Data mining methods for hydroclimatic forecasting

Skillful streamflow forecasts at seasonal lead times may be useful to water managers seeking to provide reliable water supplies and maximize hydrosystem benefits. In this study, a class of data mining techniques, known as tree-structured models, is investigated to address the nonlinear dynamics of climate teleconnections and screen promising probabilistic streamflow forecast models for river–reservoir systems. In a case study of the Lower Colorado River system in central Texas, a number of potential predictors are evaluated for forecasting seasonal streamflow, including large-scale climate indices related to the El Niño–Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), North Atlantic Oscillation (NAO), and others. Results show that the tree-structured models can effectively capture the nonlinear features hidden in the data. Skill scores of probabilistic forecasts generated by both classification trees and logistic regression trees indicate that seasonal inflows throughout the system can be predicted with sufficient accuracy to improve water management, especially in the winter and spring seasons in central Texas.     

北半球大气遥相关型与区域尺度大气扰动

北极涛动(AO)、北大西洋涛动(NAO)和太平洋-北美型(PNA)等北半球大气遥相关型,可以用大气位势高度的物理分解扰动分量解释.结果发现,AO反映的是北极地区行星尺度纬圈平均扰动分量的变化,PNA与持续性天气尺度扰动分量相联系,NAO是行星尺度纬圈平均扰动与天气尺度扰动共同作用的结果.对行星尺度纬圈平均扰动分量和天气尺度扰动分量用旋转经验正交函数(REOF)展开,不但可以证实人们已经命名的区域性大气涛动,还新发现了北极地区的两对偶极涛动、欧亚涛动(EAO)和"大西洋-欧亚型"(AEA)波列.这些涛动连接了相邻地区的异常天气和异常气候.     

Regime-dependent streamflow sensitivities to Pacific climate modes cross the Georgia–Puget transboundary ecoregion

The Georgia Basin–Puget Sound Lowland region of British Columbia (Canada) and Washington State (USA) presents a crucial test in environmental management due to its combination of abundant salmonid habitat, rapid population growth and urbanization, and multiple national jurisdictions. It is also hydrologically complex and heterogeneous, containing at least three streamflow regimes: pluvial (rainfall-driven winter freshet), nival (melt-driven summer freshet), and hybrid (both winter and summer freshets), reflecting differing elevation ranges within various watersheds. We performed bootstrapped composite analyses of river discharge, air temperature, and precipitation data to assess El Niño–Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) impacts upon annual hydrometeorological cycles across the study area. Canadian and American data were employed from a total of 21 hydrometric and four meteorological stations. The surface meteorological anomalies showed strong regional coherence. In contrast, the seasonal impacts of coherent modes of Pacific circulation variability were found to be fundamentally different between streamflow regimes. Thus, ENSO and PDO effects can vary from one stream to the next within this region, albeit in a systematic way. Furthermore, watershed glacial cover appeared to complicate such relationships locally; and an additional annual streamflow regime was identified that exhibits climatically driven non-linear phase transitions. The spatial heterogeneity of seasonal flow responses to climatic variability may have substantial implications to catchment-specific management and planning of water resources and hydroelectric power generation, and it may also have ecological consequences due to the matching or phase-locking of lotic and riparian biological activity and life cycles to the seasonal cycle. The results add to a growing body of literature suggesting that assessments of the streamflow impacts of ocean–atmosphere circulation modes must accommodate local hydrological characteristics and dynamics. Copyright © 2007 John Wiley & Sons, Ltd. The copyright in Paul H. Whitfield's contribution belongs to the Crown in right of Canada and such copyright material is reproduced with the permission of Environment Canada.     

Global ENSO-streamflow teleconnection,streamflow forecasting and interannual variability

Abstract

El Niño Southern Oscillation (ENSO) has been linked to climate anomalies throughout the world. This paper presents an overview of global ENSO-streamflow teleconnection and identifies regions where the relationship may be exploited to forecast streamflow several months ahead. The teleconnection is investigated by fitting a first harmonic to 24-month El Niño streamflow composites from 581 catchments worldwide and the potential for forecasting is investigated by calculating the lag correlation between streamflow and two indicators of ENSO. The analyses indicate clear ENSO-streamflow teleconnections in many catchments, some of which are consistent across large geographical regions. Strong and regionally consistent ENSO-streamflow teleconnections are identified in Australia and New Zealand, South and Central America, and weaker signals are identified in some parts of Africa and North America. The results suggest that the ENSO-streamflow relationship and the serial correlation in streamflow can be used to successfully forecast streamflow. The streamflow forecasts can be used to help manage water resources, particularly in systems with high interannual variability in Australia, southern and drier parts of Africa and some areas of North America.     

Influence of the El Niño/Southern Oscillation on South Korean streamflow variability

Deciphering the mechanisms through which the El Niño/Southern Oscillation (ENSO) affects hydrometeorological parameters in the tropics and extratropics is of great interest. We investigate climatic teleconnections between warm or cold phases of ENSO and streamflow patterns over South Korea using an empirical methodology designed to detect regions showing a strong and consistent hydroclimatic signal associated with ENSO. We calculate not only spatial coherence values by monthly streamflow composite formed over 2‐year ENSO cycle and the first harmonic fit to detect candidate regions but also temporal consistency rates by aggregate composite and index time series to determine core regions. As a result, the core regions, namely, the Han river basin and the Nakdong river basin, are detected with a high level of response of ENSO phenomena to streamflow patterns. The ENSO composites for both core regions indicate drier (wetter) conditions in early autumn of the warm (cold) episode years and wetter (drier) conditions from winter to spring of the following year. For both regions, the spatial coherences are over 92% (82%) and the temporal consistencies are 71% (75%) during the El Niño (La Niña) events. In addition, for the core regions identified by composite‐harmonic analysis for both extreme episodes, the results of comparative analyses by using correlation, annual cycle, and Wilcoxon rank sum test indicate that 2 opposite phases‐streamflow relationships have a tendency of sign reversal of the streamflow anomaly. Also, the positive departures during the El Niño years show more coherent and strong responses than the negative anomalies in the La Niña events. In conclusion, South Korea experiences climatic teleconnection between ENSO forcing and midlatitude streamflow patterns.     

Coherence between atmospheric teleconnections,Great Lakes water levels,and regional climate

We investigated the frequency domain relationships between four atmospheric teleconnections (Trans-Niño Index TNI, Pacific Decadal Oscillation PDO, Northern Annular Mode/Arctic Oscillation Index NAM/AO, and Pacific/North American PNA pattern) and water levels in the Great Lakes from 1948 to 2002 by quantifying the coherence between these time series. The levels in all Great Lakes are significantly correlated with the TNI in the frequency range (3–7)⁻¹ cycles year⁻¹, and with the PDO in interdecadal frequencies. The levels in Lakes Superior, Michigan, and Erie are significantly correlated with the PNA pattern in interdecadal frequencies, and the levels in all Great Lakes are significantly correlated with the NAM/AO in interannual frequencies.     

Threshold level approach for streamflow drought analysis in the Central Andes of Argentina: a climatological assessment

A streamflow drought climatology was developed over the Central Andes of Argentina, a semi-arid region highly vulnerable to climatic variations, based on the analysis of daily historical streamflow records. A threshold level approach was applied on a daily basis for three different severity levels in order to depict the main characteristics of droughts – number of drought events, mean duration and mean severity – over the period 1957–2014. Based on three annual indices that summarize the frequency of drought events, their duration and severity, we identified the main regional dry periods and the main modes of variability through an empirical decomposition. These modes are linked to La Niña conditions on inter-annual time scales and the Pacific Decadal Oscillation for the decadal variations, showing the influence of the tropical Pacific Ocean in the development of streamflow drought conditions and its relevance for potential predictability of hydroclimatic variations over the region.     

A multi‐species dendroclimatic reconstruction of Chilko River streamflow,British Columbia,Canada

Dendroclimatological data were used to reconstruct the discharge history of Chilko River, which drains a glacierized watershed in the Coast Mountains of British Columbia. We correlated ring‐width records from Engelmann spruce (ES) (Picea engelmanni) and mountain hemlock (MH) (Tsuga mertensiana) trees to historical hydroclimate data. Over the period of record, spruce and hemlock radial growth correlates significantly with temperature and snow depth, respectively. We found that a multi‐species approach provided a better model fit and reconstructive power. Using these relationships, we developed generalized linear models for mean June, July, and June‐July discharge. The proxy records provide insights into streamflow variability of a typical Coast Mountains river over the past 240 years and confirm the long‐term influence of the Pacific Decadal Oscillation (PDO) on hydroclimatic regimes in the region. A relationship also exists between the reconstructed June‐July discharge record and the North Pacific (NP) Index, suggesting that winter atmospheric patterns over the North Pacific influence the hydrology of coastal British Columbia. Copyright © 2010 John Wiley & Sons, Ltd.     

CHOSEN: A synthesis of hydrometeorological data from intensively monitored catchments and comparative analysis of hydrologic extremes

Comparative hydrology has been hampered by limited availability of geographically extensive, intercompatible monitoring data on comprehensive water balance stores and fluxes. These limitations have, for example, restricted comprehensive assessment of multiple dimensions of wetting and drying related to climate change and hampered understanding of why widespread changes in precipitation extremes are uncorrelated with changes in streamflow extremes. Here, we address this knowledge gap and underlying data gap by developing a new data synthesis product and using that product to detect trends in the frequencies and magnitudes of a comprehensive set of hydroclimatic and hydrologic extremes. CHOSEN (Comprehensive Hydrologic Observatory Sensor Network) is a database of streamflow, soil moisture, and other hydroclimatic and hydrologic variables from 30 study areas across the United States. An accompanying data pipeline provides a reproducible, semi-automated approach for assimilating data from multiple sources, performing quality assurance and control, gap-filling and writing to a standard format. Based on the analysis of extreme events in the CHOSEN dataset, we detected hotspots, characterized by unusually large proportions of monitored variables exhibiting trends, in the Pacific Northwest, New England, Florida and Alaska. Extreme streamflow wetting and drying trends exhibited regional coherence. Drying trends in the Pacific Northwest and Southeast were often associated with trends in soil moisture and precipitation (Pacific Northwest) and evapotranspiration-related variables (Southeast). In contrast, wetting trends in the upper Midwest and the Rocky Mountains showed few univariate associations with other hydroclimatic extremes, but their latitudes and elevations suggested the importance of changing snowmelt characteristics. On the whole, observed trends are incompatible with a ‘drying-in-dry, wetting-in-wet’ paradigm for climate-induced hydrologic changes over land. Our analysis underscores the need for more extensive, longer-term observational data for soil moisture, snow and evapotranspiration.     

Assessment of a hydrologic model's reliability in simulating flow regime alterations in a changing climate

It is a common practice to employ hydrologic models for assessing present and future states of watersheds and assess the degree of alterations for a range of hydrologic indicators. Previous studies indicate that the hydrologic model may not be able to replicate some of the indicators of interest, which raises questions on the reliability of model simulated changes. Hence, we initiated a study to evaluate the replicability of the streamflow changes by employing the widely used variable infiltration capacity hydrologic model for sub‐basins and mainstem of the Fraser River Basin, Canada. Given that the hydrologic regime of the region is known to be influenced by teleconnections to the Pacific Decadal Oscillation (PDO) and El Niño–Southern Oscillation (ENSO), we used hydrologic responses to the PDO and ENSO states as analogues for evaluating the model's ability to simulate climate‐induced changes. The results revealed that the qualitative patterns of response, such as lower flows for the warm PDO state compared to the cool state, and progressively higher flows for the warm, neutral and cool ENSO states, were generally well reproduced for most hydrologic indicators. Additionally, while the directions of change between the different PDO and ENSO states were mostly well replicated, the magnitude of change for some of the indicators showed considerable differences. Hence, replicability of both magnitude and direction of change need to be carefully examined before using the simulated indicators for assessing future hydrologic changes, and a reliable replication increases the confidence of projected changes. Copyright © 2016 Her Majesty the Queen in Right of Canada. Hydrological Processes. © 2016 John Wiley & Sons, Ltd.     

影响中国北方强降雪事件年际变化的典型环流背景和水汽收支特征分析

基于1961-2014年中国台站观测资料和NECP/NCAR再分析资料,对影响中国北方强降雪事件（日降雪量5 mm及以上,包括大到暴雪）年际变化的典型大尺度环流特征和水汽条件进行了综合分析.结果表明：中国北方强降雪事件主要集中在新疆北部和东北两个地区,而且强降雪日数和降雪量具有高度一致的年际变化特征.中国北方强降雪事件偏多时,对应北大西洋涛动（NAO）和北极涛动（AO）负位相;贝加尔湖上空维持异常低槽区,有利于冷空气的爆发南下;热带印度洋至热带西太平洋上空维持一条异常反气旋带,有利于暖湿气流向北输送;中国北方及以北区域高空为异常西风气流,提供有利的动力抬升条件,使得强降雪易于在中国北方发生;反之亦然.水汽收支分析显示,中国北方西边界和南边界水汽入流增强在强降雪偏多中起着主要贡献.异常西风水汽输送利于新疆北部大到暴雪偏多,异常西南风水汽输送则利于东北地区大到暴雪的发生.进一步研究揭示：与小雪相比,影响中国北方大到暴雪年际偏多的中高纬环流特征相类似,但环流经向度更大;而且大到暴雪与NAO和AO的关系更密切,并更多的受到来自中低纬地区的水汽输送影响.     

Streamflow predictability in the Saskatchewan/Nelson River basin given macroscale estimates of the initial soil moisture status

Abstract

Soil moisture estimates obtained over large spatial areas will become increasingly available through current and upcoming satellite missions and from numerous land surface parameterization schemes run at global- and continental-scale resolutions. The goal of this research was to evaluate the potential for using macroscale estimates of soil moisture for enhancing streamflow forecasts. Towards this research objective, monthly streamflow estimates were obtained from over 50 gauge locations within the Nelson basin, Canada, for the period 1979–1999. For each streamflow record, multiple linear regression models were used to remove components of the streamflow signal related to previous streamflow, climate teleconnections (e.g. ENSO and AO) and snow water equivalence. Correlations were then assessed between the macroscale soil moisture estimates and the residuals of the multiple linear regression analysis over lead times of one, two and three months. At the one- and two-month lead time, statistically significant relationships between soil moisture and the residuals of streamflow are observed over a large proportion of the gauging locations. The number of catchments with statistically significant relationships decreases significantly after two months and particularly in the months of April—June. This study demonstrates that available macroscale estimates of soil moisture have the potential to enhance streamflow prediction, although further study is suggested to improve upon the soil moisture estimates and their application in a forecast system.     

Relative importance of wind and buoyancy forcing for interdecadal regime shifts in the Pacific Ocean

Interdecadal variations in the Northern Hemisphere and the North Pacific have been documented in many studies[1 4]. The connection between the subtropical North Pacific and the tropics is regarded as the most important process triggering and maintaining t…     

Aquifer responses to El Niño-Southern Oscillation, Southwest British Columbia

We used climatological composite analysis to investigate El Ni?o-Southern Oscillation (ENSO) signals in long-term shallow ground water level observations from four wells in the lower Fraser Valley of British Columbia. Significance of differences between warm-phase, cold-phase, and neutral climate states was assessed with a Monte Carlo bootstrap technique. We also considered time series of local precipitation and streamflow for comparison. Composite annual hyetographs suggest that ENSO precipitation impacts are largely limited to winter and spring, with higher and lower rainfall occurring, respectively, under cold-phase and warm-phase episodes. This is consistent with prior work in the region and is found to be directly reflected in both streamflow and ground water level data. The mean magnitude of ENSO terrestrial hydrologic anomalies can be up to approximately 50% of the average seasonal cycle amplitude. ENSO does not appear to systematically affect annual hydrometeorological cycle timing in this study area. However, relative to the surface hydrologic systems considered, aquifers are observed to retain a stronger memory of seasonal ENSO-related precipitation anomalies, with changes potentially extending through the following summer, presumably reflecting storage effects. Most responses appear to be somewhat nonlinear.     

Coherence between lake ice cover, local climate and teleconnections (Lake Mendota, Wisconsin)

Ice duration has shortened and the ice-off date has become earlier for Lake Mendota from 1905 to 2000 as air temperatures have warmed and snowfall has increased. In addition, the ice record has cyclic components at inter-annual and inter-decadal scales. We examined the frequency domain relations between ice, local climate and the teleconnections, Southern Ocean Oscillation (SOI), Pacific Decadal Oscillation (PDO), North Atlantic Oscillation (NAO), and Northern Pacific Index (NP), through a three-tiered analysis of coherence. The coherence results provide evidence of linear relations between the three levels at inter-annual and inter-decadal frequencies. Of the three local climate variables analyzed, namely temperature, snowfall and snow depth, temperature is the variable that most significantly affects ice duration and ice-off date, at both inter-annual and inter-decadal frequencies. The most significant effect of teleconnections on local climate are the effects of PDO on snowfall and snow depth, and SOI on temperature, at inter-annual frequencies, and the effect of NAO on snowfall at inter-decadal frequencies. The teleconnections that most significantly affect ice-cover duration and ice-off date, particularly at inter-decadal frequencies, are the PDO and the NAO. The influence of PDO on ice-cover appears to be transmitted through temperature, while the influence of the NAO appears to be transmitted through temperature and snowfall. A cascading set of links between teleconnections, local climate, and lake ice explain some, but not all, of the dynamics in these time series.     

Atlantic Ocean sea-surface temperatures and regional streamflow variability in the Adour-Garonne basin,France

Abstract

The identification of Atlantic Ocean (AO) climatic drivers may prove valuable in long lead-time forecasting of streamflow in the Adour-Garonne basin in southwestern France. Previous studies have identified the Atlantic Multidecadal Oscillation (AMO) and the North Atlantic Oscillation (NAO) as drivers of European hydrology. The current research applied the singular value decomposition (SVD) statistical method to AO sea-surface temperatures (SSTs) to identify the primary AO climatic drivers of the Adour-Garonne basin streamflow. Annual and seasonal streamflow volumes were selected as the hydrological response, while average AO SSTs were calculated for three different 6-month averages (January–June, April–September and July–December) for the year preceding streamflow. The results identified a region along the Equator as the probable driver of the basin streamflow. Additional analysis evaluated the influence of the AMO and NAO on Adour-Garonne basin streamflow.

Editor Z.W. Kundzewicz; Associate editor H. Aksoy

Citation Oubeidillah, A.A., Tootle, G. and Anderson, S.-R., 2012. Atlantic Ocean sea-surface temperatures and regional streamflow variability in the Adour-Garonne basin, France. Hydrological Sciences Journal, 57 (3), 496–506.     

Interannual variability of annual streamflow and the Southern Oscillation in Costa Rica

Abstract

This study illustrates the association between annual and seasonal streamflow characteristics on six Costa Rican rivers and the Southern Oscillation Index (SOI). Annual discharge from rivers within the Pacific watershed are clearly positively associated with contemporary values of the SOI and experience significant reductions in both mean and variance in El Ninõ years. The considerable practical implications of this finding to a country in which over 60% of national electrical power comes from hydroelectric schemes is illustrated using quantile estimates from various models. Rivers draining towards the Caribbean show less clear and coherent patterns of associations. The observed associations with seasonal flows on some rivers appear to be the opposite of those on the Pacific, and may even vary during the course of a year at a site. The exact nature of the response seems to be closely related to the elevation of the gauge site. The larger the proportion of the basin at elevations above about 500–1000 m the greater the similarity to the Pacific pattern, suggesting that the marked topographic divide between the two coastal watersheds does not correspond to the divide in associations between streamflow and the SOI.     

The response in the Pacific to the sun's decadal peaks and contrasts to cold events in the Southern Oscillation

van Loon et al. [2007. Coupled air–sea response to solar forcing in the Pacific region during northern winter. Journal of Geophysical Research 112, D02108, doi:10.1029/2006JD007378] showed that the Pacific Ocean in northern winter is sensitive to the influence of the sun in its decadal peaks. We extend this study by three solar peaks to a total of 14, examine the response in the stratosphere, and contrast the response to solar forcing to that of cold events (CEs) in the Southern Oscillation. The addition of three solar peak years confirms the earlier results. That is, in solar peak years the sea level pressure (SLP) is, on average, above normal in the Gulf of Alaska and south of the equator, stronger southeast trades blow across the Pacific equator and cause increased upwelling and thus anomalously lower sea surface temperatures (SSTs). Since the effect on the Pacific climate system of solar forcing resembles CEs in the Southern Oscillation, we compare the two and note that, even though their patterns appear similar in some ways, they are particularly different in the stratosphere and are thus due to separate processes. That is, in July–August (JA) of the year leading into January–February (JF) of the solar peak years, the Walker cell expands in the Pacific troposphere, and the stratospheric wind anomalies are westerly below 25 hPa and easterly above, whereas this signal in the stratosphere is absent in CEs. Thus the large-scale east–west tropical atmospheric (Walker) circulation is enhanced, though not to the extent that it is in CEs in the Southern Oscillation, and the solar influence thus appears as a strengthening of the climatological mean regional precipitation maxima in the tropical Pacific. Additionally, CEs have a 1-year evolution, while the response to solar peaks extends across 3 years such that the signal in the Pacific SLP of the solar peaks is similar but weaker in the year leading into the peak and in the year after the peak. The concurrent negative SST anomalies develop during the year before the solar peak, and after the peak the anomalies are still present but are waning. In the stratosphere in solar peaks, the equatorial quasi-biennial oscillation (QBO) is amplified when it is in its westerly phase in the lower stratosphere and easterly phase above; and the QBO is suppressed when in its easterly phase below–westerly phase above. Such an association is not evident in CEs.     

An example of application: The ecological “natural flow regime” paradigm in hydroclimatology

According to the concept of “natural flow regime,” introduced and developed in the 1990's in aquatic ecology, streamflow can be described using five basic characteristics: magnitude, frequency, duration, period of occurrence and variability. A sixth could be added to these, namely, distribution curve. Our study, which focused exclusively on the temporal variability of these six characteristics, had these objectives: (1) to compare their stationarity, (2) to determine the links among these characteristics and (3) to analyze, for the first time, their relationship to six climatic indices (Atlantic Multidecadal Oscillation, Artic Oscillation, North Atlantic Oscillation, Niño3.4, Pacific decadal Oscillation and Southern Oscillation Index). To do this, we used the Vermillon River (2670 km²) as an example, analyzing the streamflow of heavy spring floods (equal to or greater than the annual flood streamflow), as measured between 1934 and 2000.     

The 11-year solar cycle affects the intensity and annularity of the Arctic Oscillation

We investigate the dependence of the Arctic Oscillation (AO) in winter on the solar activity by stratifying the data into overlapping intervals defined by percentiles of the 10.7 cm radio flux. The AO exhibits a complex dependence of its polarity, being weakest under low, but not minimum, solar activity, while strongest in solar maxima. The AO is more/less variable (i.e., more/less active) under a high/low solar activity. Under a moderate solar activity, its Pacific centre weakens and eventually disappears. These effects seem to be real in spite of a potential for mixing the AO with the second principal component due to sampling errors caused by insufficient spacing between the first two eigenvalues. The weakening of the Pacific centre is not a result of coincidence with major volcanic eruptions or specific phases of the El Niño-Southern Oscillation.