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Abstract Agriculture and associated sectors are one of the primary sources of living for the global population. Sustainability in agriculture will yield long-term benefits requisite to accomplish development and mitigation of resource scarcity. Hence, realistic assessment of water requirement for agricultural use or alternatively agricultural potential from available water resources is imperative to sustainable water management keeping in view of possible scarce situation in relation to freshwater availability across the Globe. The present study focuses on assessment of the water requirement for potential agricultural use for the command area of a Himalayan river project, namely Gandak river project in Northern India using extensive geo-spatial techniques. Detailed information of extensive canal network is derived from high-resolution satellite images using GIS tools, along with other spatially distributed information for relevant parameters such as rainfall, temperature, soil type, elevation, water-holding capacity and agricultural productivity. The study reasonably identifies the spatial variability in water requirement potential in the project command with rational indication of maximum water demand in north-central section of the study area where the lowest aridity index characterized by very low slope and deep sandy loam soil is recorded. Efficient usage with growing scarcity of this essential natural resource warrants efficiency optimization of water usage with realistic assessment. This approach unlike traditional method uses high-resolution satellite data that are more scientific and accurate and will undoubtedly facilitate development of rational decision support system for efficient management of available surface water use for different purposes in the region.

Abstract The evolution of regional arid/humid patterns caused by global climate change deserves attention. We investigated the changes in the area of arid/humid climate regions over Asia under the aegis of national-committed emission reductions to comply with the Paris Agreement using an ensemble of 17 global climate models (GCMs) from the Fifth Coupled Climate Model Intercomparison Project (CMIP5) archives. Our results indicated an overall trend towards aridity in a future warmer climate based on an aridity index (AI), defined as the ratio of precipitation to potential evapotranspiration (PET). In the future, the humid region will contract and the arid region and arid/humid transition zones will expand. Compared with the present period, arid/humid region switch is projected to occur in a land area of 2512.8 × 103 km2 over Asia under the Intended Nationally Determined Contributions (INDC)-pledge scenario. If global warming is controlled to the ambitious 2.0 °C and 1.5 °C scenarios instead of that of the INDC-pledge scenario, a decrease in the changes in the area of arid/humid regions by more than half would be expected. In addition, the arid/humid regions with continuous global warming are estimated to contract/expand greatly. Changes in the spatial pattern of the arid/humid zones over Asia show strong similarities between multi-model simulations, although there are some differences in detail.

The influence of climate aridization on soil salinity in the basins of the south of Eastern Siberia and Mongolia is considered in the article. The data characterizing the climate aridity of the basins of the south of Eastern Siberia over 50 years are analyzed. In the south of Eastern Siberia from 1955 to 2015, the increase in air temperature was higher than in the whole world. In the basins of Tuva, the increase in air temperature was 2.5–3.7 оС; in the Minusinsk depression – 1.7–2.8 оС, in the basins of Buryatia – 1.5–1.8 оС; the coefficient of determination for moving averages over 20 years (R2) was 0.9–0.95, the changes are significant – Student's criterion 19–35. Changes in the aridity coefficient were in the range of 0.02–0.14; according to the Student criterion, they were significant (t = 7.4 – -22), while a decrease in aridization was observed in the Minusinsk depression and its growth in other regions. Thus, in general, for the studied regions, the multidirectionality of the processes of climate aridization has been ascertained. In the Minusinsk depression, despite a slight decrease in aridization, category changes (according to the classification of Lobova et al., 1977) did not occur during this period, the territory remained in the arid and subarid categories. Despite the increase in climate aridization in the basins of Tuva and Buryatia, most of them also did not show a tendency to more arid category. Nevertheless, in a number of hollows in the south of Eastern Siberia, an increase in aridization with a transition to a more arid category was observed. This applies to the Eravnensky and Barguzinsky basins of Buryatia, which switched from weakly arid to subarid, as well as to the Ubsunur basin of Tuva, which turned from arid to strongly arid. For the basins of the south of Eastern Siberia, where climate aridization was recorded, the question arose about the possible activation of the process of soil salinization. To solve this problem, materials were collected on soil salinity in the arid regions of Mongolia. It was found that an increase in climate aridity even in the extreme arid deserts of the Gobi, where parent rocks are not saline, under automorphic conditions, the soil is practically not saline (the amount of salts does not exceed 0.1%). In areas where saline Cretaceous-Paleogene red sediments are spread, automorphic soils are saline, and the amount of salts may exceed 2.5%. Thus, in extremely arid climatic conditions, salinization of automorphic soils can range from non-saline to highly saline. Under the hydromorphic conditions of the basins of the south of Eastern Siberia, as well as in Mongolia, climate aridization inevitably leads to an intensification of the salt accumulation process, therefore, in the basins of Tuva and Buryatia experiencing climate aridization, a process of soil salinization in hydromorphic landscapes should be expected.

Serious economic damages in many regions of the world were caused by the changes in agroclimatic resources during the last 2–3 decades. The Balkan Peninsula is much affected by the temperatures rising, changes in the distribution of precipitation, and the increasing frequency of extreme events—basically, droughts and frosts. Bulgarian agriculture is developed under various agrometeorological conditions. The climate of the country is characterized by the atmosphere and soil moisture deficit in the time of active crop vegetation and yield formation. The aim of this research is to assess the changes in agrometeorological conditions for the growth of the main grain crops and the possibilities for reaction through agro-technologies. Furthermore, the features of contemporary varieties and hybrids of spring and autumn cereals will be taken into account. The next important factor is the specific requirements for hydro-thermal conditions at different phenological phases of agricultural crop development, i.e., sums of the temperatures and precipitations. Agro-technologies react to tendencies in changing agrometeorological conditions. For the adaptation of agro-technologies, the maximum use of natural agroclimatic resources should be included in activities for overcoming unfavorable conditions, as well as the increased frequency of extreme events. A detailed assessment of the agrometeorological conditions is necessary to choose the suitable agro-technology activity. The analysis of the main meteorological elements—temperatures, precipitations, air humidity, wind speed, and solar radiation for thirty years (1986–2015) was used to assess the changes in agrometeorological conditions on agricultural lands in Bulgaria. Appropriate agro-technical activities for growing the main grain crops are proposed in accordance with the observed changes.

Xinjiang is a typical continental arid climate zone and ecologically fragile zone. Drought has caused damage to the local social economy, agricultural production, and the ecological environment. However, the study of drought is more difficult due to the complex topography and the lack of monitoring information. In this paper, based on the meteorological data of 94 meteorological stations in Xinjiang from 1961 to 2020, we used the precipitation and potential evapotranspiration (ET0) to calculate the aridity index (AI); the Mann–Kendall test, Morlet wavelet analysis, and Kriging interpolation were used to identify the trend, period, and spatial distribution. The results showed that (1) the average change rate of the precipitation in Xinjiang was 8.58 mm/10a, the average change rate of the ET0 was −14.84 mm/10a, and the average change rate of the AI was −1.94/10a; (2) the periods of precipitation, ET0, and AI in Xinjiang were 39, 29, and 14 years, respectively, and the abrupt changes occurred in 1986, 1971, and 1987, respectively; (3) The Moran index of precipitation and temperature are 0.41 and 0.33, respectively, indicating that precipitation and temperature in Xinjiang are positively correlated in spatial distribution and have spatial clustering characteristics; and the z-values are both greater than 2.58 (p < 0.01), indicating that the spatial autocorrelation of precipitation and temperature in Xinjiang is significant. This study can provide a reference for the diagnosis of the meteorological drought mechanism and the coping with climate change in Xinjiang.

Variation in climatic parameters affecting water access can play a key role in the sustainable development of agriculture and the environment. Reference evapotranspiration (ET0), after precipitation, is the most important parameter affecting access to water resources in the arid and semiarid areas like Iran. In this study, data were collected from 50 synoptic weather stations for a period of 30 years (1988–2017) in the area with high population density and critical agricultural regions of Iran. Trend analysis of ET0 and climatic parameters including maximum and minimum temperature (Tmax and Tmin), sunshine duration (SD), relative humidity (RH), wind speed (WS), and air pressure (P) were investigated. Also, the effects of climatic parameters on ET0 were analyzed using dimensionless sensitivity coefficients. The aridity index (AI) was also evaluated using precipitation and ET0 data in the study area. Results showed that on an annual time scale, ET0 had a significant increasing trend (p ≤ 0.05) in 77.1% of the studied stations. In the seasonal time scale, the most increasing trend of ET0 was observed in winter. The results of sensitivity analysis showed that Tmax, RH, and WS were the most effective variables on ET0. The trend analysis of AI revealed that 92% of the stations had a significant (p ≤ 0.05) increasing trend over the study period. The spatial distribution of the annual AI indicated that only 10% of the study area meets the atmospheric evaporation demand, and in 90% of the study area, the annual ET0 was greater than the annual precipitation. These areas were highly affected by aridity and thus required additional water for crop production. These results indicated that climate change in Iran has increased ET0 and aridity, thereby increasing the water requirement for plants in agricultural lands. Hence, the optimum use of water resources for agricultural purposes is a suitable way to deal with the crisis of water shortage and aridity in Iran. [ABSTRACT FROM AUTHOR]

Global warming is already having a negative impact on vital sectors on which human development depends, such as water resource availability. In this study, the changes and abrupt change timing of climatic extreme indices, aridity and drought over the Region of South Aegean are captured using the Mann–Kendall and Pettitt tests, while the latter variables are correlated with the water volume transported by ships to the region as well as the relevant costs. The region's climate is shifting to warmer conditions with less precipitation, since significantly positive trends were noted with regard to the number of tropical nights, warm nights, warm days, the warm spell duration index and the diurnal temperature range; significant negative trends were observed in relation to the number of cool nights, cool days and the cold spell duration index, with the change-point year for the latter variables being 2006. Inaddition, 7/11 precipitation related indices exhibited a downward trend, while significantly negative trends were observed with regard to the number of consecutive dry days, with the timing of the abrupt change being 2001. The Aridity Index (AI) reveals that the region's climate characterization is changing from dry and sub-humid to semi-arid conditions, whilst the Reconnaissance Drought Index standardized (RDIst) and the Standardized Precipitation Index (SPI) indices suggests an amplification of drought phenomena over the Region. The tourism variables illustrated a significant positive trend, with the timing of the abrupt change being registered during 2006–2009, whilst the correlation analysis between tourism variables and water transfers implies that the surge on water transfer by ships to the Region occurred between 1998 and 2008. This can be mainly attributed to the changes in climate patterns. The correlation analysis documents a strong positive correlation between the water transfer dataset and the diurnal temperature range, and a moderately negative association with the precipitation related indices, annual precipitation, drought phenomena and aridity with 7/11. [ABSTRACT FROM AUTHOR]

Accurate assessment of changes in climate conditions and their impacts on different sectors including agriculture, animal husbandry, wildlife, environment, and so forth can affect the appropriate natural disaster management. The aridity index defined by the United Nations Environmental Programme (UNEP) is one of the most widely used indices in the evaluation of climate conditions based on the ratio of precipitation (P) and potential evapotranspiration (PET) parameters. In this study, the impact of changes on PET calculation methods (6 PET calculation methods) in values of UNEP aridity index were compared by analyzing the data series of 28 synoptic stations with various climate conditions on monthly and seasonal time scales in Iran from 1967 to 2017. Therefore, it is determined to apply the FAO Penman–Monteith (FPM) equation as the reference method to measure PET. According to the results, based on the GEE method (Backward Generalized Estimating Equations) within monthly and seasonal time scales, calculated UNEP aridity index based on Hargreaves–Samani (HS), Jensen–Haise (JH), and Blaney–Criddle (BC) equations, respectively had the most similarities with calculated UNEP Aridity Index based on FPM method. The clustering analysis indicated that values of calculated UNEP aridity index within the monthly and seasonal time scales using JH, HS and BC equations are strikingly similar to the values of calculated UNEP aridity index using the FPM method. The average similarity rates of the calculated UNEP aridity index using JH and HS equations and by FPM method were 98.35% and 98.34% within a 1-month time scale and 98.11% and 98.09% within a 3-month time scale, respectively. [ABSTRACT FROM AUTHOR]

Catchment baseflow is jointly controlled by climate and landscape properties. Previous studies have recognized that spatial variability of mean annual baseflow coefficient (BFC = Qb/P, ratio of baseflow to precipitation) is primarily controlled by aridity index and storage capacity. However, an analytical solution of BFC in terms of the dominant controlling factors has not yet been established. The objective of this study was to develop an analytical BFC curve to depict spatial variability of BFC based on the "limit" concept of the Budyko framework. The BFC curve relates the baseflow coefficient to aridity index and storage capacity without resolving complex interactions between evapotranspiration and baseflow generation. The proposed BFC curve showed that, in the arid catchments, baseflow coefficient was primarily limited by available water (precipitation, P) and, in the humid catchments, was jointly controlled by both the available energy (potential evapotranspiration, Ep) and catchment retention capability (ratio of catchment storage capacity to P, i.e., Sp/P). Observed hydrological data from 950 catchments in Australia, the conterminous United States and the United Kingdom with diverse hydro‐climatic conditions (BFC = 0.001–0.650) were collected to demonstrate the capability of the developed curve. Results showed that the BFC curve captured the spatial variability of observed BFC in the 950 study catchments (R2 = 0.75, RMSE = 0.058). Mean annual baseflow estimated by the BFC curve agreed well with observed baseflow (R2 = 0.86, RMSE = 0.19 mm). The developed analytical curve provides an analytical solution for understanding how aridity index and storage capacity control mean annual catchment baseflow, and will improve predictability of baseflow at ungauged basins. Key Points: An analytical curve was established to depict the spatial variability of mean annual baseflow based on the Budyko "limit" frameworkThe curve directly relates aridity index and storage capacity (Sp) to estimate baseflow and shows dominant control of Sp in humid catchmentsThe developed curve performed well with observed data from 950 catchments located in the Australia, CONUS and UK [ABSTRACT FROM AUTHOR]

Background: Sweet potato producers in Kenya practice either sole cropping of or relay cropping and rarely do intercropping which aims at maximizing on time and space. Objective. To assess the relative performance of sweet potato under various cropping systems. Methodology: This study was conducted in Katumani, Kenya for two seasons; 2018/2019 and 2019/2020. The treatments comprised of sole cropping of Kabode, sole cropping of Bungoma, Kabode + common bean, Bungoma + common bean, and sole cropping of common beans (Mwezi mbili) were laid out in a randomized complete block design (RCBD) in 3 replications. Monocropped sweet potato and beans served as the control treatment. Weather data, leaf area, leaf area index, vine length, and percent canopy cover were collected throughout the cropping period. The data were analysed by a two-way ANOVA at 0.05% significance level followed by a Pearson’s correlation analysis on the extent to which length of vines, percent canopy cover, leaf area index, and weather parameters; ETo, aridity index, and rainfall influenced the attained tuber yields. Results: Intercropping significantly (p < 0.05) reduced sweet potato yields of Kabode and Bungoma varieties by 19.3% and 44%, respectively. Monocropped Kabode yielded 31.4 t ha-1, significantly (p< 0.05) higher than monocropped Bungoma with 23.9 t ha-1 whereas their common bean intercrops yielded 26.2 t ha-1 and 18.1 t ha-1,respectively. Correlation analysis showed that rainfall, ETo, LAI, vine length, and percent canopy cover negatively affected tuber yields. Implication: Land equivalent ratio revealed that intercropping sweet potato varieties with common beans was biologically efficient and that the percentage of the land saved averagely ranged from 8% to 33%. More studies should be conducted to determine the extent of sweet potato allelopathy on companion crops and nutrient use under intercropping systems. Conclusion: Yield stability analysis showed that orange-fleshed Kabode was the most stable variety across seasons to be grown in Katumani.

Minimum data length is vital to guarantee accuracy in hydrological analysis. In practice, it is sometimes determined by the experiences of hydrologists, leading the selection of the acceptable minimum data length to an arguable issue among hydrologists. Therefore, this study aims to investigate the impact of data length on parameter estimation and hydrological model performance, especially for data-scarce regions. Using four primary datasets from river basins in Japan and USA, subsets were generated from a 28-year dataset and used to estimate data adjustment parameters based on the aridity index approach to improve the parameter estimation. The influence of their length on hydrological analysis is evaluated using the Xinanjiang (XAJ) model; also, the effectiveness of outlier removal on the parameter estimation is checked using regression analysis. Here, we present the estimation of the most acceptable minimum data length in parameter estimation for assessing the XAJ model and the effectiveness of parameter adjustment by removing the outliers in observed datasets. The results show that between 10-year to 13-year datasets are generally sufficient for the robust estimate of the most acceptable minimum data length in the XAJ model. Moreover, removing outliers can improve parameter estimation in all study basins.

A research study was undertaken to estimate reference evapotranspiration (ETO), moisture index (MI) and aridity index (AI) and analyse their trends in different locations/zones of Punjab. Annual and seasonal ETO was observed to be highest in south-west and lowest in north-east zone. North-east zone experienced increasing trend in annual as well as seasonal ETO. Districts within the central zone had large variability within the zone. MI and AI were in the order of north-east zone followed by Central zone and South-west zone indicating better moisture availability conditions in north-east. Mean difference in annual and seasonal MI and AI also indicated statistical similarities within the districts of north-east and south-west zones but different from other zones. Thus, increasing trend of ETO in north-east region and higher ETO range in south-west zone along with severe moisture availability necessitates the need for more careful planning of water resources in the region.

Unlike other crops, beans have moderate moisture requirements, but are very sensitive to moisture deficiency during flowering and grain formation. It has been established that in the short interval between these phenophases the sensitivity is maximum both in case of excess moisture and moisture deficit. Research has shown that the lack of water during flowering and fruiting greatly reduces production by shortening the duration of these phases of vegetation, by reducing pollen fertility, reducing pods and grain weight. The sensitivity of beans to the deficiency of vapor saturation in the atmosphere during flowering also has negative effects on the harvest. In order to determine to what extent the years of experimentation approach or deviate from the climatic conditions typical of the experimental field, monthly aridity indices were used for the series of years in which the experiments were performed at the studied farms, compared to indices of aridity from a longer period. The highest yields were obtained when the soil moisture at the beginning of flowering was at the field capacity for water and was maintained at the mentioned ceilings until the full formation of the grains. This paper summarizes the results of research on the influence of irrigation on production obtained in 2018-2021, at four farms located in the North Baragan Plain in Braila County. [ABSTRACT FROM AUTHOR]

A research study was undertaken to estimate reference evapotranspiration (ETO), moisture index (MI) and aridity index (AI) and analyse their trends in different locations/zones of Punjab. Annual and seasonal ETO was observed to be highest in south-west and lowest in north-east zone. North-east zone experienced increasing trend in annual as well as seasonal ETO. Districts within the central zone had large variability within the zone. MI and AI were in the order of north-east zone followed by Central zone and South-west zone indicating better moisture availability conditions in north-east. Mean difference in annual and seasonal MI and AI also indicated statistical similarities within the districts of north-east and south-west zones but different from other zones. Thus, increasing trend of ETO in north-east region and higher ETO range in south-west zone along with severe moisture availability necessitates the need for more careful planning of water resources in the region. [ABSTRACT FROM AUTHOR]

For evaluating the climatic and landscape controls on long‐term baseflow, baseflow index (BFI, defined as the ratio of baseflow to streamflow) and baseflow coefficient (BFC, defined as the ratio of baseflow to precipitation) are formulated as functions of climate aridity index, storage capacity index (defined as the ratio of average soil water storage capacity to precipitation), and a shape parameter for the spatial variability of storage capacity. The derivation is based on the two‐stage partitioning framework and a cumulative distribution function for storage capacity. Storage capacity has a larger impact on BFI than on BFC. When storage capacity index is smaller than 1, BFI is less sensitive to storage capacity index in arid regions compared to that in humid regions; whereas, when storage capacity index is larger than 1, BFI is less sensitive to storage capacity index in humid regions. The impact of storage capacity index on BFC is only significant in humid regions. The shape parameter plays an important role on fast flow generation at the first‐stage partitioning in humid regions and baseflow generation at the second‐stage partitioning in arid regions. The derived formulae were applied to more than 400 catchments where storage capacity index was found to follow a logarithmic function with climate aridity index. The role of climate forcings at finer timescales on baseflow were quantified, indicating that seasonality in climate forcings has a significant control especially on BFI. Plain Language Summary: Baseflow is a portion of streamflow from delayed storage such as groundwater, and it is crucial for human water supply and ecological environments. Studies have indicated both climate and catchment landscape have impacts on baseflow generation. However, their respective roles on mean annual baseflow are not fully understood. This study derives new functions to analyze the mediation effects of soil water storage capacity on the process of precipitation partitioning, and uses numerical simulations to evaluate the role of climate forcings at finer timescales on mean annual baseflow. Two widely used baseflow metrics are focused on here: baseflow index (BFI), defined as the ratio of baseflow to total streamflow; and baseflow coefficient (BFC), defined as the ratio of baseflow to precipitation. Our results show that the spatial variability of soil water storage capacity plays an important role in baseflow generation, and the impact of soil water storage capacity on BFI spreads across regions with different climates, while its impact on BFC is only significant in humid regions. Numerical simulation shows that seasonality in climate forcings has a vital influence on BFI. Our study advances our knowledge of physical controls on baseflow generation. Key Points: Derived baseflow index (BFI) and baseflow coefficient (BFC) as functions of aridity index, storage capacity index, and a shape parameterWhen storage capacity index is small (large), BFI is less sensitive to climate aridity index in arid (humid) regionsThe control of climate variability (particularly seasonality) on BFI is strong, but not for BFC [ABSTRACT FROM AUTHOR]

Assessing trends of hydrologic variables related to both hydrologic processes facilitates accurate water resources forecasting, especially in arid and semiarid regions with high evaporation and low rainfall volume. In this study, spatial and temporal trends of six hydrologic and climatic variables, viz. rainfall, evaporation, streamflow discharge, temperature, wind speed and relative humidity and also the ratio of annual potential evaporation to precipitation (E/P) were analysed at a monthly and annual scale. Moreover, the relationship of relative humidity, temperature, rainfall and wind speed trends with evaporation trend was investigated. Results of the study revealed the absence of significant temporal trend in precipitation, temperature and wind velocity for the majority of months, and the presence of upward trends in relative humidity and evaporation values as well as downward trend in streamflow discharge in some months. At an annual scale increasing evaporation and decreasing stream flow discharge trends were observed at most stations, which means that the region will be confronted with more severe drought conditions in future. Also, the result of Spearman's rank coefficient revealed that the temporal evaporation trend is not related to wind speed, temperature, relative humidity and rainfall trend. Moreover, the spatial trend of climatic and hydrologic variables indicated the similarity of evaporation and relative humidity trend as well as wind speed and rainfall trend.

Climate change has very significant impact on livelihoods and food security. The geospatial technology provides a better understanding of various themes related to climate change. This study examined the seasonal (kharif, rabi and zaid) long term (1970-2000) monthly climatic parameters such as precipitation, potential evapotranspiration over the country of India. The seasonal Aridity Index was computed and analyzed with respect to various agro-ecological zones of India. The analysis of long term mean precipitation (mm) during kharif, rabi and zaid season was found to be in the range of (14-7463), (0-914) and (0-1722) respectively. The analyses of the long term mean potential evapotranspiration in all seasons was found notable high in arid/semiarid zones. The Aridity Index during kharif, rabi and zaid seasons was found to be in the range of (0.19-4.27), (0.03-0.73) and (0.01-1.48) respectively. The seasonal Aridity Index in some of the agro-ecological zones of the central India in the arid and semiarid regions was found to be notably low. A concrete plan with synergic approach including integrated watershed management and traditional ecological practices will help to fulfill crop water demand and maintain adequate soil moisture for the present and future crops.

Even though climate variability, geology, and human activity are main triggers of landslides, based on earlier research, precipitation is considered the most important natural factor responsible for soil erosion in the landslide context. In this study landslide activation has been correlated with precipitation in least developed municipality of Crna Trava located in South-east Serbia. The purpose of this study is analyzing the precipitation in thirteen surrounding settlements: Vranje, Leskovac, Babušnica, Bela Palanka, Pirot, Dimitrovgrad, Kalna, Kriva Feja, Vladičin Han, Vučje, Vlasotince, Grdelica, Brestovac and finding its correlation to landslide occurrences. Precipitation for seven decades (period 1946-2017) has been interpolated by IDW method in the software ArcMap 10.5 and correlated to Crna Trava slope map. Potential locations of landslides were determined and compared to the recent landslides which occurred in July in 2018, in Bankovci village. Potential years for landslide activation were compared to calculated values of the Precipitation Concentration Index (PCI), the Modified Fournier Index (MFI), and Lang Aridity Index (AILang). The case study was done based on fieldwork which happened in a period from 20 to 26 of July 2018 in the village of Bankovci. On the 25 of July landslides were activated because of the extreme weather conditions, which affected wider region in Central and South-east Serbia: 100 liters of rain fell during the three-hour period. Habitants were interviewed about their memories on extreme floods and landslides in Crna Trava municipality, and the years they mentioned are in well agreement with our results of the extreme precipitation events.

This study examined the climatic water balance and aridity in the Western Lithoral hydrological zone of Nigeria. Monthly climatic data from 1976-2015 collected from six Nigeria Metrological Agency (NIMET) stations located in Ikeja, Ibadan, Akure, Abeokuta, Osogbo and Ilorin were used. The climatic variables are rainfall amount, temperature, sunshine hour, relative humidity and wind speed. The FAO Penman-Monteith method was adopted in estimating the potential evapotranspiration (PET). Water balance was determined from PET and rainfall amount. The spatial and temporal pattern of rainfall amount and PET were evaluated using universal kriging interpolation method, Mann-Kendall and regression trend analysis. The results of the Mann-Kendall and regression trend analysis revealed a statistically significant (Z= 2.74, P= 0.005) upward trend in rainfall amount between 1976 and 2015. Similarly, a statistically significant (Z= 4.40, p= 0.001) increasing trend was observed in PET during the same period. Six months of water surplus (May-October) and six months of water deficit (November-April) were identified. Overall, 27 years of water deficit was discovered over the 40 years period. Water balance pattern revealed the highest annual mean water surplus (324.51 mm) in the hinterland of Idanre, Akure, and Owo rather than the coastal city of Ikeja which can be attributed to orographic effect in the hinterland. The study area with a mean Aridity index (AI) of 0.94 can still be regarded as humid environment, although the spatial variability of AI indicates that the northern part is tending towards a dry sub-humid condition (AI= 0.76). This study recommends conservation of water surplus in the wet months for the augmentation of deficit in the dry months; this will not only boost agricultural production, but also alleviate water supply problem in the study area.

Climate zones fundamentally shape the patterns of the terrestrial environment and human habitation. How global warming alters their current distribution is an important question that has yet to be properly addressed. Using root-layer soil moisture as an indicator, this study investigates potential future changes in climate zones with the perturbed parameter ensemble of climate projections by the HadGEM3-GC3.05 model under the CMIP5 RCP8.5 scenario. The total area of global drylands (including arid, semiarid, and subhumid zones) can potentially expand by 10.5% (ensemble range is 0.6–19.0%) relative to the historical period of 1976–2005 by the end of the 21st century. This global rate of dryland expansion is smaller than the estimate using the ratio between annual precipitation total and potential evapotranspiration (19.2%, with an ensemble range of 6.7–33.1%). However, regional expansion rates over the mid-high latitudes can be much greater using soil moisture than using atmospheric indicators alone. This result is mainly because of frozen soil thawing and accelerated evapotranspiration with Arctic greening and polar warming, which can be detected in soil moisture but not from atmosphere-only indices. The areal expansion consists of 7.7% (–8.3 to 23.6%) semiarid zone growth and 9.5% (3.1–20.0%) subhumid growth at the expense of the 2.3% (–10.4 to 7.4%) and 12.6% (–29.5 to 2.0%) contraction of arid and humid zones. Climate risks appear in the peripheries of subtype zones across drylands. Potential alteration of the traditional humid zone, such as those in the mid-high latitudes and the Amazon region, highlights the accompanying vulnerability for local ecosystems. [ABSTRACT FROM AUTHOR]

The transitional climate zone (TCZ) over East Asia is an interface area between monsoon circulation and westerly circulation, making it highly susceptible to natural disasters and climate change. This study explores the spatial–temporal variation of the summer (May–September) TCZ during 1961–2018 and its response to monsoon rainy season. The summer Aridity Index (AI) instead of annual amount is used to recognize summer TCZ, with similar domain produced. However, differing from the annual total, the summer evaporation remains stable during the whole period, despite global warming. Hence, the summer TCZ has experienced little significant long‐term trends toward wetter or drier, since it is predominantly driven by precipitation that shows no clear tendency. The EOF decomposition reveals three key patterns accounting for 58.2% of the total variance: spatially uniform, south–north dipole and meridional tripole, which shows the complexity of spatial‐temporal variation in TCZ. TCZ is characterized by interdecadal mutations and periodical oscillations of 3 or 8 years. There exist remarkable 3 years interannual periods, with the greatest contribution stemming from the south‐central part of TCZ. In comparison, the northeast part exhibits a significant interdecadal band of about 8 years, which promotes the regime shift from wet to dry in the late 1990s over TCZ. Furthermore, the onset, retreat, and duration of the rainy season of TCZ in response to summer monsoon are examined, based on EEMD filtered 4 mm/day precipitation. All three indicators are subjected to strong interannual dispersion, without any significant overall trends. Only the retreat date of the western part of TCZ (100–110°E) is significantly correlated with the onset date. Dry‐wet condition in TCZ is more closely associated with the duration length of the monsoon influence. And we also notice that the westmost part of TCZ shows a greater sensitivity to monsoon activity than the east part. [ABSTRACT FROM AUTHOR]

Farming and afforestation in the African Sahel and Great Green Wall (GGW) regions are constrained by climate variability, water scarcity, and degradation of lands. Yet, the debate on dynamics of the Saharan boundary and vegetation productivity in these regions is ongoing. Here, we trace the most unsuitable areas for rainfed agriculture and greening in the two regions over the period 1998–2017 without specifying a crop/vegetation type. A method is devised based on combining June–October rainfall/potential evapotranspiration (aridity index) and integrated normalized difference vegetation index (productivity index). The feasibility of the currently planned GGW is placed in the context of naturally‐sound afforestation. The results show certain features of the suitable zone for planting. A seasonal aridity index of 0.1 is a minimum threshold for vegetation vigour to begin. Given the strong interannual north–south progression and retreat of this seasonal level, the northernmost aridity isoline that dictates feasibility of rainfed productivity is found to correspond to the borderline between the arid and semiarid zones. This borderline is delimited by an average aridity index of 0.2. Accordingly, 1,337,535 km2 (43.5%) and 729,576 km2 (25.6%) of the Sahel and the proposed GGW region, respectively, are not feasible for sustainable planting, that is, under rainfed and natural land fertility conditions. About 93.0% of the impractical GGW area lies east of longitude 10°E. Investing in a green belt east of this longitude is risky without supplementary irrigation. The contrasting productivity behavior across the GGW cautions the progression in this project without rigorous feasibility investigation. [ABSTRACT FROM AUTHOR]

In the Savannah region of Ghana, water scarcity appears to be a frequent occurrence, which is expected to worsen with the anticipated reductions in the quantity of rainfall received. A better estimation of future occurrences and the subsequent preparations are hinged on a solid understanding of past climatic patterns. Given that, trends in rainfall were analysed using the non-parametric Mann-Kendal test for nine (9) climate stations in as well as the entire Savannah zone of Ghana. from 1960 to 2015. No significant trends were observed in annual rainfall for the entire study area as well as individual climate stations except Wenchi, where a negative trend (Sen's slope = -3.30, p-value = 0.01) was recorded at a 0.05 level of significance The Standardised Precipitation Index (SPI) was used to study rainfall anomalies. Droughts were observed to be a regular feature of the climate, occurring at alternating intervals with wet periods. Recovery of the wet periods from the droughts was observed to be declining post the year 2000. For most locations, 1983 recorded the most intense drought while a few others like Navrongo and Wa also saw 2015 being hardly hit by another. Aridity in the study area was found to be intensifying, with aridity index values increasing at a rate of 0.2/decade, although this was not found to be significant (p-value = 0.06) at a 0.05 level of significance. Similar to rainfall, aridity for most of the stations appeared to be increasing although these changes were not statistically significant except for Wenchi, which again recorded a significant increase (p-value of 0.02).

In order to deeply understand the effect mechanism of rapid drought stress on the physiological and biochemical properties of crop leaves and determine drought thresholds, the potted spring wheat under two water treatments, adequate water supply and continuous drought stress, was researched. In the early stage of drought, the parameters of leaves decreased in the order of stomatal conductance (gs), intercellular CO2 concentration (Ci), maximum electron transfer rate (Jmax), mesophyll conductance (gm), photosynthetic rate (Pn,) leaf water content (LWC), triose phosphate utilization rate (TPU), transpiration rate (Tr), and maximum carboxylation rate (Vcmax). Photosynthesis was dominated by stomatal limitation and also limited by carboxylation and mesophyll limitation. The carboxylation limitation was mainly caused by the reduction of electron transport capacity. In the late stage of drought, stomatal limitation first decreased, and then mesophyll limitation decreased. During extreme drought, carboxylation limitation also decreased. With the decrease of relative soil moisture (RSM), except for Ci, which first decreased and then increased, other physicochemical parameters of leaves all showed an S-shaped, decreasing trend. Mild and severe drought thresholds were determined to be 56.6% and 43.6% of the RSM, respectively, according to the curve’s inflection point, corresponding to 16.6% and about 52.2% of the average initial decrease amplitude among all parameters. This will provide a reference for monitoring as well as an early warning of rapid drought in spring wheat.

The rangelands of Crete island (Greece) are typical Mediterranean habitats under high risk of degradation due to long-term grazing and harsh climatic conditions. We explored the effect of abiotic (climatic conditions, altitude) and biotic factors (long-term grazing by small ruminants) on the floristic composition and diversity of selected lowland (Pyrathi, Faistos) and highland (Vroulidia, Nida) rangelands. In each rangeland, the ground cover was measured, and the floristic composition was calculated in terms of five functional groups: grasses, legumes, forbs, phrygana, and shrubs. The aridity index, species turnover, species richness, Shannon entropy, and Gini–Simpson index (with the latter two converted to the effective number of species) were calculated. Our results reveal that highlands are characterized by the highest aridity index (wetter conditions). Lowland rangelands, compared to highland, exhibited a higher percentage contribution of grasses, legumes, and forbs, while species turnover decreased along the altitudinal gradient. The Shannon entropy index was correlated (a) positively with Gini–Simpson and mean annual temperature and (b) negatively with mean annual precipitation, aridity index, and altitude. Moreover, the Gini–Simpson index correlated positively with mean annual temperature and negatively with altitude. Our results could help to understand the effects of grazing on rangeland dynamics and sustainability in semi-arid regions in the context of climatic change.

Based on the homogenized daily data of 2255 meteorological stations during the past 60 years from 1961 to 2020, the potential evapotranspiration was calculated using the revised FAO56 Penman–Monteith model, and then the annual AI (aridity index, the ratio of annual potential evapotranspiration to annual precipitation) was employed to analyze the dry-wet climate change in China. The GCM models’ prediction data was used to analyze the possible trends of dry-wet climate in China by the end of this century. The results showed that in the past 60 years, the climate in China was getting wetter, especially in the western regions of China, including Xinjiang, western Qinghai, Gansu, western Inner Mongolia, and northwestern Tibet. In the last 10 years, China’s climate has become more humid. Compared with the 1960s, the total area of aridity has decreased by about 650,000 square kilometers. The changes of different climate zones have regional and periodical characteristics. There was a tendency to get wet periods in all four seasons, especially in summer. Analysis of GCM model projection data shows that by the end of this century, the climate in China would have a general trend of becoming drier. The drier regions are mainly located in the central and eastern parts of China, while the western regions of China continue to maintain the wetting trends. In the case of high emissions, the trends of drying in the central and eastern and wetting in the west are more significant than in the case of medium emission.

Desertification is a serious threat to human development and sustainability. This process is characterized by land degradation over areas with dry sub‐humid, semi‐arid and arid climate. In this work, climate susceptibility to desertification was identified for the state of Rio de Janeiro (SRJ), Brazil, the third most populated state in the country. The state is characterized by complex topography, and diverse climate and land uses. Two formulations for the aridity index were used: Ia, defined by Thornthwaite (1948, Geographical Review, 38(1), 55–94) and Penman (1953, Horticultural Congress, 2, 913–924), and D, a modification of Ia by Hare (1983, Climate and Desertification: A Revised Analysis, Geneva: World Meteorological Organization). Both estimates of the aridity require annual rainfall and potential evapotranspiration, which were calculated from the climatological water balance using times series of rainfall and air temperature (1961–2010) from 98 stations over the SRJ. Annual rainfall, evapotranspiration, water deficit and the aridity indices were then spatially interpolated over a 5 × 5‐km grid using a spline tension method. Both indices agree on the driest regions of the SRJ: Norte and Baixada Litorânea, near the northern coast, both under sub‐humid and semi‐arid climate. The index Ia indicated susceptibility to desertification over 2,305 km2 on the Norte and Baixada Litorânea regions, which correspond to 5% of SRJ area; similarly, the index D classified a smaller area over the Norte region under desertification (431 km2). These subregions, among the others also considered in this study, are of great importance for the agricultural, forestry and tourism industries and contribute immensely to the economic development of the state. Hence, the evaluation of susceptibility to desertification in those areas is essential to help prevent further land degradation and support policies formulation on long‐term sustainable management of land and water resources, especially under regional and global climate change scenarios. The methodology used in this work can be applied to studies of desertification in other regions of the world. [ABSTRACT FROM AUTHOR]

In this study, we project the global terrestrial changes in Aridity Index (AI), as defined by the ratio of annual precipitation to potential evapotranspiration (PET), at 2 and 4°C levels of global warming above the preindustrial conditions based on the outputs from 21 Coupled Model Intercomparison Project Phase 5 models under the Representative Concentration Pathways 8.5 (RCP8.5) scenario. Compared to the preindustrial period, the global terrestrial annual precipitation will increase by an average of 0.02% (3%), the annual PET will increase by 6% (15%) and AI will decrease by 0.1 (0.2) at the 2°C (4°C) warming level. More remarkable decreases in the annual AI are seen in the northern high latitudes, where will also experience greater increases in PET and precipitation. In general, the seasonal changes in AI display a similar spatial pattern to the annual changes and are characterized by the greatest decrease in December–January–February and the smallest in June–July–August. The largest expansion of drylands occurs in semi‐arid regions, followed by the expansion of arid regions, with area changes of 4% (7%) and 3% (4%) under the 2°C (4°C) scenario, respectively. Further analyses indicate that the AI changes are determined by PET in the northern high latitudes, and the contribution of PET to AI increases from the 2 to 4°C warming levels. Furthermore, changes in thermodynamic factors contribute most to the PET, and at a higher level of global warming, the contribution of thermodynamic factors increases and that of dynamic factors decreases. [ABSTRACT FROM AUTHOR]

Water flow in the Polish Carpathians was exemplified by long-term (1988-2017) analysis of two foothill catchments (of the Skawinka and Stobnica) and two catchments in the Beskidy Mountains (of the Soła and Osława). The work allowed for the determination of the duration of low flows and outflow deficits in relation to changes in thermal and precipitation conditions, as well as land use and land cover. In the selected catchments, the 30-year period brought a decrease in the area of arable land and an increase in the area of grassland and forest. In addition built-up areas increased by 495% between 1990 and 2018. A greater susceptibility to the occurrence of total drought was noted for the Beskidy Mountains catchments, in which the duration of low flows and outflow deficit was greater than in the foothill catchments. At the same time, the mountain catchments proved less susceptible to the emergence of deep drought, on account of their higher levels of forest cover and levels of soil permeability. In regional terms, the durations of low flows and outflow deficits were greater in the catchments located in the eastern part of the Carpathians (those of the Stobnica and Osława), in line with this area's intensified features of a continental climate. [ABSTRACT FROM AUTHOR]

Information about the past evolutionary changes in the soil cover is essential as a retrospective basis for long-term forecasts of soil development under the changing climatic conditions, and also for understanding the present-day problems of desertification and land degradation in the south of the East European Plain. The principal task of the present study was to estimate quantitatively the shift of the boundary between the steppe and desert-steppe zones in this region during the late Holocene under the impact of global climate variations. The properties of about 100 paleosols of archaeological sites widely represented in the region were used for quantitative reconstruction of paleoprecipitation, paleotemperature, and climate aridity. To obtain regional calibrations, the dependences of the magnetic properties of modern soils on climatic parameters in the south of the East European Plain were analyzed in detail. Samples of 35 soil profiles along the 1500-km-long Voronezh–Volgograd–Astrakhan–Elista–Voronezh transect were used. This transect crosses several natural climatic zones with gradients in the annual precipitation of about 500 mm/yr and in the annual temperatures of about 3°C, which allowed us to obtain reliable relationships between the climatic parameters and the properties of recent soils. Limitations for paleoclimate reconstructions based on the magnetic properties of soils in the range of mean annual precipitation <600 mm/year were identified. Cartographic reconstruction of changes in the De Martonne aridity index (IDM) using GIS modeling methods and paleopedological data indicates that the Volga–Don interfluve has undergone repeated changes in the climatic situation over the past 5000 years resulting in the shifts of the boundaries between soil-geographical zones to distances of up to 200–300 km. [ABSTRACT FROM AUTHOR]

Machine learning (ML) models have been applied to monthly streamflow forecasting in recent decades. In this study, forecasting skills of eight ML models are evaluated based on the Model Parameter Estimation Experiment (MOPEX) dataset. We consider two skill scores, i.e., the Nash–Sutcliffe efficiency (NSE) and the adjusted NSE (ANSE), and the latter is the skill score based on the interannual mean monthly value (MMV) as the reference (benchmark) model. Furthermore, NSE of the MMV model (NSEmmv) is used as a measure of the seasonality of monthly streamflow, as it is the ratio of variance explained by the MMV process. An important result is that forecasting skills of ML models for monthly streamflow are largely controlled by NSEmmv. Moreover, based on comparisons of different ML models, we have found that the selection of models is not a dominating factor impacting the final skill. Three key factors influencing NSE, i.e., NSEmmv, the base flow index (BFI) and the aridity index (AI), are explored in this paper. Specifically, NSEmmv impacts NSE directly and is the predominant factor; BFI influences the memory of the monthly streamflow and therefore influences NSE. The relationship between AI and NSE is much complex and indirect. Firstly, basins with higher AI tend to have lower NSEmmv, and this will lead to lower NSE; secondly, basins with higher AI tend to have lower BFI, which will also lead to lower NSE; thirdly, for a given BFI level, basins with higher AI tend to have higher memory and higher NSE. For ANSE, basins with AI between 1 and 2 show higher ANSE, which corresponds to higher autocorrelation coefficients. [ABSTRACT FROM AUTHOR]

Previous studies that observed the fact that Middle Palaeolithic sites mainly were concentrated in arid and semi-arid areas in Africa and Southwest Asia, concluded that climate factors determined the distribution patterns. We argue that biological factors could have been equally important. In present-day sub-Saharan Africa, mosquito-borne diseases and especially falciparum malaria have a serious impact on human populations. This study was aimed to investigate the possible former effect of falciparum malaria on Middle Palaeolithic site distribution patterns and explain why ancient humans avoided the humid areas in the tropical and subtropical regions. It was found that the early human settlements situated in those regions of Africa and Southwest Asia where the potential annual development period of falciparum parasites was short in the mosquitoes, the area was not too humid, and the potential falciparum malaria incidence values were low or moderate. In the Indian Peninsula, precipitation played a less significant role in determining human settlements. The number of the months when the extrinsic development of Plasmodium falciparum parasites was possible showed the strongest structural overlap with the modelled malaria incidences according to the spatial occurrence of the Middle Paleolithic archaeological sites in the case of Africa and in Southwest Asia. In the Indian Peninsula, climatic factors showed the strongest structural overlap with the modelled malaria incidences according to the occurrence patterns of the Middle Palaeolithic archaeological sites. Image 1 [ABSTRACT FROM AUTHOR]

The monthly precipitations obtained during 51 years of measurement in 24 stations of Soummam watershed in Algeria were analyzed to describe rainfall trends and aridity state of the area using statistical modeling. The choice of distribution laws was justified by comparing fitting results of different distributions laws used in literature reviews. Hence, the p values proved that Generalized Extreme Value, Weibull (3) and Logistic the distribution law are more adequate to analyze rainfall frequencies in different part of the watershed. The diagnostic given by Q‐Q plot, P‐P plot and survival regression curve showed the period of wetness and dryness in the northeastern and the southwestern part of the watershed, respectively. Moreover, the study given by the De Martonne index explains the consequences of climate change by a new form of aridity in the watershed between 1994 and 2018. Recommendations for Resource ManagersThe annual rainfall of Soummam watershed has a moderate and irregular rainfall distribution between 1967 and 2018.Using distribution function on monthly rainfall in each bioclimatic floor to analyze the trend of rainfall frequency gives a spatio‐temporal description of climate in the area.Fitting by Kolmogorov‐Smirnov test allows us to choose generalized extreme value, Weibull (3) and Logistic for modeling monthly rainfall variability in each part of the watershed.The diagnostic obtained by P‐P plot, Q‐Q plot and survival regression curve proved a change of aridity in the northeastern and southwestern part of the watershed between 1994 and 2018. [ABSTRACT FROM AUTHOR]

Droughts being a regional phenomenon has a vicious impact on agricultural production as well as on the socioeconomic status of an area. Meteorological drought is not only the result of rainfall deficit but also influenced by temperature in the form of evapotranspiration. There are several indices that could assess meteorological drought. Because of the complex phenomenon underling in the interaction between climatic, hydrological and ecological variables hampers to ascertain the suitability of a drought index to a particular region. The present work aims to compare different meteorological drought indices for a given climatic condition at the regional level. The Standardized Precipitation Index (SPI), Reconnaissance Drought Index (RDI) and Standardized Precipitation Evapotranspiration Index (SPEI) were employed to study the variation of drought characteristics calculated from these indices. The study was implemented in the Ghataprabha river basin, which is one of the potential lands for agriculture in the basin of river Krishna. The study area possesses negative trends in rainfall and significant increasing trends in the temperature when tested with the Mann-Kendell trend test. Several drought events were observed through SPI, RDI, and SPEI over the basin. SPEI identified the highest number of drought events with high duration and severe intensity as compared to SPI and RDI. The alike performance was noticed between RDI and SPI whereas SPEI does not harmonize with them at any timescale of the study period. The study recommends to consider RDI and SPI in the humid (subhumid) region and SPEI at the semiarid (arid) region to assess the impact of drought effectively. The study also suggests to use an appropriate drought index for analysis of drought, which could lead to an adequate preparedness for the future drought hazards. [ABSTRACT FROM AUTHOR]

Drought in the Mongolian Plateau (MP) has gradually intensified in recent decades. The energy and water cycles are key factors affecting drought. However, there are few quantitative studies on the mechanism of aridity change in this region. This study uses the ERA5, Moderate Resolution Imaging Spectroradiometer (MODIS) and Himawari 8 datasets and investigated the mechanism of drought change over the MP. The aridity index (the ratio of potential evaporation and total precipitation) is employed to detect drought changes. The results showed that the annual mean of aridity index increased by 0.73% per year (increased significantly since 1999) during the period 1979–2020. Moreover, the drought was most severe in the January to April of 2016–2020, mainly concentrated in the central and western parts of the MP. The potential evaporation increased (0.72% per year) and total precipitation decreased (0.16% per year) from 1979 to 2020. However, the surface temperature continued increasing from August to December in the period 2016–2020 (1.67% per year). This may result in an increase in potential evaporation and a decrease in volumetric soil water from August to December last year. The decrease of volumetric soil water resulted in the decrease of total cloud cover (0.25% per year) and total precipitation from January to April. The surface net radiation (increased by 0.42% per year) and the potential evaporation increased, which may aggravate the drought from January to April. The evaporation paradox is studied over the MP. The results show that the variation in evaporation is consistent with that of total precipitation, and the surface temperature will promote an increase in evaporation and potential evaporation. This study reveals that global warming, desertification and increased surface net radiation contribute to the increase in potential evaporation and reduced volumetric soil water, which together contribute to drought.

Drought (similarly as flooding) is considerably the gravest agrometeorological extreme connected with climate change and bringing the highest losses in an agricultural production. The objective of this paper is to study the spatial and temporal variability of the Aridity Index (AI) in the Czech Republic, per decade, during the 55‑year period (1961–2015). AI is a climatic index, which is important for recording of the drought phenomenon evolution. The climatic data used, include monthly precipitation totals and air temperature from 120 meteorological stations operated by the Czech Hydrometeorological Institute. The potential evapotranspiration was calculated based on the modified algorithm Penman‑Monteith. The data processing was done by the statistical tools of Microsoft Excel and the Geographical Information Systems (Clidata GIS, ArcGIS 10). The results of the analysis showed, that during the decade 1961–1970, almost the whole area of the Czech Republic is classified as “wet” with AI values ranging above 0.60, but over the next years (1971–2015), areas of the south Moravia (e.g. Dyjsko‑svratecký ravine, Valticko‑lednický area, surroundings of Brno city), and also Prague city and Poohří river basin shifted gradually to “sub‑humid” climate zone with AI < = 0.60. Especially, during the pre‑last decade of the study period 1991–2000.

The distribution pattern of the characteristics of spring–summer droughts during periods of increased and decreased annual wetting in 12 administrative entities of the south of European Russia in 1901–2018 are studied. During this time, four periods of different humidification conditions (alternating wetter, dry, wet and again dry periods) of different durations are well traced according to anomalies in the aridity index in seven regions: Kursk, Belgorod, Voronezh, Saratov, Volgograd, and Rostov oblasts and the Republic of Kalmykia. A desiccation period was noted in Samara and Astrakhan oblasts from the beginning to the middle of the 20th century. The desiccation period then gave way to a wetter one. The most frequent change of periods with different moisture conditions was observed in Stavropol krai, where five alternating periods were identified. It has been established that the frequency of spring–summer droughts is consistent with the long-term humidification conditions. According to the standardized precipitation index, it increases on average by 1.5 times in the dry period with a slight increase in drought intensity. The conditions of increased humidification observed in all of the examined administrative subjects in the second half of the 20th century were replaced by drier conditions at the beginning of the 21st century. The spread of more arid conditions began in the eastern oblasts. The development of the dry period in the 21st century is confirmed by the distribution of the NDVI vegetation index in the negative trend. In the absence of statistically significant aridization trends for more than a century, all of the considered oblasts of the south of European Russia undergo long, intracentury periods of aridization strengthening and weakening, which are characterized by significant differences in the frequency and intensity of spring–summer droughts. [ABSTRACT FROM AUTHOR]

Arid regions are highly vulnerable to climate change and human activity, and global warming in particular has the potential to increase the arid land area. One traditional way to evaluate the extent of climate change in dryland regions is to use the aridity index (AI), defined as the ratio of annual rainfall to annual potential evapotranspiration. However, the AI is a climatic index; it does not represent actual conditions of aridity in arid regions. In contrast, the satellite-based aridity index (SbAI), which is based on day/night land surface temperature changes, is considered to represent actual conditions of moisture availability. Arid regions during 2001–2013 were classified at global scale by comparing the SbAI with the AI, that is, within Turc space, which is based on the water balance concept. In addition, factors contributing to aridification or wetness changes detected in different global regions were examined by comparing the SbAI and AI result with the yearly maximum normalized difference vegetation index and past land use. As a result, dryland regions were newly classified into five zones. In the stable zone, land areas were classified into hyper-arid, arid, semi-arid, or dry sub-humid regions by both the SbAI and the AI. Areas in the transition zone toward dryness are moderately dry. Areas in the transition zone toward wetness include large river basins, oases, and wadis with little rainfall. In the moist zone, rainfed or irrigated farming is being successfully conducted. Many parts of the dry zone, however, are extremely dry. [ABSTRACT FROM AUTHOR]

The 100th meridian is a conceptual arid‐humid divide that effectively bisects the continent of the United States into the humid east and arid west. Here, we examine the historical and future shifts of the 100th meridian from atmospheric, hydrologic, and agroecological perspectives. We find that the effective arid‐humid divide regarding vegetation greenness and runoff has been moving toward west with a mean shift of 0.73° (1982–2015) and 2.08° (1961–2010), respectively, suggesting decreased agroecological and hydrologic aridity in the region. For future periods, the agroecological divide shows a persistent westward movement, whereas eastward shifts of the 100th meridian are detected from the atmospheric and hydrologic perspectives. Nevertheless, the eastward movements of the atmospheric and hydrologic divide substantially slow down when the vegetation response to elevated atmospheric CO2 is accounted for. This finding demonstrates that CO2 fertilization on vegetation could largely alleviate the warming‐induced drying tendency around the 100th meridian region. Plain Language Summary: The 100th meridian is a conceptual arid‐humid divide in the physical climate and landscape of the central United States continent and has exerted a profound influence on human settlement and agriculture developments. Using climate projections and aridity index, a previous study reported an eastward movement of the 100th meridian, indicating an overall drying trend in the region. Here, we reexamine the historical and future shifts of the 100th meridian from the atmospheric, hydrologic, and agroecological perspectives. We find that the movements of the 100th meridian are strongly modified by the vegetation response to elevated atmospheric CO2 concentration that CO2 fertilization on vegetation could largely alleviate the warming‐induced drying tendency and effectively slows down the eastward movement of the arid‐humid divide. Key Points: Historical and future shifts of the 100th meridian from atmospheric, hydrologic, and agroecological perspectives are assessedObserved hydrologic and agroecological 100th meridian have been moving toward west over the past few decadesProjected agroecological divide moves toward west whereas hydrologic and atmospheric divides move toward east in the coming century [ABSTRACT FROM AUTHOR]

Understanding the complex relationship between evapotranspiration and climate conditions and land surface characteristics is important within the context of global warming and increasing anthropogenic stressors. Based on the Budyko theory, we derived general frameworks for describing how the evapotranspiration ratio (actual evapotranspiration/precipitation, AET/P) responds to changes in the aridity index (potential evapotranspiration/precipitation, PET/P) and watershed characteristics (m). The frameworks show that the sensitivity of AET/P to PET/P decreases with increasing aridity but such decreasing pattern also depends on different watershed characteristics. The sensitivity coefficient tends to be greater in the energy‐limited regimes (above 0.3) than in the water‐limited regimes. The slope of the sensitivity curve becomes steeper for larger m values (e.g., m > 2). In addition, the sensitivity of the AET/P to m shows an asymmetrical unimodal curve, while the strongest sensitivity (inflection point) of evapotranspiration ratio to m occurs at PET/P > 1. We further examined spatial patterns of these sensitivities and the relative roles of PET/P (RCPET/P) and m (RCm) to AET/P over 91 hydrological basins worldwide. The tropical humid basins present the strongest sensitivity of AET/P to PET/P, while higher sensitivity coefficients of AET/P to m can be found in very cold basins. The changes in the sensitivity of evapotranspiration ratio to PET/P and m between 1930–1970 and 1971–2008 were assessed for these basins across broad climatic gradients. Most of these basins show a positive change in RCPET/P but a negative shift in RCm in the warming world. Key Points: General frameworks are derived to describe how the evapotranspiration ratio responds to the aridity index and watershed characteristicsSensitivity of the evapotranspiration ratio to watershed characteristics (m) shows an asymmetrical unimodal curveSpatial patterns of these sensitivity coefficients and the relative roles of PET/P and m to AET/P over global basins were identified [ABSTRACT FROM AUTHOR]

The evolution of regional arid/humid patterns caused by global climate change deserves attention. We investigated the changes in the area of arid/humid climate regions over Asia under the aegis of national-committed emission reductions to comply with the Paris Agreement using an ensemble of 17 global climate models (GCMs) from the Fifth Coupled Climate Model Intercomparison Project (CMIP5) archives. Our results indicated an overall trend towards aridity in a future warmer climate based on an aridity index (AI), defined as the ratio of precipitation to potential evapotranspiration (PET). In the future, the humid region will contract and the arid region and arid/humid transition zones will expand. Compared with the present period, arid/humid region switch is projected to occur in a land area of 2512.8 × 103 km2 over Asia under the Intended Nationally Determined Contributions (INDC)-pledge scenario. If global warming is controlled to the ambitious 2.0 °C and 1.5 °C scenarios instead of that of the INDC-pledge scenario, a decrease in the changes in the area of arid/humid regions by more than half would be expected. In addition, the arid/humid regions with continuous global warming are estimated to contract/expand greatly. Changes in the spatial pattern of the arid/humid zones over Asia show strong similarities between multi-model simulations, although there are some differences in detail. [ABSTRACT FROM AUTHOR]

Agriculture and associated sectors are one of the primary sources of living for the global population. Sustainability in agriculture will yield long-term benefits requisite to accomplish development and mitigation of resource scarcity. Hence, realistic assessment of water requirement for agricultural use or alternatively agricultural potential from available water resources is imperative to sustainable water management keeping in view of possible scarce situation in relation to freshwater availability across the Globe. The present study focuses on assessment of the water requirement for potential agricultural use for the command area of a Himalayan river project, namely Gandak river project in Northern India using extensive geo-spatial techniques. Detailed information of extensive canal network is derived from high-resolution satellite images using GIS tools, along with other spatially distributed information for relevant parameters such as rainfall, temperature, soil type, elevation, water-holding capacity and agricultural productivity. The study reasonably identifies the spatial variability in water requirement potential in the project command with rational indication of maximum water demand in north-central section of the study area where the lowest aridity index characterized by very low slope and deep sandy loam soil is recorded. Efficient usage with growing scarcity of this essential natural resource warrants efficiency optimization of water usage with realistic assessment. This approach unlike traditional method uses high-resolution satellite data that are more scientific and accurate and will undoubtedly facilitate development of rational decision support system for efficient management of available surface water use for different purposes in the region. [ABSTRACT FROM AUTHOR]

Aridity index reflects the exchanges of energy and water between the land surface and the atmosphere, and its variation can be used to forecast drought and flood patterns, which makes it of great significance for agricultural production. The ratio of potential evapotranspiration and precipitation is applied to analyse the spatial and temporal distributions of the aridity index in the Belt and Road region under the 1.5°C and 2.0°C global warming scenarios on the basis of outputs from four downscaled global climate models. The results show that: (1) Under the 1.5°C warming scenario, the area-averaged aridity index will be similar to that in 1986–2005 (around 1.58), but the changes vary spatially. The aridity index will increase by more than 5% in Central-Eastern Europe, north of West Asia, the monsoon region of East Asia and northwest of Southeast Asia, while it is projected to decrease obviously in the southeast of West Asia. Regarding the seasonal scale, spring and winter will be more arid in South Asia, and the monsoon region of East Asia will be slightly drier in summer compared with the reference period. While, West Asia will be wetter in all seasons, except winter. (2) Relative to 1986–2005, both areal averaged annual potential evapotranspiration and precipitation are projected to increase, and the spatial variation of aridity index will become more obvious as well at the 2.0°C warming level. Although the aridity index over the entire region will be maintained at approximately 1.57 as that in 1.5°C, the index in Central- Eastern Europe, north of West Asia and Central Asia will grow rapidly at a rate of more than 20%, while that in West Siberia, northwest of China, the southern part of South Asia and West Asia will show a declining trend. At the seasonal scale, the increase of the aridity index in Central-Eastern Europe, Central Asia, West Asia, South Asia and the northern part of Siberia in winter will be obvious, and the monsoon region in East Asia will be drier in both summer and autumn. (3) Under the scenario of an additional 0.5°C increase in global temperature from 1.5°C to 2.0°C, the aridity index will increase significantly in Central Asia and north of West Asia but decrease in Southeast Asia and Central Siberia. Seasonally, the aridity index in the Belt and Road region will slightly increase in all other seasons except spring. Central Asia will become drier annually at a rate of more than 20%. The aridity index in South Asia will increase in spring and winter, and that in East Asia will increase in autumn and winter. (4) To changes of the aridity index, the attribution of precipitation and potential evapotranspiration will vary regionally. Precipitation will be the major influencing factor over southern West Asia, southern South Asia, Central-Eastern Siberia, the non-monsoon region of East Asia and the border between West Asia and Central Asia, while potential evapotranspiration will exert greater effects over Central-Eastern Europe, West Siberia, Central Asia and the monsoon region of East Asia. [ABSTRACT FROM AUTHOR]

Investigating the spatiotemporal distribution of climate data and their impact on the allocation of the regional aridity and meteorological drought, particularly in semi-arid and arid climate, it is critical to evaluate the climate variability effect and propose sufficient adaptation strategies. The coefficient of variation, precipitation concentration index and anomaly index were used to evaluate the climate variability, while the Mann-Kendall and Sen's slope were applied for trend analysis, together with homogeneity tests. The aridity was evaluated using the alpha form of the reconnaissance drought index (Mohammed & Scholz, Water Resour Manag 31(1):531–538, 2017c), whereas drought episodes were predicted by applying three of the commonly used meteorological drought indices, which are the standardised reconnaissance drought index, standardized precipitation index and standardized precipitation evapotranspiration index. The Upper Zab River Basin (UZRB), which is located in the northern part of Iraq and covers a high range of climate variability, has been considered as an illustrative basin for arid and semi-arid climatic conditions. There were general increasing trends in average temperature and potential evapotranspiration and decreasing trends in precipitation from the upstream to the downstream of the UZRB. The long-term analysis of climate data indicates that the number of dry years has temporally risen and the basin has experienced succeeding years of drought, particularly after 1994/1995. There was a potential link between drought, aridity and climate variability. Pettitt's, SNHT, Buishand's and von Neumann's homogeneity test results demonstrated that there is an evident alteration in the mean of the drought and aridity between the pre- and post-alteration point (1994). [ABSTRACT FROM AUTHOR]