preinstrumental past and strengthen capacity to study shorter‐duration and season‐specific events like atmospheric rivers.

A multidisciplinary drought catalogue for southwestern Germany dating back to 1801

Abstract. Droughts are multidimensional hazards that can lead to substantial environmental and societal impacts. To understand causes and impacts, multiple perspectives need to be considered. Many studies have identified past drought events and investigated drought propagation from meteorological droughts via soil moisture to hydrological droughts, and some studies have included the impacts of these different types of drought. However, it is not certain whether the increased frequency and severity of drought events in the past decade is unprecedented in recent history. Therefore, we analyze different droughts and their impacts in a regional context using a multidisciplinary approach. We compile a comprehensive and long-term dataset to investigate possible temporal patterns in drought occurrence and place recent drought events into a historical context. We assembled a dataset of drought indices and recorded impacts over the last 218 years in southwestern Germany. Meteorological and river-flow indices were used to assess the natural drought dynamics. In addition, tree-ring data and recorded impacts were utilized to investigate drought events from an ecological and social perspective. Since 1801, 20 extreme droughts have been identified as common extreme events when applying the different indices. All events were associated with societal impacts. Our multi-dataset approach provides insights into similarities but also the unique aspects of different drought indices.

Model evaluation and uncertainties in projected changes of drought over northern China based on CMIP5 models

AbstractIn recent decades, severe and long duration drought events have serious impacts on northern China. Consequently, this study is motivated by investigating the projection and uncertainties of drought change over northern China based on 20 CMIP5 multi‐model ensemble (AMME) and best multi‐model ensemble (BMME) under middle and high emission scenarios. BMME selected in term of the spatial patterns and interannual variability of aridity index (AI) against the observations shows better performance on the simulation of dryland especially for hyper‐arid areas in Northwest China (NWC) and sub‐humid regions in North China (NC). In the middle of 21st century, the projections from two model ensembles illustrate the aggravation of drought in loess plateau and west of Xinjiang but reduction of acridity over NWC. Northeast China (NEC) becomes more arid under RCP8.5 that is sensitive with the high emission. The uncertainties increase between two model ensembles at the end of 21st century when the opposite trend can be found over NC under RCP4.5 and NEC under RCP8.5, respectively. The increasing rate of precipitation and PET is the key factor for AI change. The larger contribution of precipitation than PET results in the humid tendency over NWC. Moreover, the equivalent contributions of precipitation and PET induce the increased uncertainties in AI change over NC and NEC. Similarly, the temporal evaluation of AI indicates decreasing trend of drought over NWC but the large uncertainties can be found after middle of this century over NEC and in the early of the century over NC.

The Groundwater Drought Initiative (GDI): Analysing and understanding groundwater drought across Europe

Abstract. In Europe, it is estimated that around 65 % of drinking water is extracted from groundwater. Worryingly, groundwater drought events (defined as below normal groundwater levels) pose a threat to water security. Groundwater droughts are caused by seasonal to multi-seasonal or even multi-annual episodes of meteorological drought during which the drought propagates through the river catchment into the groundwater system by mechanisms of pooling, lagging, and lengthening of the drought signals. Recent European drought events in 2010–2012, 2015 and 2017–2018 exhibited spatial coherence across large areas, thus demonstrating the need for transboundary monitoring and analysis of groundwater level fluctuations. However, such monitoring and analysis of groundwater drought at a pan-European scale is currently lacking, and so represents a gap in drought research as well as in water management capability. To address this gap, the European Groundwater Drought Initiative (GDI), a pan-European collaboration, is undertaking a large-scale data synthesis of European groundwater level data. This is being facilitated by the establishment of a new network to co-ordinate groundwater drought research across Europe. This research will deliver the first assessment of spatio-temporal changes in groundwater drought status from ∼1960 to present, and a series of case studies on groundwater drought impacts in selected temperate and semi-arid environments across Europe. Here, we describe the methods used to undertake the continental-scale status assessment, which are more widely applicable to transboundary or large-scale groundwater level analyses also in regions beyond Europe, thereby enhancing groundwater management decisions and securing water supply.

Spatiotemporal analysis of meteorological drought in a Mediterranean dry land: case of the Cheliff basin–Algeria

Drought is amongst the most significant natural hazards threatening human societies and ecosystems. The present study concerns monitoring the spatiotemporal evolution of meteorological drought in the Cheliff Basin northwestern Algeria based on available rainfall data that covers a period of 73 years from 1936 to 2008. The procedure employed herein involved analyzing the homogeneity of rainfall series along with the calculation of the standardized precipitation index (SPI). Results of homogeneity analysis revealed important inter-annual variability and a generalized decreasing trend of annual rainfall amounts accompanied by shifts of stationarity observed between 1974 and 1980. The analysis of the temporal evolution of the SPI revealed significant changes in the characteristics of drought events, arguably after 1976 the observed drought events were characterized by significantly higher intensities, durations and frequencies. The spatial distribution maps of mean SPI before and after 1976 generated in a geographic information system (GIS), enhanced the appreciation of the significant changes of drought conditions during the studied period and, more important, emphasized the strong spatial component of the recent drought events. The results of this study may help decision-makers of the local authorities in planning and managing water resources over the Cheliff basin.

Quantifying Ground Subsidence Associated with Aquifer Overexploitation Using Space-Borne Radar Interferometry in Kabul, Afghanistan

Rapid population growth combined with recent drought events and decades of political instability have left the residents of Kabul facing water scarcity, significantly relying on groundwater. Groundwater overexploitation might have induced various magnitudes of ground subsidence, however, to date, no comprehensive study of ground subsidence in Kabul has been conducted. In this study, we investigated the spatio-temporal evolution of ground deformation phenomena and its main governing processes in Kabul from 2014 to 2019 using C-Band Sentinel-1 derived Interferometric Synthetic Aperture Radar (InSAR) time-series from both ascending and descending orbits to extract the two-dimensional (2D) surface displacement field. Four subsidence bowls were distinguished with highly variable spatial extents and deformation magnitudes over four separate aquifer basins, with the maximum value of −5.3 cm/year observed in the Upper Kabul aquifer basin. A wavelet analysis suggests that there is a strong correlation between the groundwater level variations and subsidence. Investigation of hydrogeological data further reveals that the observed subsidence could be attributed to the presence of highly compressible clayey soils. This detailed space-borne regional survey provides new insights into the main governing mechanism of land subsidence in Kabul and may direct better mitigation plans of potential hazards.

Measuring the Transaction Costs of Historical Shifts to Informal Drought Management Institutions in Italy

Coase shows how costly resources are (re)allocated via costly institutions, and that transaction costs must therefore be positive. However, Coase did not elaborate on transitions between institutions which incur positive transaction costs that are characterized by numerous institutional complementarities; that is, feedback loops that inform the need for, and pathways toward, institutional change. Economic investigations of complementary modes of (re)allocation are rarely undertaken, let alone studies of transitions between modes. However, modes of (re)allocation that achieve similar results at less cost are generally viewed as having production-raising value. This paper measures the costs of transitioning drought management institutions in Italy toward informal, participatory, and consensus-based approaches during several recent drought events. The chosen model is Drought Steering Committees, which offer a substitute for current formal (less flexible) planning approaches, and where lower transaction costs that are associated with the transition are inferred. Our results highlight the relevance of empirical assessments of ‘costly’ transitions based on a historical study of transaction costs, as well as supporting previous works that highlight the value of contextual analysis in economic studies, in order to identify the benefits of institutional investment.

Causes and Changes of Drought in China: Research Progress and Prospects

Drought is one of the most serious and extensive natural hazards in the world. Subject to monsoon climate variability, China is particularly influenced by drought hazards, especially meteorological drought. Based on a comprehensive understanding of the current status of international drought research, this paper systematically reviews the history and achievements of drought research in China since the founding of the People’s Republic of China, from four main perspectives: characteristics and spatiotemporal distribution of historical and recent drought events, drought formation mechanism and change trend, drought hazard risk, and the particular flash drought. The progress and problems of drought research in China are analyzed and future prospects are proposed, with emphasis on the multi-factor synergetic effect for drought formation; the effect of land-atmosphere interaction; identification, monitoring, and prediction of flash drought; categorization of drought and characteristics among various types of drought; the agricultural drought development; drought response to climate warming; and assessment of drought hazard risks. It is suggested that strengthening scientific experimental research on drought in China is imperative. The present review is conducive to strategic planning of drought research and application, and may facilitate further development of drought research in China.

Uncovering episodic influence of oceans on extreme drought events in Northeast Brazil by ordinal partition network approaches

Since 2012, the semiarid region of Northeast Brazil (NEB) has been experiencing a continuous dry condition imposing significant social impacts and economic losses. Characterizing the recent extreme drought events and uncovering the influence from the surrounding oceans remain to be big challenges. The physical mechanisms of extreme drought events in the NEB are due to varying interacting time scales from the surrounding tropical oceans (Pacific and Atlantic). From time series observations, we propose a three-step strategy to establish the episodic coupling directions on intraseasonal time scales from the ocean to the precipitation patterns in the NEB, focusing on the distinctive roles of the oceans during the recent extreme drought events of 2012-2013 and 2015-2016. Our algorithm involves the following: (i) computing drought period length from daily precipitation anomalies to capture extreme drought events; (ii) characterizing the episodic coupling delays from the surrounding oceans to the precipitation by applying the Kullback-Leibler divergence (KLD) of complexity measure, which is based on ordinal partition transition network representation of time series; and (iii) calculating the ratio of high temperature in the ocean during the extreme drought events with proper time lags that are identified by KLD measures. From the viewpoint of climatology, our analysis provides data-based evidence of showing significant influence from the North Atlantic in 2012-2013 to the NEB, but in 2015-2016, the Pacific played a dominant role than that of the Atlantic. The episodic intraseasonal time scale properties are potential for monitoring and forecasting droughts in the NEB in order to propose strategies for drought impacts reduction.

Recent droughts in the Kruger National Park as reflected in the extreme climate index

Associated with the 2015/2016 El Niño, extreme drought occurred over the Lowveld of South Africa. The area includes the Kruger National Park (KNP). Significant die-offs of a mega herbivore species occurred, corroborated by census data in KNP. The drought situation and impact were likely exacerbated by a frequency of recorded extreme temperatures never observed before together with increased numbers of herbivores. Here we consider this recent drought and places it into context with previous El Niño-related droughts. We use an index of climate extremes, based simply on derivatives of temperature and rainfall, to identify the most extreme recent drought events and consider other observed datasets to verify the ability of the index to identify the most extreme cases. We also further explore the characteristics of extreme droughts in the KNP, according to insights gained by applying the index.

Drought and food security in the middle east: An analytical framework

Natural disasters may act as harmful causes of food insecurity in the Middle East. Frequent drought events, water scarcity, and unsustainable intensive agricultural practices may impact food security in the region. This paper investigates a causal relationship between drought and food security across the Middle East. Meteorological, agricultural, and hydrological droughts are analyzed at multiple timescales over the region for seven decades during the period of 1948–2017. We simulate food security in the Middle East as a function of drought (representing a water stress factor) as well as several other socio-economic drivers. A Bayesian approach is implemented to integrate these drivers in order to accurately predict food security in the region. Results reveal that hydrological drought is the most intensified drought type over the region, especially in Egypt, during the study period. Moreover, the results demonstrate the significant impacts of livestock, population growth, agricultural products, and drought on food security in the Middle East. Our findings further indicate that the agricultural products decreased in the Middle East following the recent drought event that happened in 2010.

Extremeness of recent drought events in Switzerland: dependence on variable and return period choice

Abstract. The 2018 drought event had severe ecological, economic, and social impacts. How extreme was it in Switzerland? We addressed this question by looking at different types of drought, including meteorological, hydrological, agricultural, and groundwater drought, and at the two characteristics deficit and deficit duration. The analysis consisted of three main steps: (1) event identification using a threshold-level approach, (2) drought frequency analysis, and (3) comparison of the 2018 event to the severe 2003 and 2015 events. In Step 2 the variables precipitation, discharge, soil moisture, and low-flow storage were first considered separately in a univariate frequency analysis; pairs of variables were then investigated jointly in a bivariate frequency analysis using a copula model for expressing the dependence between the two variables under consideration. Our results show that the 2018 event was especially severe in north-eastern Switzerland in terms of soil moisture, with return periods locally exceeding 100 years. Slightly longer return periods were estimated when discharge and soil moisture deficits were considered together. The return period estimates depended on the region, variable, and return period considered. A single answer to the question of how extreme the 2018 drought event was in Switzerland is therefore not possible – rather, it depends on the processes one is interested in.

The limits of resilience in US community responses to recent drought events

ABSTRACT Drought threatens many facets of community life, including food security, agricultural and tourism livelihoods, recreation, esthetic appeal, and social cohesion. Many policy responses to a drought crisis are enacted at the municipal level, including voluntary water conservation, burn bans, outdoor watering restrictions, municipal water source expansion, and drought contingency plans. Though communities have many reasons to limit their vulnerability to future drought events, it is questionable whether these measures do. In a comprehensive survey of more than 450 news media reports on drought response in communities across the United States, this study defines 27 common response approaches. Results show that responses tend to be short-term emergency coping measures. Temporary water restrictions may not leave communities prepared to address future water crises. Furthermore, restrictions can create tension amongst levels of governance. Recommendations based in resilience theory suggest that collaboration, engagement, and forward-looking planning processes are necessary to address community drought vulnerability.

Role of Moisture Transport and Recycling in Characterizing Droughts: Perspectives from Two Recent U.S. Droughts and the CFSv2 System

Abstract We investigate the role of moisture transport and recycling in characterizing two recent drought events in Texas (2011) and the Upper Midwest (2012) by analyzing the precipitation, evapotranspiration, precipitable water, and soil moisture data from the Climate Forecast System version 2 (CFSv2) analysis. Next, we evaluate the CFSv2 forecasts in terms of their ability to capture different drought signals as reflected in the analysis data. Precipitation from both sources is partitioned into recycled and advected components using a moisture accounting–based precipitation recycling model. All four variables reflected drought signals through their anomalously low values, while precipitation and evapotranspiration had the strongest signals. Drought in Texas was dominated by the differences in moisture transport, whereas in the Upper Midwest, the absence of strong precipitation-generating mechanisms was a crucial factor. Reduced advection from the tropical and midlatitude Atlantic contributed to the drought in Texas. The Upper Midwest experienced reduced contributions from recycling, terrestrial sources, the midlatitude Pacific, and the tropical Atlantic. In both cases, long-range moisture transport from oceanic sources was reduced during the corresponding drought years. June and August in Texas and July and August in the Upper Midwest were the driest months, and in both cases, drought was alleviated by the end of August. Moisture from terrestrial sources most likely contributed to alleviating drought intensity in such conditions, even with negative anomalies. The forecasts showed noticeable differences as compared to the analysis for multiple variables in both regions, which could be attributed to several factors as discussed in this paper.