The effect of fire on annual streamflow has been examined in numerous watershed studies, with some studies observing postfire increases in streamflow while other have observed no conclusive change. ...Despite this inherent variability in streamflow response, the management of water resources for flood protection, water supply, water quality, and the environment necessitates an understanding of postfire effects on streamflow at regional scales. In this study, the regional effect of wildfire on annual streamflow was investigated using 12 paired watersheds in central and southern California. A mixed model was used to pool and statistically examine the combined paired‐watershed data, with emphasis on the effects of percentage area burned, postfire recovery of vegetation, and postfire wetness conditions on postfire streamflow change. At a regional scale, postfire annual streamflow increased 134% (82%–200%) during the first postfire year assuming 100% area burned and average annual wetness conditions. Postfire response decreased with lower percentages of percentage area burned and during subsequent years as vegetation recovered following fire. Annual streamflow response to fire was found to be sensitive to annual wetness conditions, with postfire response being smallest during dry years, greatest during wet years, and slowly decreasing during very wet years. These findings provide watershed managers with a first‐order estimate for predicting postfire streamflow response in both gauged and ungauged watersheds.
Key Points:
Regional effect of fire on annual streamflow was estimated using a mixed model
Annual streamflow in California increased following fire at regional scale
Postfire streamflow change was sensitive to postfire wetness conditions
Cervical dystonia is a neurological disorder characterized by sustained, involuntary movements of the head and neck. Most cases of cervical dystonia are idiopathic, with no obvious cause, yet some ...cases are acquired, secondary to focal brain lesions. These latter cases are valuable as they establish a causal link between neuroanatomy and resultant symptoms, lending insight into the brain regions causing cervical dystonia and possible treatment targets. However, lesions causing cervical dystonia can occur in multiple different brain locations, leaving localization unclear. Here, we use a technique termed 'lesion network mapping', which uses connectome data from a large cohort of healthy subjects (resting state functional MRI, n = 1000) to test whether lesion locations causing cervical dystonia map to a common brain network. We then test whether this network, derived from brain lesions, is abnormal in patients with idiopathic cervical dystonia (n = 39) versus matched controls (n = 37). A systematic literature search identified 25 cases of lesion-induced cervical dystonia. Lesion locations were heterogeneous, with lesions scattered throughout the cerebellum, brainstem, and basal ganglia. However, these heterogeneous lesion locations were all part of a single functionally connected brain network. Positive connectivity to the cerebellum and negative connectivity to the somatosensory cortex were specific markers for cervical dystonia compared to lesions causing other neurological symptoms. Connectivity with these two regions defined a single brain network that encompassed the heterogeneous lesion locations causing cervical dystonia. These cerebellar and somatosensory regions also showed abnormal connectivity in patients with idiopathic cervical dystonia. Finally, the most effective deep brain stimulation sites for treating dystonia were connected to these same cerebellar and somatosensory regions identified using lesion network mapping. These results lend insight into the causal neuroanatomical substrate of cervical dystonia, demonstrate convergence across idiopathic and acquired dystonia, and identify a network target for dystonia treatment.
Higher global temperatures and increased levels of disturbance are contributing to greater tree mortality in many forest ecosystems. These same drivers can also limit forest regeneration, leading to ...vegetation type conversion. For the Sierra Nevada of California, little is known about how type conversion may affect streamflow, a critical source of water supply for urban, agriculture and environmental purposes. In this paper, we examined the effects of tree-to-shrub type conversion, in combination with climate change, on streamflow in two lower montane forest watersheds in the Sierra Nevada. A spatially distributed ecohydrologic model was used to simulate changes in streamflow, evaporation, and transpiration following type conversion, with an explicit focus on the role of vegetation size and aspect. Model results indicated that streamflow may show negligible change or small decreases following type conversion when the difference between tree and shrub leaf areas is small, partly due to the higher stomatal conductivity and the deep rooting depth of shrubs. In contrast, streamflow may increase when post-conversion shrubs have a small leaf area relative to trees. Model estimates also suggested that vegetation change could have a greater impact on streamflow magnitude than the direct hydrologic impacts of increased temperatures. Temperature increases, however, may have a greater impact on streamflow timing. Tree-to-shrub type conversion increased streamflow only marginally during dry years (annual precipitation < 800 mm), with most streamflow change observed during wetter years. These modeling results underscore the importance of accounting for changes in vegetation communities to accurately characterize future hydrologic regimes for the Sierra Nevada.
Extreme wildfires are increasing in frequency globally, prompting new efforts to mitigate risk. The ecological appropriateness of risk mitigation strategies, however, depends on what factors are ...driving these increases. While regional syntheses attribute increases in fire activity to both climate change and fuel accumulation through fire exclusion, they have not disaggregated causal drivers at scales where land management is implemented. Recent advances in fire regime modeling can help us understand which drivers dominate at management-relevant scales. We conducted fire regime simulations using historical climate and fire exclusion scenarios across two watersheds in the Inland Northwestern U.S., which occur at different positions along an aridity continuum. In one watershed, climate change was the key driver increasing burn probability and the frequency of large fires; in the other, fire exclusion dominated in some locations. We also demonstrate that some areas become more fuel-limited as fire-season aridity increases due to climate change. Thus, even within watersheds, fuel management must be spatially and temporally explicit to optimize effectiveness. To guide management, we show that spatial estimates of soil aridity (or temporally averaged soil moisture) can provide a relatively simple, first-order indicator of where in a watershed fire regime is climate vs. fuel-limited and where fire regimes are most vulnerable to change.
The effect of wildfire on peak streamflow and annual water yield has been investigated empirically in numerous studies. The effect of wildfire on baseflow recession rates, in contrast, is not well ...documented. The objective of this paper was to quantify the effect of wildfire on baseflow recession rates in California for both individual watersheds and for all the study watersheds collectively. Two additional variables, antecedent groundwater storage and potential evapotranspiration, were also investigated for their effect on baseflow recession rates and postfire baseflow recession rate response. Differences between prefire and postfire baseflow recession rates were modeled statistically in 8 watersheds using a mixed statistical model that accounted for fixed and random effects. For the all‐watershed model, antecedent groundwater storage, potential evapotranspiration, and wildfire were each found to be significant controls on baseflow recession rates. Wildfire decreased baseflow recession rates 52.5% (37.6% to 66.0%), implying that postfire reductions in above‐ground vegetation (e.g., decreased interception, decreased evapotranspiration) were a stronger control on baseflow recession rate change than hydrophobicity. At an individual watershed scale, baseflow recession rate response to wildfire was found to be sensitive to intraannual differences in antecedent groundwater storage in 2 watersheds, with the effect of wildfire on baseflow recession rates being greater with lower levels of antecedent groundwater storage. Examination of burn severity for a subset of the study watersheds pointed to riparian zone burn severity as a potential primary control on postfire recession rate change. This study demonstrates that wildfire may have a substantial impact on fluxes to and from groundwater storages, altering the rate at which baseflow recedes.
Climate and wildfire are closely linked. Climate regulates wildfire directly over short timescales through its effect on fuel aridity and indirectly over long timescales through vegetation ...productivity and the structure and abundance of fuels. Prediction of future wildfire regimes in a changing climate often uses empirical studies that presume current relationships between short‐term climate variables and wildfire activity will be stationary in the future. This is problematic because landscape‐scale wildfire dynamics exhibit non‐stationarity, with both positive and negative feedback loops that operate at different temporal and spatial scales. This requires that such feedbacks are accommodated in a model framework from which wildfire dynamics are emergent rather than pre‐specified. We use a new model, RHESSys‐WMFire, that integrates ecohydrology with fire spread and effects to simulate a 60‐yr time series of vegetation, fuel development, and wildfire in a 6572‐ha watershed in the Southern Sierra Nevada, USA, with a factorial design of increased temperature and severe drought. All climate scenarios had an initial pulse of elevated area burned associated with high temperature, low precipitation, and high fine fuel loading. There were positive correlations between annual area burned and mean annual maximum temperature and negative correlations with annual precipitation, consistent with understood direct effects of climate on wildfire in this system. Decreased vegetation productivity and increased fine fuel decomposition were predicted with increased temperature, resulting in long‐term reduced fine fuels and area burned relative to baseline. Repeated extreme drought increased area burned relative to baseline and over the long‐term had substantially reduced overstory biomass. Overstory biomass was resilient to repeat wildfire under baseline climate. The model system predicts that the short‐term direct effects of climate on wildfire can differ from long‐term indirect effects such that the simple maxim hotter/drier equals more wildfire can be both true and false, depending on scale.
The water balance is an essential tool for hydrologic studies and quantifying water‐balance components is the focus of many research catchments. A fundamental question remains regarding the ...appropriateness of water‐balance closure assumptions when not all components are available. In this study, we leverage in‐situ measurements of water fluxes and storage from the Southern Sierra Critical Zone Observatory (SSCZO) and the Kings River Experimental Watersheds (KREW) to investigate annual water‐balance closure errors across large (1016–5389 km2) river basins and small (0.5–5 km2) headwater‐catchment scales in the southern Sierra Nevada. The results showed that while long‐term water balance in river basins can be closed within 10% of precipitation, in the smaller headwater catchments as much as a quarter of precipitation remained unaccounted for. A detailed diagnosis of this water‐balance closure error using distributed soil moisture measurements in the top 1 m suggests an unaccounted deeper storage and a net groundwater export from the headwater catchments. This imbalance was also found to be very sensitive to the timescales over which water‐balance closures were attempted. While some of the closure errors in the simple water balance can be attributed to measurement uncertainties, we argue for a broader consideration of groundwater exchange when evaluating hydrological processes at headwater scales, as the assumption of negligible net groundwater exchange may lead to an overestimation of fluxes derived from the water balance method.
We quantified the variation in water balance closure across multiple spatial and temporal scales and argue for a broader consideration of groundwater exchange terms when evaluating hydrological processes, particularly at small headwater scales. The current assumption of water balance closure by forcing net groundwater exchange to zero may lead to an overestimation of the other unknown water fluxes.
Vitamin D2 (ergocalciferol) and sterols were analyzed in mushrooms sampled nationwide in the United States to update the USDA Nutrient Database for Standard Reference. Vitamin D2 was assayed using ...HPLC with 3H-vitamin D3 internal standard and sterols by GC-FID mass spectrometric (MS) confirmation. Vitamin D2 was low (0.1–0.3 μg/100 g) in Agaricus bisporus (white button, crimini, portabella) and enoki, moderate in shiitake and oyster (0.4–0.7 μg/100 g), and high in morel, chanterelle, maitake (5.2–28.1 μg/100 g) and UV-treated portabella (3.4–20.9 μg/100 g), with significant variability among composites for some types. Ergosterol (mg/100 g) was highest in maitake and shiitake (79.2, 84.9) and lowest in morel and enoki (26.3, 35.5); the range was <10 mg/100 g among white button composites but 12–50 mg/100 g among samples of other types. All mushrooms contained ergosta-5,7-dienol (22,23-dihydroergosterol) (3.53–18.0 mg/100 g) and (except morel) ergosta-7-enol. Only morel contained brassicasterol (28.6 mg/100 g) and campesterol (1.23–4.54 mg/100 g) and no ergosta-7,22-dienol. MS was critical in distinguishing campesterol from ergosta-7,22-dienol.
Forest biomass reductions in overgrown forests have the potential to provide hydrologic benefits in the form of improved forest health and increased streamflow production in water‐limited systems. ...Biomass reductions may also alter evaporation. These changes are generated when water that previously would have been transpired or evaporated from the canopy of the removed vegetation is transferred to transpiration of the remaining vegetation, streamflow, and/or non‐canopy evaporation. In this study, we combined a new vegetation‐change water‐balance approach with lumped hydrologic modelling outputs to examine the effects of forest biomass reductions on transpiration of the remaining vegetation and streamflow in California's Sierra Nevada. We found that on average, 102 mm and 263 mm (8.0% and 20.6% of mean annual precipitation MAP) of water were made available following 20% and 50% forest biomass‐reduction scenarios, respectively. This water was then partitioned to both streamflow and transpiration of the remaining forest, but to varying degrees depending on post‐biomass‐reduction precipitation levels and forest biomass‐reduction intensity. During dry periods, most of the water (approximately 200 mm 15.7% on MAP for the 50% biomass‐reduction scenario) was partitioned to transpiration of the remaining trees, while less than 50 mm (3.9% on MAP) was partitioned to streamflow. This increase in transpiration during dry periods would likely help trees maintain forest productivity and resistance to drought. During wet periods, the hydrologic benefits of forest biomass reductions shifted to streamflow (200 mm 15.7% on MAP) and away from transpiration (less than 150 mm 11.8% on MAP) as the remaining trees became less water stressed. We also found that streamflow benefits per unit of forest biomass reduction increased with biomass‐reduction intensity, whereas transpiration benefits decreased. By accounting for changes in vegetation, the vegetation‐change water balance developed in this study provided an improved assessment of watershed‐scale forest health benefits associated with forest biomass reductions.
We developed a new vegetation‐change water‐balance approach to examine the effects of biomass reductions on forest health and streamflow. During dry periods, most of the water made available from biomass reductions was partitioned to transpiration of the remaining trees. During wet periods, this partitioning shifted to streamflow.
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