Dry Events Research Articles

Impact of drought conditions on air pollution over Turkey

AbstractAs a natural disaster, drought affects many sectors such as agriculture and hydrology, as well as having an effect on air quality. In terms of air pollution, drought can reduce wet scavenging of pollutants and change their chemical production/loss and lifetime. This study investigates the relationship between drought events and air pollutants in Turkey. As a drought indicator, the Standardized Precipitation‐Evapotranspiration Index (SPEI)‐1 monthly values for dry (SPEI < −0.99), normal (−0.99 < SPEI < 0.99) and wet (SPEI < 0.99) conditions were used to investigate the changes in PM10, PM2.5, O3 concentration levels. Monthly mean PM10 values of 80 stations for the period 2010–2018, PM2.5 and O3 values of 10 and 12 stations, respectively, were used for the analysis throughout the 2014–2018 period. According to the results, while frequency occurrence of normal conditions decreased in the last period (2010–2018) when compared to the first (1901–2009), drought conditions have significantly increased in each region of Turkey in the last decade. Highest increase in drought events occurred in the inner/southern parts of Turkey. In dry events, while PM10 levels of the stations show above‐normal values, highest regional increase in PM10 was found in the Central Anatolia (CAR), Mediterranean (MeR), Aegean (AR) and Marmara (MR) regions of the country. In fall, high daily temperatures and cloudless days in CAR and MeR regions are seen under deep surface low over continental Europe and surface high over Caspian Sea, which result in severe dryness events and associated high PM10 values in the air quality stations. On the other hand, as a consequence of the expanding Asiatic monsoon low to the eastern part of Turkey, significant amount of moisture is transferred from the Eastern Mediterranean Sea surface to the CAR and MeR regions by southerly flows (wetness SPEI conditions in fall) and cause to appear below‐normal PM10 values in the southern stations.

Continuous precipitation loss induced more pronounced compositional and diversity changes in the lotic phytobenthos than one-off drought events

Changing precipitation dynamics is one of the most important mechanisms that, by affecting the water regime, modifies the physical and chemical environment of aquatic assemblages. Thus, hydrological extremes can be considered as key drivers that shape algal assemblages and lead to diversity changes even in large rivers. Here, we investigated the long-term changes in the benthic diatom composition of the Rába River (River Raab), the watershed of which experienced continuous loss of precipitation in the last five years. We aim to answer the main question: Do one-off drought events and trend-like (continuous) precipitation decrease result in similar changes within diatom assemblages of this perennial river? Because, it has been already demonstrated that resilience and resistance of assemblages may vary depending on whether the drought occurs regularly or only occasionally. Our results demonstrated that one-off dry events hardly affected either assemblages’ composition or biodiversity. In contrast, continuously decreasing precipitation (drying period) had a pronounced effect on taxa and trait distribution and resulted in a significant decrease in taxonomic diversity and in functional richness. It is important to stress that the observed deteriorating diversity anticipates that a lasting drought period is likely to upset the ecological balance of the ecosystem and lead to remarkable natural damage. Since the climate scenarios project extremes in water regime in the near future, including longer periods of low precipitation, any knowledge that predicts changes in microflora can help to develop action plans by authorities to save lotic ecosystems.

Observing the recent floods and drought in the Lake Victoria Basin using Earth observations and hydrological anomalies

The Lake Victoria Basin, home of Africa’s largest freshwater lake, experienced extensive floods in 2019–2020 and anomalous drought conditions in early 2022. Both antithetical hydrological events raised concerns for an estimated 35 million people within the basin who are vulnerable to these continually recurrent hydrometeorological extremes. While there is a need for high-resolution spatial and temporal hydrological monitoring, in-situ observations are limited and insufficient within the basin. This study assesses the capability of publicly available Earth observations and models to capture the occurrence of recent hydrological extremes within the Lake Victoria Basin. Spatial and temporal comparisons of the following hydrological variables are conducted within the Lake Victoria Basin from June 2002 – June 2022: precipitation, evapotranspiration, runoff, soil moisture, lake height, and total water storage anomaly (TWSA). Results from the time series and spatial analyses confirm that the anomalous wet and dry events respectively occurred from October 2019 – March 2020 and November 2021 – March 2021. The observations also indicated a quick recovery from the drought event by June 2022. Additionally, a comparison of 9-km soil moisture and 1-km downscaled near-surface soil moisture products improves understanding of wetness spatial variability within the basin. These results were validated using in-situ soil moisture data available through the International Soil Moisture Network, making this the first study to validate the downscaled 1-km soil moil moisture product within the African continent. Methods from this study demonstrate the utility of a diverse array of publicly available Earth observation and model data to improve understanding of recent hydrological anomalies and extreme events within the Lake Victoria Basin. This can be applied to water resources management, particularly in regions lacking sufficient in-situ hydrological data.

Drought increase since the mid-20th century in the northern South American Altiplano revealed by a 389-year precipitation record

Abstract. Given the short span of instrumental precipitation records in the South American Altiplano, longer-term hydroclimatic records are needed to understand the nature of climate variability and to improve the predictability of precipitation, a key natural resource for the socioeconomic development in the Altiplano and adjacent arid lowlands. In this region grows Polylepis tarapacana, a long-lived tree species that is very sensitive to hydroclimatic changes and has been widely used for tree-ring studies in the central and southern Altiplano. However, in the northern sector of the Peruvian and Chilean Altiplano (16–19∘ S) still exists a gap of high-resolution hydroclimatic data based on tree-ring records. Our study provides an overview of the temporal evolution of the late-spring–mid-summer precipitation for the period 1625–2013 CE at the northern South American Altiplano, allowing for the identification of wet or dry periods based on a regional reconstruction from three P. tarapacana chronologies. An increase in the occurrence of extreme dry events, together with a decreasing trend in the reconstructed precipitation, has been recorded since the 1970s in the northern Altiplano within the context of the last ∼4 centuries. The average precipitation over the last 17 years stands out as the driest in our 389-year reconstruction. We reveal a temporal and spatial synchrony across the Altiplano region of dry conditions since the mid-1970s. Independent tree-ring-based hydroclimate reconstructions and several paleoclimatic records based on other proxies available for the tropical Andes record this synchrony. The influence of El Niño–Southern Oscillation (ENSO) on the northern Altiplano precipitation was detected by our rainfall reconstruction that showed past drier conditions in our study region associated with ENSO warm events. The spectral properties of the rainfall reconstruction showed strong imprints of ENSO variability at decadal, sub-decadal, and inter-annual timescales, in particular from the Pacific NIÑO 3 sector. Overall, the recent reduction in precipitation in comparison with previous centuries, the increase in extreme dry events and the coupling between precipitation and ENSO variability reported by this work is essential information in the context of the growing demand for water resources in the Altiplano. This study will contribute to a better understanding of the vulnerability and resilience of the region to the projected evapotranspiration increase for the 21st century associated with global warming.

Hydroclimatic variation over central China during the 4.2 ka event and its implications for cultural transformation

The 4.2 ka climate event, which marks the start of the late Holocene (Meghalayan), is linked to disruption to human cultures across a wide belt from the eastern Mediterranean to the Yangtze River Valley. Here we present a high-resolution stalagmite δ13C record for the middle Yangtze Valley from 4.4 to 3.0 ka BP, and identify two humid pulses and two dry episodes associated with the 4.2 ka event. Similar hydroclimate fluctuations associated with the 4.2 ka event also occur in the Chinese Loess Plateau and Central Plains of China, and may be at least partly responsible for the decline of the Neolithic culture in these regions. Although the 4.2 ka event marks the internationally recognised boundary between the middle and late Holocene, our stalagmite-based evidence shows that regime shift in hydrological variability occurred at ∼3.5 ka BP in the middle Yangtze Valley. Regime shift correlates with inflection points of temperature in the extratropical Northern Hemisphere and tropical El Niño Southern Oscillation (ENSO) systems, indicating teleconnections between local and global climate change at this time. Following regime shift, precipitation fluctuated with a larger amplitude. Two dry events and one humid rebound event correspond to the early, late, and middle phases of the Shang Dynasty, respectively. In summary, we propose that frequent climatic alternations and their increased amplitudes impacted late Holocene cultural evolution in China.

Assessment of the Potential Hydrological Impacts of Climate Change in Quebec—Canada, a Refined Neutral Approach

There is currently much discussion as to whether probabilistic (top–down) or possibilistic (bottom–up) approaches are the most appropriate to estimate potential future climate impacts. In a context of deep uncertainty, such as future climate, bottom-up approaches aimed at assessing the sensitivity and vulnerability of systems to changes in climate variables have been gaining ground. A refined framework is proposed here (in terms of coherence, structure, uncertainty, and results analysis) that adopts the scenario–neutral method of the bottom–up approach, but also draws on some elements of the top–down approach. What better guides the task of assessing the potential hydroclimatological impacts of changing climatic conditions in terms of the sensitivity of the systems, differential analysis of climatic stressors, paths of change, and categorized response of the scenarios: past, changing, compensatory, and critical condition. The results revealed a regional behavior (of hydroclimatology, annual water balances, and snow) and a differential behavior (of low flows). We find, among others, the plausible scenario in which increases in temperature and precipitation would generate the same current mean annual flows, with a reduction of half of the snow, a decrease in low flows (significant, but differentiated between basins), and a generalized increase in dry events.

Longer dry and wet spells alter the stochasticity of microbial community assembly in grassland soils

Climate change is increasing the duration of alternating wet and dry spells. These fluctuations affect soil water availability and other soil properties which are crucial drivers of soil microbial communities. While soil microbial communities have a moderate capacity to recover once a drought ceases, the expected alternation of strongly opposing regimes can challenge their capacity to adapt. Here, we set up experimental grassland mesocosms where precipitation frequency was adjusted along a gradient while holding total precipitation constant. The gradient varied the duration of wet and dry spells from 1 to 60 days during a total of 120 days, where we hypothesized that especially intermediate durations would increase the importance of stochastic community assembly due to frequent alternation of opposing environmental regimes. We examined bacterial and fungal community composition, diversity, co-occurrence patterns and assembly mechanisms across these different precipitation treatments. Our results show that 1) intermediate regimes of wet and dry spells increased the stochasticity of microbial community assembly whereas microbial communities at low and high regimes were subjected to more deterministic assembly, and 2) more persistent precipitation regimes (>6 days duration) reduced the fungal diversity and network connectivity but had little effect on bacterial communities. Collectively, these findings indicate that longer alternating wet and dry events lead to a less predictable and connected soil microbial community. This study provides new insight into the likely mechanisms through which precipitation persistence alters soil microbial communities and their predictability.

Concordant changes in late Holocene hydroclimate across southern Patagonia modulated by westerly winds and the El Niño–Southern Oscillation

AbstractThe southern westerly winds influence weather patterns and water resources across the southern high-latitude regions, with important socioeconomic impacts. The strengthening and poleward migration of these winds since the late 20th century also have implications for regional environmental change, including drought, wildfire, and sea-ice loss. However, it is challenging to recognize the natural variability of the westerlies and predict their future behavior, as those recent changes have been influenced by anthropogenic factors. We present a 4200-yr-long record from a southern Patagonian peatland in a location that is sensitive to changes in the position and/or strength of the westerlies. Our δ13C record shows a 6‰ increasing trend from 4200 to 1200 cal. yr B.P., indicating a progressive, millennial-scale increase in peatland moisture. This long-term trend is attributed to an increase in moisture induced by strengthening southern westerly winds associated with a change in the mean state of the El Niño–Southern Oscillation (ENSO) system. Superimposed on this millennial trend, centennial-scale shifts in hydroclimate persist into modern times. We suggest that a “paleo”–Southern Annular Mode, which is linked to tropical Pacific climate, with dry events contemporaneous with positive phases and La Niña–like conditions, is responsible for this enhanced hydroclimate variability. Overall, our results point to millennial- and centennial-scale changes in hydroclimate during the late Holocene that link tropical Pacific climate variability with the Southern Annular Mode and the southern westerlies, with far-reaching implications for future changes in the southern high latitudes, including CO2 ventilation from the Southern Ocean.

A new hydrological climatic proxy in arid lake sediments: Iodine‑uranium concentrations

Hydrological variation in the past ∼2 kyr is important for understanding the impact and driving forces of climate changes in the present and future, especially in arid areas. Sediment is one of the most useful archives in such a time period, and selection and validation of qualified hydrological proxies is the key point for reconstruction of hydrology in the past centuries. However, such research still faces a challenge due to limited knowledge of physiochemical implications of the traditional proxies in the specific lake, and difficulties to discriminate dry-wet from warm-cold signals. Here, a sediment core collected from Keluke Lake, Qaidam Basin, Northwest China was analyzed for iodine and uranium concentrations, to explore their potential as a new hydrological proxy in the arid regions for reconstructing the dry-wet changes during the past ∼2200 years. A significant correlation between iodine and uranium concentrations (r = 0.62, P < 0.01) was observed in the sediment core, and four peak events of synchronously varied iodine and uranium concentrations occurred in the studied sediment core. This indicates similar physiochemical behaviors of the two elements from the catchment to the sediments via lake water. During drier periods, as vegetation degradation and soil organic substance content decreased, water-soluble iodine and uranium were intensively leached, and fine particle associated iodine and uranium were seriously eroded from catchment soils. Meanwhile, the suspended matter concentrations and organic substance content in lake water increased as well, which facilitated more iodine and uranium to be deposited and recorded in the sediment as peak events. The four dry events coincide with the reported climatic changes in other lake sediments, ice core and aeolian sediments, and also correspond with the society evolution in this area, including the establishment of Tuyuhun Kingdom (313–663 CE), Tubo Empire (618–842 CE), Mongolian tribes (1495–1591 CE, and the Han population immigration driven by a severe drought disaster in 1876–1879.

Sub-seasonal to seasonal drivers of dry extreme rainfall events over Northeast Thailand

The interannual El Niño-Southern Oscillation (ENSO) and the Boreal Summer Intraseasonal Oscillation (BSISO) strongly modulate sub-seasonal to seasonal rainfall variability, leading to dry extreme rainfall events (DEREs) over Northeast (NE) Thailand. In this study, the ability of climate models to simulate the ENSO-BSISO-induced DEREs and associated synoptic features are evaluated using self-organizing maps. Observed DEREs occur most frequently during ENSO Neutral and La Niña conditions, when enhanced convection is located over central India and the Bay of Bengal. The intensity of observed DEREs are strengthened during El Niño when enhanced convection is observed over the western Pacific region. The climate models exhibit a diverse frequency of DEREs during ENSO phases, with some models showing better skill than others. On intraseasonal time scales, observed DEREs are favored when enhanced BSISO convection in phases 3–5 is located over the Bay of Bengal and the western Pacific region. Five models out of the 19 examined capture the observed pattern during BSISO phases 4 and 5, while only three models capture the BSISO phase 3 behavior. Composite maps of observed DEREs during the combined BSISO and ENSO conditions indicate that BSISO convection increases (decreases) DERE frequency during El Niño and Neutral (La Niña) phase(s). Climate models can simulate the occurrence of dry events associated with the combined BSISO and ENSO phases, but they do so in different BSISO phases.

Intraseasonal‐to‐seasonal evolution of soil moisture‐based droughts and floods in observation‐based datasets and Coupled Model Intercomparison Project Phase 6 models

AbstractDroughts and floods are extreme events that have tremendous socioeconomic impact. Many studies have investigated their possible variations under the effects of climate changes, while their intraseasonal‐to‐seasonal characteristics have received less attention. Based on observation‐constrained monthly soil moisture (SM) datasets since 1980, we analysed the spatiotemporal characteristics of global SM at the intraseasonal‐to‐seasonal time scales and the associated influencing factors. The results were then used to evaluate the performance of simulations by Coupled Model Intercomparison Project Phase 6 (CMIP6) models. It is found that the frequencies of extreme wet events are slightly higher than those of extreme dry events, but their spatial distributions are similar and are both affected by precipitation variability. Extreme events tend to have longer durations than nonextreme events, and their global mean durations are 4–5 months. Globally, dry events persist longer than wet events. Maximum SM anomalies are strongly affected by earlier precipitation and this effect is stronger in a transitional climate. The onset and peak times of SM anomalies in a year occur most frequently near the peak time of precipitation rather than that of SM. Approximately half of CMIP6 models overestimate the durations of both dry and wet events and approximately one third of models only underestimate wet events durations. Different versions of the same model produce similar event durations. The findings of this study enhance understanding of the intraseasonal‐to‐seasonal variabilities of global droughts and floods and could provide guidance for future study of land–atmosphere interactions and prediction of extreme events.

Spatiotemporal analysis of drought occurrence in the Ouergha catchment, Morocco

&lt;abstract&gt; &lt;p&gt;Although the spatiotemporal characterization of droughts is a key step in the design and implementation of practical measures to mitigate their impacts, it is hampered by the lack of hydro-climatic data with sufficient spatial density and duration. This study aimed to assess the trends and spatial patterns of drought occurrence in the Ouergha catchment in northern Morocco, which has been identified as a hot spot for climate change and variability. The study combined data from various sources, including the North Atlantic Oscillation Index (NAOi); Western Mediterranean Oscillation Index (WeMOi); a meteorological index (SPI), calculated using precipitation data; a hydrological index (SDI), calculated using precipitation data; and satellite images to calculate the Normalized Difference Vegetation Index (NDVI) and Normalized Difference Moisture Index (NDMI) from 1984/85 to 2016/17. The results showed that the adopted statistical analyses were effective in detecting the linearity and trend of drought in the Ouergha catchment scale. The correlations between various indices were moderate to strong between NAOi and SPI, WeMoi and SPI, as well as SPI and SDI, while the Mann-Kendall tests indicate an increasing trend of drought intensity in the catchment. During dry events, vegetation cover and moisture were maintained due to the presence of dam reserves. Overall, the study provides empirical evidence that confirms the severe drought conditions experienced in the Ouergha catchment. The unique set of data adds to the growing body of knowledge about drought in the region and underscores the urgency of preserving dam resources for sustainable use during future droughts.&lt;/p&gt; &lt;/abstract&gt;

Persistent Wet and Dry Spells of Indian Summer Monsoon Rainfall: A Reexamination of Definitions of “Active” and “Break” Events

Abstract Persisting wet events (PWEs) and persisting dry events (PDEs) over central India (CI), defined by rain spells lasting for 5 days or more above and below climatology, respectively, represent an important component of the Indian summer monsoon’s intraseasonal variability. However, half of such PREs and PDEs that do not overlap with conventionally defined “active” and “break” spells over CI while contributing about 20% to the seasonal mean remained poorly studied. Here we find that, in contrast to more abundant longer (&gt;5 days) wet and dry spells over the CI, the intraseasonal rainfall variability over northeast India (NEI) is characterized by higher abundance of intense shorter spells (&lt;5 days). Physically, the difference is linked to the fact that monsoon intraseasonal oscillations with a 30–60-day time scale dominate subseasonal variability over the CI, whereas the 10–20-day quasi-biweekly mode dominates subseasonal variability over NEI. While non-overlapping PDEs are associated with large-scale but lower-intensity breaks, non-overlapping PWEs are associated with synoptic events with relatively smaller spatial scales rather than large-scale active events. Here, a percentile-based definition of active and break spells as daily rainfall in excess of the 90th percentile and below the 30th percentile, respectively, persisting for more than 3 days is proposed; this encompasses almost all non-overlapping PWEs and PDEs and is expected to be more useful to the users. Contributions of the subseasonal fluctuations to the seasonal mean and their association with predictable drivers indicate that the seasonal mean rainfall over the NEI is significantly less predictable than that over the CI. Significance Statement Farmers eagerly await the extended range projections of “wet” and “dry” phases of Indian monsoon intraseasonal variability for planting, harvesting, and water resource management. The prevailing definitions for “active” and “break” spells, however, ignored the less intense persisting wet or dry events that contribute roughly equally to the seasonal mean rainfall. To facilitate the process, a new percentile-based definition of the Indian summer monsoon rainfall’s intraseasonal spells is proposed that includes nearly all non-overlapping PWEs and PDEs. The subseasonal fluctuations’ contributions to the seasonal mean and its association with predictable drivers suggest that the seasonal mean rainfall over the NEI is much less predictable than that over the CI, and thus illustrates the contrasting features of spells within these two regions.

Austral and Subtropical Gyre Radiolaria – latest Jurassic to Early Cretaceous Leg 123, Site 765, Argo Abyssal Plain revisited: Southern Hemisphere paleobiogeography and global climate change

The aim of this report is to 1) to formally describe Austral and Subtropical Gyre Radiolaria recovered from ODP Hole 123-765C), 2) to compare them with published records of Southern Hemisphere “non-Tethyan” assemblages and 3) to discuss radiolarian paleobiogeography of the Southern Hemisphere and its implications for global climate change during the Jurassic–Cretaceous transition. The Tithonian to Aptian/early Albian radiolarian record recovered from Hole 765C, Cores -62R to -36R in the Argo Abyssal Plain (AAP) is unique in its density of well-preserved samples and in its faunal contents. Radiolaria recovered from claystones yielded the low diversity, ecologically tolerant “Crypto-Archaeo” Assemblage, (chiefly cryptocephalic and cryptothoracic nassellarians and Archeodictyomitra spp.) interpreted herein as originated in the Subtropical Gyre (STG). In contrast, assemblages extracted from radiolarite layers, interpreted as pelagic turbidites derived from the deeper Australian margin, are dominated by Austral taxa. Neotethyan taxa are very rare to absent before the late Hauterivian/Barremian, when they gradually gain in diversity and abundance. Described Austral and STG taxa include 10 families, of which Fusitanellidae n. fam. and Windaliinae n. subfam. are new. Of 18 genera 7 are new (Nodosphaera, Praewindalia, Pachycingula, Archaeotanella, Morchella, Fusitanella, Argofusus) and of 55 species 30 new ones are formally described and 14 new ones are left in open nomenclature. The southern hemisphere Late Jurassic to Early Cretaceous radiolarian biogeography is defined from low- to high latitude: 1. the Neotethyan (NT) and 2. the Central Panthalassan (CP) realms, 3. Eastern Boundary Current (EBC) realm, 4. the Subtropical Gyre (STG) and the Austral (A) circum south-polar realm. Radiolarian biogeography and plate tectonic models support a scenario of palaeoceanographic and global climatic change during the Jurassic–Cretaceous transition related to progressive Pangea break-up with the following consequences: 1. an increased heat transfer to the Southern hemisphere which caused cooling of Neotethyan regions during the Late Tithonian dry event. 2. A northward shift of the southern summer Intertropical Conve nience Zone reduced the Neotethyan monsoon area and allowed the establishment of a southern Neotethyan subtropical gyre documented by the “Crypo-Archaeo” Assemblage. 3. The south-polar West Wind Drift may have forced a circum Antarctic-Australian cold current through the epicontinental rift between India and Antarctica-Australia since the Berriasian (140 my), transporting Austral Radiolaria into the AAP where they accumulated in radiolarite layers.

Evaluación del índice de precipitación estandarizado (SPI) con datos de alta resolución en clima histórico y futuro en el centro de México

Introduction: Drought monitoring needs good quality meteorological data, but records frequently face problems. Therefore, satellite precipitation datasets are an alternative. Objective: Evaluation of three high-resolution datasets (compared with observed precipitation) to capture wet and dry periods. In addition, the influence of the selection of the dataset to downscale future climate simulations is evaluated in the estimation of drought indicators. Methodology: Precipitation products (NOAA, CHIRPS and PERSIANN-CDR) were compared with observations from seven meteorological stations (1983-2013). The 12-month standard precipitation index (SPI) was selected to evaluate drought conditions. Also, precipitation estimates from CanESM2 were downscaled and bias-corrected with each dataset. Results: The annual precipitation cycle is well capture, but underestimation is noted. The datasets have a good correlation, but less variability. Regarding the SPI, results show good correlation, but extremely dry events are generally underestimated with CHIRPS and PERSIANN-CDR. The NOAA dataset performs better in terms of categorical scores, especially for wet events. Similar median values were found in the drought indicators in future; however, the datasets lead to less variability than observations, especially in the drought frequency indicator. Study limitations: Limited number of good quality meteorological records. Originality: Selected precipitation datasets are tested under different climatic conditions for the first time in Mexico. Also, the influence of the reference precipitation dataset for bias correction is evaluated on future drought projections. Conclusions: Precipitation products should be tested before their use in monitoring droughts in the historical period, as well as in estimating droughts with future projections.

Citizen science data validates aerial imagery to track the ‘rise and fall’ of woody vegetation through extremes of climate

Context Ground truthing remotely sensed imagery for detecting changes in wetland vegetation can be time-consuming and costly for monitoring. Harnessing the resources of citizen scientists (CS) using mobile devices has been under utilised in Australia. Aims The project aimed to test the feasibility and practicality of using CS to collect data using mobile devices to ground truth remotely sensed imagery. Methods Using high-resolution aerial imagery, we detected the establishment of woody vegetation over a 20-year dry phase from 2000 to 2020 in Thirlmere Lakes National Park, NSW, Australia. To ground truth these woody species, we engaged with a local community group using a customised, freely available mobile device application. Key results During the dry event of 2020, CS documented well-established woody species, such as Melaleuca linariifolia (flax-leaved paperbark), amongst the Lepironia articulata grey rush. With the La Niña wet events in early 2020–22 and subsequent higher water levels, the CS documented the survival of M. linariifolia but the dieback of eucalypts, and other woody species. Conclusions Observations at higher temporal frequencies by CS using mobile devices, augmented with researchers’ observations, proved to be a valuable, quality-controlled method to ground truth high-resolution aerial imagery. Implications This case study showed that monitoring the phenology of vegetation in a peat wetland can be supplemented by the inclusion of a CS programme. This under-utilised resource can increase coverage and frequency of data observations, lower costs as well as create community awareness, capability and engagement in scientific research.

Attribution of the 2015 drought in Marathwada, India from a multivariate perspective

The agricultural region of Marathwada in India incurred significant loss of crops and lives during the summer of 2015, which was characterised by persistent hot and dry conditions. We use observations and large ensembles of regional climate model simulations to understand and attribute this joint occurrence of deficient rainfall and high temperature in a novel, multivariate framework. Highly unlikely in a world without anthropogenic climate change (1-in-256 year), the event is found to be frequent (1-in-38 year) in the actual world. Thus, the risk of this event is found to be atleast quintupled due to anthropogenic factors, implying that the 2015 event is more likely due to anthropogenic climate change. Interestingly, the 2015 dry event is not unprecedented (∼1-in-15 year) based on observed records and for either of the model scenarios, suggesting that risk assessments based on rainfall alone may not be enough to reconcile the observed impacts. Further, such compound drought events are projected to become even more frequent under future end-of-the-century warming targets of 1.5 °C and 2 °C above pre-industrial levels, with expected doubling and tripling of the probability of the 2015 hot-dry conditions, respectively. Our findings highlight the role of human-induced warming on increased incidences of compound extreme events, thereby warranting adaptation strategies that aim at alleviating associated risks.

Assessment of Wet and Dry Spells Over North Western Zone of Tamil Nadu Using WASP

Rainfall is the most dependent weather factor that decides the success or failure of a crop in a location. The behaviour of rainfall plays a major role in the selection of crop, cropping system and cropping pattern. It is also essential for planning of water resource management structures. Hence it is essential to study the anomaly in rainfall over a long period of time to identify the deviation in rainfall pattern over the region. Weighted Anomaly of Standardized Precipitation Index (WASP) is an index that can help in identifying the occurrence of dry or wet spells over different time scales (tri, hexa, nona and dodeca-monthly). The analysis was carried out for Salem district of Tamil Nadu over a period of 30 years (1991-2020) which has an average rainfall of 990 mm per year with bimodal distribution. The analysis shows an increase in near normal events, decrease in wet as well as dry events with 3 m, 6 m, 9 m and 12 m WASP. The 3 m-WASP indicates the north east monsoon have more variability in rainfall since more number of wet as well as dry events have occurred during this season. With 6 m WASP During, in all the 3 decades, the consecutive wet as well as dry events have been occurred during the winter and NE monsoon seasons. This shows the risk in crop cultivation during NEM season because of higher instability in rainfall. Considering the longer time scale of 9 m and 12 m WASP indicates the occurrence of prolonged extreme dry or extreme wet events to be very minimal. The negative effects of these events can be handled easily by adopting proper drainage, water harvesting and storage structure within the farms. These structures can also help in recharging the ground water table in addition to supplementing water needs for the crops.

Droughts Reduce Growth Rates and Increase Vulnerability to Increasingly Frequent and Severe Drying Events in an Aquatic Ectotherm

Many aquatic organisms are experiencing increasingly severe and frequent droughts and drying events. Simultaneously, drought effects are carrying over to nondrought years as ecosystems remain in incomplete states of recovery. Aquatic organisms are thus faced with fewer sequential years under degraded environmental conditions to prepare for increasingly severe droughts and potential drying events. We assessed the effect of droughts and sex on the growth, mass, and mass-dependent estivation potential of long-lived aquatic salamanders (Greater Sirens, Siren lacertina) that estivate during drying events brought on by severe droughts. We calculated growth rates of S. lacertina based on mark–recapture data spanning 11 yr of a severe drought local minimum (of past 50 yr) in the southeastern United States. Sirens showed a distinct seasonal gain in body length and mass from March through September and little growth for the rest of the year. Gains during the growth season were strongly reduced by drought conditions. Although male and female sirens were predicted to reach a similar maximum body size, females grew much slower. Recruitment into drying event “size refugia” is constrained by drying event severity (determines minimum size required), frequency (determines available time between events to grow), and environmental conditions between drying events (determines the rate of growth). Thus, increases in drying event severity and frequency will require faster growth to a larger body size for successful recruitment into a size class that is resistant to drying events. The slower growth of females and reduction of growth during suboptimal years (mild to moderate droughts) suggest that the life history strategy of Greater Sirens for persisting through drying events potentially increases their demographic susceptibility to the predicted effects of climate change.

A research agenda for nonvascular photoautotrophs under climate change.

Nonvascular photoautotrophs (NVP), including bryophytes, lichens, terrestrial algae, and cyanobacteria, are increasingly recognized as being essential to ecosystem functioning in many regions of the world. Current research suggests that climate change may pose a substantial threat to NVP, but the extent to which this will affect the associated ecosystem functions and services is highly uncertain. Here, we propose a research agenda to address this urgent question, focusing on physiological and ecological processes that link NVP to ecosystem functions while also taking into account the substantial taxonomic diversity across multiple ecosystem types. Accordingly, we developed a new categorization scheme, based on microclimatic gradients, which simplifies the high physiological and morphological diversity of NVP and world-wide distribution with respect to several broad habitat types. We found that habitat-specific ecosystem functions of NVP will likely be substantially affected by climate change, and more quantitative process understanding is required on (1) potential for acclimation, (2) response to elevated CO2 , (3) role of the microbiome, and (4) feedback to (micro)climate. We suggest an integrative approach of innovative, multimethod laboratory and field experiments and ecophysiological modelling, for which sustained scientific collaboration on NVP research will be essential.