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Baez-Villanueva, O. M., Zambrano-Bigiarini, M., Miralles, D. G., Beck, H. E., Siegmund, J. F., Alvarez-Garreton, C., et al. (2024). On the timescale of drought indices for monitoring streamflow drought considering catchment hydrological regimes. Hydrol. Earth Syst. Sci., 28(6), 1415–1439.
Abstract: There is a wide variety of drought indices, yet a consensus on suitable indices and temporal scales for monitoring streamflow drought remains elusive across diverse hydrological settings. Considering the growing interest in spatially distributed indices for ungauged areas, this study addresses the following questions: (i) What temporal scales of precipitation-based indices are most suitable to assess streamflow drought in catchments with different hydrological regimes? (ii) Do soil moisture indices outperform meteorological indices as proxies for streamflow drought? (iii) Are snow indices more effective than meteorological indices for assessing streamflow drought in snow-influenced catchments? To answer these questions, we examined 100 near-natural catchments in Chile with four hydrological regimes, using the standardised precipitation index (SPI), standardised precipitation evapotranspiration index (SPEI), empirical standardised soil moisture index (ESSMI), and standardised snow water equivalent index (SWEI), aggregated across various temporal scales. Cross-correlation and event coincidence analysis were applied between these indices and the standardised streamflow index at a temporal scale of 1 month (SSI-1), as representative of streamflow drought events. Our results underscore that there is not a single drought index and temporal scale best suited to characterise all streamflow droughts in Chile, and their suitability largely depends on catchment memory. Specifically, in snowmelt-driven catchments characterised by a slow streamflow response to precipitation, the SPI at accumulation periods of 12-24 months serves as the best proxy for characterising streamflow droughts, with median correlation and coincidence rates of approximately 0.70-0.75 and 0.58-0.75, respectively. In contrast, the SPI at a 3-month accumulation period is the best proxy over faster-response rainfall-driven catchments, with median coincidence rates of around 0.55. Despite soil moisture and snowpack being key variables that modulate the propagation of meteorological deficits into hydrological ones, meteorological indices are better proxies for streamflow drought. Finally, to exclude the influence of non-drought periods, we recommend using the event coincidence analysis, a method that helps assessing the suitability of meteorological, soil moisture, and/or snow drought indices as proxies for streamflow drought events.
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Ramajo, L., Prado, L., Rodriguez-Navarro, A. B., Lardies, M. A., Duarte, C. M., & Lagos, N. A. (2016). Plasticity and trade-offs in physiological traits of intertidal mussels subjected to freshwater-induced environmental variation. Mar. Ecol.-Prog. Ser., 553, 93–109.
Abstract: Environmental gradients play an important role in shaping geographic variability in coastal marine populations. Thus, the ability of organisms to cope with these changes will depend on their potential to acclimatize, or adapt, to these new environmental conditions. We investigated the spatial variability in biological responses shown by Perumytilus purpuratus mussels collected from 2 intertidal areas experiencing contrasting freshwater input influences (river-influenced vs. marine conditions). To highlight the role of plasticity and adaptive potential in biological responses, we performed a reciprocal-transplant experiment and measured relevant phenotypic traits including mortality, growth, calcification, metabolism, and chemical composition of the shell periostra cum. We determined that mussels exposed to river-influenced conditions had increased metabolic rates and reduced growth rates, as compared to mussels experiencing marine conditions (p < 0.05). While the energy investment strategies of the 2 local populations resulted in similar net calcification rates, these rates decreased significantly when mussels were transplanted to the river-influenced site. Stressful conditions at the river-influenced site were evidenced by decreased survivorship across treatments. Freshwater inputs modify the organic composition of the shell periostracum through a significant reduction in polysaccharides. Although our field experiment did not identify specific environmental factors underlying these contrasting phenotypic changes, the results imply that plasticity plays a strong role when P. purpuratus is exposed to some combination of natural (e.g. salinity) and anthropogenic influences (e.g. pollution), and that the lack of exposure to freshwater may promote less tolerant mussels with greater potential for local adaptation.
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