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Reliable knowledge of the near-future climate change signal of extremes is important for adaptation and mitigation strategies. Especially compound extremes, like heat and drought occurring simultaneously, may have a greater impact on society than their univariate counterparts and have recently become an active field of study. In this paper, we use a 12-member ensemble of high-resolution (7 km) regional climate simulations with the regional climate model COSMO-CLM over central Europe to analyze the climate change signal and its uncertainty for compound heat and drought extremes in summer by two different measures: one describing absolute (i.e., number of exceedances of absolute thresholds like hot days), the other relative (i.e., number of exceedances of time series intrinsic thresholds) compound extreme events. Changes are assessed between a reference period (1971–2000) and a projection period (2021–2050). Our findings show an increase in the number of absolute compound events for the whole investigation area. The change signal of relative extremes is more region-dependent, but there is a strong signal change in the southern and eastern parts of Germany and the neighboring countries. Especially the Czech Republic shows strong change in absolute and relative extreme events. [ABSTRACT FROM AUTHOR]

The second West African Monsoon Modeling and Evaluation Project Experiment (WAMME II) is designed to improve understanding of the possible roles and feedbacks of sea surface temperature (SST), land use land cover change (LULCC), and aerosols forcings in the Sahel climate system at seasonal to decadal scales. The project's strategy is to apply prescribed observationally based anomaly forcing, i.e., 'idealized but realistic' forcing, in simulations by climate models. The goal is to assess these forcings' effects in producing/amplifying seasonal and decadal climate variability in the Sahel between the 1950s and the 1980s, which is selected to characterize the great drought period of the last century. This is the first multi-model experiment specifically designed to simultaneously evaluate such relative contributions. The WAMME II models have consistently demonstrated that SST forcing is a major contributor to the twentieth century Sahel drought. Under the influence of the maximum possible SST forcing, the ensemble mean of WAMME II models can produce up to 60 % of the precipitation difference during the period. The present paper also addresses the role of SSTs in triggering and maintaining the Sahel drought. In this regard, the consensus of WAMME II models is that both Indian and Pacific Ocean SSTs greatly contributed to the drought, with the former producing an anomalous displacement of the Intertropical Convergence Zone before the WAM onset, and the latter mainly contributes to the summer WAM drought. The WAMME II models also show that the impact of LULCC forcing on the Sahel climate system is weaker than that of SST forcing, but still of first order magnitude. According to the results, under LULCC forcing the ensemble mean of WAMME II models can produces about 40 % of the precipitation difference between the 1980s and the 1950s. The role of land surface processes in responding to and amplifying the drought is also identified. The results suggest that catastrophic consequences are likely to occur in the regional Sahel climate when SST anomalies in individual ocean basins and in land conditions combine synergistically to favor drought. [ABSTRACT FROM AUTHOR]

This paper analyzed the drought situation in southwestern China with the standardized precipitation index (SPI) and the standardized precipitation–evapotranspiration index (SPEI) on multiple time scales. The spatial distribution, seasonal variation and features of drought in southwestern China were examined separately by drought frequency, probability of non-exceedance and runs theory. The results showed that the precipitation sequence will change suddenly near 2073 and an obvious, long-term drought will occur after 2073 due to the decline in precipitation. The spatial distribution of drought frequency indicated that the drought frequency will grow obviously in 2071–2100, and the growth rate will increase from the peripheral to the center of the region. The probability of non-exceedance for SPEI-1 less than − 1.0 will be 14.6% in the spring of 2011–2040, grow in 2041–2070 and reach 25.9% in 2071–2100, while that of SPEI in winter will gradually increase in all periods. When the SPEI-12 is smaller than − 1.0, the non-exceedance probability of the index in all seasons of 1981–2100 was and will be growing gradually, indicating that climate change has and will cause severe droughts in spring and winter from 1981 through 2100, especially the medium- and long-term drought. Through the analysis of the SPI and SPEI time sequences by runs theory, it is observed that the drought severity predicted by SPI-12 was and will be increasing over time, and the long-term drought will become more serious. On all time scales, if the SPEI is smaller than − 1.0, the drought duration will gradually increase from 1981–2010 to 2071–2100, indicating the drought in the study region will worsen due to climate change. [ABSTRACT FROM AUTHOR]

The North Atlantic Oscillation (NAO) is responsible for the climatic variability in the Northern Hemisphere, in particular, in Europe and is related to extreme events, such as droughts. The purpose of this paper is to study the correlation between precipitation and winter (December-January-February-March (DJFM)) NAO both for the historical period (1951-2000) and two future periods (2001-2050 and 2051-2100). NAO is calculated for these three periods by using sea level pressure, while precipitation data from seven climate models following the representative concentration pathway (RCP) 8.5 are also used in this study. An increasing trend in years with positive DJFM NAO values in the future is defined by this data, along with higher average DJFM NAO values. The correlation between precipitation and DJFM NAO is high, especially in the Northern (high positive) and Southern Europe (high negative). Therefore, higher precipitation in Northern Europe and lower precipitation in Southern Europe are expected in the future. Cross-spectral analysis between precipitation and DJFM NAO time series in three different locations in Europe revealed the best coherence in a dominant cycle between 3 and 4 years. Finally, the maximum drought period in terms of consecutive months with drought is examined in these three locations. The results can be used for strategic planning in a sustainable water resources management plan, since there is a link between drought events and NAO. [ABSTRACT FROM AUTHOR]

Nuclear energy is a very important component of overall power supply in France. If the effects of future extreme weather events or climate shifts are not addressed, energy systems will be highly vulnerable to extreme weather events or shifts in weather patterns, such as changes in precipitation. Because of the deep uncertainties involved in climate projections and response strategies, any strategy implementation should perform adequately regardless of which scenario actually materialises. In this paper, we analyse the effects of drought and heat wave in the French nuclear energy sector using the Strategy Robustness Visualisation Method. The key feature of the method is the modelling of uncertainty of the quantitative indicators by (min, max) values plotted on radar plots such that each strategy option’s performance can be visually inspected for robustness. The method can be utilised as a “module” of its own in different uncertainty management approaches. Based on the case study, the presented adaptation strategies “Maintaining industrial production and final demand” and “Smart grid infrastructure” were more robust than the “No planned or automatic adaptation”. [ABSTRACT FROM AUTHOR]

This paper is a response to a recent special issue of Regional Environmental Change, “Quantifying vulnerability to drought from different disciplinary perspectives” (vol. 8, number 4, 2008). In this paper, we examine some of the challenges facing efforts to understand vulnerability to drought through quantification as they are manifest in some of the articles in this special issue. [ABSTRACT FROM AUTHOR]

The objective of this paper is to analyse the impacts of climate change on a pine forest stand in Central Siberia (Zotino) to assess benefits and risks for such forests in the future. We use the regional statistical climate model STARS to develop a set of climate change scenarios assuming a temperature increase by mid-century of 1, 2, 3 and 4 K. The process-based forest growth model 4C is applied to a 200-year-old pine forest to analyse impacts on carbon and water balance as well as the risk of fire under these climate change scenarios. The climate scenarios indicate precipitation increases mainly during winter and decreases during summer with increasing temperature trend. They cause rising forest productivity up to about 20 % in spite of increasing respiration losses. At the same time, the water-use efficiency increases slightly from 2.0 g C l HO under current climate to 2.1 g C l HO under 4 K scenario indicating that higher water losses from increasing evapotranspiration do not appear to lead to water limitations for the productivity at this site. The simulated actual evaporation increases by up to 32 %, but the climatic water balance decreases by up to 20 % with increasing temperature trend. In contrast, the risk of fire indicated by the Nesterov index clearly increases. Our analysis confirms increasing productivity of the boreal pine stand but also highlights increasing drought stress and risks from abiotic disturbances which could cancel out productivity gains. [ABSTRACT FROM AUTHOR]

The Eastern Mediterranean region has been exposed to drought episodes, which have been occurring more frequently during the last decades. The objective of the present paper is to study the precipitation regime of the Damascus (Mazzeh) meteoric station by analysing drought characteristics using the Standardized Precipitation Index (SPI) and comparing this with the drought in Cyprus. The cumulative drought conceptis proposed to characterize long-term hydrologic drought, which affects the shallow groundwater productivity in terms of quantity and quality. Gamma probability distribution was fitted to the long-term annual precipitation in Damascus from 1918-1919 to 2007-2008 ( n = 90 years). Generally, a decreasing trend of 17% to the mean annual rainfall of Damascus and 13% to the mean annual rainfall of Cyprus was estimated between 1970 and 2000. The SPI identifies three major extended drought periods: (1) 9 years of severe drought (1954-1963) with an average 20% precipitation deficit per year compared to the mean. (2) 8 years of severe drought (1983-1991) with a 27% deficit per year on average. (3) 9 years of extreme drought (1993-2002) with a 31% deficit per year on average. The cumulative standardized precipitation index (SPI 30) demonstrates positive values for the first period and is indicative of having no effect on the global water balance. SPI 30 exhibits sensitive equilibrium with near zero values / a near zero value (±1.5) for the second period. For the third period, however, the SPI 30 decreases below −10 indicating an extreme hydrological drought that has negative consequences on the recent groundwater recharge. It is required to develop and implement a sustainable groundwater management strategy to reduce long-terms drought risks. Generally, the SPI 30 in Cyprus is parallel to that in Damascus with a 3-5 year delay. Thus, the central zone of the Eastern Mediterranean region is facing big challenges and has been suffering from three decades of moderate to severe hydrological drought (SPI 30=−5 to −10) causing a severe decrease in springs discharges of the region. Therefore, in order to reduce the climate change effects on water resources, it is necessary to adopt a sustainable proactive management plan during the frequent severe droughts. [ABSTRACT FROM AUTHOR]

Worldwide climate is likely to become more variable or extreme with increases in intense precipitation. In Mediterranean areas, climate change will increase the risks of droughts, flash floods and soil erosion. Despite rainfall intensity being a key factor in erosive processes, in these areas information on extreme rainfall intensity and the associated erosivity, based on high-temporal resolution data, is either non homogeneous or scarce. These parameters thus need to be assessed in order to highlight suitable adaptation strategies. In this paper, an hourly rainfall intensity (RI) data series is analyzed together with the corresponding 1-min rainfall intensity maximum (RIm) of 23 rainfall gauges located in Tuscany, Italy, in an area highly vulnerable to erosion. The aim is to look for temporal trends (1989-2010) in extreme rainfall intensity and erosivity. Fixed effect logistic regression shows statistically significant temporal increases in the number of RI and RIm exceedances over the 95th percentile threshold. Winter is shown to be the season with the strongest increasing trend in coastal and inland rainfall gauge groups, followed by spring for the coastal group and autumn for the inland group. Linear regressions show that in the inland group there is a temporal increase in rainfall erosivity and on a seasonal basis, the highest increase is observed in autumn. By contrast, for the coastal group this increasing trend is only detectable for spring and winter. Such an increase in rainfall erosivity and its potential continuation could have a strong adverse effect on Mediterranean land conservation. [ABSTRACT FROM AUTHOR]

This paper analyzes the meteorological drought events in Paraguay in the period of 1964 to 2011, using the Standardized Precipitation Index (SPI). The objective is to determine if the frequency and/or severity of droughts has increased or decreased in the last years, in response of climate change. They The southernmost parts of the country are affected by severe droughts producing damage to soybean and corn crop during the rainy season (October-March) especially during the summer of 2008-2009. The years of 1967, 1968, 1978, 1979, 2000 and 2008 was identified as severe to extreme drought events and coincides with La Niña event. However, the relationship between all drought events, especially those agricultural droughts and La Niña is not clear, suggesting the necessity of new research, focusing on new drivers to explain the cause of the droughts. The economy of Paraguay, based for good part on agriculture, is clearly vulnerable to droughts. Even though no undeniable increasing trend in drought frequency/severity was detected, contingency plans to diminish drought impacts ought to be elaborated. [ABSTRACT FROM AUTHOR]

An Inconvenient Truth (AIT) has earned Al Gore an Oscar and a share of the 2007 Nobel Peace Prize and has been widely acclaimed by the mass media. However, significant errors exist in the film, owing to alarmism and exaggeration. As this forum does not provide for a detailed examination of these errors, this paper will focus only on the portrayal of the hydrologic cycle by AIT--precipitation and floods, soil moisture and droughts, and storminess. AIT argues that precipitation and intense rainfalls, floods, droughts, and the total number, intensity, and duration of tropical cyclones have all increased due exclusively to anthropogenically-driven climate change; indeed, AIT paints a picture of near scientific certainty with an overwhelming bias toward catastrophe scenarios. A closer look at the science, however, reveals that the data do not support these claims and that the scientific community is divided as to what the impact of anthropogenic climate change on the hydrologic cycle will be. Thus, the film gives a false impression of both the current state of climate change and that 'the science is settled'. [ABSTRACT FROM AUTHOR]

Three consecutive dry summers in western Europe (2018–2019–2020) had widespread negative impacts on society and ecosystems, and started societal debate on (changing) drought vulnerability and adaptation measures. We investigate the occurrence of multi-year droughts in the Rhine basin, with a focus on event probability in the present and in future warmer climates. Additionally, we investigate the temporally compounding physical drivers of multi-year drought events. A combination of multiple reanalysis datasets and multi-model large ensemble climate model simulations was used to provide a robust analysis of the statistics and physical processes of these rare events. We identify two types of multi-year drought events (consecutive meteorological summer droughts and long-duration hydrological droughts), and show that these occur on average about twice in a 30 year period in the present climate, though natural variability is large (zero to five events can occur in a single 30 year period). Projected decreases in summer precipitation and increases in atmospheric evaporative demand, lead to a doubling of event probability at 1 ∘ C additional global warming relative to present-day and an increase in the average length of events. Consecutive meteorological summer droughts are forced by two, seemingly independent, summers of lower than normal precipitation and higher than normal evaporative demand. The soil moisture response to this temporally compound meteorological forcing has a clear multi-year imprint, resulting in a relatively larger reduction of soil moisture content in the second year of drought, and potentially more severe drought impacts. Long-duration hydrological droughts start with a severe summer drought followed by lingering meteorologically dry conditions. This limits and slows down the hydrological recovery of soil moisture content, leading to long-lasting drought conditions. This initial exploration provides avenues for further investigation of multi-year drought hazard and vulnerability in the region, which is advised given the projected trends and vulnerability of society and ecosystems. [ABSTRACT FROM AUTHOR]

This study aims to evaluate the performance of six models from the Coupled Model Intercomparison Project Phase 6 (CMIP6) models in reproducing the monthly cycle of precipitation and maximum surface air temperature of the Hodna region in central Algeria during the baseline period 1901–2014. The six climate models selected are as follows: ACCESS-ESM4, BCC-CSM2-MR, CanESM5, GFDL-ESM1-5, IPSL-EM6A-LR, and MIROC6. The best-performing models are determined by comparing observation (CRU-TS) and historical data. The evaluation procedure is performed using the compromise programming method and multiple statistical metrics including mean bias error (MB), root mean square error (RMSE), and pattern determination coefficient (R2). The first two best-performing models are used for precipitation (IPSL-EM6A-LR) and maximum surface air temperature (GFDL-ESM4). Four future periods are considered: 2021–2040, 2041–2060, 2061–2080, and 2081–2100 for SSP1-2.6 and SSP3-7.0. For the most optimist scenario, the maximum surface air temperature may increase in the next decades in comparison with observed and simulated values by 2 °C, but then almost stabilizes and reaches an average monthly increase of 28.53 °C. The same is shown in the precipitation projection of 48.75 mm/month by 2100. Eventually, the SSP1-2.6 scenario does not show any current signs in the current Hodna basin climate on a global scale. Future precipitation projections under Hodna's SSP3-7.0 may decrease with an average value of 10 mm in a monthly scale. This decrease becomes mostly in the center and southeastern parts. Maximum surface air temperature can rise steadily from 28 to 31 °C and reach its maximum of 4.5 °C by 2100. The outcomes of this study will evaluate how projected changes will affect droughts and floods. [ABSTRACT FROM AUTHOR]

The influence of increased horizontal resolution on regional climate models simulations of 1961-1990 period was investigated with a focus on precipitation. The main attention was paid to the annual cycle of precipitation described by a special characteristic, precipitation half-time. Two models (RegCM3 and ALADIN-CLIMATE/CZ), both of them in two horizontal resolutions (25 and 10 km), were used. An evaluation of model simulations with 25 km resolution on the European domain is presented as well as a more detailed evaluation of both 25 and 10 km versions on the area of the Czech Republic. Generally, the effects of increased horizontal resolution vary with climate model and evaluated characteristic. For the precipitation amount and the dependence of precipitation amount on altitude, the increase in horizontal resolution decreases the accuracy of results in both models. For the simulation of annual precipitation cycle and the precipitation half-time, RegCM3 results improved with the increased horizontal resolution, whereas ALADIN-CLIMATE/CZ results worsened. [ABSTRACT FROM AUTHOR]

Climate change is a main driving force that affects the hydrological cycle, leading to an increase in natural hazards. Among these natural hazards, drought is one of the most destructive and becomes more complex considering climate change. Therefore, it is necessary to investigate the effect of climate change on different types of drought. In this study, we examined the propagation probability of meteorological drought into hydrological drought using a probabilistic graphical model across South Korea. We performed correlation analyses among meteorological drought represented by Standardized Precipitation Index (SPI) and Standardized Precipitation Evapotranspiration Index (SPEI) and hydrological drought by Standardized Runoff Index (SRI) on different time scales. Drought characteristics were examined under a baseline period, RCP 4.5, and 8.5 climate change scenarios, and the results illustrated that drought characteristics varied spatially. On average, drought severity of SPI increased in P1 (2011–2040) and then deceased in P2 (2041–2070) and P3 (2071–2099) under RCP 4.5, whereas drought severity also increased in P1 under RCP 8.5. However, average drought severity of SPEI increased in P3, whereas that of SRI showed a decreasing trend for all the periods. Finally, propagation occurrence probabilities of different states of meteorological drought resulting in different states of hydrological drought were examined under climate change scenarios. The average propagation probability of extreme state of meteorological drought resulting in moderate and severe condition of hydrological drought increased by 13% and 2%, respectively, under RCP 4.5; while average propagation probability of extreme state of meteorological drought resulting in severe and extreme conditions of hydrological drought increased by 1.5% and 84%, respectively, under RCP 8.5. We concluded that propagation probability of meteorological drought into hydrological drought increased significantly under climate change. These findings will be helpful for early mitigation of hydrological drought. [ABSTRACT FROM AUTHOR]

The sensitivity of plant production to precipitation underlies the functioning of ecosystems. Studies that relate long-term mean annual precipitation and production across multiple sites (spatial relationship) or examine interannual linkages within a site (temporal relationship) can reveal biophysical controls over ecosystem function but have limited ability to infer responses to extreme changes in precipitation that may become more common under climate change. To overcome limitations of using a single approach, we integrated satellite- and ground-based estimates of production with a standardized, multi-site precipitation manipulation experiment across a grassland elevation gradient in the southwestern USA. The responsiveness of production to changes in precipitation followed the order: temporal (0.06–0.13 g m−2 mm−1) < spatial (0.21 g m−2 mm−1) < experimental relationship (0.25–0.42 g m−2 mm−1), suggesting that spatial and temporal relationships determined with satellite- and ground-based estimates cannot be extrapolated to determine the effect of extreme events. A strong production response to differences in mean annual precipitation across sites reinforces a regional control of water availability. Interannual sensitivity to precipitation was strongest at the low elevation grasslands, and the high elevation mixed conifer meadow had a large reduction in production in a drought year. Extreme experimental drought strongly reduced production in low elevation grasslands, but water addition had mixed effects. High elevation meadows were insensitive to both extreme drought and water addition. Our results highlight the importance of accounting for extreme climate regimes and site-level factors when scaling climate change effects up to regional and global scales. [ABSTRACT FROM AUTHOR]

Drought is the most complex climate-related disaster issue in South Asia, because of the various land-cover changes, vegetation dynamics, and climates. The aims of the current research work were to analyze the performance of AVHRR Normalized Difference Vegetation Index (NDVI) and spatiotemporal differences in vegetation dynamics on a seasonal basis by correlating the results with NASA's MERRA precipitation and air temperature for monitoring vegetation dynamics and drought over South Asia. Our approach is based on the use of AVHRR NDVI data and NASA's MERRA rainfall and air temperature data (1990–2011). Due to the low vegetation and dryness, the NDVI is more helpful in describing the drought condition in South Asia. There were rapid increases in NDVI, VHI, and VCI from April to October. Monthly NDVI, VHI, and VCI stabilize in September and improved once more in October and then show a declining trend in December. The monthly PCI, TCI, VHI, and VCI values showed that the South Asia goes through an extreme drought in 2000, which continues up to 2002, which lead the highest water stress. Spatial correlation maps among NDVI, precipitation, air temperature, VHI, and VCI on a seasonal basis. The correlation between NDVI and precipitation showed a significantly higher correlation value in JJA and SON seasons; the spatial correlation between NDVI and air temperature showed significant high values in DJF, JJA, and SON periods, while the correlation between VHI and TCI showed a significantly higher values in MAM and SON seasons, which indicated a good sign for dryness monitoring, mainly for farming regions during these seasons in South Asia. It was confirmed that these indexes are a comprehensive drought monitoring indicator and a step to monitoring the climate change in South Asia, which will play a relevant role ongoing studies on vegetation types, monitoring climate change, and drought over South Asia. [ABSTRACT FROM AUTHOR]

Single- to multiple-year drought episodes posed significant challenges for agrarian communities across southern Africa during the nineteenth century and hence are widely recorded in a variety of historical documents. However, the ways in which droughts are articulated, and the focus of individual accounts, vary considerably between different authors and historical source types. This study draws on a range of documentary source types—specifically newspapers, letters, reports and diaries—to explore the varied narratives associated with three protracted droughts (those of 1861–1863, 1876–1879 and 1895–1897) that affected large areas of the subcontinent. The analysis spans four case study areas—present day KwaZulu-Natal (South Africa), Lesotho, Malawi and the southern Kalahari (Botswana and South Africa)—which were investigated as part of different interdisciplinary projects. We explore issues common to all case study areas, including (i) how specific drought events are framed and (ii) what is and is not reported about individual droughts across different source types. We conclude that different source types in the subcontinent may be more or less appropriate for addressing the specific objectives of historical climatology, particularly in relation to historical drought. Sources such as newspapers and weather diaries are rich in qualitative and quantitative observations suitable for the reconstruction of temporal and spatial patterns of weather and climate, as well as climate-related natural disasters. In contrast, letters, reports and personal journals, especially those written by missionaries, provide additional qualitative narratives through which to investigate the vulnerability of past societies and economies to climate variations, and to explore past discourses and social representations of climate. While studies of this kind have been published for European and American source types, this is the first systematic exploration of documentary sources for the historical climatology of Africa. It should therefore provide a guide for climate history studies elsewhere in the continent, or other regions where written records are absent prior to the arrival of European colonists. [ABSTRACT FROM AUTHOR]

The study aims at regional and probabilistic evaluation of bivariate drought characteristics to assess both the past and future drought duration and severity in Bangladesh. The procedures involve applying (1) standardized precipitation index to identify drought duration and severity, (2) regional frequency analysis to determine the appropriate marginal distributions for both duration and severity, (3) copula model to estimate the joint probability distribution of drought duration and severity, and (4) precipitation projections from multiple climate models to assess future drought trends. Since drought duration and severity in Bangladesh are often strongly correlated and do not follow same marginal distributions, the joint and conditional return periods of droughts are characterized using the copula-based joint distribution. The country is divided into three homogeneous regions using Fuzzy clustering and multivariate discordancy and homogeneity measures. For given severity and duration values, the joint return periods for a drought to exceed both values are on average 45% larger, while to exceed either value are 40% less than the return periods from the univariate frequency analysis, which treats drought duration and severity independently. These suggest that compared to the bivariate drought frequency analysis, the standard univariate frequency analysis under/overestimate the frequency and severity of droughts depending on how their duration and severity are related. Overall, more frequent and severe droughts are observed in the west side of the country. Future drought trend based on four climate models and two scenarios showed the possibility of less frequent drought in the future (2020–2100) than in the past (1961–2010). [ABSTRACT FROM AUTHOR]

Understanding the effects of climate change, in particular, climate extremes on plant functional traits can provide a mechanistic basis for predicting how plant communities may be altered in the future. Here, we focused on a dominant species in Inner-Mongolia typical temperate steppe, Leymus chinensis (Trin.) Tzvei, to examine the responses of plant functional traits to experimentally imposed extreme drought at three sites along an aridity gradient. When comparing the driest (high aridity) to the wettest sites (low aridity), plant height, leaf dry matter content and δ13C (water use efficiency) were increased at the intermediate and low aridity sites, whereas specific leaf area and leaf nitrogen content were reduced at the high-aridity site. When extreme drought (~ 66% reduction in the growing season precipitation) was experimentally imposed at all sites, plant height decreased and δ13C of L. chinensis increased at the intermediate and low aridity sites. The extreme drought of 66% precipitation reduction also increased leaf dry matter content in high- and low-aridity sites. Compared to the control (ambient precipitation), extreme drought increased the strength of the positive association between plant height and δ13C, as well as the negative associations of specific leaf area with plant height and leaf dry matter content. Thus, extreme drought altered key functional traits of the dominant grass of Inner Mongolia steppe, particularly at the low-aridity site where the drought decreased plant size and increased water use efficiency and affected relationships between these traits. [ABSTRACT FROM AUTHOR]

The Wetness Index was calculated using gridded monthly precipitation and potential evapotranspiration in China during 1924-2013. Variations of dry and wet periods in different areas and the impact of meteorological factors were analyzed. The results show the following: (1) Drought areas (W ≤ 0.5) and wet areas (W > 0.65) in China constituted 33-56% and 35-55%, respectively, of the total land area and there were no secular trends during 1924-2013. During this period, the areas of drought and wet were inversely proportional, but had different changes among seven regions. (2) Since 1954, the overall trend in China has changed from wet to dry. Drought areas increased significantly (p < 0.05) during 1954-1983. Drought areas increased (not significantly) during 1984-2013, but the rate of drought/wetness clearly decreased (tendency rates were between − 0.05 and 0.05/30 year, and accounted for 54.79% of China). (3) Dry/wet variation in North, Northeast, Central, and Southwest China played major roles. (4) Except in the North region, drought/wet conditions were affected by surface warming. [ABSTRACT FROM AUTHOR]

Over the past decades, drought has become a major concern in Morocco due to the importance of agriculture in the economy of the country. In the present work, the standardized precipitation index (SPI) is used to monitor the evolution, frequency, and severity of droughts in the High Atlas basins (N'Fis, Ourika, Rhéraya, Zat, and R'dat), located south of Marrakech city. The spatiotemporal characterization of drought in these basins is performed by computing the SPI with precipitation spatially interpolated over the catchments. The Haouz plain, located downstream of these basins, is strongly dependent on water provided by the mountain ranges, as shown by the positive correlations between the normalized difference vegetation index (NDVI) in the plain and the 3, 6, and 12-month SPI in the High Atlas catchments. On the opposite, no significant correlations are found with piezometric levels of the Haouz groundwater due to intensified pumping for irrigation in the recent decades. A relative SPI index was computed to evaluate the climate change impacts on drought occurrence, based on the projected precipitation (2006-2100) from five high-resolution CORDEX regional climate simulations, under two emission scenarios (RCP 4.5 and RCP 8.5). These models show a decrease in precipitation towards the future up to − 65% compared to the historical period. In terms of drought events, the future projections indicate a strong increase in the frequency of SPI events below − 2, considered as severe drought condition. [ABSTRACT FROM AUTHOR]

Climate change projections were evaluated over both the whole Iran and six zones having different precipitation regimes considering the CORDEX South Asia dataset, for assessing space-time distribution of drought occurrences in the future period 2070-2099 under RCP4.5 scenario. Initially, the performances of eight available CORDEX South Asia Regional Climate Models (RCMs) were assessed for the baseline period 1970-2005 through the GPCC v.7 precipitation dataset and the CFSR temperature dataset, which were previously selected as the most reliable within a set of five global datasets compared to 41 available synoptic stations. Though the CCLM RCM driven by the MPI-ESM-LR General Circulation Model is in general the most suitable for temperature and, together with the REMO 2009 RCM also driven by MPI-ESM-LR, for precipitation, their performances do not overwhelm other models for every season and zone in which Iranian territory was divided according to a principal component analysis approach. Hence, a weighting approach was tested and adopted to take into account useful information from every RCM in each of the six zones. The models resulting more reliable compared to current climate show a strong precipitation decrease. Weighted average predicts an overall yearly precipitation decrease of about 20%. Temperature projections provide a mean annual increase of 2.4 °C. Future drought scenarios were depicted by means of the self-calibrating version of the Palmer drought severity index (SC-PDSI) model. Weighted average predicts a sharp drying that can be configured as a real shift in mean climate conditions, drastically affecting water resources of the country. [ABSTRACT FROM AUTHOR]

Flash drought is a rapidly intensifying drought with abnormally high temperature, which has greatly threatened crop yields and water supply, and aroused wide public concern in a warming climate. However, the preferable hydrometeorological conditions for flash drought and its association with conventional drought at longer time scales remain unclear. Here, we investigate two types of flash drought over China: one is high-temperature driven (Type I), while the other is water-deficit driven (Type II). Results show that the frequencies of the two types of flash drought averaged over China during the growing season are comparable. Type I flash drought tends to occur over southern China, where moisture supply is sufficient, while Type II is more likely to occur over semi-arid regions such as northern China. Both types of flash drought increase significantly (p < 0.01) during 1979-2010, with a doubled rise in Type I as compared with Type II. Composite analysis shows that high temperature quickly increases evapotranspiration (ET) and reduces soil moisture from two pentads before the onset of Type I flash drought. In contrast, there are larger soil moisture deficits two pentads before the onset of Type II flash drought, leading to a decrease in ET and increase in temperature. For flash drought associated with seasonal drought, there is a greater likelihood of occurrence during the onset and recovery phases of seasonal drought, suggesting perfect conditions for flash drought during transition periods. This study provides a basis for the early warning of flash drought by connecting multiscale drought phenomena. [ABSTRACT FROM AUTHOR]

Heilongjiang Province is a major grain production base in China, and its agricultural development plays an important role in China’s social economy. Drought and flood events are the primary disasters in Heilongjiang Province and have considerable impacts on agriculture. In this study, relatively complete monthly precipitation data from 26 meteorological stations in Heilongjiang Province during the period of 1958-2013 were analyzed using the standardized precipitation index (SPI) combined with principal component analysis, Mann-Kendall trend analysis and Morlet wavelet analysis to determine the spatial and temporal distributions of drought and flood events in this province. The results were as follows: (1) the whole of Heilongjiang exhibited an aridity trend. In northern Heilongjiang, spring and summer experienced a wetting trend, and autumn and winter experienced an aridity trend. (2) The SPI3 exhibited 8- and 16-year periodic variation characteristics in spring, 10- and 22-year periodic variation characteristics in summer, and 10- and 32-year periodic variation characteristics in autumn. In addition to the 10-year periodic variation characteristics in winter, other periodic variation characteristics were observed. (3) The increasing trend in the percentage of stations affected by flood was more obvious than that affected by drought. Therefore, Heilongjiang Province is more vulnerable to flooding. (4) The influence of drought and flood disasters in Heilongjiang Province showed a growth trend, but the flood effect was more remarkable. (5) The agricultural area affected by drought and flood disasters in Heilongjiang Province showed an increasing trend. Although there was a greater increase in flood disaster area, the main types of disasters were drought-dominated. [ABSTRACT FROM AUTHOR]

Summer 2012 was very wet in northern Europe, and unusually dry and hot in southern Europe. We use multiple approaches to determine whether anthropogenic forcing made the extreme European summer of 2012 more likely. Using a number of observation- and model-based methods, we find that there was an anthropogenic contribution to the extremes in southern Europe, with a qualitative consensus across all methodologies. There was a consensus across the methodologies that there has been a significant increase in the risk of hot summers in southern Europe with climate change. Most approaches also suggested a slight drying, but none of the results were statistically significant. The unusually wet summer in northern Europe was made more likely by the observed atmospheric circulation pattern in 2012, but no evidence was found for a long-term trend in circulation. [ABSTRACT FROM AUTHOR]

Projections for near-surface soil moisture content in Europe for the 21st century were derived from simulations performed with 26 CMIP5 global climate models (GCMs). Two Representative Concentration Pathways, RCP4.5 and RCP8.5, were considered. Unlike in previous research in general, projections were calculated separately for all four calendar seasons. To make the moisture contents simulated by the various GCMs commensurate, the moisture data were normalized by the corresponding local maxima found in the output of each individual GCM. A majority of the GCMs proved to perform satisfactorily in simulating the geographical distribution of recent soil moisture in the warm season, the spatial correlation with an satellite-derived estimate varying between 0.4 and 0.8. In southern Europe, long-term mean soil moisture is projected to decline substantially in all seasons. In summer and autumn, pronounced soil drying also afflicts western and central Europe. In northern Europe, drying mainly occurs in spring, in correspondence with an earlier melt of snow and soil frost. The spatial pattern of drying is qualitatively similar for both RCP scenarios, but weaker in magnitude under RCP4.5. In general, those GCMs that simulate the largest decreases in precipitation and increases in temperature and solar radiation tend to produce the most severe soil drying. Concurrently with the reduction of time-mean soil moisture, episodes with an anomalously low soil moisture, occurring once in 10 years in the recent past simulations, become far more common. In southern Europe by the late 21st century under RCP8.5, such events would be experienced about every second year. [ABSTRACT FROM AUTHOR]

Evapotranspiration ( ET) plays an important role in exchange of water budget and carbon cycles over the Inner Mongolia autonomous region of China (IMARC). However, the spatial and decadal variations in terrestrial ET and drought over the IMARC in the past was calculated by only using sparse meteorological point-based data which remain quite uncertain. In this study, by combining satellite and meteorology datasets, a satellite-based semi-empirical Penman ET (SEMI-PM) algorithm is used to estimate regional ET and evaporative wet index (EWI) calculated by the ratio of ET and potential ET ( PET) over the IMARC. Validation result shows that the square of the correlation coefficients $$(R^{2})$$ for the four sites varies from 0.45 to 0.84 and the root-mean-square error (RMSE) is $$0.78$$ mm. We found that the ET has decreased on an average of 4.8 mm per decade ( $$p=0.10$$ ) over the entire IMARC during 1982-2009 and the EWI has decreased on an average of 1.1% per decade ( $$p=0.08$$ ) during the study period. Importantly, the patterns of monthly EWI anomalies have a good spatial and temporal correlation with the Palmer Drought Severity Index (PDSI) anomalies from 1982 to 2009, indicating EWI can be used to monitor regional surface drought with high spatial resolution. In high-latitude ecosystems of northeast region of the IMARC, both air temperature $$(T_{a})$$ and incident solar radiation $$(R_{s})$$ are the most important parameters in determining ET. However, in semiarid and arid areas of the central and southwest regions of the IMARC, both relative humidity (RH) and normalized difference vegetation index (NDVI) are the most important factors controlling annual variation of ET. [ABSTRACT FROM AUTHOR]

Estimation of drought in a certain temporal and spatial scale is crucial in climate change studies. The current study targets on three agricultural areas widespread in Greece, Ardas River Basin in Northeastern Greece, Sperchios River Basin in Central Greece, and Geropotamos River Basin in Crete Island in South Greece that are characterized by diverse climates as they are located in various regions. The objective is to assess the spatiotemporal variation of drought conditions prevailing in these areas. The Standardized Precipitation Index (SPI) was used to identify and assess the present and future drought conditions. Future simulated data were derived from a number of Regional Climatic Models (RCMs) from the ENSEMBLES European Project. The analysis was performed for the future periods of 2021-2050 and 2071-2100, implementing A1B and B1 scenarios. The spatial analysis of the drought conditions was performed using a combined downscaling technique and the Ordinary Kriging. The Mann-Kendall test was implemented for trend investigation. During both periods and scenarios, drought conditions will tend to be more severe in the upcoming years. The decrease of the SPI values in the Sperchios River Basin is expected to be the strongest, as it is the only study area that will show a negative balance (in SPI values), regarding the drought conditions. For the Ardas and the Geropotamos River Basins, a great increase of the drought conditions will occur during the 2021-2050 period, while for 2071-2100 period, the decrease will continue but it will be tempered. Nevertheless, the situation in all study areas according to the SPI classification is characterized as 'Near-normal', in terms of drought conditions. [ABSTRACT FROM AUTHOR]

Drought variability and change was assessed across the Iberian Peninsula over more than 100 years expanding through the twentieth century and the first decade of the twenty-first century. Daily temperature and precipitation data from 24 Iberian time series were quality controlled and homogenized to create the Monthly Iberian Temperature and Precipitation Series (MITPS) for the period 1906-2010. The Standardized Precipitation Index (SPI), driven only by precipitation, and the Standardized Precipitation Evapotranspiration Index (SPEI), based on the difference between the precipitation and the reference evapotranspiration (ET), were computed at annual and seasonal scale to describe the evolution of droughts across time. The results confirmed that a clear temperature increase has occurred over the entire Iberian Peninsula at the annual and seasonal scale, but no significant changes in precipitation accumulated amounts were found. Similar drought variability was provided by the SPI and SPEI, although the SPEI showed greater drought severity and larger surface area affected by drought than SPI from 1980s to 2010 due to the increase in atmospheric evaporative demand caused by increased temperatures. Moreover, a clear drying trend was found by the SPEI for most of the Iberian Peninsula at annual scale and also for spring and summer, although the SPI did not experience significant changes in drought conditions. From the drying trend identified for most of the Iberian Peninsula along the twentieth century, an increase in drought conditions can also be expected for this region in the twenty-first century according to future climate change projections and scenarios. [ABSTRACT FROM AUTHOR]

Drought is a critical issue, and it has a pressing, negative impact on agriculture, ecosystems, livelihoods, food security, and sustainability. The problem has been studied globally, but its regional or even local dimension is sometimes overlooked. Local-level drought assessment is necessary for developing adaptation and mitigation strategies for that particular region. Keeping this in understanding, an attempt was made to create a detailed assessment of drought characteristics at the local scale in Bangladesh. Standardized precipitation evapotranspiration (SPEI) is a new drought index that mainly considers the rainfall and evapotranspiration data set. Globally, SPEI has become a useful drought index, but its local scale application is not common. SPEI (0.5° grid data) for 110 years (1901-2011) was utilized to overcome the lack of long-term climate data in Bangladesh. Available weather data (1955-2011) from Bangladesh Meteorology Department (BMD) were analyzed to calculate SPEI using the SPEI calculator. The drivers for climate change-induced droughts were characterized by residual temperature and residual rainfall data from different BMD stations. Grid data (SPEI) of 26 stations of BMD were used for drought mapping. The findings revealed that the frequency and intensity of drought are higher in the northwestern part of the country which makes it vulnerable to both extreme and severe droughts. Based on the results, the SPEI-based drought intensity and frequency analyses were carried out, emphasizing Rangpur (northwest region) as a hot spot, to get an insight of drought assessment in Bangladesh. The findings of this study revealed that SPEI could be a valuable tool to understand the evolution and evaluation of the drought induced by climate change in the country. The study also justified the immediate need for drought risk reduction strategies that should lead to relevant policy formulations and agricultural innovations for developing drought adaptation, mitigation, and resilience mechanisms in Bangladesh. [ABSTRACT FROM AUTHOR]

Despite large increases in national cereal production in recent decades, Ethiopia continues to experience regular acute food insecurity crises, often associated with drought events. However, the meteorology of these events is poorly defined and local populations frequently experience food insecurity crises in years when national rainfall and cereal production totals are high. Therefore, looking at national, or even to some extent sub-national, rainfall variability is a misappropriation of climate as a causal factor in food insecurity in Ethiopia. The distinction between 'drought' as catch-all driver of food insecurity and a more nuanced view of the relationship between rainfall variability and food security is necessary both for addressing food insecurity now and for interpreting long-term climate model projections. The on-going recurrence of acute food insecurity is a feature of the heterogeneity of climate and climate variability in Ethiopia, but only in the context of a food system dominated by smallholder farming and climate-sensitive livelihoods. Climate variability has the greatest adverse impact in the most marginal livelihood zones in the drier east of the country. Increasing the resilience of smallholder farmers and pastoralists to climate variability and improvements in early warning and disaster risk response could reduce the frequency and severity of food security crises. However, unless the food system in Ethiopia undergoes transformational adaptation, food insecurity crises will continue to occur, and the opportunity to achieve zero hunger by 2030 will be missed. [ABSTRACT FROM AUTHOR]

The impact of climate change on a variety of scales and on land-use policies across sectors is well-established. There will be climate-related changes to which land use must adapt, although Europe and Germany may not be as affected as other regions. Therefore, we must evaluate how climate change is perceived on a regional scale and across land-use sectors. The aim of this study is to gather information from regional land-use experts regarding their perceptions of climate change to highlight the impact of climate change on land use and to identify the risks and opportunities associated with climate change that these experts observe. With these objectives in mind, we conducted 60 semi-structured interviews and a questionnaire survey with regional land-use experts in agriculture, forestry, and water management in four case study regions in the North German Plain. Climate change is clearly acknowledged by the experts throughout the regions and across the sectors. Drought (particularly in the spring) and increased occurrences of extreme weather events are the most severe regional issues identified. Furthermore, with very few exceptions, climate change is mostly understood as a risk. The results of this study confirm the results from other models and prognoses but with more detail and precision at the regional level. Differences among the sectors and regions were also noted. Unlike most studies, the regional experts in our sample have already noted the impacts and risks of climate change cross-sectorally, which might be a good basis from which to begin regional adaptation. [ABSTRACT FROM AUTHOR]

Tibetan Plateau is the headwater region of many major Asian rivers and very susceptive to climate change. Therefore, knowledge about climate and its spatiotemporal variability in this area is very important for ecological conservation, water resource management and social development. The aim of this study was to reconstruct and analyze the hydroclimate variation on eastern Tibetan Plateau (ETP) over many centuries and explore possible forcing factors on regional hydroclimate variability. We used 118 tree-ring chronologies from ETP to reconstruct the gridded May-July Standardized Precipitation Evapotranspiration Index for the ETP over the last millennium. The reconstruction was developed using an ensemble point-by-point reconstruction method, and a searching region method was used to locate the candidate tree-ring chronologies. The reconstructions have nicely captured the spatial and temporal features of the regional drought variation. The drought variations in south and north of 32.5°N are notably different, which may be related to the divergence influence of North Atlantic Oscillation on the climate systems in the south and north, as well as differences in local climate. Spectral analysis and series comparison suggest that the drought variation in the northeastern Tibetan Plateau has been possibly influenced by solar activity on centurial and longer time scale. [ABSTRACT FROM AUTHOR]

This study reveals the impacts of climatic variable trends on drought severity in Xinjiang, China. Four drought indices, including the self-calibrating Palmer drought severity index (sc-PDSI), Erinç's index ( I ), Sahin's index ( I ), and UNEP aridity index (AI), were used to compare drought severity. The ensemble empirical mode decomposition and the modified Mann-Kendall trend test were applied to analyze the nonlinear components and trends of the climatic variable and drought indices. Four and six climatic scenarios were generated in sc-PDSI, I , I , and AI with different combinations of the observed and detrended climatic variables, respectively. In Xinjiang, generally increasing trends in minimal, average, and maximal air temperature ( T , T , T ) and precipitation ( P) were found, whereas a decreasing trend in wind speed at 2 m height ( U ) was observed. There were significantly increasing trends in all of the four studied drought indices. Drought relief was more obvious in northern Xinjiang than in southern Xinjiang. The strong influences of increased P on drought relief and the weak influences of increased T , T , and T on drought aggravation were shown by comparing four drought indices under different climate scenarios. Decreased U had a weak influence on drought, as shown by the AI in different climate scenarios. The weak influences of T and U were considered to be masked by the strong influences of P on droughts. Droughts were expected to be more severe if P did not increase, but were likely milder without an increase in air temperature and with a decrease in U . [ABSTRACT FROM AUTHOR]

Under the exacerbation of climate change, climate extreme events, especially for drought, happened frequently and intensively across the globe with greater spatial differences. We used the Standardized Precipitation-Evapotranspiration Index computed from the routine meteorological observations at 269 sites in Southwest China (SWC) to study the drought characteristics (e.g., extent, duration and intensity) and their decadal variations during 1971-2012. It was revealed that the drought, in responses to the coupling between decadal precipitation and potential evapotranspiration (PET) anomalies, differed among regions and periods. For the entire SWC, droughts in 1970s and 2000s+ was generally stronger than in 1980s and 1990s with respect to their spatial extent, duration and intensity, especially in 2000s+. It was well-known that drought was closely related with a lack of precipitation; however, the impact of atmospheric demand of evaporation (reflected by PET here) on drought (e.g., duration and intensity) was rarely paid enough attentions. To that end, a spatial multi-linear regression approach was proposed in this study for quantifying the contributions of decadal PET and precipitation variations to drought duration and intensity. We have found that the contributions of decadal PET anomalies to drought duration and intensity could exceed those of precipitation, e.g., during 1980s and 1990s in SWC. Additionally, despite the strongest droughts in 2000s+, it was suggested that PET could exert comparable impacts on drought anomalies as precipitation. All these findings implied that PET plays a critical role in drought event, which acts to amplify drought duration and intensity. To sum up, this study stressed the need for enough attentions for PET processes in drought studies. [ABSTRACT FROM AUTHOR]

Given the severe impacts of hot summers on human and natural systems, we attempt to quantify future changes in extreme hot summer frequency in China using the Coupled Model Intercomparison Project Phase 5 (CMIP5) projections. Unlike previous studies focusing on fixed future time slices, we investigate the changes as a function of global mean temperature (GMT) rise. Analyses show that extreme hot summers (June-July-August mean temperature higher than 90 % quantile of 1971-2000 climatology) are projected to occur at least 80 % of the time across China with a GMT rise of 2 °C. The fraction of land area with extreme hot summers becoming the norm (median of future summer temperatures exceed the extreme) will increase from ~15 % with 0.5 °C of GMT rise to ~97 % with 2.5 °C GMT rise, which is much greater than for the global land surface as a whole. A distinct spatial pattern of the GMT rise threshold over which the local extreme hot summer first becomes the norm is revealed. When averaged over the country, the GMT rise threshold is 0.96 °C. Earth system models exhibit comparable results to climate system models, but with a relatively larger spread. Further analysis shows that the concurrence of hot and dry summers will increase significantly with the spatial structure of responses depending on the definition of drying. The increase of concurrent hot and dry conditions will induce potential droughts which would be more severe than those induced by only precipitation deficits. [ABSTRACT FROM AUTHOR]

Portugal is on a climate change hot spot region, where precipitation is expected to decrease with important impacts regarding future water availability. As one of the European countries affected more by droughts in the last decades, it is important to assess how future precipitation regimes will change in order to study its impacts on water resources. Due to the coarse scale of global circulation models, it is often needed to downscale climate variables to the regional or local scale using statistical and/or dynamical techniques. In this study, we tested the use of a generalized linear model, as implemented in the program GLIMCLIM, to downscale precipitation for the center of Portugal where the Tagus basin is located. An analysis of the method performance is done as well as an evaluation of future precipitation trends and extremes for the twenty-first century. Additionally, we perform the first analysis of the evolution of droughts in climate change scenarios by the Standardized Precipitation Index in the study area. Results show that GLIMCLIM is able to capture the precipitation's interannual variation and seasonality correctly. However, summer precipitation is considerably overestimated. Additionally, precipitation extremes are in general well recovered, but high daily rainfall may be overestimated, and dry spell lengths are not correctly recovered by the model. Downscaled projections show a reduction in precipitation between 19 and 28 % at the end of the century. Results indicate that precipitation extremes will decrease and the magnitude of droughts can increase up to three times in relation to the 1961-1990 period which can have strong ecological, social, and economic impacts. [ABSTRACT FROM AUTHOR]

Together with affected areas of crops from 1978 to 2008, the daily precipitation of 110 stations located in the Huai River Basin during 1959-2008 was used to study the critical conditions when drought and flood occur, based on which the quantitative relationship between the critical condition and the affected area of crops was further studied. Based on the research on the hazard-formative factor of precipitation and the damage degree of crops, the spatial-temporal characteristics of disasters were analyzed, the drought and flood disaster-causing threshold was determined, and the quantitative relationship between the disaster-causing threshold and affected area of crops was established. The results are as the follows: (1) During 1959-2008, extreme precipitation levels were high in the eastern and western part of the Huai River Basin and were low in its central part; the spatial distribution of the coefficient of variation (CV) differed greatly from average extreme precipitation: the series of most stations were located in the central basin, and especially there was a positive trend in Anhui and Henan Provinces. (2) The cumulative precipitation during the disaster period of each station was divided by its mean cumulative precipitation during the same period in 1959-2008 to obtain the disaster-causing threshold, which has shown a good effect on reflecting the actual grade and affected areas in disasters. (3) The relationship among disaster grade, disaster-causing threshold and damage area of crops was established; this threshold can be used as a tool for agricultural disaster assessment and early warning, and can effectively improve the ability to prevent and mitigate disaster in the Huai River Basin. (4) The disaster-causing threshold can be an important input parameter for hazard assessment; other underlying surface indicators can be good supplements for determining the threshold in hazard assessment. [ABSTRACT FROM AUTHOR]

The effects of future temperature and hence evapotranspiration increases on drought risk over North America, based on ten current (1970-1999) and ten corresponding future (2040-2069) Regional Climate Model (RCM) simulations from the North American Regional Climate Change Assessment Program, are presented in this study. The ten pairs of simulations considered in this study are based on six RCMs and four driving Atmosphere Ocean Coupled Global Climate Models. The effects of temperature and evapotranspiration on drought risks are assessed by comparing characteristics of drought events identified on the basis of Standardized Precipitation Index (SPI) and Standardized Precipitation Evapotranspration Index (SPEI). The former index uses only precipitation, while the latter uses the difference (DIF) between precipitation and potential evapotranspiration (PET) as input variables. As short- and long-term droughts impact various sectors differently, multi-scale (ranging from 1- to 12-month) drought events are considered. The projected increase in mean temperature by more than 2 °C in the future period compared to the current period for most parts of North America results in large increases in PET and decreases in DIF for the future period, especially for low latitude regions of North America. These changes result in large increases in future drought risks for most parts of the USA and southern Canada. Though similar results are obtained with SPI, the projected increases in the drought characteristics such as severity and duration and the spatial extent of regions susceptible to drought risks in the future are considerably larger in the case of SPEI-based analysis. Both approaches suggest that long-term and extreme drought events are affected more by the future increases in temperature and PET than short-term and moderate drought events, particularly over the high drought risk regions of North America. [ABSTRACT FROM AUTHOR]

Tendencies of climatic variability indicate that northern Mexico will soon suffer from severe drought. Modeling the influence of climate and ecological processes would help researchers better understand the future implication of climatic variations. Here, we reconstructed historical seasonal precipitation using dendrochronological indices of Pinus cooperi and El Niño southern oscillation (ENSO). Correlation analysis was conducted to establish the precipitation response period; then a reconstruction model using independent variables was constructed using regression procedures. Available data were calibrated and verified to strengthen and validate the modeled reconstruction. Precipitation from the previous winter was best correlated with tree growth. Regression procedures showed that the residual chronology associated in a linear model with El Niño 3.4 explained 47 % of seasonal precipitation variability. This study contributes to a better understanding of historical variations in precipitation and the influence of ENSO in common tree species of northern Mexico to help land managers improve local forest management in a climate change scenario. [ABSTRACT FROM AUTHOR]

The interpretations of trend behaviour for dry and wet events are analysed in order to verify the dryness and wetness episodes. The fitting distribution of rainfall is computed to classify the dry and wet events by applying the standardised precipitation index (SPI). The rainfall amount for each station is categorised into seven categories, namely extremely wet, severely wet, moderately wet, near normal, moderately dry, severely dry and extremely dry. The computation of the SPI is based on the monsoon periods, which include the northeast monsoon, southwest monsoon and inter-monsoon. The trends of the dry and wet periods were then detected using the Mann-Kendall trend test and the results indicate that the major parts of Peninsular Malaysia are characterised by increasing droughts rather than wet events. The annual trends of drought and wet events of the randomly selected stations from each region also yield similar results. Hence, the northwest and southwest regions are predicted to have a higher probability of drought occurrence during a dry event and not much rain during the wet event. The east and west regions, on the other hand, are going through a significant upward trend that implies lower rainfall during the drought episodes and heavy rainfall during the wet events. [ABSTRACT FROM AUTHOR]

Albedo plays an important role in land-atmosphere interactions and local climate. This study presents the impact on simulating regional climate, and the evolution of a drought, when using the default climatological albedo as is usually done in regional climate modelling, or using the actual observed albedo which is rarely done. Here, time-varying satellite derived albedo data is used to update the lower boundary condition of the Weather Research and Forecasting regional climate model in order to investigate the influence of observed albedo on regional climate simulations and also potential changes to land-atmosphere feedback over south-east Australia. During the study period from 2000 to 2008, observations show that albedo increased with an increasingly negative precipitation anomaly, though it lagged precipitation by several months. Compared to in-situ observations, using satellite observed albedo instead of the default climatological albedo provided an improvement in the simulated seasonal mean air temperature. In terms of precipitation, both simulations reproduced the drought that occurred from 2002 through 2006. Using the observed albedo produced a drier simulation overall. During the onset of the 2002 drought, albedo changes enhanced the precipitation reduction by 20 % on average, over locations where it was active. The area experiencing drought increased 6.3 % due to the albedo changes. Two mechanisms for albedo changes to impact land-atmosphere drought feedback are investigated. One accounts for the increased albedo, leading to reduced turbulent heat flux and an associated decrease of moist static energy density in the planetary boundary layer; the other considers that enhanced local radiative heating, due to the drought, favours a deeper planetary boundary layer, subsequently decreasing the moist static energy density through entrainment of the free atmosphere. Analysis shows that drought related large-scale changes in the regional climate favour a strengthening of the second mechanism. That is, the second mechanism is stronger in a drought year compared to a normal year and this difference is larger than for the first mechanism. When both mechanisms are active, the second mechanism tends to dominate across the model domain, particularly during the 2002 drought period. The introduction of observed inter-annual variations in albedo produces an enhancement of the first mechanism and a weakening of the second mechanism during the onset of the drought. [ABSTRACT FROM AUTHOR]

The Standardized Precipitation Index (SPI) is a well-established drought index that is based on transforming the interannual distribution of precipitation to a standard normal distribution. Because of its robust statistical basis, SPI is readily applicable to different regions making comparisons between locations and time windows possible. Nevertheless, the usability of SPI results is undermined by shortcomings that are partly resultant from data and model uncertainties. One such shortcoming is the inability of the existing SPI model to include change in variability of interannual precipitation from non-stationary normal - mostly caused by climate change. In addition, epistemic uncertainty in the form of incompleteness in station-wide precipitation records results in heterogeneity and inconsistency in SPI results. The effects of such epistemic uncertainty on the accuracy of estimations of long-term changes in drought frequency are mostly unknown. Given such deficiency, SPI's procedure and subsequent results remain deterministic and inadequately informative. Here, we introduce modifications to the traditional SPI using Dempster-Shafer theory (DST) to enable modeling and propagation of variability and epistemic uncertainty with the regular SPI procedure. By generalizing the SPI model from a deterministic setting to an 'uncertainty-driven setting' provided by DST, this work makes possible: (a) efficiently propagating data uncertainty in interpolation of station-wide precipitation and SPI, and (b) modeling the effects of shift in precipitation normals (due to e.g., climate change) on drought frequency. In addition, the significance of this shift may then be evaluated with respect to the epistemic uncertainty by measuring how much of the surrounding epistemic uncertainty this shift encloses (i.e., 'probability of enclosing'). The latter is especially important due to large unknowns already associated with climate change modeling. We implement the model on summer extreme drought for the Okanagan Basin, BC, Canada. For a single general circulation model and scenario (CGCM3 A2) a maximum 7 % increase in summer extreme drought (for 2080s, as per current definition) is estimated with a maximum probability of enclosing of 36 %. [ABSTRACT FROM AUTHOR]

Within Canada, the Canadian Prairies are particularly drought-prone mainly due to their location in the lee of the western cordillera and distance from large moisture sources. Although previous studies examined the occurrence of Canadian Prairie droughts during instrumental, pre-instrumental and to a lesser extent, future periods, none have specifically focused on all time three scales. Using two different drought indicators, namely the Palmer Drought Severity Index (PDSI) and Standardized Precipitation Index (SPI), this investigation assesses the variability of summer drought duration and intensity over a core region of the Prairies during (a) the pre-instrumental record extending back several centuries (inferred from tree rings), (b) the instrumental record (1901-2005), and (c) the twenty-first century using statistically downscaled climate variables from several Atmosphere-Ocean Global climate models with multiple emission scenarios. Results reveal that observed twentieth century droughts were relatively mild when compared to pre-settlement on the Prairies, but these periods are likely to return (and even worsen) in the future due to the anticipated warming during the course of the twenty-first century. However, future drought projections are distinctly different between the two indices. All PDSI-related model runs show greater drought frequency and severity mainly due to increasing temperatures. Conversely, the precipitation-based SPI indicates no significant changes to future summer drought frequency although there tends to be a higher persistence of multi-year droughts in central and southern portions of Canadian Prairies. These findings therefore stress the importance of considering anticipated warming trends when assessing future regional-scale drought, especially given the uncertainties and lack of consistency in future precipitation signals among climate models. This study can be considered an initial step toward quantifying and understanding Canadian Prairie drought occurrence and severity over several centuries as determined from paleo, instrumental, and climate model data sources. [ABSTRACT FROM AUTHOR]

Climate change involves warmer temperatures, altered precipitation patterns, increased climatic variability and, in Mediterranean regions, increased frequency and severity of droughts. Tree species may show different growth responses to these components of climatic change, which may trigger changes in forest composition and dominance. We assessed the influence of recent climatic changes on secondary growth of mature trees from four species co-occurring in a Mediterranean continental forest: Quercus ilex, Quercus faginea, Pinus nigra and Juniperus thurifera. We used dendrochronology to relate radial-growth variables [earlywood and latewood widths, basal area increment (BAI)] to annual and seasonal climatic variables for the period 1977-2007. Our results showed that Q. faginea BAI has declined, whereas J. thurifera BAI has increased over time while Q. ilex and P. nigra have maintained their growth rates. Growth was mainly favored by higher precipitations and tree size for all species. Reduced growth during extremely dry years was observed for all study species, but all of them except Q. faginea recovered their growth levels 2 years after drought. Our findings illustrate how the effects of climatic changes on growth should include analyses of seasonal climatic trends and extreme events such as severe droughts. We conclude that the seasonal timing of warming and precipitation alterations leading to drought events caused contrasting effects on growth of co-occurring Mediterranean tree species, compromising their future coexistence. [ABSTRACT FROM AUTHOR]

Drought is expected to increase in frequency and severity in the future as a result of climate change, mainly as a consequence of decreases in regional precipitation but also because of increasing evaporation driven by global warming. Previous assessments of historic changes in drought over the late twentieth and early twenty-first centuries indicate that this may already be happening globally. In particular, calculations of the Palmer Drought Severity Index (PDSI) show a decrease in moisture globally since the 1970s with a commensurate increase in the area in drought that is attributed, in part, to global warming. The simplicity of the PDSI, which is calculated from a simple water-balance model forced by monthly precipitation and temperature data, makes it an attractive tool in large-scale drought assessments, but may give biased results in the context of climate change. Here we show that the previously reported increase in global drought is overestimated because the PDSI uses a simplified model of potential evaporation that responds only to changes in temperature and thus responds incorrectly to global warming in recent decades. More realistic calculations, based on the underlying physical principles that take into account changes in available energy, humidity and wind speed, suggest that there has been little change in drought over the past 60 years. The results have implications for how we interpret the impact of global warming on the hydrological cycle and its extremes, and may help to explain why palaeoclimate drought reconstructions based on tree-ring data diverge from the PDSI-based drought record in recent years. [ABSTRACT FROM AUTHOR]

We utilize a variety of climate datasets to examine impacts of two mechanisms on precipitation in the Greater Horn of Africa (GHA) during northern-hemisphere summer. First, surface-pressure gradients draw moist air toward the GHA from the tropical Atlantic Ocean and Congo Basin. Variability of the strength of these gradients strongly influences GHA precipitation totals and accounts for important phenomena such as the 1960s-1980s rainfall decline and devastating 1984 drought. Following the 1980s, precipitation variability became increasingly influenced by the southern tropical Indian Ocean (STIO) region. Within this region, increases in sea-surface temperature, evaporation, and precipitation are linked with increased exports of dry mid-tropospheric air from the STIO region toward the GHA. Convergence of dry air above the GHA reduces local convection and precipitation. It also produces a clockwise circulation response near the ground that reduces moisture transports from the Congo Basin. Because precipitation originating in the Congo Basin has a unique isotopic signature, records of moisture transports from the Congo Basin may be preserved in the isotopic composition of annual tree rings in the Ethiopian Highlands. A negative trend in tree-ring oxygen-18 during the past half century suggests a decline in the proportion of precipitation originating from the Congo Basin. This trend may not be part of a natural cycle that will soon rebound because climate models characterize Indian Ocean warming as a principal signature of greenhouse-gas induced climate change. We therefore expect surface warming in the STIO region to continue to negatively impact GHA precipitation during northern-hemisphere summer. [ABSTRACT FROM AUTHOR]

Climate change in the twenty-first century, projected by a large ensemble average of global coupled models forced by a mid-range (A1B) radiative forcing scenario, is downscaled to Climate Divisions across the western United States. A simple empirical downscaling technique is employed, involving model-projected linear trends in temperature or precipitation superimposed onto a repetition of observed twentieth century interannual variability. This procedure allows the projected trends to be assessed in terms of historical climate variability. The linear trend assumption provides a very close approximation to the time evolution of the ensemble-average climate change, while the imposition of repeated interannual variability is probably conservative. These assumptions are very transparent, so the scenario is simple to understand and can provide a useful baseline assumption for other scenarios that may incorporate more sophisticated empirical or dynamical downscaling techniques. Projected temperature trends in some areas of the western US extend beyond the twentieth century historical range of variability (HRV) of seasonal averages, especially in summer, whereas precipitation trends are relatively much smaller, remaining within the HRV. Temperature and precipitation scenarios are used to generate Division-scale projections of the monthly palmer drought severity index (PDSI) across the western US through the twenty-first century, using the twentieth century as a baseline. The PDSI is a commonly used metric designed to describe drought in terms of the local surface water balance. Consistent with previous studies, the PDSI trends imply that the higher evaporation rates associated with positive temperature trends exacerbate the severity and extent of drought in the semi-arid West. Comparison of twentieth century historical droughts with projected twenty-first century droughts (based on the prescribed repetition of twentieth century interannual variability) shows that the projected trend toward warmer temperatures inhibits recovery from droughts caused by decade-scale precipitation deficits. [ABSTRACT FROM AUTHOR]