Evapotranspiration Conditions Research Articles

Drought intensification in Brazilian catchments: implications for water and land management

Droughts exert widespread impacts on both natural and social systems, and there is accumulating evidence that this situation may worsen in the context of global warming. Despite the importance of assessing changes in droughts to understand their potential future impacts on society, studies are unevenly distributed worldwide. In this study, utilizing bias-corrected CMIP6 simulations and a standard precipitation-evaporation index based approach, we quantified expected changes in future drought properties across 735 Brazilian catchments under SSP2-4.5 and SSP5-8.5 scenarios. Beyond evaluating the statistical properties of future droughts, we assessed their occurrence under both land use and water demand perspectives and propose a new framework to better understand their link with changes in long- and short-term conditions of precipitation ( P ) and potential evapotranspiration ( PET ). Our results indicate that drought events are projected to become more frequent and severe in the future, with high CMIP6 model agreement. According to the SSP5-8.5 scenario, at least half of Brazilian cropland and pasture areas will experience an increase of over 30% in drought properties by the end of the century. Furthermore, among the 85% of catchments expected to experience more severe droughts, nearly 90% are also projected to exhibit increased water demand, which will likely exacerbate future water scarcity. The investigation of the relationship between droughts changes and climate variables suggests that catchments with augmented droughts in the future will likely exhibit increased long-term average PET and P -variability, but not necessarily long-term average P . For instance, over 50% of evaluated Brazilian catchments are expected to experience an intensification of drought properties even with increases in Pmean . We believe this study may contribute (a) to improve Brazilian water resiliency by helping achieve the objectives of the National Water Security Plan and (b) to deepen our understanding of droughts in an uncertain future.

Effect of Water Regime and Soil Maintenance Mode on Vegetative Growth and Peach Tree Production

The peach tree is a very water-demanding species that is affected by water stress, which is worsening due to global warming. The soil environment is also influenced by tillage and cropping methods, which affect the water content, temperature, aeration, and organic matter of the soil. Weed control is one of the most crucial cultural practices in arboriculture since weeds can compete with fruit trees for resources. This paper aims to measure the impact of water stress combined with different soil maintenance methods on vegetative growth and peach tree production. Different evapotranspiration conditions (ETc) were used. Two irrigation doses R1 (80% of ETc) and R2 (100% of ETc) were combined with three soil maintenance modes T1 (Sapping), T2 (Sickle tillage), and T3 (Chemical maintenance). The findings highlighted water stress reduces the growth and development of the peach tree but did not have a significant impact on yield when the irrigation dose was reduced by 20%. The sapping and sickle maintenance modes recorded the best results for most of the parameters, while the chemical maintenance mode had a positive effect on the total number of fruits and yield under the 100% of ETc water regime.

Assessing the impact of climatic factors on biosphere dose conversion factors in long-term safety assessment of radioactive waste disposal

Climate factors from different regions were employed to assess the impact on Biosphere Dose Conversion Factors (BDCF) in the biosphere assessment of radioactive waste disposal. Climate characteristics of tropical and subtropical regions were considered alongside diverse climatic regions, observing the influence of different radionuclides. Data on annual rainfall, monthly rainfall distribution, temperature, and sunlight were collected for various regions. The relationship between rainfall and the processes of flooding, as well as erosion, was also established. Furthermore, the Water Budget Model (WBM) was used to calculate the required surface water flow parameters for the biosphere model. The results indicated limited effects from flooding and erosion, which could be evaluated using simplified methods. Under conditions of high evapotranspiration, low rainfall, or uneven rainfall distribution, specific radionuclides exhibited higher BDCF values. For regions currently and prospectively aligning with these climate characteristics, a comprehensive investigation into climate factors and their correlation with surface and near-surface hydrology is recommended to mitigate uncertainty.

Apparent fractionation of hydrogen isotope from precipitation to leaf wax n-alkanes from natural environments and manipulation experiments

Knowledge of hydrogen isotopic fractionation (ε) of plant leaf waxes is the foundation for applying hydrogen isotope values (δ2H) in environmental reconstructions. In this work, we systematically investigated plant ε values (εalk/precipitation, εalk/soil water, εalk/leaf water and εalk/lake water, representing the isotopic fractionation between plant n-alkane δ2H and precipitation δ2H, soil water δ2H, leaf water δ2H and lake water δ2H) from the natural environments and manipulation experiments. The results show that the εalk/precipitation values of terrestrial plants have large variations (from −190 ‰ to −20 ‰) and become more negative with increasing aridity index. This phenomenon is possibly caused by the δ2H changes in source water (from precipitation to soil water and then to leaf water) during plant leaf wax synthesis under various evapotranspiration conditions in different climatic zones. The rainfall manipulation experiments show that leaf water δ2H values are generally higher than soil water δ2H values, and the latter are higher than precipitation δ2H values. This finding further demonstrates that the evapotranspiration effect on source water δ2H affects the quantification of the leaf wax apparent ε values (εalk/leaf water < εalk/soil water < εalk/precipitation). The εalk/lake water values of submerged plants display a smaller range (−153 ± 5 ‰) than the εalk/precipitation values of terrestrial plants, which is close to the terrestrial εalk/precipitation values in humid areas. Therefore, the biosynthetic ε value of terrestrial plant leaf waxes is relatively constant (ca. –153 ± 5 ‰), and the observed variable apparent εalk/precipitation values are possibly caused by the varied degree of evapotranspiration effect on the water that plants used in different climatic conditions. This effect should be considered when applying δ2H values of leaf waxes to trace environmental changes.

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Water consumption of agricultural plants can be considered one of the main elements of the assessment needed for irrigation. Covering water needs during the growing season is done by applying irrigation. Quantitative studies on evapotranspiration performed on maize and sunflower crops showed different values. The average water consumption calculated according to the Thornthwaite method recorded the highest values in June, July and August. For the maize crop, the highest water consumption was reached in July (1480 m3 / ha or 27.1% of the total consumption), during which time the pollination, the growth of the cobs and the formation of the grain take place. In sunflower cultivation, the highest consumption was recorded in July (1302 m3 / ha or 28.2% of total consumption) and correspond to the phases of growth of the flowering head (inflorescence) and seed formation. The purpose of this paper is to establish the need for hydro-amelioration arrangements through a correct irrigation regime during the growing season following the results obtained based on water consumption in the crops studied. The present paper presents the results of water consumption in maize and sunflower crops, calculated according to the Thornthwaite method, as well as the correction coefficients for potential evapotranspiration conditions on the upper Prut river basin.

Incorporating ECOSTRESS evapotranspiration in a paired catchment water balance analysis after the 2018 Holy Fire in California

Ecohydrological processes such as evapotranspiration (ET) and streamflow are highly variable after fire in Mediterranean systems and require accurate assessments to improve long-term risk mitigation of erosion and peak flows and revegetation strategies, especially at the small catchment scale. Using the case of the 2018 Holy Fire in southern California, we characterized 1) pre-fire rainfall and evapotranspiration conditions and 2) recovery of ecohydrological processes using a paired analysis between an unburned (Santiago) and burned (Coldwater) catchment. ECOsystem Spaceborne Thermal Radiometer Experiment on Space Station (ECOSTRESS), Operational Simplified Surface Energy Balance Model (SSEBop), vegetation indices, and local rainfall-runoff data were used to characterize the sites and investigate spatial and temporal patterns of post-fire ET. Consistent with the drought conditions in California, we observed low precipitation and ET prior to the fire. Additionally, compared to other vegetation types, montane hardwood species were more likely to be classified as high soil burn severity. We also found that the high spatial and temporal resolution of ECOSTRESS provided more information about the general ET patterns. After the fire, ECOSTRESS ET was sensitive to parameters such as slope aspect, soil burn severity, and vegetation species, which has implications for post-fire vegetation recovery and water storage. This work demonstrates opportunities to apply ECOSTRESS ET across globally diverse ecoregions and small catchment scales to identify potentially high-risk areas and improve fire risk and vegetation recovery assessments.

Variability of potential evapotranspiration and moisture conditions in Srikakulam district of Andhra Pradesh

In the present study, evapotranspiration and moisture adequate index for the 37 mandals of the Srikakulam district for the year 2018 has been estimated. The PET values were very high in the summer season of all the mandals than in the other seasons. The normal PET values were lower than that of the actual PET values showing location specific and better estimation characteristics. This estimation of location-specific PET can be helpful for the drought classification and water management planning within the district. Moisture adequate index of all the mandals has indicated that the district as a whole has a humid/temperate climate; but within the district, mandals report different conditions. This makes it a more relevant tool for drought, microclimatic classification and annual water planning for sustainable agriculture.

Analysis of the variation in potential evapotranspiration and surface wet conditions in the Hancang River Basin, China

Evapotranspiration is an important component of the water cycle, and possible trends in evapotranspiration can, among others, influence water management and agricultural production. Potential evapotranspiration (ETp) is a measure of the ability of the atmosphere to remove water from the surface through the processes of evaporation and transpiration. It plays an important role in assessing regional dry–wet conditions and variations in meteorological conditions. This study analyzed the change trends of monthly ETp and surface dryness and wetness in the Hancang River Basin and, through principal component analysis and correlation analysis, explored the main meteorological factors that affected ETp and the interactions between meteorological factors; ETp values were estimated using the FAO-56 Penman–Monteith method. The results showed that there was a large gap in ETp between different months in the Hancang River Basin, with a trend of first increasing and then decreasing within a year. The highest monthly evapotranspiration was 114.119 mm (July), and the lowest was 42.761 mm (January). The maximum relative humidity index was 0.822 (August), and the minimum was -0.979 (January). The average temperature, precipitation, average relative humidity, and solar radiation are positive factors that affect ETp, while average air pressure is a negative factor that affects ETp. This study provides a reference for the wet conditions of small watersheds and for countermeasures to address climate change.

Effects of climate anomalies on warm-season low flows in Switzerland

Abstract. Switzerland has faced extended periods of low river flows in recent years (2003, 2011, 2015 and 2018), with major economic and environmental consequences. Understanding the origins of events like these is important for water resources management. In this work, we provide data illustrating the individual and joint contributions of precipitation and evapotranspiration to low flows in both typical and dry years. To quantify how weather drives low flows, we explore how deviations from mean seasonal climate conditions (i.e., climate anomalies) of precipitation and potential evapotranspiration correlate with the occurrence and magnitude of annual 7 d lowest flows (Qmin) during the warm season (May through November) across 380 Swiss catchments from 2000 through 2018. Most warm-season low flows followed periods of below-average precipitation and above-average potential evapotranspiration, and the lowest low flows resulted from both of these drivers acting together. Low-flow timing was spatially variable across Switzerland in all years, including the driest (2003, 2011, 2015 and 2018). Low flows in these driest years were associated with much longer-lasting climate anomalies than the ≤2 month anomalies which preceded typical warm-season low flows in other years. We found that snow water equivalent and winter precipitation totals only slightly influenced the magnitude and timing of warm-season low flows in low-elevation catchments across Switzerland. Our results provide insight into how precipitation and potential evapotranspiration jointly shape warm-season low flows across Switzerland and potentially aid in assessing low-flow risks in similar mountain regions using seasonal weather forecasts.

Prediction of coupled hydromechanical behavior of unsaturated soils based on seasonal variations in hydrologic conditions

Seasonal variations in hydrologic conditions greatly influence the hydromechanical properties of unsaturated soils. There are several models available to estimate shear strength of unsaturated soil under various hydrologic conditions. However, many of these existing models provide little to no data regarding the deformations associated with wetting and drying of unsaturated soils. The incremental hydromechanical behavior for an unsaturated soil is generally described by a constitutive framework. In this study, a modified Sheng, Fredlund, and Gens (SFG) soil constitutive model was utilized with in situ hydrologic data to simulate fully coupled mechanical behavior for an unsaturated slope over different hydrologic events. This paper also presents a hydrological prediction approach to estimate hydrologic characteristics of unsaturated soils over several wetting and drying events using only the soil-water characteristics parameters of the main drying curve. The proposed approach provides a possibility of describing long-term hydrologic behavior of unsaturated soils by means of a limited amount of in situ hydrologic data. The outcome of this study provides geotechnical engineers with the capability of estimating deformational behavior of unsaturated soils under various real-time rainfall–evapotranspiration conditions and implementing more effective emergency planning.

A conterminous United States analysis of the impact of Landsat 5 orbit drift on the temporal consistency of Landsat 5 Thematic Mapper data

The Landsat 5 orbit changed more than expected over its three-decade mission life. Previous modelling research indicated that the resulting Landsat 5 overpass time and so acquisition solar zenith differences will have caused non-negligible reflectance and normalized difference vegetation index (NDVI) temporal differences. Rather than use a modelling approach this paper presents the results of a comprehensive examination of the Landsat 5 Thematic Mapper (TM) data. Ten years of summer Landsat 5 TM Analysis Ready Data (ARD) sampled at >19.3 million 30 m pixel locations across the conterminous United States (CONUS) are considered. The acquisition solar zenith, red, near infrared (NIR), shortwave infrared (SWIR) (~2.1 μm) surface reflectance, and NDVI, are compared between five consecutive periods (1995 versus 2006, 1996 versus 2007, 1997 versus 2008, 1998 versus 2009, and 1999 versus 2010) that span years with very different Landsat 5 overpass times, and are also compared between 1998 and 1999 that have similar overpass times. The different years of Landsat 5 TM data are plotted against each other and reduced major axis (RMA) regressions passing though the origin are developed and compared with the acquisition solar geometry changes. The red, SWIR and NDVI RMA slopes are proportional to the magnitude of solar zenith change between years and are indicative of CONUS-wide differences due to orbit drift. The greatest differences occurred between 1995 and 2006, the years with the greatest solar zenith differences (median CONUS difference 8.43°) with RMA regression slopes quite far from unity (1.14 for the red and SWIR bands, 0.91 for NDVI). In years with smaller solar zenith differences the RMA slopes are closer to unity. As agricultural crops may be managed inconsistently through time, and as drought may have pronounced effects on reflectance, the analysis is also undertaken masking out crop pixels and considering locations that have similar precipitation and evapotranspiration conditions between years. These experiments indicate that, at CONUS scale, the cause of the changing RMA regression slopes between years is not due to agricultural changes or to the influence of above normal drought or wetness. The results confirm previous published modelling based findings but are based on direct examination of CONUS Landsat 5 TM data. They indicate that certain research and applications that require temporally consistent red, SWIR and NDVI data may need to take Landsat 5 orbit drift effects into account.

The Sensitivity of Satellite Solar‐Induced Chlorophyll Fluorescence to Meteorological Drought

AbstractSolar‐induced chlorophyll fluorescence (SIF) could provide information on plant physiological response to water stress (e.g., drought). There are growing interests to study the effect of drought on SIF. However, to what extent SIF responds to drought and how the responses vary under different precipitation, temperature, and potential evapotranspiration conditions are not clear. In this regard, we evaluated the relationship between satellite‐based SIF product and four commonly used meteorological drought indices (Standardized Precipitation‐Evapotranspiration Index, Standardized Precipitation Index, Temperature Condition Index, and Palmer Drought Severity Index) under diverse climate regions in the continental United States. The four drought indices were used because they estimate meteorological drought conditions based on either single or combined meteorological factors such as precipitation, temperature, and potential evapotranspiration, representing different perspectives of drought. The relationship between SIF and meteorological drought varied spatially and differed for different ecosystem types. The high sensitivity occurred in dry areas characterized by a high mean annual growing season temperature and low vegetation productivity. Through random forest regression analyses, we found that temperature, gross primary production, precipitation, and land cover are the major factors affecting the relationships between SIF and meteorological drought indices. Taken together, satellite SIF is highly sensitive to meteorological drought, but the high sensitivity is constrained to dry regions.

Warming Alters Hydrologic Heterogeneity: Simulated Climate Sensitivity of Hydrology‐Based Microrefugia in the Snow‐to‐Rain Transition Zone

AbstractIn complex terrain, drifting snow contributes to ecohydrologic landscape heterogeneity and ecological refugia. In this study, we assessed the climate sensitivity of hydrological dynamics in a semiarid mountainous catchment in the snow‐to‐rain transition zone. This catchment includes a distinct snow drift‐subsidized refugium that comprises a small portion (14.5%) of the watershed but accounts for a disproportionate amount (modeled average 56%) of hydrological flux generation. We conducted climate sensitivity experiments using a physically based hydrologic model to assess responses of a suite of hydrologic metrics across the watershed. Experiments with an imposed 3.5 °C warming showed reductions in average maximum snow water equivalent of 58–68% and deep percolation by 72%. While relative decreases were similar across the watershed, much greater absolute decreases in snowpack occurred in the drift‐subsidized site than the surrounding landscape. In drift‐subsidized locations, warming caused a shift from a regime that included both energy‐ and water‐limited evapotranspiration conditions to exclusively water‐limited conditions. Warming also resulted in altered interannual variability of hydrologic metrics. The drift‐subsidized unit was more sensitive to warming than the surrounding landscape, with reduced potential for the effects of warming to be offset by increased precipitation. Despite spatially homogeneous changes in climate, the effects of climate change on the hydrological dynamics were spatially heterogeneous in this watershed due to the presence of lateral water transport in the form of drifting snow. These findings suggest an increase in hydrologic homogeneity across the landscape and relatively large changes in snow drift‐subsidized refugia.

Foliar gas exchange, fruit quality and water use efficiency of cape Gooseberry under different irrigation depths and mulching at greenhouse conditions

Abstract The current study aimed at evaluating gas exchanges, yield, water use efficiency and fruit quality of cape gooseberry in response to different irrigation depths with or without mulching of oat residues on pots at greenhouse conditions. Four irrigation depths were tested: 50%, 100%, 125% e 150% of reference evapotranspiration (ETo). Leaf gas exchanges were evaluated by an infrared gas analyzer at different stages of the crop. Throughout the harvest, yield per plant and yield components were assessed in conjunction with water-use efficiency (WUE) and fruit quality responses. Stomata conductance at the flowering and fructification stages showed a smaller limitation under the treatments 125 and 150%ETo. It should be noticed that the aforementioned treatments increased in 83% fresh fruit mass per plant in comparison to 50%ETo. We found a higher instantaneous water-use efficiency throughout flowering under 150%ETo, as well as at the fructification under 125%ETo treatments. Nevertheless, under 125%ETo conditions without mulching the greatest WUE was found, whereas the lowest WUE was obtained under the 50%ETo treatment with no mulching. The treatment 125%ETo resulted in the highest SS and pH, whilst the treatment 150%ETo with mulching evidenced the highest Ratio along with the lowest total acidity observed.

Determination of the Water Potential Threshold at Which Rice Growth Is Impacted

Rice feeds 50% of the world’s population. Flooding is the most common irrigation system used for growing rice, a practice responsible for a large amount of water loss. Climate changes may affect water availability in irrigated agriculture, and it will be necessary to develop more sustainable irrigation practices. The aim of this work was to determine, in controlled conditions, the threshold when water potential begins to decrease plant growth. Two independent greenhouse experiments were conducted during middle summer and fall, in order to validate the results for high and low evapotranspiration conditions. Rice plants were grown in hydroponics and the water potential was adjusted with polyethylene glycol 6000, varying from −0.04 MPa (control) to −0.19 MPa. Leaf water potential, water use efficiency, leaf area, and root and shoot biomass were evaluated. All assayed parameters decreased as the water potential was decreased. The water potential threshold which starts to negatively affect rice growth was between −0.046 and −0.056 MPa, which are values close to those observed in the field in previous research. The definition of a critical value may help to improve water management in rice cultivation and to maintain productivity.

Effects of excessive irrigation of date palm on soil salinization, shallow groundwater properties, and water use in a Saharan oasis

In arid oases, soil salinity and a rise in shallow groundwater are serious threats to long-term sustainability of irrigated agriculture. Understanding the impacts of irrigation practices on soil salinity and shallow groundwater dynamics is critical for improving soil conditions and water efficiency. In this study, the impacts of excessive irrigation of date palms with low-quality water on soil salinization and shallow groundwater properties (depth and electrical conductivity) were evaluated for a 10-year period (2005–2015) in a Saharan Tunisian oasis. The study included three phases: (1) assessment of the suitability of groundwater for irrigating date palms; (2) quantification of the long-term water use of date palm plantations; and (3) quantification of dynamic patterns of soil electrical conductivity and shallow saline groundwater in the studied oasis for a 10-year period (2005–2015). Results of this study indicated that under high evapotranspiration conditions, the identified low-quality water resources (leading to high soil salinization risk) coupled with rapidly rising shallow groundwater at critical depths (<1.5 m) (resulting from the high water use) were key factors of the rapid increase in soil salinization within the oasis. The soil electrical conductivity built up to levels that exceeded the salt tolerance of date palms, estimated at 4 dS m−1. Although the excessive use of irrigation water dilutes the groundwater, and its salinity decreases, the risk of increasing soil salinity is greater because of rising water table.

English

The use of different water depths and soil surface soil surface wetted areas by micro-sprinkler irrigation systems results different wetted soil volumes and evapotranspiration conditions, which may cause changes in fruit production quality and quantity. The objective of this study was to evaluate yield, fruit physical characteristics and leaf area of ​​banana cv. Grand Naine under different irrigation depths and soil surface wetted areas in Northern Minas Gerais State, Brazil. The experiment was conducted in the period 2003 to 2006, involving three production cycles of &#39;Grand Naine&#39; banana with planting spacing of 3.0 m &times; 2.7 m irrigated by micro-sprinklers. The experimental design was a randomized block with four replicates in a split-plot arrangement with three soil surface wetted areas in the plot and five irrigation depths as subplots. The irrigation levels were taken as fractions of crop evapotranspiration (ETc): 0.70; 0.85; 1.00; 1.15 and 1.30 ETc, and the soil surface wetted areas (Wa) were: Wa 1 of 10.17 m2, with emitter of 20 L h-1 and radius of throw of 1.8 m; Wa 2 of 23.74 m2, with emitter of 63.6 L h-1 and radius of throw of 2.7 m and Wa 3 of 28.26 m2, with emitter of 60 L h-1 and radius of throw of 3.0 m. Central fruit diameter and mean weight, leaf area and yield of &#39;Grand Naine&#39; banana were not influenced by irrigation depths. On the other hand, smaller soil surface wetted area causes reduction in central fruit length and weight, leaf area and yield of &#39;Grand Naine&#39; banana. Key words: Musa spp., irrigation management, soil surface wetted area.

Integrative Effects of Vine Water Relations and Grape Ripeness Level of Vitis vinifera L. cv. Shiraz/Richter 99. I. Physiological Changes and Vegetative-Reproductive Growth Balances

The water relations and physiological status of the grapevine are critical for obtaining a quality product and for fully exploring vineyard and grape potential. The objective of this investigation was to determine the effect of grapevine water status (induced by means of two field water capacity-based irrigation levels, 75% and 100%, applied at single and combined vine developmental stages) on morphological and physiological changes in Vitis vinifera L. cv. Shiraz/Richter 99 grapevines and grapes (harvested at different soluble solid levels) under field conditions. The integrative effects of vine water relations and grape ripeness level, specifically in a Mediterranean high winter rainfall area, have not yet been investigated systematically. The terroir affected the reaction of the vines to treatments. The soil displayed high water-holding capacity and a buffer against favourable evapotranspiration conditions, even with a western aspect and being subjected to long and relatively dry seasons, with frequent occurrence of high temperatures and grapevines with fully developed canopies. The vines did not seem overly stressed – in line with the relatively high base soil water fractions of mostly more than 50% of field water capacity. Primary and secondary leaf water potential and stem water potential displayed similar patterns and the water potential of the primary and secondary leaves was similar. Despite relatively high base soil water contents that prevented excessively low plant water potential and classic leaf and berry behaviour to surface, the vines still responded in a noticeable way to volume and timing of irrigation in relation to the grape ripeness level status. Water relations, ripeness level and terroir conditions showed an integrated, steering impact on physiological, vegetative and reproductive behaviour. Post-veraison irrigated vines were expected to maintain relatively high water potential during the last weeks of the ripening period, but this seemed not to be the case. All vines seemed to have recuperated/stabilised during this time, maintaining their water balances. Physical, physiological and compositional changes in the berry during late ripening under field conditions were clarified further. New information was obtained on the relationships between the behaviour of the root system, canopy and grapes and the changing terroir conditions during the ripening period.

Comparison of SPI and SPEI applicability for drought impact assessment on crop production in the Danubian Lowland and the East Slovakian Lowland

Drought belongs among the main impact factors considering crop yields. Therefore, this paper is focused on the assessment of drought occurrence and intensity as well as on its impact on crop yields on the Danubian and the East Slovakian lowlands with the spatial resolution at district level. Yield data were the main limitation of the study, which resulted in the limited length of the assessed period (1996–2013). The standardized yields of ten crops (winter wheat, spring wheat, winter barley, spring barley, rye, maize, potatoes, oilseed rape, sunflower, and sugar beet) were correlated with monthly, 2-, and 3-monthly standardized precipitation index (SPI) and standardized precipitation and evapotranspiration index (SPEI). For this purpose, the common significance level of alpha = 0.05 was used. The temporal evolution of both indices and drought occurrence during the period 1961–2013 were assessed for each district. Most crops show a higher correlation with the SPEI than with the SPI in contrast to potatoes, which reached a higher significant correlation using the SPI. The correlation also increases with increasing number of months within a time step. The highest correlation can be seen between maize and the 3-monthly SPEI in August representing summer precipitation and potential evapotranspiration conditions. Furthermore, a very high correlation was recorded considering sugar beet, which is influenced mainly by summer precipitation, because the correlation coefficient between the sugar beet and the 3-monthly SPI is as high as using the 3-monthly SPEI. Crop yields in the East Slovakian Lowland do not seem to be influenced by wet/dry periods identified using the SPI and the SPEI as their correlation with both indices is quite low and insignificant.

Human activity and climate variability impacts on sediment discharge and runoff in the Yellow River of China

We analyze the variability of sediment discharge and runoff in the Hekou–Longmen segment in the middle reaches of the Yellow River, China. Our analysis is based on Normalized Difference Vegetation Index (NDVI), sediment discharge, runoff, and monthly meteorological data (1961–2010). The climate conditions are controlled via monthly regional average precipitation and potential evapotranspiration (ET0) that are calculated with the Penman–Monteith method. Data regarding water and soil conservation infrastructure and their effects were investigated as causal factors of runoff and sediment discharge changes. The results indicated the following conclusions: (1) The sediment concentration, sediment discharge, and annual runoff, varied considerably during the study period and all of these factors exhibited larger coefficients of variation than ET0 and precipitation. (2) Sediment discharge, annual runoff, and sediment concentration significantly declined over the study period in a linear fashion. This was accompanied by an increase in ET0 and decline in precipitation that were not significant. (3) Within paired years with similar precipitation and potential evapotranspiration conditions (SPEC), all pairs showed a decline in runoff, sediment discharge, and sediment concentration. (4) Human impacts in this region were markedly high as indicated by NDVI, and soil and water measurements, and especially the soil and water conservation infrastructure resulting in an approximately 312 Mt year−1 of sediment deposition during 1960–1999.