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Modern changes in the precipitation and air temperature regime in the mountainous regions of the Dagestan republic
Abstract
The study focuses on the local dynamics of precipitation and temperature in the mountainous regions of the Dagestan Republic (North Caucasus, eastern part). A shift in the secondary maximum of the precipitation annual distribution in the low-mountainous part of the region from August to September was found. The wettest years in the highlands in the periods 1966--1978 and 1996--2013 are discovered. The period from the beginning of the current century until now is identified as the wettest in the low-mountain zone. It was found that the trends of seasonal temperatures are positive. At the same time, the dynamics of spring temperatures remained insignificant in the low-mountain zone until 2010. It was revealed that the statistically reliable increase of temperature in February and March and unidirectional tendencies in the daily characteristics of precipitation is the local pattern of the climate change in this part of the North Caucasus. In this season the increase in the average and maximum daily precipitation intensity is reliable.
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This study examines the changing behavior of summer dry spell duration in response to increasing air temperatures at 517 Russian stations during 1966-2010. We found that the frequency distribution of dry spell duration (as represented by histograms) is becoming skewed toward longer dry spells. This asymmetrical shift is accompanied by mean increases in dry spell duration. This asymmetry is also reflected in exponentially higher increasing rates of dry spell duration toward higher percentiles. Consequently, across Russia, summers have experienced significant increases in 7-day-or-longer dry spells (at 6.1%/°C of warming) and fewer occurrences of 3-day-or-shorter dry spells (at 2.4%/°C). This study suggests that hotter summers favor more frequent prolonged dry spells, exacerbating drought and heat wave conditions during Russian summers as air temperatures continue to rise.
Climate change has led to concerns about increasing river floods resulting from the greater water-holding capacity of a warmer atmosphere¹. These concerns are reinforced by evidence of increasing economic losses associated with flooding in many parts of the world, including Europe². Any changes in river floods would have lasting implications for the design of flood protection measures and flood risk zoning. However, existing studies have been unable to identify a consistent continental-scale climatic-change signal in flood discharge observations in Europe³, because of the limited spatial coverage and number of hydrometric stations. Here we demonstrate clear regional patterns of both increases and decreases in observed river flood discharges in the past five decades in Europe, which are manifestations of a changing climate. Our results—arising from the most complete database of European flooding so far—suggest that: increasing autumn and winter rainfall has resulted in increasing floods in northwestern Europe; decreasing precipitation and increasing evaporation have led to decreasing floods in medium and large catchments in southern Europe; and decreasing snow cover and snowmelt, resulting from warmer temperatures, have led to decreasing floods in eastern Europe. Regional flood discharge trends in Europe range from an increase of about 11 per cent per decade to a decrease of 23 per cent. Notwithstanding the spatial and temporal heterogeneity of the observational record, the flood changes identified here are broadly consistent with climate model projections for the next century4,5, suggesting that climate-driven changes are already happening and supporting calls for the consideration of climate change in flood risk management.
The study of climate, in such a diverse climatic region as the Caucasus, is necessary in order to evaluate the influence of local factors on the formation of temperature and precipitation regimes in its various climatic zones. This study is based on the instrumental data (temperatures and precipitation) from 20 weather stations, located on the territory of the Caucasian region during 1961–2011. Mathematical statistics, trend analysis, and rescaled range Methods were used. It was found that the warming trend prevailed in all climatic zones, it intensified since the beginning of global warming (since 1976), while the changes in precipitation were not so unidirectional. The maximum warming was observed in the summer (on average by 0.3 °C/10 years) in all climatic zones. Persistence trends were investigated using the Hurst exponent H (range of variation 0–1), which showed a higher trend persistence of annual mean temperature changes (H = 0.8) compared to annual sum precipitations (H = 0.64). Spatial-correlation analysis performed for precipitations and temperatures showed a rapid decrease in the correlation between precipitations at various weather stations from R = 1 to R = 0.5, on a distance scale from 0 to 200 km. In contrast to precipitation, a high correlation (R = 1.0–0.7) was observed between regional weather stations temperatures at a distance scale from 0 to 1000 km, which indicates synchronous temperature changes in all climatic zones (unlike precipitation).
Despite evidence of increasing precipitation extremes, corresponding evidence for increases in flooding remains elusive. If anything, flood magnitudes are decreasing despite widespread claims by the climate community that if precipitation extremes increase, floods must also. In this commentary we suggest reasons why increases in extreme rainfall are not resulting in corresponding increases in flooding. Among the possible mechanisms responsible, we identify decreases in antecedent soil moisture, decreasing storm extent, and decreases in snowmelt. We argue that understanding the link between changes in precipitation and changes in flooding is a grand challenge for the hydrologic community and is deserving of increased attention.
Weather extremes have widespread harmful impacts on ecosystems and human communities with more deaths and economic losses from flash floods than any other severe weather-related hazards. Flash floods attributed to storm runoff extremes are projected to become more frequent and damaging globally due to a warming climate and anthropogenic changes, but previous studies have not examined the response of these storm runoff extremes to naturally and anthropogenically driven changes in surface temperature and atmospheric moisture content. Here we show that storm runoff extremes increase in most regions at rates higher than suggested by Clausius-Clapeyron scaling, which are systematically close to or exceed those of precipitation extremes over most regions of the globe, accompanied by large spatial and decadal variability. These results suggest that current projected response of storm runoff extremes to climate and anthropogenic changes may be underestimated, posing large threats for ecosystem and community resilience under future warming conditions.
Based on observational data from 70 hydrological stations in the North Caucasus an evaluation of present values of mean annual runoff, minimum monthly winter and summer runoff was carried out. Series of maps was drawn. Significant changes in mean annual. minimum monthly and maximum runoff during last decades have been revealed in the North Caucasus. A rise in both amount of water availability and potential natural hazard is characteristic of the most of the North Caucasus that is considered to be caused by recent climate change. Mean annual runoff during 1978-2010 increased compared to 1945-1977 by 5-30 % in the foothills and by 30-70% in the plain area. An increase in winter minimum monthly runoff is as well most intensive in the plain part of study area (>100%). Within the foothills it amounts to 50-100%. In mountainous area long-term oscillation of winter minimum monthly discharge strongly depends on local factors, such as geological structure. The rate of the increase in summer minimum monthly discharge regularly grows from central foothill part of Northern Caucasus (30-50%) to the Western plain territory (70-100%). In Kuban river basin 30% of analyzed gauging stations show positive trend in maximum instantaneous discharge, while 9% negative. On the contrary, in the Eastern part – Terek river basin – negative trend in maximum instantaneous discharge is prevalent: 38% of gauging stations. Positive trend in Terek river basin is characteristic of 9.5% of analyzed gauging stations.
There is overwhelming consensus that the intensity of heavy precipitation events is increasing in a warming world. It is generally expected such increases will translate to a corresponding increase in flooding. Here, using global data sets for non-urban catchments, we investigate the sensitivity of extreme daily precipitation and streamflow to changes in daily temperature. We find little evidence to suggest that increases in heavy rainfall events at higher temperatures result in similar increases in streamflow, with most regions throughout the world showing decreased streamflow with higher temperatures. To understand why this is the case, we assess the impact of the size of the catchment and the rarity of the event. As the precipitation event becomes more extreme and the catchment size becomes smaller, characteristics such as the initial moisture in the catchment become less relevant, leading to a more consistent response of precipitation and streamflow extremes to temperature increase. Our results indicate that only in the most extreme cases, for smaller catchments, do increases in precipitation at higher temperatures correspond to increases in streamflow.
We analyzed the changes in precipitation regime in the Altai Mountains for 1959-2014 and estimate the influence of atmospheric circulations on these changes. Our study showed that during last 56 years the changes in the precipitation regime had a positive trend for the warm seasons (April-October), but weakly positive or negative trends for the cold seasons (November-March). It was found that these changes correspond to the decreasing contribution of “Northern meridional and Stationary anticyclone (Nm-Sa)” and “Northern meridional and East zonal (Nm-Ez)” circulation groups and to the increasing contribution of “West zonal and Southern meridional (Wz-Sm)” circulation groups, accordingly to the Dzerdzeevskii classification. In addition, it was found that the variation of precipitation has a step change point in 1980. For the warm seasons, the precipitation change at this point is associated with the reduced influence of “West zonal (Wz)”, “Northern meridional and Stationary anticyclone (Nm-Sa)” and “Northern meridional and Southern meridional (Nm-Sm)” circulation groups. For the cold seasons, a substantial increase of “Wz-Sm” and a decrease of “Nm-Sa”, “Nm-Ez” circulation groups are responsible for the precipitation change in the two time periods (1959-1980 and 1981-2014).
This study investigated the anthropogenic influence on the temporal variability of annual precipitation for the period 1950-2005 as simulated by the CMIP5 models. The temporal variability of both annual precipitation amount (PRCPTOT) and intensity (SDII) was first measured using a metric of statistical dispersion called the Gini coefficient. Comparing simulations driven by both anthropogenic and natural forcings (ALL) with simulations of natural forcings only (NAT), we quantified the anthropogenic contributions to the changes in temporal variability at global, continental and sub-continental scales as a relative difference of the respective Gini coefficients of ALL and NAT. Over the period of 1950-2005, our results indicate that anthropogenic forcings have resulted in decreased uniformity (i.e., increase in unevenness or disparity) in annual precipitation amount and intensity at global as well as continental scales. In addition, out of the 21 sub-continental regions considered, 14 (PRCPTOT) and 17 (SDII) regions showed significant anthropogenic influences. The human impacts are generally larger for SDII compared to PRCTOT, indicating that the temporal variability of precipitation intensity is generally more susceptible to anthropogenic influence than precipitation amount. The results highlight that anthropogenic activities have changed not only the trends but also the temporal variability of annual precipitation, which underscores the need to develop effective adaptation management practices to address the increased disparity.
Extreme precipitation intensities have increased in all regions of the Contiguous United States (CONUS) and are expected to further increase with warming at scaling rates of about 7% per degree Celsius (ref.), suggesting a significant increase of flash flood hazards due to climate change. However, the scaling rates between extreme precipitation and temperature are strongly dependent on the region, temperature, and moisture availability, which inhibits simple extrapolation of the scaling rate from past climate data into the future. Here we study observed and simulated changes in local precipitation extremes over the CONUS by analysing a very high resolution (4 km horizontal grid spacing) current and high-end climate scenario that realistically simulates hourly precipitation extremes. We show that extreme precipitation is increasing with temperature in moist, energy-limited, environments and decreases abruptly in dry, moisture-limited, environments. This novel framework explains the large variability in the observed and modelled scaling rates and helps with understanding the significant frequency and intensity increases in future hourly extreme precipitation events and their interaction with larger scales. © 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved.
Практика отслеживания колебаний климата основана на анализе рядов наблюдаемых на метеостанциях значений приземной температуры воздуха и сумм атмосферных осадков. Исследования режима осадков на Западном Кавказе показывают, что при ощутимых климатических изменениях расчеты не выявляют статистически достоверной динамики в среднегодовых суммах осадков. Цель настоящей работы – исследовать современные изменения характеристик суточных сумм атмосферных осадков на Западном Кавказе. Материалы и методы. Основой для расчетов являются наблюдения на метеостанциях, представленные в специализированных массивах ВНИИГМИ-МЦД. Метод исследования – математико-статистическое моделирование. Результаты и обсуждение. Установлено, что, несмотря на существенные локальные различия в режиме осадков, рост числа дней с осадками различной интенсивности, увеличение средних и/или максимальных значений их суточной интенсивности в октябре являются общими тенденциями на исследуемой территории. В большинстве пунктов выявлены тенденции увеличения количества дней с осадками различной интенсивности и средних суточных и максимальных сумм в марте. Статистически достоверные тенденции к снижению различных характеристик суточной интенсивности на Западном Кавказе обнаружены зимой, в апреле и в августе. Заключение. Несмотря на локальные особенности режима осадков можно отметить некоторые общие тенденции. Во-первых, повсеместно обнаружен рост значений различных характеристик режима осадков в октябре, увеличение числа дней с осадками различной интенсивности, рост средних и/или максимальных значений их суточной интенсивности. А поскольку в регионе наводнения в октябре явление довольно частое, то обнаруженные статистически достоверные тенденции свидетельствуют, что вероятность наступления зависимых от интенсивности и частоты осадков опасных природных явлений в этом месяце не снижается. Во-вторых, увеличение количества дней с осадками и суточных характеристик в марте (исключение составляет метеостанция Шаджатмаз). В-третьих, снижение суточной интенсивности осадков зимой, в апреле и в августе. На фоне отсутствия значимых изменений в годовых суммах осадков установлено их перераспределение внутри года и выявлены статистически достоверные линейные тренды суточных характеристик осадков, способные повлиять на режим стока рек в регионе и формирование на них опасных гидрологических явлений.
How precipitation and its extremes change as the climate changes are examined. There is a direct influence of global warming on changes in precipitation. Increased heating leads to greater evaporation and thus surface drying, thereby increasing intensity and duration of drought. However, the water holding capacity of air increases by about 7 % per 1ºC warming, which leads to increased water vapor in the atmosphere. Hence storms, whether individual thunderstorms, extratropical rain or snow storms, or tropical cyclones and hurricanes, supplied by increased moisture, produce more intense precipitation events that are widely observed to be occurring, even in places where total precipitation is decreasing: “it never rains but it pours! ” In turn this increases the risk of flooding. A discussion is given of the critical role of the energy budget in the hydrological cycle and why total precipitation amount changes at a slower rate than for total column water vapor. The processes involved are also discussed. With modest changes in winds, patterns of precipitation do not change much but result in dry areas becoming drier (generally throughout the subtropics) and wet areas becoming wetter, especially in mid to high latitudes: the “rich get richer and the poor get poorer ” syndrome. This pattern is simulated by climate
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