Drought-prone Regions Research Articles

Tule elk selection of surface water and forage is mediated by season and drought

Climate change is expected to affect arid-system ungulate populations by altering the distribution and availability of critical resources such as water and forage, particularly through more frequent and extreme droughts. Tule elk (Cervus canadensis nannodes), a subspecies of North American elk endemic to the Mediterranean climate regions of California, USA, can provide insight into the habitat selection behaviors arid-system ungulate populations use in response to changing resource availability. We used location data collected between 2005⁠–⁠2017 from GPS-collared tule elk to model elk response to surface water sources, forage dynamics (i.e., spatio-temporal changes in forage quality and abundance), and drought in the wet and dry seasons. These data spanned the extreme drought that occurred from 2012–⁠2017, a time when survival was apparently stable in the population. We found that, in the dry season, tule elk localized around water sources but selected areas farther from water with greater forage abundance. In the wet season, high quality forage and road avoidance were the primary factors influencing selection. These patterns were intensified by the extreme drought, with elk selecting areas closer to water in the dry season and farther from water sources in the wet season. Tule elk appeared to modify their behavior to minimize the impacts of drought on their survival. These findings suggest that water source availability and the relationship between water sources and other landscape features, including forage and roads, are a critical component of ungulate management in drought-prone regions.

Ecological niche, genetic variation in natural populations, and harvest maturity of Senegalia macrostachya (Rchb. ex DC) Kayl. & Boatwr., a promising wild and perennial edible-seeded crop

Senegalia macrostachya is a wild, perennial, and promising legume that can help alleviate food insecurity in sub-Saharan Africa’s drought-prone regions. However, it has been for a long time overlooked, underutilized, and scarcely studied. This study shed light on its ecological niche, genetic variation in natural populations, and seeds’ harvest maturity. Three populations of S. macrostachya were selected along an environmental gradient, and their structures, based on their plants’ pod characteristics (i.e., unique morphological differentiation trait amongst the plants), were assessed. Then, the seeds’ development was investigated following their morphological transformation, mass accumulation, and the mobilization of their proteins and secondary metabolites. S. macrostachya has revealed low genetic variation and fitness to poor soils, warm and semi-arid climates in sub-Saharan Africa, prone to droughts and low to medium agricultural productivity. The maturation of the seeds involved the accumulation of specific late embryogenesis abundant proteins (60, 48, and 14 kDa), identified as chilling-responsive dehydrins, and the degradation of the chlorophylls and carotenoids, which could be used as biochemical landmarks of the harvest maturity. Besides, an aging symptom (high seed abortion rate (14–20%)) was observed in the study populations. This work provides unprecedented information that will assist in predicting the eco-climate suitability and climate resilience, identifying the conservation strategies, and planning the harvesting, reforestation programs, and domestication of S. macrostachya. In parallel, the dehydrins identified from S. macrostachya can be tapped into for drought-resistant crop development. Further research is needed to evaluate the impacts of the mother plants’ aging and larger climate gradient on the performance (i.e., seed productivity and regeneration ability) of S. macrostachya.

Blue is the fashion in Mediterranean pines: New drought signals from tree-ring density in southern Europe

Long-term records of tree-ring width (TRW), latewood maximum density (MXD) and blue intensity (BI) measurements on conifers have been largely used to develop high-resolution temperature reconstructions in cool temperate forests. However, the potential of latewood blue intensity (LWBI), less commonly used earlywood blue intensity (EWBI), and delta (difference between EWBI and LWBI, dBI) blue intensity in Mediterranean tree species is still unexplored. Here we developed BI chronologies in moist-elevation limits of the most southwestern European distribution of Pinus nigra subsp. salzmanii Arnold. We tested whether BI variables derived from tree rings of black pine are better proxies than ring-width variables to reconstruct long-term changes in climatic factors and water availability. For this we applied correlations and regression analyses with daily and monthly climate data, a spatial and temporal drought index (Standardized Precipitation-Evapotranspiration Index-SPEI) and Vapour Pressure Deficit (VPD), as well as atmospheric circulation patterns: North Atlantic Oscillation (NAO), Southern Oscillation Index (SOI) and Western Mediterranean Oscillation (WeMO). We found a positive relation between black pine growth (RW) and temperature during the winter preceding the growing season. Among all variables LWBI and dBI were found to be more sensitive than TRW to SPEI at low-elevation site, with EWBI series containing an opposite climatic signal. LWBI and dBI were significantly related to June and September precipitation at high-elevation site. Winter VPD was related with higher EWI and LWI series, whereas dBI and EWBI were related with January SOI and February NAO. We confirm the potential of long-term dBI series to reconstruct climate in drought-prone regions. This novel study in combination with other wood anatomical measurements has wide implications for further use of BI to understand and reconstruct environmental changes in Mediterranean conifer forests.

A Simulation Study Using Machine Learning and Formula Methods to Assess the Soybean Groundwater Contribution in a Drought-Prone Region

Groundwater contributes to the delivery of phreatic water to crop aeration zones via evapotranspiration, which is important for crop growth in drought-prone regions. Most studies on groundwater contribution have not considered the influence of crop growth stage or daily evapotranspiration. In this study, a neural network based on a genetic algorithm and the Levenberg–Marquardt backpropagation algorithm, as well as formula methods based on an accelerated genetic algorithm, were built to assess soybean groundwater contribution; in addition, a performance comparison was conducted. The results indicated that machine learning had the best performance for fitting errors, with values for relative mean error (RME), root mean square percentage error (RMSPE), and correlation coefficient of 1.088, 2.165, and 0.762, respectively; in addition, for validation errors, it had values for RME, RMSPE, and correlation coefficient of 1.069, 2.136, and 0.735, respectively. The machine learning method is recommended for readers seeking to calculate groundwater contribution.

New evidence for population-specific responses to drought events from tree ring chronologies of Pinus nigra ssp. laricio across the entire distribution range

• Growth-climate relationships were analysed in black pine (ssp. laricio ). • Drought effects on stem radial growth were studied in representative populations. • Positive impacts of precipitation in spring/summer, but negative in winter, were found. • Corsican populations were more sensitive to drought than populations in southern Italy. • Older trees were more resistant to drought events than younger trees. The increased frequency and severity of drought events due to climate warming is negatively affecting tree radial growth, particularly in drought-prone regions, such as, e.g., the Mediterranean. In this climate change hotspot, populations of the same tree species may show different growth responses to climate, due to the great variety of microclimates and environments that characterise this biogeographic region. In this study, we analysed growth-climate relationships and growth responses to drought events (i.e., resistance, recovery, and resilience) in 13 forest stands of black pine ( Pinus nigra Arnold), encompassing the whole and peculiar distribution range of the ssp. laricio (Calabria, Sicily, Sardinia, and Corsica). Analysis focussed on the 1981–2010 period, which is commonly covered at all sites. Stem radial growth of trees increased under a positive spring/summer water balance. However, abundant winter precipitation had a negative impact on stem radial growth. Populations in Corsica were more sensitive to drought, showing lower resistance and resilience than those in Sicily and Sardinia. Older trees were more resistant to drought events than younger trees. Our results highlight that population-specific responses to drought events are mainly explained by tree age and local environment, suggesting geographically related patterns in tree growth and forest productivity correspond to different populations. Intraspecific variability in sensitivity to drought events should be included in species distribution models to predict the range of forest productivity responses to climate change.

ANALYSING THE STATUS OF WATER RESOURCES AND THEIR CONSERVATION: KEY STRATEGIES FOR SUTAINABLE DEVELOPMENT IN MAHOBA DISTRICT OF UTTAR PRADESH (INDIA)

Water is one of the most important natural resources on the earth surface. It is the base not only for survival of human beings but to operate different types of activities for existence of biotic and abiotic eco-system. Although, water is abundant on the earth but the usable water is considerably very limited. The Mahoba district of Uttar Pradesh is water stressed district which is part of Bundelkhand region, known as a water deficit and drought prone region in the country. Therefore, water crisis is the main issue of the entire region. Due to the less annual rainfall, the availability of water resources is very limited in Mahoba district of Uttar Pradesh. Consequently, there is an urgent need to conserve and manage all type of water resources in order to quench the thirst of large population of the region and to operate different types of agricultural activities including tremendous anthropogenic activities for livelihood security and to feed millions of people. Hence, it is also very important to conserve and manage the water resources of the target area. By applying different types of methods and techniques including traditional and modern, we may not only conserve and manage the water resources of the region by involving local people, farmers, youth and women but also provide drinking water to the millions of people of the area as well as to irrigate farm lands. An attempt has also been made in the research paper to know the people’s perception for management and conservation of water resources.

Integrated assessment of drought vulnerability for water resources management of Bina basin in Central India

Drought is an extreme event and its frequency is expected to increase in future under the imminent threats of climate change. The areas vulnerable to drought are increasing due to increase in the spatial extent and severity of droughts. This necessitates the need for development of an integrated framework for assessment of drought vulnerability, which will be vital for water resources management policies focused towards such vulnerable areas. An integrated drought vulnerability assessment framework has been developed considering the physical indicators that vary spatially, social indicators that vary spatially but their temporal variation may be at longer time-frames, and spatio-temporal drought indicators that vary spatially and temporally during various months during drought years. This framework has been tested for Bina basin located in the drought prone Bundelkhand region of Madhya Pradesh. The drought indicators used in the study include (i) Standardized Precipitation Index (SPI) for evaluating meteorological drought characteristics, (ii) Surface water Drought Index (SDI) for evaluating streamflow drought characteristics, and (iii) Groundwater Drought Index (GDI) for evaluating groundwater drought characteristics. Groundwater levels arebeing observed at quarterly (3 monthly) time steponly. So the relationships between GDI and 3-m SPI, 6-m SPI, and 12-m SPI have been investigated. Based on the best correlation, the 12-m SPI can be used to represent the groundwater drought in Bina basin and has therefore been used to assess the monthly variability in the groundwater drought characteristics. The spatially varying physical indicators including basin reach (elevation band), land use pattern and soil type; the spatio-temporal drought indicators including soil moisture drought, surface water drought and groundwater drought, rainfall departure and number of consecutive dry days; and the spatially varying social indicators including infants and young children, illiterate population, marginal workers and rural population have been used for the development of a Drought Vulnerability Index (DVI). The integrated drought vulnerability assessment framework has been conceptualized on the basis of DVI. Four vulnerability classes have been defined and the study area falls in mild to moderate vulnerable class, based on the analysis carried out for the various drought years in the basin. Appropriate drought management plans and mitigation strategies need to be developed to target these vulnerable areas in Bina basin.

Divergent roles of deep soil water uptake in seasonal tree growth under natural drought events in North China

Understanding the ecophysiological mechanisms underlying tree adaptation in drought-prone regions is crucial for predicting forest health in the face of future climate changes. However, little is known about how tree hydraulic adaptations modulate the responses of seasonal tree growth to water deficits along a large climate gradient. In this study, the spatially divergent responses of tree growth to natural drought events were assessed through observations of water uptake patterns, leaf water potentials, sap flow rates, and tree stem radial variations in Chinese pine (Pinus tabulaeformis) plantations along a climate gradient in North China. Higher proportions of water were absorbed from the middle and deep soil layers during dry spells compared to the growing season across all study sites. However, at the semiarid and subhumid sites, increased water uptake from deeper soil layers did not completely alleviate drought stress. Instead, the trees adopted strong stomatal control over transpiration at the expense of reduced growth. In contrast, at the humid site, seasonal shifts in water uptake effectively compensated for the negative impacts of seasonal drought on tree growth. Given that intensified climatic droughts are expected under climate warming, the establishment of an early warning drought system is increasingly urgent for plantations in regions prone to drought stress.

Biosolids and conservation tillage for rainfed wheat farming in dry Mediterranean climates

Biosolids are used in dryland wheat (Triticum aestivum L.) production in eastern Washington and other regions of the world as a source of nutrients and to increase soil organic carbon (SOC). Moreover, conservation tillage is promoted to reduce erosion and soil degradation. We explored the impacts of biosolids vs synthetic fertilizer in combination with undercutter (UC) conservation tillage vs tandem disk (TD) traditional tillage in an 8-yr field experiment in drought-prone region near Lind, WA (244 mm avg. annual precipitation). There were two sets of plots to allow for data collection each year in a 2-yr winter wheat (WW)-fallow rotation. Biosolids were applied at 6.5 mt/ha dry weight to meet the nutrient needs of two WW crops. Synthetic fertilizer plots received 56 kg N plus 11 kg S/ha for every wheat crop. Biosolids increased WW grain yield vs synthetic fertilizer by 25% one year but with no differences in other years or the 8-yr avg. Tillage method had no effect on WW grain yield nor grain yield components. Wheat kernel weight was lower and grain protein higher than desirable in biosolids plots, indicating excessive N because the application rate was too high for such a dry environment. Consistent year-long surface residue cover > 30% was achieved with UC tillage for government farm program conservation compliance, but this was not attained with TD tillage. In addition to highly desirable levels of P, biosolids provided significant quantities of the important soil micronutrients Zn, Mn, Cu, Fe. Biosolids application did not increase SOC in the surface 30 cm. This study demonstrated the application of biosolids combined with low-disturbance UC conservation tillage is an agronomically- and environmentally sound practice for dryland wheat production. We believe this is the driest rainfed environment in which biosolids for crop production have yet been evaluated.

Community livelihood vulnerability to drought in semi-arid areas of northern Cameroon

Drought is a devastating recurring climate hazard, with enormous impacts on livelihoods and attainment of sustainable development goals (SDGs) in semi-arid areas. The current study was conducted to evaluate households’ livelihood vulnerability to droughts in an African semi-arid region. A total of 384 households from a drought-prone region in Northern Cameroon were randomly sampled and interviewed using a structured questionnaire. Livelihood vulnerability was evaluated from the collected households’ data using the Livelihood Vulnerability Index (LVI) and Intergovernmental Panel on Climate Change Vulnerability Index (IPCC-VI) methods. The LVI results showed that food insecurity, livelihood strategy and social networking were the major drivers of livelihood vulnerability. This was because almost all of the interviewed households relied on rain-fed agriculture and there was limited early drought warning information, which limited the achievements of some SDGs such as zero hunger, water accessibility and poverty alleviation. Adoption of drought-resilient and early maturing crops together with the use of agriculture extension officers to disseminate drought warnings are advised to reduce the effects of the livelihood vulnerability drivers and ensure sustainable development. The IPCC-VI showed that drought exposure and adaptive capacity were low while drought sensitivity was high among the surveyed households. The high sensitivity was due to food and water insecurity, while low adaptive capacity was due to a lack of formal education and a high dependency rate. Heavy investment in education and reducing the number of dependents through family planning and campaigning against polygamy could enhance households’ adaptive capacity. It was concluded that households’ livelihood vulnerability in the study area was due to high sensitivity and low adaptive capacity to drought. Drought reversed positive steps that had been taken to achieve various SDGs; however, heavy investment in other SDGs such as quality education and health could enhance households’ adaptive capacity and system sustainability in African semi-arid regions.

Unraveling the Multiple Drivers of Greening-Browning and Leaf Area Variability in a Socioeconomically Sensitive Drought-Prone Region

The complex attribution of climatic, hydrologic, and anthropogenic drivers to vegetation and agricultural production and their consequential societal impacts are not well understood, especially in socioeconomically sensitive states like Maharashtra, India. Here, we analyzed trends and variability in the MODIS leaf area index (LAI) time series, along with spatiotemporal patterns in precipitation, groundwater storage, agriculture statistics, and irrigation infrastructure, to identify their influences on the vegetation response and discuss their implications for farmers. The state showed greening in all biomes except forests, with a net gain of 17.478 × 103 km2 of leaf area during 2003–2019, where more than 70% of the trend in LAI is represented in croplands. Maximum greening was observed in irrigated croplands, attributable to increased crop productivity, whereas inadequate irrigation facilities with erratic rainfall patterns and droughts were primarily responsible for cropland browning. We discerned the dynamics and variability of vegetation response by incorporating a spectrum of synergistic feedbacks from multiple confounding drivers and found that uneven distribution of water availability across the administrative divisions governed the quantitative distinction in leaf area change. Despite the observed greening trends, the state witnessed a high number of farmer suicides related to droughts and agriculture failures hampering their socioeconomic security; therefore, improved irrigation infrastructure and comprehensive policy interventions are crucial for abatement of farmer distress.

Abnormal depletion of terrestrial water storage and crustal uplift owing to the 2019 drought in Yunnan, China

SUMMARYDroughts are natural disasters that cause severe economic and social impacts. Analysing changes in terrestrial water storage (TWS) before and after typical drought events is important for understanding the principles of the regional terrestrial water transport law and drought response, and for providing scientific agricultural production guidance. Yunnan is a drought-prone region, and high temperatures and low rainfall in 2019 led to a severe drought. Precipitation data showed that the wet season in Yunnan started 1 month later than usual in 2019. Moreover, 52 per cent (205 000 km2) of the total area of Yunnan experienced a cumulative precipitation anomaly (PA; in percentage) of −30 per cent between January and May. In this study, we used data from the Gravity Recovery and Climate Experiment (GRACE) and Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) missions to identify the spatial and temporal variations in TWS before and after the 2019 drought. Our results show that the drought led to an average reduction of 125 mm (equivalent water height) in the TWS, with the greatest loss in southern Yunnan, with a maximum loss of 272 mm. The reduced TWS caused by the delayed and anomalously weak southwest monsoon in 2019 gradually spread from the southwest to the northeast. By comparing with the drought in 2009–2010, we find that the southern Yunnan with abundant rainfall is more vulnerable to drought and has a relatively larger deficit in TWS. Furthermore, we used GRACE and GRACE-FO data to invert the crustal uplift caused by terrestrial water unloading in the 2019 drought, and found a maximum uplift of 8.4 mm. This showed a consistent spatial distribution with displacement variations recorded by 26 continuous Global Positioning System (GPS) stations in Yunnan during the same period, albeit slightly different in magnitude, indicating the potential of GPS for monitoring regional TWS changes.

Tree growth response to drought partially explains regional-scale growth and mortality patterns in Iberian forests.

Tree-ring data has been widely used to inform about tree growth responses to drought at the individual scale, but less is known about how tree growth sensitivity to drought scales up driving changes in forest dynamics. Here, we related tree-ring growth chronologies and stand-level forest changes in basal area from two independent data sets to test if tree-ring responses to drought match stand forest dynamics (stand basal area growth, ingrowth, and mortality). We assessed if tree growth and changes in forest basal area covary as a function of spatial scale and tree taxa (gymnosperm or angiosperm). To this end, we compared a tree-ring network with stand data from the Spanish National Forest Inventory. We focused on the cumulative impact of drought on tree growth and demography in the period 1981-2005. Drought years were identified by the Standardized Precipitation Evapotranspiration Index, and their impacts on tree growth by quantifying tree-ring width reductions. We hypothesized that forests with greater drought impacts on tree growth will also show reduced stand basal area growth and ingrowth and enhanced mortality. This is expected to occur in forests dominated by gymnosperms on drought-prone regions. Cumulative growth reductions during dry years were higher in forests dominated by gymnosperms and presented a greater magnitude and spatial autocorrelation than for angiosperms. Cumulative drought-induced tree growth reductions and changes in forest basal area were related, but initial stand density and basal area were the main factors driving changes in basal area. In drought-prone gymnosperm forests, we observed that sites with greater growth reductions had lower stand basal area growth and greater mortality. Consequently, stand basal area, forest growth, and ingrowth in regions with large drought impacts was significantly lower than in regions less impacted by drought. Tree growth sensitivity to drought can be used as a predictor of gymnosperm demographic rates in terms of stand basal area growth and ingrowth at regional scales, but further studies may try to disentangle how initial stand density modulates such relationships. Drought-induced growth reductions and their cumulative impacts have strong potential to be used as early-warning indicators of regional forest vulnerability.

Ridge-furrow plastic film mulching enhances grain yield and yield stability of rainfed maize by improving resources capture and use efficiency in a semi-humid drought-prone region

Soil mulching, e.g. straw mulching (SM) and ridge-furrow plastic film mulching (RP), has been reported to promote rainfed crop production in semi-arid regions, but its applicability in improving maize yield and especially yield stability in semi-humid drought-prone regions has been rarely explored. The capture and utilization of thermal, light, water and nutrients resources by maize plants under various soil mulching conditions are also poorly understood. A consecutive five-season field experiment was conducted on rainfed maize in a semi-humid drought-prone region of China during 2015–2019 to assess the effects of SM and RP on soil hydrothermal conditions, radiation interception, photosynthesis, evapotranspiration and grain yield stability, profitability and resources use efficiency compared with non-mulching (NM). The results showed that RP enhanced soil hydrothermal conditions, promoted the conversion of water from soil evaporation to plant transpiration and improved water productivity by 10.9%−203.2% compared with NM (P < 0.05). Although the growth duration was shortened, the accumulative soil thermal time and intercepted photosynthetically active radiation under RP were still 4.4% and 3.9% higher, with average increases in thermal time use efficiency by 23% and radiation use efficiency by 24%, which resulted in significantly higher nutrients accumulation (by 6.7%−19.7% for nitrogen and 4.1%−42.0% for phosphorous), grain yield (by 9.5%−186.4%) and yield stability (by 38.1%). These improvements were particularly pronounced in normal and dry years (2015, 2016 and 2017). No significant difference existed in maize’s capacity of absorbing water and nutrients and maize productivity between SM and RP under sufficient precipitation supply (2018 and 2019). The average net profit was highest under RP, especially in dry and normal years, while SM could achieve comparable net profit to RP in wet years. Overall, RP was preferable for rainfed maize production in semi-humid drought-prone regions in any precipitation year, while SM can be an alternative mulching practice in wet years. These results can improve our understanding of how RP and SM enhance rainfed maize productivity by improving resources capture and use efficiency.

Short-Term and Long-Term Replenishment of Water Storage Influenced by Lockdown and Policy Measures in Drought-Prone Regions of Central India

Central India faces a freshwater shortage due to its diverse terrain, sudden change in precipitation patterns and crystalline rock covered subsurface. Here, we investigate the patterns in terrestrial water storage anomaly (TWSA) over the last two decades, and also study the influence of the COVID-19 lockdown on TWSA in the drought-prone regions of central India, mostly covering the Vidarbha region of the Indian state of Maharashtra. The Vidarbha region is arguably the most drought-affected region in terms of farmer suicides due to crop failure. Our forecast data using multiple statistical approaches show a net TWSA rise in the order of 3.65 to 19.32 km3 in the study area in May 2020. A short-term rise in TWSA in April–May of 2020 is associated with lockdown influenced human activity reduction. A long-term rise in TWSA has been observed in the study region in recent years; the rising TWSA trend is not directly associated with precipitation patterns, rather it may be attributed to the implementation of water management policies.

Differential response of photosynthetic activity, leaf nutrient content and yield to long-term drought in cacao clones

Cacao (Theobroma cacao L.) is not frequently cropped in water limited environments, however it is cultivated in several drought-prone regions, where soil water is gradually depleted on an annual cycle. In regions where cacao is subjected to long periods without precipitation, the physiological responses under field conditions may differ between cacao clones. Evaluation of these responses are required to select potential clones that could be used for breeding programs in the context of future climatic scenarios. In order to identify physiological and yield responses to drought of 10 Ecuadorian cacao clones, relative leaf water content (RWC), CO2 assimilation rate (A), transpiration (E), stomatal conductance (gs), water use efficiency (WUE), relative quantum yield of photosystems II (ΦPSII), non-photochemical quenching (NPQ), leaf nutrient content (N, P K, Ca, and Mg) and yield were assessed during the dry (DS) and rainy seasons (RS). On average, A and E decreased by 33 and 22 %, respectively under drought, whereas WUE was higher during RS. Clones exhibited an increase in NPQ during DS, suggesting greater energy dissipation. Clones showed differences in macronutrient content and in most cases drought caused a reduction in Ca and Mg content. Two groups were established according to yield: one which maintained higher yields during RS, while the other had higher yields during drought. This offers strategic alternative in order to maintain a relatively high yield throughout the year with combination of clones in the plantations.

Yield, irrigation water productivity and nutrient uptake of arbuscular mycorrhiza inoculated sesame under drought stress conditions

According to yield evaluations performed in drought stress experiments, soil microorganisms have been considered sustainable solutions to reduce drought stress damage and enhance crop production in drought-prone regions. Thus, a two-year experiment was conducted to evaluate the impacts of sesame (Sesamum indicum L.) root colonization by two mycorrhizal fungal species (i.e., Rhizophagus intraradices and Funneliformis mosseae) under various irrigation regimes on nutrients uptake, grain yield, seed oil content and irrigation water productivity. The experiment was conducted at Seed and Plant Improvement Institute, Karaj, located in the semi-arid region of Iran, during the 2017 and 2018 growing seasons. Drought stress was induced at moderate and severe water shortage levels through irrigation after 65% and 85% available water depletion, and irrigation after 45% available water depletion was regarded as normal irrigation (no stress). Despite drought stress, mycorrhizal inoculation resulted in higher grain yield and seed oil content than noninoculated sesame. F. mosseae-inoculated plants had remarkably higher grain yield under each irrigation treatment than R. intraradices-inoculated or noninoculated plants. Although leaves and seeds N percentage was reduced due to drought stress, it was enhanced by mycorrhizal fungi, especially when plants were inoculated with F. mosseae. Moreover, the F. mosseae-inoculated plants showed the greatest P percentage in the leaves and seeds. The results revealed that different arbuscular mycorrhizal fungi (AMF) species have distinct effects on sesame performance even within the same genus. The results indicated that F. mosseae better supports sesame and is more effective under drought stress. Therefore, the use of this microorganism could be critical in the farming of sesame under semi-arid and arid conditions, where water is the main factor in determining crop yield.

Drivers of drought-induced shifts in the water balance through a Budyko approach

Abstract. An inconsistent relationship between precipitation and runoff has been observed between drought and non-drought periods, with less runoff usually observed during droughts than would be expected based solely on precipitation deficit. Predictability of these shifts in the precipitation–runoff relationship is still challenging, largely because the underlying hydrologic mechanisms are poorly constrained. Using 30 years of data for 14 basins in California, we show how the Budyko framework can be leveraged to decompose shifts in precipitation versus runoff during droughts into “regime” shifts, which result from changes in the aridity index along the same Budyko curve, and “partitioning shifts”, which imply a change in the Budyko parameter ω and thus in the relationship among water balance components that governs partitioning of available water. Regime shifts are primarily due to measurable interannual changes in precipitation or temperature, making them predictable based on drought conditions. Partitioning shifts involve further nonlinear and indirect catchment feedbacks to drought conditions and are thus harder to predict a priori. We show that regime shifts dominate changes in absolute runoff during droughts but that gains or losses due to partitioning shifts are still significant. Low aridity, high baseflow, a shift from snow to rain, and resilience of high-elevation runoff correlate with higher annual runoff during droughts than would be predicted by the precipitation–runoff ratio during non-drought years. Differentiating between these shifts in the precipitation–runoff relationship using a Budyko approach will help water resource managers, particularly in arid, drought-prone regions, to better project runoff magnitudes during droughts based on available climate data and, furthermore, understand under what circumstances and to what extent their forecasts may be less reliable due to nonlinear basin–climate feedbacks.

Development and evaluation of hybrid deep learning long short-term memory network model for pan evaporation estimation trained with satellite and ground-based data

Evaporation, as a core process within the global hydrological cycle, requires reliable methods to monitor its variation, for decision-making in agriculture, irrigation systems and dam operations, also in other areas of hydrology and water resource management. Accurate monitoring of pan evaporation (Ep) is one the most popular approaches to understand the evaporative process. This work aims to construct a hybrid Long Short-Term Memory (LSTM) predictive model that is coupled with Neighbourhood Component Analysis for feature selection to predict Ep in drought-prone regions in Queensland, Australia (Amberley, Gatton, Oakey, & Townsville). Utilizing the daily-scale dataset [31 August 2002 to 22 September 2020], the performance of the proposed deep learning (DL) hybrid model, denoted as NCA-LSTM, is compared with competitive benchmark models, i.e., standalone LSTM, other types of DL, single hidden layer neuronal architecture and decision tree-based method. The testing results reveal the lowest Relative Root Mean Square Error ≤20%, Absolute Percentage Bias ≤14.5% and the highest Kling-Gupta Efficiency ≥87% attained by the NCA-LSTM hybrid model (relative to benchmark models) tested for Amberley, Gatton, and Oakey sites. In respect to the predictive efficiency, the proposed NCA-LSTM hybrid model, improved with feature selection, outperforms all benchmark models, indicating its future utility in the prediction of daily Ep. In practical sense, the predictive model developed for Ep estimation provides an accurate estimation of evaporative water loss in hydrological cycle and therefore, can be implemented in areas of irrigation management, planning of irrigation-based agriculture, and mitigation of financial losses to agricultural and related sectors where, regular monitoring and forecasting of water resources are a vital part of sustainable livelihood and business.

Attribution of the Extreme Drought in the Horn of Africa during Short-Rains of 2016 and Long-Rains of 2017

The Horn of Africa (HOA) is one of the most drought-prone regions in the world with many arid and semiarid areas, and even some extremely arid areas. Primarily affected by the marine continental climate systems, this zone is really sensitive to global warming. Drought is the main type of natural disaster affecting this region, which triggers famine, civil conflict, and even deterioration of food security. The present study examined changes in droughts in the HOA during 1979–2019 based on Standardized Precipitation Evapotranspiration Index (SPEI). Results show that frequency, duration, and intensity of droughts exhibited an increasing trend over the past decades. Moreover, in October to December (called locate “short rains”) 2016 and March to May (called locate “long rains”) 2017, the HOA experienced the most severe drought. Based on Generalized Extreme Value (GEV) fitting, the 2016/2017 SPEI index corresponds to a drought that occurs every 250 years in the observational records. However, considering the precipitation in short rains of 2016 (long rains of 2017) was only 27.1% (11.8%) less than normal, it is hard to explain the formation of this extreme drought only from precipitation anomalies. Further statistical result shows that the evaporation in 2016/2017 corresponds to a 1-in-131 years event in the observed records. The abnormally high temperature (1.02 °C higher than normal) as well as the greatest potential evaporation since 1979 are the more important causes for the formation of drought. Thus, the extreme drought in 2016/2017, probably caused by the combined effect of dry condition and high temperature simultaneously, and the latter, played a leading role. In other words, droughts can be exacerbated by the co-occurrence of extreme high temperature. With continuous warming caused by anthropogenic activities in the next decades, the Horn of Africa may be a hotspot of the compound droughts and, therefore, it is especially important to considering the combined impacts from less precipitation and high temperature when predicting the future drought trend and making adaptation measures.