Months Of Drought Research Articles

Drought projection based on a hybrid drought index using Artificial Neural Networks

AbstractThe Tarim River Basin is a special endorheic arid drainage basin in Central Asia, characterized by limited rainfall and high evaporation as common in deserts, while water is supplied mainly by glacier and snow melt from the surrounding mountains. The existing drought indices can hardly capture the drought features in this region as droughts are caused by two dominant factors (meteorological and hydrological conditions). To overcome the problem, a new hybrid drought index (HDI), integrating the meteorological and hydrological drought regimes, was developed and tested in the basin in the work. The index succeeded in revealing the drought characteristics and the ensemble influence better than the single standardized precipitation index or the hydrological index. The Artificial Neural Network approach based on temperature and precipitation observations was set up to simulate the HDI change. The method enabled constructing scenarios of future droughts in the region using climate simulation of the GCMs under four RCP scenarios from the latest CMIP5 project. The simulations in the study have shown that the water budget patterns in the Tarim River Basin are more sensitive to temperature than to precipitation. Dominated by temperature rise causing an accelerating snow/glacier melt, the frequency of drought months is projected to decrease by about 14% in the next decades (until 2035). The drought duration is expected to be shortened to 3 months on average, with the severity alleviated. However, the region would still suffer more severe droughts with a high intensity in some years. The general decrease in drought frequency and intensity over the region in the future would be beneficial for water resources management and agriculture development in the oases. Copyright © 2014 John Wiley & Sons, Ltd.

Temporal nestedness in Chironomidae and the importance of environmental and spatial factors in species rarity

Biological communities are composed of a few common and many rare species. An understanding of the mechanisms that govern the distribution of these species is fundamental to knowledge regarding community ecology. Our hypothesis is that chironomid larvae follow a nested distribution in relation to hydrological periods in Neotropical floodplain lakes, whereby the flood period composition is a subset of the drought periods with a predominance of common species. We collected samples from 18 lakes in 2011 in a flood month and three drought months. The community followed a nested distribution where the spatial factors were more important for rare and common species during the flood and for the common species during all months. Thus, with the increasing connectivity and similarity of environments during the flood, neutral processes, as the dispersal, would govern the community. Conversely, environmental factors were more important for rare species in the drought, which suggest that these species are more specialists, largely influenced by niche-related processes. Thus, our study emphasizes the complexity of biological communities specifically concerning how environmental, spatial, and temporal factors influence community dynamics among species groups.

Carbohydrate dynamics and mortality in a piñon-juniper woodland under three future precipitation scenarios.

Drought-induced forest mortality is an increasing global problem with wide-ranging consequences, yet mortality mechanisms remain poorly understood. Depletion of non-structural carbohydrate (NSC) stores has been implicated as an important mechanism in drought-induced mortality, but experimental field tests are rare. We used an ecosystem-scale precipitation manipulation experiment to evaluate leaf and twig NSC dynamics of two co-occurring conifers that differ in patterns of stomatal regulation of water loss and recent mortality: the relatively desiccation-avoiding piñon pine (Pinus edulis) and the relatively desiccation-tolerant one-seed juniper (Juniperus monosperma). Piñon pine experienced 72% mortality after 13-25 months of experimental drought and juniper experienced 20% mortality after 32-47 months. Juniper maintained three times more NSC in the foliage than twigs, and converted NSC to glucose and fructose under drought, consistent with osmoregulation requirements to maintain higher stomatal conductance during drought than piñon. Despite these species differences, experimental drought caused decreased leaf starch content in dying trees of both species (P < 0.001). Average dry-season leaf starch content was also a good predictor of drought-survival time for both species (R(2) = 0.93). These results, along with observations of drought-induced reductions to photosynthesis and growth, support carbon limitation as an important process during mortality of these two conifer species.

STUDY OF CLIMATIC DROUGHT STATUS IN QUANG TRI PROVINCE

Quang Tri province is an area where drought rather often occurs, and severely occurred in many years. Climatic drought had been studied and analyzed based on 28-year data in the period 1985-2012. Monthly dry-wet status of this period had been compiled and presented in distribution graphs. The interpretation and analysis have shown that the drought frequency situation in the province is as follows: 7.87 drought week per year, 0.66 drought week per month (in average two drought weeks per 3 months); 3 drought period per year; drought month frequency is: (1) 13.8% for dry months; (2) 12.1% for wet months; (3) 12.2% for all seasonal months; drought season (dry or wet season) almost only ccurs in dry seasons (excepts 2006 was drought year) with frequency 17.9% (about 5.6 years one time). Drought months determined by accumulative rainfall criteria and drought coefficient have given higher frequency in compare to other drought criteria. Quang Tri has almost every year drought weeks and drought period, approximately during 8.2 years there is one year with drought month, and during 5.6 years there is one year with drought season.ReferencesNguyễn Duy Chinh (chủ biên), 2002. Đánh giá đặc điểm khí hậu tỉnh Quảng Trị. Đề tài nhánh thuộc đề tài “Xây dựng cơ sở dữ liệu và đánh giá đặc điểm khí tượng thủy văn phục vụ phát triển kinh tế - xã hội tỉnh Quảng Trị”. UBND tỉnh Quảng Trị.Nguyễn Trọng Hiệu, 1998. Phân bố hạn và tác động của chúng ở miền Trung. Báo cáo kết quả đề tài nghiên cứu khoa học Tổng cục Khí tượng Thủy văn (từ tháng 8/2002 là Trung tâm Khí tượng Thuỷ văn Quốc gia - Bộ TNMT; từ tháng 3/2013 là Cục Khí tượng Thủy văn và Biến đổi Khí hậu - Bộ TNMT).Nguyễn Thị Nga, Nguyễn Phương Nhung, 2009. Tài nguyên nước mặt tỉnh Quảng Trị. Tạp chí Khoa học ĐHQGHN-Khoa học Tự nhiên và Công nghệ 25, Số 3S. Trang 472‐483.Nguyễn Thám, Nguyễn Hoàng Sơn, 2011. Đánh giá tài nguyên sinh thái khí hậu phục vụ phát triển du lịch tỉnh Quảng Trị. Tạp chí Khoa học Đại học Huế, số 65.Ban chỉ huy PCLB &amp; TKCN tỉnh Quảng Trị UBND tỉnh Quảng Trị, 2011. Báo cáo tổng kết công tác PCLB &amp; Giảm nhẹ thiên tai 1998 - 2010.Trung tâm Dự báo Khí tượng Thủy văn Trung ương-Bộ Tài nguyên và Môi trường. Dữ liệu khí tượng thủy văn Quảng Trị 1985-2012.

Temporal-spatial characteristics of severe drought events and their impact on agriculture on a global scale

To identify the world's severely drought-prone areas, given that the corresponding ground area for a 0.5-degree grid in different latitudes is different, we proposed a more precise spherical area-based statistical method. The corresponding ground area per 0.5-degree grid is obtained by integral calculation in latitude and longitude directions. The analysis of the drought based on the global Standardized Precipitation Evapotranspiration Index dataset from 1902 to 2008, where global, Northern Hemisphere, Southern Hemisphere, and major crop-planting regions from six continents are treated as statistical units. The interannual variability characteristics of the severe drought area for each statistical unit are investigated. To study the spatial distribution characteristics of the global frequency of severe drought, the drought frequency was calculated based on drought events identified by continuous drought months on a grid level. Six major crops (wheat, maize, rice, soybean, barley, and sorghum) were chosen to study the impact of drought events on agriculture. The results suggested that severe droughts in global, Northern Hemisphere, and Southern Hemisphere areas have indicated a downward trend since 1990, but an upward trend overall in all continents except Oceania. The identified drought-prone areas show a patchy distribution and frequently drought-prone areas (with 10–20% occurrence probability of drought) were distributed in regions surrounding chronically drought-prone areas (with more than 20% probability). Global chronically drought-prone areas have increased significantly, from 16.19% in 1902–1949 to 41.09% in 1950–2008. Chronically drought-prone areas of agriculture are located in the center of southern Europe, South America, and eastern Asia.

Seasonality in the dung beetle community in a Brazilian tropical dry forest: Do small changes make a difference?

Dung beetle (Coleoptera: Scarabaeoidea: Scarabaeinae) activity is influenced by rainfall seasonality. We hypothesized that rainfall might also play a major role in regulating the community structure of this group. In this study, we describe seasonal changes in the richness, composition, and structure of the Scarabaeinae community in a Brazilian tropical dry forest. A fragment of arboreal Caatinga was sampled using baited pitfall traps during the early dry season (EDS), late dry season (LDS), early wet season (EWS), and middle wet season (MWS). We compared the dung beetle community in each season in relationship to species richness, rank-dominance, curves, and composition. We collected 1352 Scarabaeinae individuals , belonging to 15 species. Dichotomius aff. laevicollis Felsche (Coleoptera: Scarabaeidae) was the dominant species, representing 73.89% of the individuals. There were no seasonal changes in the rank dominance curves; all had a single dominant species and a few species with low abundance, typical for arid areas. Estimated richness was highest in MWS, followed by EWS. Dry-season samples (EDS and LDS) had lower richness, with no significant difference between the dry seasons. Although species richness increased as the habitat became wetter, the difference between the wet and dry seasons was small, which differs completely from the findings of other studies in Neotropical dry forests, where almost all species cease activities in the dry season. Species composition changes were found in non-metric multidimensional scaling and sustained by analysis of similarity. All the seasons had pairwise differences in composition, with the exception of EDS and MWS, which indicates that the dung beetle community in this fragment requires more than three months of drought to trigger changes in species composition; this is probably due to small changes in the forest canopy. There was no difference in composition between EDS and MWS. As in other tropical dry forests, although to a lesser extent, the dung beetle community of this fragment responded to rainfall seasonality with changes in species composition and reduced species richness. Such responses, even to this lesser extent, may occur because of small changes in tree cover and minor microclimate changes.

Temporal Variation of the Concentration of Carbon Monoxide in the Center West of Brazil

South Mato Grosso has been developing very rapidly in recent decades, and it is clearly leaving behind the status of being solely an agricultural region to become an important state in the areas of commerce and industry. Nevertheless, it is still possible to observe the harmful effects of atmospheric pollution due to biomass burning activities, even if those actions are being systematically reduced in the state throughout the past several years. This kind of pollution persists not only due to local activities but also due to the pollution of other states and even other border countries. Satellite remote sensing has proven to be an important tool of environmental control vis-à-vis the ease of data acquisition, accuracy and wide temporal range. A study has been conducted of spatial and temporal concentration of carbon monoxide (CO) in the state of South Mato Grosso from 2001 through 2012 using the MOPITT sensor onboard the TERRA satellite. The carbon monoxide comes principally from the incomplete combustion of vehicles engines and biomass burnings. A direct correlation of the CO concentration in the state of South Mato Grosso is observed precisely during the months of drought (August to October), for which the number of fire outbreaks is the highest of the year.

Hydrological Modeling of the Jiaoyi Watershed (China) Using HSPF Model

A watershed hydrological model, hydrological simulation program-Fortran (HSPF), was applied to simulate the spatial and temporal variation of hydrological processes in the Jiaoyi watershed of Huaihe River Basin, the heaviest shortage of water resources and polluted area in China. The model was calibrated using the years 2001–2004 and validated with data from 2005 to 2006. Calibration and validation results showed that the model generally simulated mean monthly and daily runoff precisely due to the close matching hydrographs between simulated and observed runoff, as well as the excellent evaluation indicators such as Nash-Sutcliffe efficiency (NSE), coefficient of correlation (R 2), and the relative error (RE). The similar simulation results between calibration and validation period showed that all the calibrated parameters had a certain representation in Jiaoyi watershed. Additionally, the simulation in rainy months was more accurate than the drought months. Another result in this paper was that HSPF was also capable of estimating the water balance components reasonably and realistically in space through the whole watershed. The calibrated model can be used to explore the effects of climate change scenarios and various watershed management practices on the water resources and water environment in the basin.

Does a rainfall-based drought index simulate hydrological droughts?

The drought severity index (DSI) is applied at 3-, 6-, 12- and 24-month time scales to both monthly gridded rainfall and monthly river flow datasets to evaluate if a rainfall-based drought index is able to simulate hydrological droughts. Time series of the rainfall-based and the flow-based DSIs are analysed at different drought severities and seasons at seven benchmark catchments in England. The analysis also includes the ability of the indices to reproduce the statistics of three drought characteristics, namely drought intensity, frequency of drought months and frequency of drought events at a given duration. Results of this study show that: (1) the rainfall-based DSI is able to capture periods of low flows as can be seen in its ability to represent major hydrological drought events as simulated by the flow-based DSI, (2) the rainfall-based DSIs generally represent moderate hydrological droughts better than extremes as shown by the smaller difference between the rainfall-based and the flow-based DSIs in terms of the statistics of the three drought characteristics and (3) there is a positive relationship between the time scale of DSI and the intensity (and duration) of the drought event it produces. As a secondary objective, the study has shown that the monthly gridded rainfall is a good proxy for monthly catchment rainfall and can therefore be considered a reliable dataset against which climate change experiments can be evaluated. The study concludes that the DSI is a credible index in estimating hydrological droughts. The strong positive correlation between the rainfall-based and the flow-based DSI time series suggests that changes and trends in rainfall-based DSIs can provide useful inferences for understanding changes in future hydrological droughts, as well as meteorological droughts. It is hoped that results from this study provide useful information when utilizing the DSI for assessment of drought impacts and future planning and management of water resources.

Representation of Soil Moisture Feedbacks during Drought in NASA Unified WRF (NU-WRF)

Abstract Positive soil moisture–precipitation feedbacks can intensify heat and prolong drought under conditions of precipitation deficit. Adequate representation of these processes in regional climate models is, therefore, important for extended weather forecasts, seasonal drought analysis, and downscaled climate change projections. This paper presents the first application of the NASA Unified Weather Research and Forecasting Model (NU-WRF) to simulation of seasonal drought. Simulations of the 2006 southern Great Plains drought performed with and without soil moisture memory indicate that local soil moisture feedbacks had the potential to concentrate precipitation in wet areas relative to dry areas in summer drought months. Introduction of a simple dynamic surface albedo scheme that models albedo as a function of soil moisture intensified the simulated feedback pattern at local scale—dry, brighter areas received even less precipitation while wet, whereas darker areas received more—but did not significantly change the total amount of precipitation simulated across the drought-affected region. This soil-moisture-mediated albedo land–atmosphere coupling pathway is structurally excluded from standard versions of WRF.

陶粒覆盖对土壤水分、植物光合作用及生长状况的影响

In this study,we investigated the effects of a combination of surface coverage and planting as well as the effects of ceramsite mulching on soil water content and the photosynthetic physiological characteristics of plants located in the central isolation belt of Langzhuo Highway in Hebei Province. The results were as follows:(1) Ceramsite mulching increased the soil water content,reduced the soil water content disparity among soil depths and months,and provided a more stable environment for growth. In addition,two layers of ceramsite(M2) had better effects than did a single layer of ceramsite(M1). The overall order of soil water content in soil at different depths or during different months was as follows:two layers of ceramsite(M2) a single layer of ceramsite(M1) bare soil(MD). The effects of ceramsite mulching on soil water content decreased with soil depth from 10 to 60 cm,while the difference in soil water content between bare soil and areas subject to ceramsite mulching was gradually reduced at these depths. During greater drought months,the effects of ceramsite mulching on soil water were obvious.(2) Moreover,ceramsite mulching had an impact on the net photosynthesis(P n),transpiration(T r) and water use efficiency(WUE) of Euonymus japonicus and Rosa chinensis. Specifically,the order of net photosynthesis(P n) of the two plants at any time of the measurement day was two layers of ceramsite(M2) a single layer of ceramsite(M1) bare soil(MD). Furthermore,the average net photosynthesis(P n) of the two plants was greatly improved under two layers of ceramsite(M2). The average transpiration(T r) of the two plants also improved,and the spike times changed in response to ceramsite mulching. Variations in the water use efficiency(WUE) among the two plants were affected by ceramsite mulching,with the order of diurnal averages being two layers of ceramsite(M2) a single layer of ceramsite(M1) bare soil(MD); however,the differences between each other were not significant. Moreover,the effects of ceramsite mulching on water use efficiency(WUE) were much lower than the effects on net photosynthesis(P n)and transpiration(T r). Because the drought-resistance of Euonymus japonicus was worse than that of Rosa chinensis,the effects of ceramsite mulching on Euonymus japonicus were greater than on Rosa chinensis.(3) Ceramsite mulching affected plant survival and growth through its effects on soil and the other conditions of plant growth. Specifically,ceramsite mulching greatly improved the survival rates of Euonymus japonicus L,Platycladus orientalis Franco,Rosa chinensis Jacq,Berberis thumbergii cv.atropurpurea and Euonymus japonicus L and increased the growth of diameter at breast height and the height of all five of these plants. The order of survival rates,growth of diameter at breast height and height of the five plants were as follows: two layers of ceramsite(M2) a single layer of ceramsite(M1) bare soil(MD). M2 showed better results than M1,but there were no significant differences between two layers of ceramsite(M2) and a single layer of ceramsite(M1).

Assessment of drought frequency, duration, and severity and its impact on pasture production in Mongolia

Drought frequency, duration, and severity and its impact on pasture productivity in the four main vegetation zones of Mongolia were analyzed using meteorological, soil moisture, and vegetation data during the growing season (April–August) of 1965–2010. Meteorological and pasture drought characteristics were explored using the Standardized Precipitation Index (SPI), the soil moisture anomalies percentile index (W p), and Palmer Drought Severity Index (PDSI) on 1-month timescale. Generally, 35–37 (15–16 %) by SPI for meteorological drought while 27–29 (12–13 %) by W p, and 16–21 (7–9 %) by PDSI for pasture drought with different durations were identified over the four vegetation zones during the study period. Most of these droughts (80 % by SPI and 50–60 % by both W p and PDSI) observed during the entire events occurred on a 1-month duration with moderate intensity. Drought frequencies were not significantly (p > 0.05) different within the four zones. The frequency of the short-term meteorological droughts was observed relatively greater than pasture droughts; however, pasture droughts were more persistent and severe than meteorological droughts. The three indices show that the frequency and severity of droughts have slightly increased over the 46 years with significant (p < 0.05) dry conditions during the last decade of 2001–2010 in the four zones (except in the high mountain). The results showed the W p was more highly significantly correlated with the precipitation anomalies (r = 0.68) and pasture production (r = 0.55) than PDSI (r = 0.51, p < 0.05 and r = 0.38, p < 0.10, respectively). A statistical model, based on pasture production and the W p, suggested that the consecutive drought months contribution during the growing season was 30 % (p < 0.05) and that pasture production was more sensitive to the occurrence of droughts during June–August (R 2 = 0.32, p < 0.05) as seen in 2000–2002 and 2007. We concluded that a greater severity and frequency of growing-season droughts, during the last decade of 2001–2010, have driven a reduction in pasture production in Mongolia.

Bioacumulation of Cyanotoxins in Hypophthalmichthys molitrix (Silver Carp) in Paranoá Lake, Brasilia-DF, Brazil

Three individuals of silver carp (Hypophthalmichthys molitrix) were collected biweekly from Paranoá Lake (DF, Brazil) for analysis of microcystin (MC) concentrations in their muscle and liver tissue. Analysis by high performance liquid chromatography and mass spectrometry revealed MC masses and fragmentation patterns that were identified as MC-LR (995.04m/z), MC-LA (909.01m/z) and an unknown MC (987.07m/z). Concentrations were calculated as MC-LR equivalents using a calibration curve prepared with a standard of MC-LR. May/06 was the month with the highest MC-LR equivalent concentrations in muscle and liver (3.83±2.78, and 12.94±10.51μgg(-1), respectively). Our results show that during the drought months (April-September), consumption of fish with these MC concentrations would result in exposure to MCs that greatly exceed the World Health Organization's recommended tolerable daily intake limit of 0.04μg MC kg(-1) body weight.

21st Century Drought Scenarios for the UK

A 6-month drought severity index (DSI6) is applied to each of the 11-member perturbed-physics ensemble (HadRM3-PPE-UK) monthly precipitation dataset from 1950 to 2100 to investigate projected 21st century droughts in the UK. Four main drought characteristics are investigated: intensity, drought covariance, frequency of drought months and frequency of drought events at a given duration. Changes in these characteristics are analysed for 30-year periods: 1970–1999 (1980s), 2010–2039 (2020s), 2040–2069 (2050s) and 2070–2099 (2080s) and described in terms of their seasonal behaviour, for both moderate and extreme droughts. Projections of drought characteristics are expressed in the forms of ensemble-mean change relative to the 1980s and model consensus, and analysed over 23 water resource regions. In general, drought characteristics show profound increases (and widespread) for the 2050s and 2080s with larger change occurring during the wet season and under moderate drought conditions. Drought covariance sees greater increase during the dry season with greater change magnitude (but less widespread) under extreme drought conditions. Results also show that droughts can persist over long durations. However, the projected frequency of droughts at longer durations is low compared with droughts with shorter duration of persistence. Water resource regions (WWRs) mostly show negative change in drought characteristics, except for drought covariance. However, intensity and duration of droughts also generally increase over most of the WRRs in England, which are already highly exploited. Of particular relevance to water management, results from this ensemble have a strong influence on dry season water availability, especially in parts of England.

Drought impacts on vegetation in the pre- and post-fire events over Iberian Peninsula

Abstract. The present work aims to study the combined effect of drought and large wildfires in the Iberian Peninsula relying on remotely sensed data of vegetation dynamics and leaf moisture content, in particular monthly NDVI, NDWI and NDDI time series from 1999–2009, derived from VEGETATION dataset. The impact of the exceptional 2004/2005 drought on vegetation was assessed for vegetation recovering from the extraordinary fire season of 2003 and on the conditions that contributed to the onsetting of the fire season of 2005. Drought severity was estimated by the cumulative negative effect on photosynthetic activity (NDVI) and vegetation dryness (NDDI), with about 2/3 of Iberian Peninsula presenting vegetative stress and low water availability conditions, in spring and early summer of 2005. Furthermore, NDDI has shown to be very useful to assess drought, since it combines information on vegetation and water conditions. Moreover, we show that besides looking at the inter-annual variability of NDVI and NDDI, it is useful to evaluate intra-annual changes (δNDVI and δNDDI), as indicators of change in vegetation greenness, allowing a detailed picture of the ability of the different land-cover types to resist to short-term dry conditions. In order to assess drought impact on post-fire regeneration, recovery times were evaluated by a mono-parametric model based on NDVI data and values corresponding to drought months were set to no value. Drought has shown to delay recovery times for several months in all the selected scars from 2003. The analysis of vegetation dynamics and fire selectivity in 2005 suggests that fires tended to occur in pixels presenting lower vegetative and water stress conditions during spring and early summer months. Additionally, pre-fire vegetation dynamics, in particular vegetation density and water availability during spring and early summer, has shown to influence significantly the levels of fire damage. These results stress the role of fuel availability in fire occurrence and impact on the Iberian Peninsula.

A Centuary (1901-2000) of Rainfall climatology – A tool for crop planning

Crop production in changing environment especially under rainfed ecosystem is very difficult. One such important varying environmental factor is rainfall which affects plant growth most vitally and directly. India with its large population predominantly depends on rainfed agriculture, need timely and adequate rainfall for successful crop raising. The study on the temporal and special variations would help to design a viable cropping pattern for a specific location. In this context, monthly rainfall may be useful for planning a viable cropping pattern and related component technologies. An attempt was made to analyse therainfall data of Dharmapuri District,( lies between 11° 45’and 13° 01’ N latitudes and 77° 13’ and 78° 45’ E longitudes with an altitude of 400 meter MSL with mean annual rainfall of 851mm; mean maximum temperature of 32° C ; mean minimum temperature of 20.8° C; mean maximum relative humidity of 89.5 %; mean minimum relative humidity of 53.9 %)Tamil Nadu, India, with a purpose of identification of viable cropping pattern.Analysis of rainfall data for 100 years (1901 – 2000) for Dharmapuri district was done to find out the occurrence of Normal, abnormal and drought months and years. Monthly mean and probability analysis were also made to compute effective growing period. The data revealed that 56.3 percent of months fall under normal rainfall distribution while 34.1 % of months are drought months. Only 9.6%o months fall under excessive rainfall months and it could be observed that the occurrence of normal rain was with 71 % probability in the district. A growing period of 120 days may be planned for annual cropping from second week of August to first week of December. Double cropping could be possible with Millets / Oilseeds/ Pulses as first crop followed by Horse gram as second crop.

Bacterial community dynamics in the hyporheic zone of an intermittent stream

The dynamics of in situ bacterial communities in the hyporheic zone of an intermittent stream were described in high spatiotemporal detail. We assessed community dynamics in stream sediments and interstitial pore water over a two-year period using terminal-restriction fragment length polymorphism. Here, we show that sediments remained saturated despite months of drought and limited hydrologic connectivity. The intermittency of stream surface water affected interstitial pore water communities more than hyporheic sediment communities. Seasonal changes in bacterial community composition was significantly associated with water intermittency, phosphate concentrations, temperature, nitrate and dissolved organic carbon (DOC) concentrations. During periods of low- to no-surface water, communities changed from being rich in operational taxonomic units (OTUs) in isolated surface pools, to a few OTUs overall, including an overall decline in both common and rare taxa. Individual OTUs were compared between porewater and sediments. A total of 19% of identified OTUs existed in both porewater and sediment samples, suggesting that bacteria use hyporheic sediments as a type of refuge from dessication, transported through hydrologically connected pore spaces. Stream intermittency impacted bacterial diversity on rapid timescales (that is, within days), below-ground and in the hyporheic zone. Owing to the coupling of intermittent streams to the surrounding watershed, we stress the importance of understanding connectivity at the pore scale, consequences for below-ground and above-ground biodiversity and nutrient processing, and across both short- and long-time periods (that is, days to months to years).

Analysis of dry periods along a pluviometric gradient in Mediterranean southern Spain

AbstractIn southern Spain a longitudinal pluviometric gradient occurs under Mediterranean climatic conditions in an area that has at least two months of drought each year and very irregular rainfall. From the Strait of Gibraltar to the Cabo de Gata in Almería there is a reduction of more than 1,000 mm year−1 in the mean annual rainfall. Analysis of the frequency and intensity of drought periods is necessary in regions where water resources are scarce and the ecosystem is highly dependent on water availability. Drought periods in the region described above were analysed using the DDSLR (Dry Days Since Last Rain) index to i) characterize trends in number of dry days and the amount of rainfall along the pluviometric gradient, ii) assess how the DDSLR index changes along the gradient from semiarid to humid Mediterranean regions, and iii) contribute to studies addressing the importance of climatic gradients in relation to the dynamics of various ecosystems. The DDSLR method enables calculation of the probability of the occurrence of dry days (days without rain) at any time of the year, assessment of the risk of water deficits for vegetation during plant growth periods, and evaluation of the temporal variability of hydrological/geomorphological processes that depend on soil moisture throughout the year. The results showed that there is a critical period of rainfall scarcity during September and October, which has implications for the availability of soil water resources for vegetation.In short‐term, the major problems are predicted for the Spanish Southern Mediterranean due to the increasing irregularity in precipitations: the number of days with no rains and drought periods are increased, but also a significant increment in the probabilities of extreme rainfalls exceeding 30 mm day−1. Copyright © 2011 Royal Meteorological Society

The impact of forest to urban land conversion on streamflow, total nitrogen, total phosphorus, and total organic carbon inputs to the converse reservoir, Southern Alabama, USA

High total organic carbon (TOC) concentrations in Converse Reservoir, a water source for Mobile, Alabama, have concerned water treatment officials due to the potential for disinfection byproduct (DBP) formation. TOC reacts with chlorine during drinking water treatment to form DBPs. This study evaluated how increased urbanization can alter watershed-derived total nitrogen (TN), total phosphorus (TP) and TOC inputs to the Converse Reservoir. Converse Watershed, on the urban fringe of Mobile, is projected to undergo urbanization increasing watershed urban land from 3% in 1992 to 22% urban land by 2020. A pre-urbanization scenario using 1992 land cover was coupled with 2020 projections of land use. The Loading Simulation Program C++ watershed model was used to evaluate changes in nutrient concentrations (mg L−1) and loads (kg) to Converse Reservoir. Urban and suburban growth of 52 km2 simulated from 1991 to 2005 (15 year) caused overall TN and TP loads to increase by 109 and 62%, respectively. Simulated urban growth generally increased monthly flows by 15%, but resulted in lower streamflows (2.9%) during drought months. Results indicate that post-urbanization median TN and TP concentrations were 59 and 66% higher than corresponding pre-urbanization concentrations, whereas TOC concentrations were 16% lower. An increase in urban flow caused TOC loads to increase by 26%, despite lower post-urbanization TOC concentrations.

Beehive fences as effective deterrents for crop-raiding elephants: field trials in northern Kenya

Increasing elephant populations in Kenya since 1989 have been widely praised as a conservation success story. However, where elephants and agricultural land overlap, incidents of human‐elephant conflict are on the increase. Wildlife managers and farmers are now trying different farm-based deterrents to keep elephants out of crops. Here, we present data on the effectiveness of a novel beehive fence deployed in a Turkana community of 62 communally run farms in Kenya. Specifically, 1700 m of beehive fences semi-surrounded the outer boundaries of seventeen farms, and we compared elephant farm invasion events with these and to seventeen neighbouring farms whose boundaries were ‘protected’ only by thorn bush barriers. We present data from 45 farm invasions, or attempted invasions, recorded over 2 years. Thirteen groups of elephants approached the beehive fences and turned away. Of the 32 successful farm invasions, only one bull elephant broke through the beehive fences. These results demonstrate that beehive fences are more effective than thorn bush barriers at deterring elephants and may have a role to play in alleviating farmer‐elephant conflict. Additionally, the harvesting of 106 kg of honey during the trial period suggests that beehive fences may also improve crop production and enhance rural livelihoods through honey sales.