Multi-year Drought Research Articles

Two millennia of Main region (southern Germany) hydroclimate variability

Abstract. A reconstruction of hydroclimate with an annual resolution covering millennia for a geographically limited region in continental Europe significantly improves our knowledge of past climate dynamics. With the use of an extensive collection of oak ring-width series (Quercus robur and Quercus petraea) from living trees, historic timbers and subfossil alluvial wood deposits from the Main River region in southern Germany, a regional, 2000-year long, seasonally resolved hydroclimate reconstruction for the Main region has been developed. Climate-growth response analysis has been performed with daily climate records from AD 1900 onwards. To test the stability of the developed transfer function, a bootstrapped transfer function stability test (BTFS) as well as a classical calibration/verification approach have been implemented to study climate-growth model performance. Living oak trees from the Main River region show a significant sensitivity to the precipitation sum from 26 February to 6 July (spring to midsummer) during the full (r=0.49, p<0.01, N=116) and split (r=0.58, p<0.01, N=58) calibration periods. BTFS confirmed the stability of the developed transfer function. The developed precipitation reconstruction reveals high variability on a high- to mid-frequency scale during the past two millennia. Very dry spring to midsummer seasons lasting multiple years appeared in the decades AD 500/510s, 940s, 1170s, 1390s and 1160s. At the end of the AD 330s, a persistent multi-year drought with drastically reduced rainfall (with regard to 1901–2000) could be identified, which was the driest decade over the past 2000 years in this region. In the AD 550s, 1050s, 1310s and 1480s, multi-year periods with high rainfall hit the Main region. In spring to midsummer of AD 338, precipitation was reduced by ∼38 % and in AD 357 it increased by ∼39 %. The presented hydroclimate reconstruction and its comparison to other records reveal interesting insights into the hydroclimate dynamics of the geographically limited area over the Common Era, in addition to revealing noticeable temporal differences.

Ocean‐Atmosphere Trajectories of Extended Drought in Southwestern North America

AbstractMultiyear droughts are a common occurrence in southwestern North America (SWNA), but it is unclear what causes these persistent dry periods. The ocean‐atmosphere conditions coinciding with droughts have traditionally been studied using correlation and composite methods, which suggest that cool conditions in the tropical Pacific are associated with SWNA droughts and warm conditions are associated with wet periods in SWNA. Nevertheless, the extent to which multiyear droughts are truly consistent with this paradigm remains unknown. This is, in part, because the temporal trajectory of ocean‐atmosphere conditions during these dry periods have not been sufficiently characterized. Here we examine the continuum of ocean‐atmosphere trajectories before, during, and after multiyear droughts in SWNA using observation‐based data and an ensemble of climate model simulations from the Community Earth System Model. An examination of sea surface temperature patterns at the beginning, middle, and end of SWNA droughts shows that an El Niño event tends to precede SWNA droughts, a cool tropical Pacific occurs during droughts, and central Pacific El Niño events end droughts. However, moderate El Niño events can occur in the middle of persistent droughts, so a warm tropical Pacific does not always end these dry periods. These findings are important for drought predictability and emphasize the need to improve simulations of the magnitude, life cycle, and frequency of occurrence of El Niño events.

The Cape Town \u201cDay Zero\u201d drought and Hadley cell expansion

In early 2018, Cape Town (population ~3.7 million) was at risk of being one of the first major metropolitan areas in the world to run out of water. This was due to a severe multi-year drought that led to the levels of supply dams falling to an unprecedented low. Here we analyze rainfall data from the city catchment areas, including rare centennial records from the surrounding region, to assess the severity of the 2015–2017 drought. We find that there has been a long-term decline in the number of winter rainfall days, but this trend has been generally masked by fluctuations in rainfall intensity. The recent drought is unprecedented in the centennial record and represents a combination of the long-term decline in rainfall days and a more recent decline in rainfall intensity. Cold fronts during the winter months are responsible for most of the rainfall reaching Cape Town and our analysis shows no robust regional trend in the number of fronts over the last 40 years. Rather, the observed multidecadal decline in rainfall days, which threatens to increase the occurrence of severe drought, appears to be linked to a decrease in the duration of rainfall events associated with cold fronts. This change in rainfall characteristics associated with fronts appears to be linked to Hadley Cell expansion seen across the Southern Hemisphere and an increasing trend in post-frontal high-pressure conditions that suppress orographically enhanced rainfall.

Legacies of more frequent drought in ponderosa pine across the western United States.

Despite widespread interest in drought legacies-multiyear impacts of drought on tree growth-the key implication of reported drought legacies remains unaddressed: as impaired growth and slow recovery associated with drought legacies are pervasive across forest ecosystems, what is the impact of more frequent drought conditions? We investigated the assumption that either multiple drought years occurring during a short period (multiyear droughts), or droughts occurring during the recovery period from previous drought (compounded droughts), are detrimental to subsequent growth. There is evidence that drought responses may vary among populations of widespread species, leading us to examine regional differences in responses of the conifer Pinus ponderosa to historic drought frequency in the western United States. More frequent drought conditions incurred additional growth declines and shifts in growth-climate sensitivities in the years following drought relative to single-drought events, with 'triple-droughts' being worse than 'double-droughts'. Notably, prediction skill was not strongly reduced when ignoring compounded droughts, a consequence of the temporally comprehensive formulation of our stochastic antecedent model that accounts for the climatic memory of tree growth. We argue that incorporating drought-induced temporal variability in tree growth sensitivities can aid inference gained from statistical models, where more simplistic models could overestimate the severity of drought legacies. We also found regional differences in response to repeated drought, and suggest plastic post-drought sensitivities and climatic memory may represent beneficial physiological adjustments in interior regions. Within-species variability may thus mediate forest responses to increasing drought frequency under future climate change, but experimental approaches using more species are necessary to improve our understanding of the mechanisms that underlie drought legacy effects on tree growth.

Quantifying Disconnection of Groundwater From Managed‐Ephemeral Surface Water During Drought and Conjunctive Agricultural Use

AbstractThe physics of disconnection between interrelated surface and groundwater has evolved considerably in recent years, especially since conjunctive use of water resources is increasingly dependent on groundwater resilience, but methods to measure disconnection on a river basin scale are lacking especially for managed‐ephemeral and irrigated‐agricultural systems. Multiyear drought limited surface water along Rincon Valley within the Elephant Butte Irrigation District (EBID) in the arid, Lower Rio Grande Basin of south‐central New Mexico, USA, and effects were compounded by continued extraction of groundwater to meet crop requirements. Average year‐end water table elevations in recent years have been below the average elevation of the riverbed, indicating potential disconnection between the river and the aquifer even when the river flows during the irrigation season. This study analyzed data from EBID groundwater monitoring wells adjacent to the river, infiltration determined from river flows, and riverbed measurements along the Rincon Valley reach to determine net annual seepage discharge to the aquifer and annual average pressure head below the river. Annual assessment from 2010 to 2017 confirmed that the drought shifted the system from connection to transition and then to disconnection. Nonlinear regression was used to quantify this shift to disconnection and back, enabled determination of several disconnection process metrics, and was also used to confirm that nonlinear disconnection behavior was reversible without significant hysteresis. The method developed herein confirms that the total head difference transition threshold can be determined from river/riparian monitoring sites over reach to basin scales.

Widespread Initiation, Reactivation, and Acceleration of Landslides in the Northern California Coast Ranges due to Extreme Rainfall

Episodically to continuously active slow‐moving landslides are driven by precipitation. Climate change, which is altering both the frequency and magnitude of precipitation worldwide, is therefore predicted to have a major impact on landslides. Here we examine the behavior of hundreds of slow‐moving landslides in northern California in response to large changes in annual precipitation that occurred between 2016 and 2018. We quantify the landslide displacement using repeat‐pass radar interferometry and pixel offset tracking techniques on a novel data set from the airborne NASA/JPL Uninhabited Aerial Vehicle Synthetic Aperture Radar. We found that 312 landslides were moving due to extreme rainfall during 2017, compared to 119 during 2016, which was the final year of a historic multiyear drought. However, with a return to below to average rainfall in 2018, only 146 landslides remained in motion. The increased number of landslides during 2017 was primarily accommodated by landslides that were smaller than the landslides that remained active between 2016 and 2018. Furthermore, by examining a subset of 51 landslides, we found that 49 had increased velocities during 2017 when compared to 2016. Our results show that slow‐moving landslides are sensitive to large changes in annual precipitation, particularly the smaller and thinner landslides that likely experience larger basal pore‐water pressure changes. Based on climate model predictions for the next century in California, which include increases in average annual precipitation and increases in the frequency of dry‐to‐wet extremes, we hypothesize that there will be an overall increase in landslide activity.

Interaction between mountain pine beetle-caused tree mortality and fire behavior in subalpine whitebark pine forests, eastern Sierra Nevada, CA; Retrospective observations

The 1351 ha Walker Fire burned in late August 2015 on the eastern Sierra Nevada, California escarpment from sagebrush steppe and pinyon pine woodlands (2150 m) through mid-elevation forests into subalpine whitebark pine (WBP; 3310 m). Fuels were particularly dry due not only to the season but as a result of a record multi-year drought (2012–2015). The fire burned into stands heavily impacted by a mountain pine beetle outbreak (MPB) during a prior drought (2007–2010). Using plot data, we report 100% mortality due to fire of understory vegetation and trees in pinyon pine, aspen, white fir, and lodgepole pine forest types. Fire-caused tree mortality was lower in Jeffrey pine forests (80%), although 100% of the understory was killed by the fire. For WBP plots in areas that had not been affected by MPB, 100% of understory and tree layers also burned. Where the fire burned through plots within the former MPB-outbreak area, 2 of 15 plots had 100% understory vegetation and trees burned by the fire, while the remaining 13 had varying levels of survivorship. In those plots, pines dead from prior beetle-kill as well as live trees remained unburned, as did understory vegetation. Whereas such “gray-stage” stands have been found to reduce fire severity in other regions and forest types, the observed reduction of surface fire was unexpected. In that fires in the subalpine WBP zone and bark beetle-fire interactions have not been studied in California, these preliminary observations suggest that subalpine forests are vulnerable to fire where continuous fuels exist below them. However, in xeric, Mediterranean landscapes, MPB outbreaks in WBP may reduce subsequent burn severity in unexpected ways. These findings may be important given current concerns for WBP’s rangewide vulnerability.

The worst drought in 50 years in a South African savannah: Limited impact on vegetation

AbstractSouth Africa experienced a severe multiyear drought from 2014 to 2016. Here, we explore the response of a South African savannah ecosystem to this drought focusing on tree and grass dynamics. We used open long‐term monitoring plots established in 2000 and distributed across broad rainfall gradients in the Hluhluwe‐iMfolozi Park in KwaZulu‐Natal. Analysis showed negligible tree mortality due to drought in 2016 (0.03%) and 2017 (0.49%). However, there was an apparent increase in the tree population especially among the small size classes (0.1–0.3 m) in 2016 and 2017 relative to the predrought 2012 census. Drought effects may be confounded with changes in browser populations. The impala population declined in a mesic savannah (Hluhluwe), as measured with dung counts; however, this decline started before the drought. Impala decline in a semi‐arid savannah (iMfolozi) was more coincident with drought. Grass biomass and cover decreased in 2016 compared to predrought 2012 but showed rapid recovery once rains began. In iMfolozi grass species, composition improved from a grazing perspective as a result of the recovery of the decreaser species, an increase in palatable species and a marked decline of unpalatable species. The minor changes in woody plants and grasses from before the drought until rain resumed and the rapid recovery of grasses suggest that this South African savannah ecosystem was resilient to severe drought.

A linked surface water-groundwater modelling approach to more realistically simulate rainfall-runoff non-stationarity in semi-arid regions

Interactions between surface water (SW) and groundwater (GW) have been identified as a major contributing factor to non-stationarity in rainfall-runoff relationships. However, because existing rainfall-runoff models do not realistically account for these SW-GW interactions, they fail to robustly simulate runoff during multi-year droughts, especially in arid and semi-arid catchments that are relatively flat. Therefore, this study introduces a linked SW-GW modelling approach and tests it under different climatic conditions (Average, Dry and Wet periods) in two heterogeneous, semi-arid catchments in southeast Australia (SEA). The linked SW-GW modelling approach includes a fully-distributed SW (i.e. rainfall-runoff) model (SWATgrid) and a three-dimensional finite-difference GW model (MODFLOW). The results show that the linked SW-GW modelling approach produces highly improved runoff simulations for the study catchments, especially during dry conditions. These findings demonstrate the importance of accounting for SW-GW interactions when conducting rainfall-runoff modelling and highlights that failing to do so will result in overestimation of runoff during droughts – this is salient given projections for hotter and drier futures in many semi-arid regions. Although the study is focused on SEA, the insights gained are highly applicable for water managers in any region that experience high hydroclimatic variability or change.

Effect of Grazing and Drought on Seed Bank in Semiarid Patchy Rangelands of Northern Patagonia, Argentina

Premise of research. The soil seed bank (SSB) plays a critical role in vegetation regeneration after stress and/or disturbance events. Here, we analyzed how drought and grazing influence the SSB of shrub patches and interpatches in a rangeland from northern Patagonia.Methodology. Soil samples were collected from shrub patches and interpatches on heavily grazed, moderately grazed, and ungrazed sites at the end of a multiyear drought and 2 yr after the end of the drought. Sampling was done immediately before seed dispersion of the dominant species in order to study the persistent seed bank. Seeds were separated from the mineral soil by elutriation and grouped into four life-forms: annual grasses, perennial grasses, forbs, and shrubs.Pivotal results. In all sampling conditions, the SSB was markedly dominated by forbs. Total seed density and seed density of every life-form were higher in shrub patches than in interpatches. Seed density of grasses and shrubs was not influenced by drought and grazing in both shrub patches and interpatches. In contrast, seed density of forbs was negatively influenced by drought in interpatches and positively influenced by grazing in shrub patches.Conclusions. The results suggest that in patchy rangelands of northern Patagonia the SSB of shrub patches is less severely depleted than that of interpatches during multiyear droughts, particularly for forbs under high grazing intensity. However, the growth of the SSB after drought is a slow process in both shrub patches and interpatches. Our results highlight the importance of grazing pressure alleviation during drought conditions to safeguard the SSB, which is the only source of seedling recruitment for most species in northern Patagonia rangelands.

A crop yield change emulator for use in GCAM and similar models: Persephone v1.0

Abstract. Future changes in Earth system state will impact agricultural yields and, through these changed yields, can have profound impacts on the global economy. Global gridded crop models estimate the influence of these Earth system changes on future crop yields but are often too computationally intensive to dynamically couple into global multi-sector economic models, such as the Global Change Assessment Model (GCAM) and other similar-in-scale models. Yet, generalizing a faster site-specific crop model's results to be used globally will introduce inaccuracies, and the question of which model to use is unclear given the wide variation in yield response across crop models. To examine the feedback loop among socioeconomics, Earth system changes, and crop yield changes, rapidly generated yield responses with some quantification of crop response uncertainty are desirable. The Persephone v1.0 response functions presented in this work are based on the Agricultural Model Intercomparison and Improvement Project (AgMIP) Coordinated Climate-Crop Modeling Project (C3MP) sensitivity test data set and are focused on providing GCAM and similar models with a tractable number of rapid to evaluate dynamic yield response functions corresponding to a range of the yield response sensitivities seen in the C3MP data set. With the Persephone response functions, a new variety of agricultural impact experiments will be open to GCAM and other economic models: for example, examining the economic impacts of a multi-year drought in a key agricultural region and how economic changes in response to the drought can, in turn, impact the drought.

Tolerance of ozone and drought in common waterhemp (Amaranthus tuberculatus)

ABSTRACTBiological invasions in established cropping systems impact biodiversity and agricultural sustainability. Under conditions of multi-year drought and elevated tropospheric ozone (O3), several Amaranthus species have recently become problematic weeds in California. We examined responses of common waterhemp (A. tuberculatus) to 12-h mean O3 exposures of 4, 59, or 114 nmol O3 mol air−1, with two levels of irrigation, 33% (deficit irrigation, DI) or 100% (well-watered, WW) of field capacity. Daytime stomatal conductance (gs) was reduced by O3 but not by DI. Nocturnal gs was uncommonly large but unaffected by either treatment. Plant productivity was not affected by O3 or DI. Leaf mass per unit area and root mass per unit leaf area were reduced by O3 but not by DI. Tolerance of this species to O3 and deficit irrigation may increase its competitiveness with crops. High night-time water loss may reduce water availability for competing crops. The competitiveness of common waterhemp may increase, as climate change creates conditions that are adverse to major crops.

Multiyear weather anomalies associated with range shifts by the mountain pine beetle preceding large epidemics

The recent range expansion of the mountain pine beetle, Dendroctonus ponderosae Hopk. (Coleoptera: Curculionidae), into evolutionarily naïve lodgepole and jack pine forests of northwestern Canada has triggered concern that continued eastward expansion through the boreal forest will threaten other pine species native to eastern North America. This unprecedented breach of a historic geoclimatic barrier was precipitated by a “hyperepidemic” west of the Rocky Mountains comprising the largest mountain pine beetle eruption in recorded history. We assessed climate-related latitudinal shifts of pre-outbreak populations of mountain pine beetle in western Canada over a 26-year period preceding the hyperepidemic, as movements of pre-outbreak populations determine, in part, the extent of subsequent outbreaks. We used digitized records of annual aerial overview surveys (1965–1979, 1986–1996) of tree-killing activity, comprising > 122,000 individual infestation polygons, and temperature and aridity data to associate trends in deviations of weather variables from historical averages with latitudinal shifts by the insect. Overall, we found that seasonal and multiyear weather phenomena such as anomalous temperature increases in a stable aridity regime, or vice-versa, and warmer-than-normal winter temperatures explained small but significant variation in northward annual range shifts after factoring out spatial and temporal variation. The numbers of discrete, tree-killing infestations increased rapidly during 1965–1979, and northward range shifts of 300 km in the early 1970s coincided with abnormally dry conditions. Mountain pine beetle populations advanced northward by 391 km from 1965 to 1996. Consistently high infestation levels of the mountain pine beetle occurred simultaneously with above-average temperatures that extended for nearly a decade immediately preceding the hyperepidemic. Climate-associated range shifts can provide gateways to rapid range expansions, and evoke concern with regard to future impacts of other bark beetle species inhabiting regions likely to experience multiyear droughts and/or temperature increases under climate change.

Conserving resources during chronic disaster: Impacts of religious and meaning-focused coping on Botswana drought survivors.

This study explored the trauma symptoms of those who have endured a multiyear drought in Botswana, an arid, pastoral, and primarily Christian Southern African nation. Particularly, this study used conservation of resources theory to consider the effects of disaster-related resource loss (DRL) and the psychology of religion literature to investigate the roles of religious or spiritual (R/S) and meaning-focused coping. Three hundred undergraduates in Botswana completed culturally adapted measures of their DRL, positive and negative R/S coping, search for meaning in life (meaning-focused coping), lifetime trauma exposure, and current trauma symptoms. Data were collected in the 4th year of the record-setting drought. Hierarchical regression analysis was used to add predictors sequentially and demonstrated that both DRL of energies (e.g., time, money) and coping behaviors (both negative R/S and meaning-focused) positively predicted current trauma symptoms beyond one's personal trauma exposure. Further, positive R/S coping was observed to moderate (buffer) the influence of DRL on trauma symptoms, whereas negative R/S and meaning-focused coping appeared to partially mediate the influence of DRL. This study extends research on DRL and coping to the context of chronic disasters. A nuanced treatment of resource loss (accounting for specific item wordings) suggests that although DRL in general may influence negative R/S coping, only some types of resource loss (energetic) from an ongoing-chronic disaster affect both one's current meaning-focused coping and trauma symptoms. In contrast to negative R/S coping behaviors (e.g., doubt), positive ones (e.g., seeking divine connection) were shown to mitigate those effects. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Phenology and productivity in a montane bird assemblage: Trends and responses to elevation and climate variation.

Climate variation has been linked to historical and predicted future distributions and dynamics of wildlife populations. However, demographic mechanisms underlying these changes remain poorly understood. Here, we assessed variation and trends in climate (annual snowfall and spring temperature anomalies) and avian demographic variables from mist-netting data (breeding phenology and productivity) at six sites along an elevation gradient spanning the montane zone of Yosemite National Park between 1993 and 2017. We implemented multi-species hierarchical models to relate demographic responses to elevation and climate covariates. Annual variation in climate and avian demographic variables was high. Snowfall declined (10mm/year at the highest site, 2mm at the lowest site), while spring temperature increased (0.045°C/year) over the study period. Breeding phenology (mean first capture date of juvenile birds) advanced by 0.2day/year (5days); and productivity (probability of capturing a juvenile bird) increased by 0.8%/year. Breeding phenology was 12days earlier at the lowest compared to highest site, 18days earlier in years with lowest compared to highest snowfall anomalies, and 6 d earlier in relatively warm springs (after controlling for snowfall effects). Productivity was positively related to elevation. However, elevation-productivity responses varied among species; species with higher productivity at higher compared to lower elevations tended to be species with documented range retractions during the past century. Productivity tended to be negatively related to snowfall and was positively related to spring temperature. Overall, our results suggest that birds have tracked the variable climatic conditions in this system and have benefited from a trend toward warmer, drier springs. However, we caution that continued warming and multi-year drought or extreme weather years may alter these relationships in the future. Multi-species demographic modeling, such as implemented here, can provide an important tool for guiding conservation of species assemblages under global change.

Assessment of Caatinga response to drought using Meteosat-SEVIRI Normalized Difference Vegetation Index (2008–2016)

The Caatinga semi-arid vegetation in Northeast region of Brazil (NEB) provides a unique opportunity for studying the vegetation in response to recurring droughts, because of its negative impacts on soil erosion. Surprisingly, however, the response of Caatinga vegetation to a recent multi-year drought across the entire semi-arid NEB has not been studied in detail. This study analyses the spatiotemporal patterns of drought impact on the Caatinga vegetation between 2008 and 2016. Yet previous research has shown that a linear relationship exists between rainfall and Caatinga vegetation at interannual timescale. Because of the strong large-scale control of precipitation, year-to-year rainfall variations have a notable degree of spatiotemporal heterogeneity in semi-arid NEB. We exploit this relationship by developing the local-to regional-scale rainfall-Normalized Difference Vegetation Index (NDVI) distribution over the Caatinga vegetation, using daily rainfall time series from in situ weather stations, and daily Meteosat Second Generation (MSG) NDVI time series. Results showed that the drought impact (2012–2015) through the rainfall deficit dynamics influenced the dynamics of vegetative drought in the Caatinga vegetation where exhibit a strong decrease in vegetation activity, contrasting with irrigated croplands that exhibit little sensitivity to drought. It is the longest, continuous drought on the historical record (1901 onwards). The severe drought year of 2012 affected more than 26% of the vegetated area in the region. Over the 2012–2016 period, the positive trend observed in vegetation greenness is largely explained by a positive trend in the rainfall over 45% of the Caatinga vegetation, with the three months lagged rainfall (R2 = 0.62 with p < 0.05). This suggests that the vegetation greenness occurs in some portions of Caatinga region is mainly due to inadequate land management practices (i.e., irrigation with poor drainage, crop planting, bush encroachment, grazing-converted, pasture, etc.) often in combination with recurring droughts.

Littoral habitat loss caused by multiyear drought and the response of an endemic fish species in a deep desert lake

Abstract Multiyear drought is projected to increase in frequency and duration in arid and semiarid regions across the world, threatening native species and ecosystem function. The effects of multiyear drought are often exacerbated by human water use for consumption, energy production, and agriculture, which, in lentic ecosystems, manifest in reduced lake elevation and altered habitat for aquatic species. Here, we demonstrate that decreasing lake levels, associated with drought and water management, reduce the availability of littoral cobble habitat to fishes by creating an elevation‐explicit littoral habitat map. We combined long‐term fish catch data and a lake elevation time series with our elevation‐explicit littoral habitat map to test whether fish species population demographics are related to drought‐driven changes in littoral habitat. We surveyed the littoral zone of Bear Lake, Utah and Idaho, U.S.A., from full pool to a depth of &gt;12 m, totalling 94.86 km2 surveyed. As lake elevation decreased &gt;6 m from full pool to the lowest historical elevation, the area of littoral cobble decreased by &gt;97%. Bear Lake sculpin (Cottus extensus, Cottidae), a cold‐water fish species which relies on cobble for reproduction, catch per unit effort decreased by &gt;75% with littoral cobble, and year class strength declined by as much as 86%, but varied across age. We predicted the response of age‐0 to age‐4 sculpin under high and low cobble availability. Our simulations predict a 60%–85% decline in juvenile sculpin CPUE (age‐2 and younger) when cobble availability decreases from the 95th to 5th percentile. Our study provided a unique opportunity to identify quantitative linkages between climate‐driven littoral habitat loss and an ecologically important profundal fish species, expanding our understanding of potential future pathways through which climate change may affect lentic ecosystems and fishes.

Winter Storm Conditions Leading to Excessive Runoff above California’s Oroville Dam during January and February 2017

AbstractDuring winter 2016/17, California experienced numerous heavy precipitation events linked to land-falling atmospheric rivers (ARs) that filled reservoirs and ended a severe, multiyear drought. These events also caused floods, mudslides, and debris flows, resulting in major socioeconomic disruptions. During 2–11 February 2017, persistent heavy precipitation in the northern Sierra Nevada culminated in a rapid increase in the water level on Lake Oroville, necessitating the activation of an emergency spillway for the first time since the Oroville Dam was installed and forcing the evacuation of 188,000 people. The precipitation, which mostly fell as rain due to elevated freezing levels, was focused on the western slope of the Sierra Nevada in connection with orographic forcing linked to two successive ARs. Heavy rain fell on saturated soils and a snowpack produced by antecedent storms and thereby resulted in excessive runoff into Lake Oroville that led to a damaged spillway and complicated reservoir operations.

Decline in body condition and high drought mortality limit the spread of wild chital deer in north-east Queensland, Australia

Chital deer (Axis axis) were introduced to the Burdekin district of northern Queensland, Australia in 1886. Compared with most successful ungulate introductions they have been slow to expand their distribution and increase in abundance (Moriarty 2004). In this study we consider the possibility that forage shortages caused by periodic droughts have caused sufficient mortalities to limit the increase and spread of chital in the region. The Burdekin district experiences fluctuations in forage according to seasonal rainfall as well as multi-year droughts. This study recorded the decline in body condition, measured as kidney fat index (KFI) and bone marrow fat (BMF), over the wet and dry seasons of two successive years in two chital deer populations during a period when annual rainfall was ~40% below average. We relate the falls in mean KFI from ~45–15%, and mean BMF from ~80–50% to the surveyed decline in chital populations of ~80%. The extent of the decline implies increased mortalities in all age classes as well as reduced reproductive output. We propose that it is likely that chital populations have experienced several such drought mortality events since the 1890s which have contributed to their limited spread.

Multistate occupancy modeling improves understanding of amphibian breeding dynamics in the Greater Yellowstone Area.

Discerning the determinants of species occurrence across landscapes is fundamental to their conservation and management. In spatially and climatologically complex landscapes, explaining the dynamics of occurrence can lead to improved understanding of short‐ vs. long‐term trends and offer novel insight on local vs. regional change. We examined the changes in occupancy for two species of anurans with different life histories over a decade using hundreds of wetland sites in Yellowstone and Grand Teton National Parks. To account for the joint dynamics of wetland drying and amphibian breeding, we adopted a multistate occupancy model as a means to investigate mechanistic relationships of observed occurrence patterns with climatological drivers of wetland hydrologic variability. This approach allowed us to decompose occupancy dynamics into habitat changes caused by wetland drying and amphibian breeding activity, conditional on available water and previous breeding state. Over our 10‐yr time series, we observed considerable variability in climate drivers and the proportion of dry wetlands. Boreal chorus frogs (Pseudacris maculata) were more responsive to changes in wetland inundation status than Columbia spotted frogs (Rana luteiventris), as indicated by higher breeding colonization probabilities under favorable (wet) conditions. Both species had high probabilities of breeding persistence in permanently inundated wetlands with prior breeding. Despite the absence of multi‐year drought in our time series, mechanistic relationships described here offer insights on how future climate variation may result in reduced and/or shifted occurrence patterns for pond‐breeding anurans in the Greater Yellowstone Area. Further, our modeling approach may prove valuable in evaluating determinants of occurrence for other species that are dependent on wetlands or other dynamic habitats.