Drought and Water Stress

This study analyses tests influencing the selection of nonwovens for water absorbing geocomposites. The task of the nonwoven is to capture water infiltrating into the soil and to direct it to the superabsorbent located inside. The best results in the tests of water permeability (88 mm/s) and water absorption (1116.85 g/m 2) were obtained for nonwoven of the lowest surface weight-112.8 g/m 2 and the largest average pore diameter-206.5 μm. The lowest water absorption capacity (478.91 g/m 2) and the smallest thickness changes under a load (19.3%) was noted in needle-punched nonwoven that had been subject to the calandering process. For one nonwoven, the presence of other significant fractions was noted, which proves that it is heterogeneous. For nonwovens applied in the unsaturated zone, not only water permeability should be taken into account, but also the size and fraction distribution of pores, in order to avoid breaking the continuity of capillaries.

Sunflower (Helianthus annuus L.) is the most important oil crop in Turkey with the preference of sunflower oil mostly and an increasing of vegetable oil deficit (4.3 billion $ in 2014). Despite of larger planting potential, low labor use and the government support, sunflower planting areas could not reach to desired level. The most important reason for that sunflower production can vary depending on the years due to extreme heat and drought in the growth period affected seed yield severely (for instance, 30-35% yield loss in 2012) as a summer crop. The study was conducted to determine the drought tolerance of some male inbred lines developed lately in National Sunflower Project conducting by Trakya Agriculture Research Institute (TARI). Based on the results under controlled conditions, some inbred lines exhibited positive responses in the research and some important yields affected less in these lines. While some inbred lines got lost 60% of the control in seed yield, some of them influenced less from drought stress about 9-10%. Drought tolerance of male inbred lines against stress conditions changed between 50-100% in 1000 seed weight and 70-100% in oil yield. However, oil content of inbred lines was not adversely influenced from drought stress; conversely, most of their oil content was increased in stress conditions.

Drought stress is one of the most important abiotic stress limiting the plant survival and growth in the Mediterranean environment. In this work, two species typically grown in Mediterranean areas with different drought responses were used. Two shrubs, with slow (Photinia × fraseri Dress 'Red Robin') or fast (Eugenia uniflora L. 'Etna Fire') adaptation ability to drought, were subjected to three water regimes: well-watered (WW), moderate (MD), and severe (SD) drought stress conditions for 30 days. Net photosynthetic rate, stomatal conductance, maximum quantum efficiency of PSII photochemistry (Fv/Fm), relative water content (RWC), chlorophyll content, proline, malondialdehyde (MDA), and antioxidant enzyme activities (superoxide dismutase, catalase, and peroxidase) were measured. Results showed that RWC and proline were higher in Eugenia than in Photinia, demonstrating the greater tolerance of the latter to the water stress. The drought stress levels applied did not compromise photosynthetic efficiency through stomatal regulation, while a reduction of Fv/Fm ratio was observed at the end of the experimental period. MDA significantly increased after 30 days in both species. The antioxidant enzyme activities showed different responses to water stress conditions. In both species, the water stress scores showed positive, while proline content showed negative correlations with all physiological parameters.

Plant age and size, seasonal growth patters and crop load, among other factors, have been reported to
decrease the usefulness of trunk diameter variation (TDV) derived indices as water stress indicators in
olive trees. Our hypothesis, however, is that indices derived from TDV records in old, big olive trees are
sensitive enough to detect levels of water stress in trees of orchards under deficit irrigation that, although
severe, are below the threshold for fruit shrivelling. This is of importance for the production of good
quality oils, since fruit shrivelling may affect oil quality. The aim of this work was to assess different TDVderived
indices as water stress indicators in 40-year-old ‘Manzanilla’ olive trees with heavy crop load.
We derived the maximum daily shrinkage (MDS), daily growth (DG) and daily recovery (DR) from TDV
records taken during the 2008 dry season both in well-irrigated FAO trees and in deficit-irrigated RI trees.
Measurements of volumetric soil water content (v), leaf water potential (l), stomatal conductance (gs),
net CO2 assimilation rate (A), water and oil accumulation in the fruits and yield parameters were made
for both treatments. The trunks did not grow during the experimental season, either in the FAO or RI
trees, likely because of the heavy crop load. Therefore, DG was useless as water stress indicator. For MDS
and DR, which were responsive to the increase of the trees’ water stress, we calculated the variability,
quantified by the coefficient of variation (CV), the signal intensity (SI) and the sensitivity (SI/CV) values.
In addition, we derived reference equations for irrigation scheduling from the relationships between
MDS values in the FAO trees and main meteorological variables. Values both of SI-MDS and SI-DR were
steady until September 9, despite of increasing differences in v between treatments from early in the
dry season. The l vs v values showed an outstanding capacity of the RI trees to take up water from the
drying soil, and the l vs gs values showed a near-isohydric behaviour of those deficit-irrigated trees.
These results explain, at least in part, the lack of response of MDS and DR on that period. Both SI-MDS
and SI-DR peaked for the first time on September 9, 16 days before the appearance of fruit shrivelling.
Our results suggest that using TDV-derived indices as water stress indicators for irrigation scheduling in
old olive orchards with medium to low plant densities, i.e. with large root zones, may be useless in case
the irrigation strategy is aimed at keeping the soil close to field capacity. Nevertheless, the MDS and DR
indices may be useful indicators for the avoidance of fruit shrivelling in deficit irrigated olive orchards for
the production of good quality oil. Reliable reference equations for scheduling irrigation with the signal
intensity approach were obtained from the regression of MDS values vs the daily maximum values of
both the air temperature and the vapour pressure deficit of the air.

Bringing together the analysis of a diverse team of social scientists, this book proposes a new approach to environmental problems. Cutting through the fragmented perspectives on water crises, it seeks to shift the analytic perspectives on water policy by looking at the social logics behind environmental issues. Most importantly, it analyzes the dynamic influences on water management, as well as the social and institutional forces that orient water and conservation policies. The first work of its kind, The Field of Water Policy: Power and Scarcity in the American Southwest brings the tools of Pierre Bourdieu’s field sociology to bear on a moment of environmental crisis, with a study of the logics of water policy in the American Southwest, a region that allows us to see the contest over the management of scarce resources in a context of lasting drought. As such, it will appeal to scholars in the social and political sciences with interests in the environment and the management of natural resources.

La vulnerabilidad ante la sequía es el grado en que un sistema es susceptible e incapaz de hacer frente a los efectos adversos, daños o perjuicios causados por la sequía. En este artículo se presenta una metodología para calcular índices de vulnerabilidad ante la sequía en los Organismos de Cuenca en México, la cual se basa en la concepción de vulnerabilidad del Panel Intergubernamental sobre Cambio Climático (IPCC, 2007), quien la divide en tres componentes: grado de exposición, sensibilidad y capacidad de adaptación. Cada una de estas componentes está representada por un conjunto de indicadores relativos a escala municipal que permiten a su vez determinar tres tipos básicos de vulnerabilidad: económica, social y ambiental, las cuales en conjunto dan lugar a la vulnerabilidad global. Los resultados indican que la metodología es viable para su aplicación en los distintos Organismos de Cuenca en México, e inclusive puede ser adaptada para aplicarse a nivel estatal o nacional. Su principal ventaja es que se basa en procedimiento analítico objetivo que permite identificar los municipios más vulnerables desde los puntos de vista económico, social y ambiental, de tal manera que es factible direccionar mejor los recursos y los esfuerzos para reducir la vulnerabilidad ante la sequía en las diversas regiones del país.

The use of documentary evidence to investigate past climatic trends and events has become a recognised approach in recent decades. This contribution presents the state of the art in its application to droughts. The range of documentary evidence is very wide, including general annals, chronicles, memoirs and diaries kept by missionaries, travellers and those specifically interested in the weather; records kept by administrators tasked with keeping accounts and other financial and economic records; legal-administrative evidence; religious sources; letters; songs; newspapers and journals; pictographic evidence; chronograms; epigraphic evidence; early instrumental observations; society commentaries ; and compilations and books. These are available from many parts of the world. This variety of documentary information is evaluated with respect to the reconstruction of hydroclimatic conditions (precipitation, drought frequency and drought indices). Documentary-based drought reconstructions are then addressed in terms of long-term spatio-temporal fluctuations, major drought events, relationships with external forcing and large-scale climate drivers, socioeconomic impacts and human responses. Documentary-based drought series are also considered from the viewpoint of spatio-temporal variability for certain continents, and their employment together with hydroclimate reconstructions from other proxies (in particular tree rings) is discussed. Finally, conclusions are drawn, and challenges for the future use of documentary evidence in the study of droughts are presented.

Observed changes in precipitation patterns, rising surface temperature, increases in frequency and intensity of floods and droughts, widespread melting of ice, and reduced snow cover are some of the documented hydro-logic changes associated with global climate change. Climate change is therefore expected to affect the water supply-demand balance in the Northeast United States and challenge existing water management strategies. The hydrological implications of future climate will affect the design capacity and operating characteristics of dams. The vulnerability of water resources systems to floods and droughts will increase, and the trade-offs between reservoir releases to maintain flood control storage, drought resilience, ecological flow, human water demand, and energy production should be reconsidered. We used a Neural Networks based General Reservoir Operation Scheme to estimate the implications of climate change for dams on a regional scale. This dynamic daily reservoir module automatically adapts to changes in climate and readjusts the operation of dams based on water storage level, timing, and magnitude of incoming flows. Our findings suggest that the importance of dams in providing water security in the region will increase. We create an indicator of the Effective Degree of Regulation (EDR) by dams on water resources and show that it is expected to increase, particularly during drier months of year, simply as a consequence of projected climate change. The results also indicate that increasing the size and number of dams, in addition to modifying their operations, may become necessary to offset the vulnerabilities of water resources systems to future climate uncertainties. This is the case even without considering the likely increase in future water demand, especially in the most densely populated regions of the Northeast.

The study analyzes drought using Standardized Precipitation Index (SPI) and Mann-Kendall (MK) Trend Test in the context of the impacts of drought on  groundwater table (GWT) in the Barind area, Bangladesh during the period 1971-2011. The area experienced twelve moderate to extreme agricultural droughts in the years 1972, 1975, 1979, 1982, 1986, 1989, 1992, 1994, 2003, 2005, 2009 and 2010. Some of them coincide with El Niño events. Hydrological drought also  occurred almost in the same years. However, relationship between all after drought events and El Niño is not clear. Southern and central parts of the area frequently suffer from hydrological drought, northern part is affected by  agricultural drought. Trends in SPI values indicate that the  area has an insignificant trend towards drought, and numbers of mild and moderate drought are increasing. GWT depth shows strong correlation with rainy season SPI values such that GWT regaining corresponds with rising SPI values and vice versa. However, 2000 onwards, GWT depth is continuously increasing even with positive SPI values. This is due to over-exploitation of groundwater and changes in cropping patterns. Agricultural practice in Barind area based on groundwater irrigation is vulnerable to drought. Hence, adaptation measures to minimize effects of drought on groundwater ought to be taken.

There are numerous drought indicators used by decision makers all around the globe which have been developed to fulfill specific needs. By far, risks associated with drought and related consequences have become a bold topic for scientists in which debates still taking place everywhere. No global drought indices could provide universally accepted results since almost all of these indices are based on observed data as key performance indicators. In this respect, researchers spend a lot of effort on this issue for a better understanding on the various indices which are proposed until now. It is crucial to get a better sense on how drought can develop and how it can be monitored. It is also important to understand that, recent global challenges like climate change also amplifies the obligation on continues effort toward developing better indicators and methods to monitor droughts. As climate patterns change or a seasonal shift occurs, predefined drought indicators become useless. In this review, the concepts of drought indices and indicators are revisited and evaluated. Pros and cons of frequently used indices are addressed and the major differences between them are bolded. It is concluded that each index is applicable to fulfill expectations of a specific drought type while pre-knowledge about each case is very crucial. However, there is a need to develop a composite drought index to integrate all relevant data and drought definitions, with respect to the dominant types of monthly droughts in time and space together with climate change scenarios.

A new agricultural drought index was developed for monitoring drought impacts on agriculture in Oklahoma. This new index, called the Soil Moisture Evapotranspiration Index (SMEI), estimates the departure of aggregated root zone moisture from reference evapotranspiration. The SMEI was estimated at five locations across Oklahoma representing different climates. The results showed good agreement with existing soil moisture-based (SM) and meteorological drought indices. In addition, the SMEI had improved performance compared to other indices in capturing the effects of temporal and spatial variations in drought. The relationship with crop production is a key characteristic of any agricultural drought index. The correlations between winter wheat production and studied drought indices estimated during the growing period were investigated. The correlation coefficients were largest for SMEI (r > 0.9) during the critical crop growth stages when compared to other drought indices, and r decreased by moving from semi-arid to more humid regions across Oklahoma. Overall, the results suggest that the SMEI can be used effectively for monitoring the effects of drought on agriculture in Oklahoma.