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The Arctic rivers contribute more than one‐third of the total freshwater streamflow into the Arctic Ocean and play an essential role in the heat and mass circulation of the Arctic atmosphere/ocean system. As the Arctic is warming faster than the global average, the streamflow from Arctic basins increases. This study analyzed the streamflow of the three largest Siberian rivers: the Lena, Yenisei, and Ob', at multiple temporal scales. Results show that the annual streamflow of each river basin exhibits statistically significant increasing trends, while the seasonal streamflow of sub‐basins generally decreases in the summer but increases in the winter. Both autocorrelation and long‐term persistency are often found in the streamflow time series, which indicates significant changes in the large‐scale climatological environment. Therefore, wavelet coherence between the streamflow and large‐scale climate patterns, including the El Niño–Southern Oscillation (ENSO), North Pacific pattern (NP), Arctic Oscillation (AO), and the Pacific/North America Pattern (PNA), have been conducted. NP and ENSO are found to have positive relationships with the precipitation and the ratio of potential evapotranspiration over the precipitation. AO and the PNA are found to have positive relationships with the streamflow of the Ob' and Yenisei rivers at decadal and multidecadal scales. This study demonstrates that the existence of nonstationarities within the Siberian streamflow as the combined impact of climate change alters the hydroclimatological and terrestrial environment of Siberia. These findings provide new insights into the mechanisms underlying the hydrologic changes to warming trends and oscillations of climate patterns, which contribute to our understanding and the prediction of streamflow of these northern rivers. [ABSTRACT FROM AUTHOR]

Until now, driving mechanisms behind recurring droughts and hydroclimate variations that controls the Nile River Basin (NRB) remains poorly understood. Our results show significant hydroclimatic changes that contributed to recent increasing aridity of NRB since the 1970s. Besides climate warming, the influence of stronger ENSO and Indian Ocean dipole (IOD) in NRB has increased after 1980s, which have significantly contributed to NRB's drought severity at inter-annual to inter-decadal timescales. Our results demonstrate that warming, El Niño and IOD have played a crucial role on NRB's inter-decadal hydroclimate variability, but IOD has played a more important role in modulating NRB's hydroclimate at higher timescales than El Niño. Results also indicate that the impacts of positive phases of ENSO and IOD events are larger than the negative phases in the NRB hydroclimate. Further, the southward (westward) shift in stream functions and meridional (zonal) winds caused an enhancement in the blocking pattern, with strong anticyclonic waves of dry air that keeps moving into NRB, has resulted in drier NRB, given stream function, geopotential height and U-wind anomalies associated with El Niño shows that changes in regional atmospheric circulations during more persistent and stronger El Niño has resulted in drier NRB. After 1970s, El Niño, IOD, and drought indices shows significant anti-phase relationships, which again demonstrates that more frequent and severe El Niño and IOD in recent years has led to more severe droughts in NRB. Our results also demonstrate that IOD and and the western pole of the Indian Ocean Dipole (WIO) are better predictors of the Nile flow than El Niño, where its flow has decreased by 13.7 (upstream) and by 114.1 m3/s/decade (downstream) after 1964. In summary, under the combined impact of warming and stronger IOD and El Niño, future droughts of the NRB will worsen. [ABSTRACT FROM AUTHOR]

Under the possible impact of climate warming, recent changes in dry and wet spells have contributed significantly to climate-related hazards around the world. In this work, spatial and temporal variations in dry and wet spells over Canada are investigated using daily precipitation data from 1979 to 2018. The time-varying relationships between precipitation spells and large-scale climate anomalies are modeled using a nonstationary generalized extreme value (GEV) distribution and Bayesian quantile regression. Over the period 1979–2018, significant changes in dry and wet spells have been observed across Canada, particularly in the southern Canadian Prairies (CP), where both the number and duration of dry spells show positive trends. Dry and wet spells over many parts of Canada are nonstationary under the effects of the El Niño–Southern Oscillation (ENSO) and the Pacific–North American pattern (PNA), with PNA having stronger effects on annual maximum dry spells than ENSO, especially in the central CP and eastern Ontario. For western Canada, the influence of ENSO on dry spells tends to be relatively strong, especially for dry spells of high quantiles, as El Niño generally induces atmospheric moisture deficit. For central Canada, ENSO and PNA have a negative (positive) impact on the wet spell duration of low (high) quantiles. For eastern Canada, PNA is negatively correlated with the duration of wet spells, especially for wet spells of high quantiles. Therefore, a better understanding of the spatial and temporal variability in dry and wet spell return periods will be useful for the effective management of water resources, and for developing effective disaster mitigation measures against the possible social and economic impacts of climate-related hazards. [ABSTRACT FROM AUTHOR]

Summary A physically based land surface scheme, the Modified Interaction Soil Biosphere Atmosphere (MISBA) of Kerkhoven and Gan (2006) was used to assess the future streamflow of the South Saskatchewan River Basin (SSRB) of Alberta under the combined impacts of climate change and El Niño Southern Oscillation (ENSO). Potential impacts of climate change on the streamflows of 15 sub-basins of the SSRB for the 2010–2039 (2020s), 2040–2069 (2050s) and 2070–2099 (2080s) were simulated by MISBA based on 30 years (1961–1990) of re-analysis data of the European Centre for Mid-range Weather Forecasts (ERA-40) adjusted with climate scenarios projected by four General Circulation Models (GCMs) for three Special Report on Emissions Scenarios (SRES) emissions (A1FI, A21, B21) of Intergovernmental Panel on Climate Change (IPCC). Next, the combined impacts of climate change and ENSO are simulated by driving MISBA with the ERA-40 dataset re-sampled for active El Niño and La Niña episodes adjusted for climate projections of 2050s. Under SRES climate projections alone, MISBA simulated an overall decrease in streamflow for sub-basins of SSRB in 2020s, 2050s, and 2080s. While under a combined impact of climate change and ENSO, a further decrease (increase) in the streamflow of SSRB by 2050s was simulated if the climate anomaly considered was El Niño (La Niña). [ABSTRACT FROM AUTHOR]

Rainfall is the primary driver of basin hydrologic processes. This article examines a recently developed rainfall predictive tool that combines wavelet principal component analysis (WPCA), an artificial neural networks-genetic algorithm (ANN-GA), and statistical disaggregation into an integrated framework useful for the management of water resources around the upper Blue Nile River basin (UBNB) in Ethiopia. From the correlation field between scale-average wavelet powers (SAWPs) of the February-May (FMAM) global sea surface temperature (SST) and the first wavelet principal component (WPC1) of June-September (JJAS) seasonal rainfall over the UBNB, sectors of the Indian, Atlantic, and Pacific Oceans where SSTs show a strong teleconnection with JJAS rainfall in the UBNB ( r ≥ 0.4) were identified. An ANN-GA model was developed to forecast the UBNB seasonal rainfall using the selected SST sectors. Results show that ANN-GA forecasted seasonal rainfall amounts that agree well with the observed data for the UBNB [root-mean-square errors (RMSEs) between 0.72 and 0.82, correlation between 0.68 and 0.77, and Hanssen-Kuipers (HK) scores between 0.5 and 0.77], but the results in the foothills region of the Great Rift Valley (GRV) were poor, which is expected since the variability of WPC1 mainly comes from the highlands of Ethiopia. The Valencia and Schaake model was used to disaggregate the forecasted seasonal rainfall to weekly rainfall, which was found to reasonably capture the characteristics of the observed weekly rainfall over the UBNB. The ability to forecast the UBNB rainfall at a season-long lead time will be useful for an optimal allocation of water usage among various competing users in the river basin. [ABSTRACT FROM AUTHOR]

By applying a suit of statistical techniques, this study investigated the impacts of the El Nino-Southern Oscillation (ENSO), the Pacific-North America (PNA) pattern, the West Pacific (WP) pattern and the Pacific decadal oscillation (PDO) teleconnections on the interannual to interdecadal variability of southwestern (SW) Canadian streamflow anomalies. It is shown that El Nino (La Nina) episodes lead to significant negative (positive) streamflow anomalies in several subregions during the spring and/or summer months following the ENSO onset year. A simple composite analysis of streamflow for anomalous PNA years conditioned on non-ENSO years showed that the high phase of PNA could also produce an El Nino-like streamflow response over the region. In addition, the ENSO-streamflow relationship appears to be modulated by the interdecadal oscillation of the North Pacific (NP) climate as indexed by the PDO. The interaction between PDO and ENSO was found to be constructive when the two are in phase and destructive otherwise. The potential of using the three large-scale climate anomalies (ENSO, PNA and PDO) for long-range streamflow forecasting in SW Canada was assessed using a partial correlation analysis with the southern oscillation index (SOI), the PNA and PDO indices at lead times of up to 10 months. While partial correlations with all three indices were found to be statistically significant for several basins, the ENSO and PDO effects appear to be far more important than that of the PNA pattern. The winter season SOI, which is an indicator of the mature phase of ENSO, shows modest correlations with basins whose flow regimes are dominated by winter rain/spring snowmelt. On the other hand, the winter season PDO shows relatively strong correlations with basins originating in the Rocky Mountains, whose flow regimes are dominated by spring-summer snow/glacier melt. The modest SOI-streamflow relationships are partly attributed to nonlinearity induced by the interference from the extratropical sources of variability (i.e. PNA and PDO). Long-range streamflow forecasting strategies for this region should thus incorporate information from the three large-scale climate anomalies. Copyright © 2006 Royal Meteorological Society. [ABSTRACT FROM AUTHOR]