Persistent Drought Research Articles

Roman water management impacted the hydrological functioning of wetlands during drought periods

During the Roman domain of the Iberian Peninsula (from 201 BCE to 460 CE) water management infrastructures were built to satisfy high water demand. However, whether the Roman activities affected the hydrological balance of Iberian wetlands remains unclear. Here, we investigate the paleo-hydrology of Lake Zóñar (southern Iberia) by using the stable isotopes (16O, 17O, 18O, 1H and 2H) of its gypsum (CaSO4·2H2O) sediments and reconstruct the isotopic composition of the lake water during Roman times. A period of recurrent lake low stand occurred between 2120 and 1890 cal. yr BP (ca. 170 BCE to 60 CE), coinciding with a relatively dry climate stage recorded by most regional paleoclimate archives. The stable isotopes and hydrochemistry of the lake water during gypsum precipitation are consistent with a shallow saline lake that evaporated under relative humidity ~ 10% lower than the present annual mean and at least 20% less rainfall amount. Our analytical and archeological findings support lake level lowering during the Roman period was probably caused by combined arid climate conditions and diversion of the inlets feeding the lake. Spring capturing was likely necessary to satisfy the high water demand of nearby Roman settlements, in the framework of a period of persistent droughts.

Drought reconstruction since 1796 CE based on tree-ring widths in the upper Heilongjiang (Amur) River basin in Northeast Asia and its linkage to Pacific Ocean climate variability

Abstract. The economic and environmental impacts of persistent droughts in East Asia are of growing concern, and therefore it is important to study the cyclicity and causes of these regional droughts. The self-calibrating Palmer drought severity index (scPDSI) has been extensively employed to describe the severity of regional drought, and several scPDSI reconstructions based on tree rings have been produced. We compiled a tree-ring chronology for Hailar pine (Pinus sylvestris var. mongolica) from two sites in the Hailar region in the upper Heilongjiang (Amur) River basin. Analysis of the climate response revealed that scPDSI was the primary factor limiting tree ring growth from May to July. The mean May to July scPDSI in the Hailar region since 1796 was reconstructed from the tree-ring width chronology. The results of spatial correlation analysis revealed that the reconstructed scPDSI in this region responded significantly to climate change. Analysis of the synoptic climatology indicated that the drought in the upper Heilongjiang (Amur) River basin is closely related to El Niño–Southern Oscillation (ENSO) and the Silk Road teleconnection. The results of atmospheric water cycle analysis show that water vapor transport processes are the dominant factor in the development of drought in this region.

Molecular evidence for the adaptive evolution in euryhaline bivalves

Marine bivalves inhabiting intertidal and estuarine areas are frequently exposed to salinity stress due to persistent rainfall and drought. Through prolonged adaptive evolution, numerous bivalves have developed eurysalinity, which are capable of tolerating a wide range of salinity fluctuations through the sophisticated regulation of physiological metabolism. Current research has predominantly focused on investigating the physiological responses of bivalves to salinity stress, leaving a significant gap in our understanding of the adaptive evolutionary characteristics in euryhaline bivalves. Here, comparative genomics analyses were performed in two groups of bivalve species, including 7 euryhaline species and 5 stenohaline species. We identified 24 significantly expanded gene families and 659 positively selected genes in euryhaline bivalves. A significant co-expansion of solute carrier family 23 (SLC23) facilitates the transmembrane transport of ascorbic acids in euryhaline bivalves. Positive selection of antioxidant genes, such as GST and TXNRD, augments the capacity of active oxygen species (ROS) scavenging under salinity stress. Additionally, we found that the positively selected genes were significantly enriched in KEGG pathways associated with carbohydrates, lipids and amino acids metabolism (ALDH, ADH, and GLS), as well as GO terms related to transmembrane transport and inorganic anion transport (SLC22, CLCND, and VDCC). Positive selection of MCT might contribute to prevent excessive accumulation of intracellular lactic acids during anaerobic metabolism. Positive selection of PLA2 potentially promote the removal of damaged membranes lipids under salinity stress. Our findings suggest that adaptive evolution has occurred in osmoregulation, ROS scavenging, energy metabolism, and membrane lipids adjustments in euryhaline bivalves. This study enhances our understanding of the molecular mechanisms underlying the remarkable salinity adaption of euryhaline bivalves.

Flash drought fades away under the effect of accumulated water deficits: the persistence and transition to conventional drought

Flash drought typically refers to the rapid intensification process that would only persist for a certain amount of time. In spite of short duration, flash drought may cause destructive impacts on agricultural and ecological sectors due to the sustained drought severity during or after the rapid intensification period. Understanding the persistence of flash drought, its regional patterns, and to what extent a transition from rapid intensification to conventional drought occurs is beneficial for drought monitoring and drought management. Employing surface and root-zone soil moisture reanalysis datasets, the notion of accumulated water deficits over varying time scales (can be detected by the moving averages of daily soil moisture series from 1 to 300 d) was introduced to explore how the signal of flash drought fades away over China during the period of 1950–2021. Results show that the flash drought signal gradually attenuates under the increased time scales of water deficits. With significant spatial differences, more than 50% of flash drought on average would be lost at a 10 d time scale, and the attenuation ratio may reach 90% when the time scale increases to 100 d. Under the effects of accumulated water deficits, the majority of flash drought events may evolve into conventional drought before dissipating completely. Soil moisture memory has a finite effect on the attenuation of flash drought signal. Flash drought signal dissipates slowly in areas with strong soil moisture memory. As time scale increases, both flash drought signal and the memory of soil moisture decrease, and their correlation also weakens.

Effects of Climate Change and Drought Tolerance on Maize Growth.

Climate change is affecting all regions of the world with different climates, and the scale of damage is increasing due to the occurrence of various natural disasters. In particular, maize production is highly affected by abnormal climate events such as heat waves and droughts. Increasing temperatures can accelerate growth and shorten the growing season, potentially reducing productivity. Additionally, enhanced temperatures during the ripening period can accelerate the process, reducing crop yields. In addition, drought stress due to water deficit can greatly affect seedling formation, early plant growth, photosynthesis, reproductive growth, and yield, so proper water management is critical to maize growth. Maize, in particular, is tall and broad-leaved, so extreme drought stress at planting can cause leaves to curl and stunt growth. It is important to understand that severe drought can have a detrimental effect on the growth and reproduction of maize. In addition, high temperatures caused by drought stress can inhibit the induction of flowering in male flowers and cause factors that interfere with pollen development. It is therefore important to increase the productivity of all food crops, including maize, while maintaining them in the face of persistent drought caused by climate change. This requires a strategy to develop genetically modified crops and drought-tolerant maize that can effectively respond to climate change. The aim of this paper is to investigate the effects of climate change and drought tolerance on maize growth. We also reviewed molecular breeding techniques to develop drought-tolerant maize varieties in response to climate change.

Development of composite drought indices for the coastal areas of southeastern China: A case study of Jinjiang and Jiulongjiang River basins

Given the complexity of coastal drought events and their unique impacts on coastal ecosystems, it is vital to develop drought indices that can reflect both freshwater availability and impacts on ecological resources to better assess drought conditions over coastal regions. Existing drought indices developed for upland areas may not be suitable to capture the timing and severity of drought in the coastal regions. To explore coastal drought issue more comprehensively, this paper constructed the Coastal Composite Drought Indices (CCDIs) based on the entropy-weighted Euclidean distance method by freely combining six variables: precipitation (P), evaporation (E), runoff (R), salinity (S), Normalized Difference Vegetation Index (NDVI) and Land Surface Temperature (LST), in the Jinjiang River Basin (JJRB) and the Jiulong River Basin (JLRB). The CCDIs were later compared to the Standardized Precipitation Index (SPI) and Palmer Drought Severity Index (PDSI) to select the Optimized Drought Indices (ODIs). The results demonstrated that the Precipitation Evaporation Runoff Composite Index (PER) is more sensitive to capturing short-term coastal drought events compared to other CCDIs. PER performed better than SPI and PDSI in detecting the onset of drought development and reflecting drought persistence. The salinity exhibited mixed responses to long-term drought events in different river basins depending on the size of each coastal system and its characteristics, thus raising the issue of regional applicability. Through a series of cross-comparisons and validations, the Runoff NDVI LST Composite Index (RNL) and the Runoff Salinity NDVI Composite Index (RSN) were chosen to monitor long-term droughts in the JJRB and JLRB, respectively. Overall, all three indices have the ability to capture the dynamics and trends of the variables and provide better information on the occurrence, persistence, and end of droughts in coastal areas.

Persistent Meteorological Drought in the Yangtze River Basin during Summer–Autumn 2022: Relay Effects of Different Atmospheric Internal Variabilities

During the summer–autumn (July–October, Jul–Oct) period of 2022, the Yangtze River Basin (YRB) of China experienced an extreme meteorological drought, with Jul–Oct containing the lowest precipitation in the YRB since 1979. The possible causes of this drought were analyzed in the present study. Surprisingly, unlike many previous drought events, we found that this event was not characterized by a consistent atmospheric circulation anomaly regime throughout the entire drought period. Instead, two distinct circulation patterns were responsible for the precipitation deficit in two different stages, i.e., July–August (Jul–Aug) and September–October (Sep–Oct). In Jul–Aug, the YRB precipitation deficit primarily resulted from an intensified and northward-shifted East Asian subtropical jet, which allowed for an extremely northwestward shift of western Pacific subtropical highs, leading to an anomalous descending motion. Such circulation patterns in Jul–Aug originated from the dispersion of Rossby waves upstream from central Asia and Europe. Meanwhile, in Sep–Oct, the YRB drought was primarily attributed to a low-level cyclonic anomaly over the western North Pacific, which was closely associated with frequent tropical cyclones traveling across this region. Observational analysis and a model ensemble hindcast suggest that atmospheric internal variabilities dominated the drought process, while the SSTA, particularly the La Niña event, played a limited role. Therefore, this long-lasting extreme YRB meteorological drought was largely driven by the relay effects of different atmospheric internal variabilities in Jul–Aug and Sep–Oct, respectively, which shows limited model predictability and poses a great challenge for operational climate predictions.

Introduction

Introduction

Eco-physiological response mechanism of Tamarix chinensis to soil water changes in coastal wetlands of the Yellow River Delta

Elucidating the effect of soil moisture on the adaptation of dominant plants in coastal wetlands is important for predicting the evolution of vegetation in the region. In this paper, Tamarix chinensis, a dominant species in the Yellow River Delta, was used as the object to study the changes of its growth and physiological parameters with increasing soil salinity under different moisture conditions (normal watering, persistent drought and persistent waterlogging). Different salt stress (2‰, 5‰, 8‰, 12‰, 16‰, and 20‰) using pot experiments was also used to reveal the mechanism of soil moisture on its salt tolerance. The results showed that the relative growth rate between 5‰-8‰ soil salinity was the largest, and growth was significantly inhibited above 20‰. Among different moisture conditions, the difference in relative growth rate under normal watering and persistent drought were nonsignificant, while both were significantly lower than those under persistent waterlogging. With increasing soil salinity, relative water content and total chlorophyll content significantly decreased, and cell membrane permeability (malondialdehyde), sodium ion, osmoregulatory substances (proline, soluble protein), and protective enzyme activity (SOD) significantly increased, while changes in non-structural carbohydrates (NSC) were not significant. Compared with normal watering and persistent waterlogging, persistent drought had the lowest leaf relative water content, total chlorophyll content, and sodium ions, and the highest cell membrane permeability, osmoregulatory substances and protective enzyme activity. With increasing treatment time, the relative leaf water content and total chlorophyll content significantly decreased, and cell membrane permeability, osmoregulatory substances and protective enzyme activity increased more significantly than normal watering and persistent waterlogging. NSC increased under normal watering and persistent waterlogging, while significantly decreased under persistent drought. Correlation analysis showed that the relationships between sodium ions, total chlorophyll content and malondialdehyde were various under different moisture conditions. Under persistent drough, malondialdehyde was significantly positively correlated with relative conductivity, superoxide dismutase, proline, soluble protein and soluble sugar. Total chlorophyll content was the key indicator reflecting the salt and waterlogging tolerance of T. chinensis under normal watering and persistent waterlogging, while cell membrane damage was under persistent drought. In summary, T. chinensis has strong salt and waterlogging tolerance, but persistent drought with salt stress can have serious impacts on its growth and survival.

Spatio-Temporal Evolution of Rainfall over the Period 1981–2020 and Management of Surface Water Resources in the Nakanbe–Wayen Watershed in Burkina Faso

Spatio-temporal analysis of rainfall trends in a watershed is an effective tool for sustainable water resources management, as it allows for an understanding of the impacts of these changes at the watershed scale. The objective of the present study is to analyze the impacts of climate change on the availability of surface water resources in the Nakanbe–Wayen watershed over the period from 1981 to 2020. The analysis was conducted on in situ rainfall data collected from 14 meteorological stations distributed throughout the watershed and completed with CHIRPS data. Ten precipitation indices, recommended by the ETCCDI (Expert Team on Climate Change Detection and Indices), were calculated using the RClimDex package. The results show changes in the distribution of annual precipitation and an increasing trend in annual precipitation. At the same time, a trend towards an increase in the occurrence and intensity of extreme events was also observed over the last 4 decades. In light of these analyses, it should be emphasized that the increase in precipitation observed in the Nakanbe–Wayen watershed is induced by the increase in the occurrence and intensity of events, as a trend towards an increase in persistent drought periods (CDD) is observed. This indicates that the watershed is suffering from water scarcity. Water stress and water-related hazards have a major impact on communities and ecosystems. In these conditions of vulnerability, the development of risk-management strategies related to water resources is necessary, especially at the local scale. This should be formulated in light of observed and projected climate extremes in order to propose an appropriate and anticipated management strategy for climate risks related to water resources at the watershed scale.

Artificially applied late-terminal drought stress in the field differentially affects Ramularia leaf spot disease in winter barley

Ramularia leaf spot disease (RLS) is one of the most dominating fungal diseases in barley. The disease typically appears late in the season after flowering and results in a rapid loss of photosynthetic leaf area. A recent decline in fungicide efficacy and a lack of RLS-resistant cultivars hamper effective control. Global warming will provoke increasing droughts which influence host plant physiology and probably affect outbreak and severity of RLS. Relatively little is known about genetic resistance to RLS in winter barley and about the influence of various weather conditions and climate change on RLS pathogenesis. Hence, we evaluated severity of RLS on 15 winter barley genotypes under persistent late-terminal drought stress or controlled irrigation, respectively, in a field rainout shelter. Over three consecutive years, we observed reproducible differences in quantitative RLS field resistance of the used cultivars and variable suppression of RLS under drought. Our results support a function of drought in suppression of RLS in winter barley, but also reveal strong year effects even under semi-controlled rainout shelter conditions. Data may be relevant for genotype selection in breeding programmes for RLS resistance and for farmers in the frame of integrated disease management under a changing climate.Graphical abstract

Irrawaddy River experienced more frequent hydrological drought events with global warming: Evidence from a 400-year tree ring oxygen isotope record

Global temperature fluctuations have significantly impacted regional hydrological cycles. The Irrawaddy River (IR) is the largest river in Myanmar and has an important influence on socioeconomic conditions within its watershed and beyond. However, potential changes to the IR’s hydrological extremes under a future warming climate remain poorly understood. We reconstructed a 400-yr May–July streamflow time series for the IR using tree-ring cellulose oxygen isotopes (δ18O) and compared the variations of the hydrological extremes before and after the onset of global warming. The streamflow reconstruction shows that the IR experienced 65 extreme flood events and 67 extreme drought events during 1617–2017, with 58 extreme drought events occurred after 1850. Extreme drought events in this region have gradually increased and the frequency of extreme droughts has increased significantly since the 1850s. The occurrence of drought events in the last few decades has exceeded the natural variability. Especially, the persistent drought conditions during 2000–2017 are unprecedented compared with the record of the last 400 yr. This increase in drought events is significantly linked to the weakening of the ISM and increasing temperatures, hence the IR may experience more extreme drought events in the future under global warming.

How Unusual Is the 2022 European Compound Drought and Heatwave Event?

AbstractThe 2022 Compound Drought and Heatwave (CDHW) caused widespread crop damage, water shortages, and wildfires across Europe. Our study analyzed this event’s severity and return period (RP) and compared it with past mega CDHWs in Europe. The hardest‐hit areas were Iberian Peninsula, France, and Italy, where temperatures exceeded 2.5°C above normal, and severe droughts persisted from May to August. Using a Bayesian approach, we estimated the RP for the 2022 CDHW event, which was unprecedented in Northern Italy, Iberian Peninsula, and western parts of France, with RPs of 354, 420, and 280 years, respectively. The reduced soil moisture due to precipitation deficits and high temperatures contributed to the persistence and severity of drought, creating a positive feedback loop where dry soils led to even drier conditions. In light of our findings, it is evident that global warming poses increased risks of severe CDHW events, which are likely to increase.

Predicting extreme floods and droughts in East Africa using a deep learning approach

The East African region is highly susceptible to severe floods and persistent droughts, which greatly impact the livelihood of millions of people. Early warnings, at least a few seasons in advance, would help implement mitigation measures. However, most prediction systems using dynamical models perform poorly at long lead times. In this study, we propose a statistical deep learning approach based on a convolutional neural network (CNN) to predict extreme floods and droughts during the short rains season (October–December). The proposed CNN model captures the phase of extreme floods and droughts two to three seasons ahead, except for a few cases. By diagnosing the model’s skills using heatmaps, we find that predicted extreme floods and droughts are linked with the sea surface temperature anomalies of the Indian Ocean Dipole at shorter leads and with western and southern Indian Ocean, equatorial Pacific, and southern Atlantic Ocean at longer leads. Although there were a few poorly predicted exceptions, the superior skill of our CNN-based predictions at longer leads provides a significant advantage in developing mitigation measures.

Dissemination of climate smart agricultural knowledge through farmer field schools (FFS): analyzing the application CAS knowledge by smallholder farmers

PurposeThe purpose of this paper is to investigate the effects of climate smart agriculture knowledge transfers. As well as to examine the application of climate-smart agricultural (CSA) knowledge such as conservation agriculture, irrigation systems, integrated soil fertility management, bioenergy and agroforestry by smallholder farmers in Kenya.Design/methodology/approachThe study applied comparative research methodology to compare climate smart agriculture knowledge application between smallholder participants in farmer field schools (FFS) and no FFS participation. This study used household data from 759 randomly selected rural agricultural households in three counties in Kenya. The study applied multivariate probit model to estimate CSA knowledge application by farmers who participated in field trainings and non-FFS participation farmers.FindingsThis study established that climate smart agriculture knowledge transfer through FFS increases farmers’ application of critical aspects of climate smart agriculture knowledge practices such as irrigation system, conservation agriculture and soil and water conservation. Such aspects have been noted as effective interventions against adverse climate change effects such as persistent droughts and flooding and soil infertility. Further findings illustrated that farmers who received CSA knowledge transfers applied agricultural insurance to mitigate rising climatic risks on their farms. Knowledge transfer interventions targeting affordability through subsidizing agricultural insurance are probable and more cost-effective measures that can be used to reduce smallholder farmers’ exposure to climate change-related risks.Originality/valueThis study provides information that was previously unknown about climate smart agriculture knowledge transfers and application among farmers who participated in field trainings and non-FFS participation farmers by using empirical data.

A genotype × environment experiment reveals contrasting response strategies to drought between populations of a keystone species (Artemisia tridentata; Asteraceae).

Western North America has been experiencing persistent drought exacerbated by climate change for over two decades. This extreme climate event is a clear threat to native plant communities. Artemisia tridentata is a keystone shrub species in western North America and is threatened by climate change, urbanization, and wildfire. A drought Genotype × Environment (G × E) experiment was conducted to assess phenotypic plasticity and differential gene expression in A. tridentata. The G × E experiment was performed on diploid A. tridentata seedlings from two populations (one from Idaho, USA and one from Utah, USA), which experience differing levels of drought stress during the summer months. Photosynthetic data, leaf temperature, and gene expression levels were compared between treatments and populations. The Utah population maintained higher photosynthetic rates and photosynthetic efficiency than the Idaho population under drought stress. The Utah population also exhibited far greater transcriptional plasticity than the Idaho population and expressed genes of response pathways distinct from those of the Idaho population. Populations of A. tridentata differ greatly in their drought response pathways, likely due to differences in response pathways that have evolved under distinct climatic regimes. Epigenetic processes likely contribute to the observed differences between the populations.

Cascading effects of drought in Xilin Gol temperate grassland, China

In the context of global climate change, the cascading risk of compound natural hazards is becoming increasingly prominent. Taking Xilin Gol grassland as study area, we used the Mann–Kendall trend method, the maximum Pearson correlation coefficient method, and Partial least squares structural equations modeling to detect the characteristics of spatiotemporal pattern changes of the three types of droughts. The propagation characteristics and the cascade effects among the three types of droughts was also identified. The standardized precipitation evapotranspiration index, standardized evapotranspiration drought index, and soil moisture index were selected as indicators of meteorological drought, ecohydrological drought, and soil drought, respectively. The results show that the warm and dry trend in Xilin Gol grassland was obvious in the past 30 years. The seasonal propagation of different drought was prominent, with stronger spread relationships in summer. Persistent meteorological drought was more likely to trigger the other two types of droughts. The intensity and range both increased during the propagation from meteorological drought to ecohydrological drought. The cascade effect was differed in different time scales. The multi-year persistent climatic drought has an overwhelming cascade effect on soil drought and ecohydrological drought. For seasonal or annual drought, vegetation cover change has an amplifying or mitigating impact on the cascade effect, where soil moisture, evapotranspiration (ET), and their relationship all play important roles. In eastern areas with better vegetation cover, the reduction of vegetation in the early stage aggravated the cascading effect of meteorological drought to ecohydrological drought through reducing ET. In the northwestern sparsely vegetated areas, ET was mainly influenced by meteorological factors, and the cascade effect of meteorological factors to ecohydrological drought was more obvious than that of soil drought.

Farmer Response to Change in Irrigation Water Pricing in Khyber Pakhtunkhwa: A Multinomial Logistic Regression Analysis

The River Swat is one of Pakistan's interior rivers, lying in the Khyber Pakhtunkhwa province. Despite being semi-dry, the area is a significant grain and fruit-producing area. However, persistent drought in recent years, along with excessive water extraction, has resulted in a constant decline of water pouring into the Swat River's mainstream, resulting in serious deterioration of ecosystems along the river's lower reaches. Water pricing is the best tool to control the misuse of water resources and will lead to the optimum use of this very precious resource. 300 farmers were chosen randomly and a preliminary test of the quantitative questionnaire was conducted before data collection to ensure clarity. To analyze the quantitative dataset Multinomial Logistic Regression, a version of ordinary regression was used. Farmers in the study area who face a 100% rise in water prices were polled to gauge their reactions. The results reveal that factors that are "total land area", "age", "total farm income", "slight water shortage", & "presence of fruit plants" are statistically significant. According to the finding, many farmers reacted to the rise in irrigation water prices and they were ready to use irrigation water more efficiently. This study also observed and concluded that just raising the irrigation water price is not a realistic and permanent solution.

Human Responses to Climate Change in the Second Millennium AD

Abstract The history of past civilisations in southern Africa from AD 700 to AD 1450 has engendered unresolved debates on the social complexities and ultimate decline of these powerful states. The purpose of this paper is to examine the history of the Mapungubwe and Great Zimbabwe state systems in southern Africa through an environmental perspective by taking into consideration human responses to persistent droughts and dry spells. The theories underpinning this study are derived from contemporary societal responses to similar environmental hardships in the Bikita and Chivi districts of southern Zimbabwe. Using rainfall data, and interviews with chiefs, villagers, farmers and experts, this study notes that the occurrence of droughts and dry-spell experiences interfere with sociopolitical organisation. The concepts of sustainability, resilience and transformation are used to explain what could have transpired in societies in southern Africa in the second millennium AD in the face of persistent droughts and dry spells.

Current and historical patterns of recruitment of Yellowstone cutthroat trout in Yellowstone Lake, Wyoming, as revealed by otolith microchemistry

Yellowstone cutthroat trout inhabiting Yellowstone Lake have declined substantially over the past 25 years as a result of predation by invasive lake trout, the presence of whirling disease, and periods of persistent drought. We used otolith microchemistry to assess whether cutthroat trout recruitment patterns have changed in response to these environmental stressors. Though water chemistry variation among the 22 sampled spawning tributaries was low, we identified 9 distinct spawning stream clusters. Random forest models were developed for assessing relative recruitment, yielding a high classification accuracy of 84.4% for known-origin cutthroat trout fry otoliths and 79.0% for simulated otolith signatures based on water chemistry. Proportion of recruitment varied significantly between pre- and post-stressor samples (X2 = 15.40, P = 0.03). The majority of pre- (0.84) and post-stressor (0.77) recruitment occurred in the same three stream clusters, but there was a notable decrease in recruitment in streams with high whirling disease prevalence, and a notable increase from the tributary cluster without whirling disease and with low lake trout predation risk. Conservation efforts should be focused on protecting important spawning tributaries and improving cutthroat trout recruitment in spawning streams that in the past likely contributed much greater numbers of fish.