Hydroclimatic Data Research Articles

Scale invariance of water stress and scarcity indicators: Facilitating cross-scale comparisons of water resources vulnerability

Several indicators are commonly used to measure the degree of water resources vulnerability (e.g., water stress and scarcity) in different populations and regions. Little is known, however, about how these indicators respond to changes in the scale of data used to derive them. Two of the most widely used water resources vulnerability metrics, conventionally computed for mean annual values at the country level are Falkenmark Index (FI) for per capita water availability and the Criticality Ratio (CR) for water use to availability. This study computes FI and CR values at a wide range of scales and tests for trends with scale in three river basins: Missouri (North America), Danube (Europe) and Ganges (South Asia) Basins. Gridded sub-continental hydro-climatic data sets at 0.5° resolution are used and aggregated at multiple scales from 0.5° to 5.0°. Analytical logic and empirical evidence show that mean grid-cell values of these vulnerability metrics are in fact scale-independent (scale-invariant) for a given basin. When unscaled variables like water availability and use are ratioed to variables that depend on area, such as population, their dependency on scale may be lost and they become spatially scaled variables. For example, grid-cell mean values of water availability are scale dependent, but grid-cell mean values of the ratio of water availability to population (i.e. FI) are not. This implies that, for a particular river basin, average water resources vulnerability computed by FI and CR at one scale should apply to all scales. This has tremendous implications to applied geographic studies of water resources, and is especially interesting since the unscaled variables used to derive the two indices are scale dependent and vary greatly with scale. The paper and findings highlight the multi-scale complexities of water resources and the geographic nature of water resources and vulnerability metrics.

Regional Modeling of Climate Change Impact on Peninsular Malaysia Water Resources

The future projections of climate change by means of global climate models of the Earth provide fundamental coarse-grid-resolution hydroclimate data for studies of the effect of climate change on water resources. This paper reports on a study that was performed during 2001–2006, in which the climate change simulations of the coupled global climate model of the Canadian Center for Climate Modeling and Analysis were downscaled by a regional hydroclimate model of Peninsular Malaysia (RegHCM-PM) to the scale of the subregions and watersheds of Peninsular Malaysia (PM), to assess the effect of future climate change on its water resources. On the basis of the simulations of hydroclimatic conditions during the historical period of 1984–1993 and future periods of 2025–2034 and 2041–2050, this report concludes that the overall mean monthly streamflow is approximately the same during both the future period, and the historical period for most of the watersheds of Peninsular Malaysia, except Kelantan and Pahang. In t...

National Centers for Environmental Prediction – National Center for Atmospheric Research (NCEP–NCAR) reanalyses data for hydrologic modelling on a basin scale

This paper evaluates the National Centers for Environmental Prediction – National Center for Atmospheric Research (NCEP–NCAR) reanalyses hydroclimatic data as an initial check for assessment of hydrologic impacts of climate change at the basin scale. A reanalysis dataset for daily precipitation, maximum temperature, and minimum temperature from the NCEP–NCAR global (NNGR) and regional (North American Regional Reanalysis or NARR) reanalysis project has been used as input into the semidistributed hydrologic model (Hydrologic Engineering Center Hydraulic Modeling System or HEC–HMS) for the period 1980–2005. An extensive analysis has been performed for assessing the performance of the reanalysis data generated flows compared with the observed inputs during May–November. The stream flows generated from the NARR dataset show encouraging results in simulating summertime low flows with less variability and fewer errors. The results indicate that NNGR results are less accurate and highly variable. This study suggests that NARR can be adequately used as an alternative in data-scarce regions.

Streamflow Trends and Climate Variability Impacts in Poyang Lake Basin, China

Under the background of global warming, does the effect of the rising global surface temperature accelerate the hydrological cycle? To address this issue, we use the hydro-climatic data from five sub-basins in Poyang Lake basin in the southeast China over the past 50 years, to investigate the annual and seasonal trends of streamflow and the correlations between streamflow and climatic variables. The Theil–Sen Approach and the non-parametric Mann–Kendall test are applied to identify the trends in the annual and seasonal streamflow, precipitation and evapotranspiration series. It was found that annual and seasonal streamflow of all the stations had increasing trends except Lijiadu station in wet season. Only 37.5% hydro-stations in annual streamflow increased significantly, while most stations increased at 95% significance level in dry season. Trends in annual and seasonal precipitation during the whole period were generally not as significant as those in evapotranspiration. The correlations between streamflow and climate variables (precipitation and evapotranspiration) were detected by the Pearson’s test. The results showed that streamflow in the Poyang Lake basin are more sensitive to changes in precipitation than potential evapotranspiration.

Joint Variability of Global Runoff and Global Sea Surface Temperatures

Abstract Global land surface runoff and sea surface temperatures (SST) are analyzed to identify the primary modes of variability of these hydroclimatic data for the period 1905–2002. A monthly water-balance model first is used with global monthly temperature and precipitation data to compute time series of annual gridded runoff for the analysis period. The annual runoff time series data are combined with gridded annual sea surface temperature data, and the combined dataset is subjected to a principal components analysis (PCA) to identify the primary modes of variability. The first three components from the PCA explain 29% of the total variability in the combined runoff/SST dataset. The first component explains 15% of the total variance and primarily represents long-term trends in the data. The long-term trends in SSTs are evident as warming in all of the oceans. The associated long-term trends in runoff suggest increasing flows for parts of North America, South America, Eurasia, and Australia; decreasing runoff is most notable in western Africa. The second principal component explains 9% of the total variance and reflects variability of the El Niño–Southern Oscillation (ENSO) and its associated influence on global annual runoff patterns. The third component explains 5% of the total variance and indicates a response of global annual runoff to variability in North Atlantic SSTs. The association between runoff and North Atlantic SSTs may explain an apparent steplike change in runoff that occurred around 1970 for a number of continental regions.

Spatial and temporal variation of runoff in the Yangtze River basin during the past 40 years

Frequent floods occur in the Yangtze River basin, where the Three Gorges reservoir has been constructed. However, in recent years, it has been found that droughts have also occurred frequently. For a better understanding of the spatial and temporal variations in runoff in the Yangtze River basin, especially in the upper Three Gorges reservoir area during the past 40 years, a hydro-climate data analysis was carried out together with rainfall-runoff modeling. The trends in precipitation and river discharge were analyzed for the whole Yangtze River basin, offering a comparison upstream and downstream of the Three Gorges Dam. The results showed that both precipitation and discharge along the downstream of the dam had statistically significant increasing trends in summer. However, the upstream area had significant decreasing trends for both precipitation and discharge in autumn. To analyze the spatial-temporal variation of runoff in the upper Yangtze River, a geomorphology-based distributed hydrological model (GBHM) was used for simulating the natural runoff during 1961–2000. It was confirmed that the natural runoff increased in summer and decreased greatly in autumn. This natural change in runoff in the upper Yangtze River basin implies an increasing flood risk in summer and water shortage in autumn.

Characterizing the Hydrology of Shallow Floodplain Lakes in the Slave River Delta, NWT, Canada, Using Water Isotope Tracers

ABSTRACTThe relative importance of major hydrological processes on thaw season 2003 lakewater balances in the Slave River Delta, NWT, Canada, is characterized using water isotope tracers and total suspended sediment (TSS) analyses. A suite of 41 lakes from three previously recognized biogeographical zones—outer delta, mid-delta, and apex—were sampled immediately following the spring melt, during summer, and in the fall of 2003. Oxygen and hydrogen isotope compositions were evaluated in the context of an isotopic framework calculated from 2003 hydroclimatic data. Our analysis reveals that flooding from the Slave River and Great Slave Lake dominated early spring lakewater balances in outer and most mid-delta lakes, as also indicated by elevated TSS concentrations (>0.01 g L−1). In contrast, the input of snowmelt was strongest on all apex and some mid-delta lakes. After the spring melt, all delta lakes underwent heavy-isotope enrichment due to evaporation, although lakes flooded by the Slave River and Great Slave Lake during the spring freshet continued to be more depleted isotopically than those dominated by snowmelt input. The isotopic signatures of lakes with direct connections to the Slave River or Great Slave Lake varied throughout the season in response to the nature of the connection. Our findings provide the basis for identifying three groups of lakes based on the major factors that control their water balances: (1) flood-dominated (n = 10), (2) evaporation-dominated (n = 25), and (3) exchange-dominated (n = 6) lakes. Differentiation of the hydrological processes that influence Slave River Delta lakewater balances is essential for ongoing hydroecological and paleohydrological studies, and ultimately, for teasing apart the relative influences of variations in local climate and Slave River hydrology.

Extreme sediment delivery events recorded in the contemporary sediment record of a montane lake, southern Coast Mountains, British Columbia

The extreme sediment delivery regime of a montane catchment was examined through the analysis of recent lacustrine varve deposits recovered from a high-density sampling program. Years of anomalously high sediment yield from the Green Lake watershed were identified over a 70-year period (1930–2000) based on whole-lake varve deposit volumes. Intra-annual sediment delivery events were categorized and described for those anomalous years using historical hydroclimatic data and the stratigraphic record observed within inflow proximal sediment cores. Extreme sediment delivery coincided with high discharge conditions and elevated sediment availability resulting from (1) rapid glacier recession of the early twentieth century, (2) late-summer and autumn rainstorm-generated floods, and (3) freshet floods caused by unusual snowmelt conditions. The thickness and physical characteristics of varves vary among years that experienced different types of moderate and extreme sediment delivery events in relation to the defined average-regime depositional model. Several hydroclimatic factors can interact to produce composite varve units of anomalous thickness. In some cases, geomorphic events, such as landslides and channel changes, contributed to extreme sediment delivery in the Green Lake catchment. The interaction of these geomorphic effects, coupled with the variable nature of associated hydroclimatic functions, complicate paleoenvironmental assessments based on the lacustrine varve record.

Recent Variations in Temperature, Precipitation, and Streamflow in the Rio Grande and Pecos River Basins of New Mexico and Colorado

Trends in climatic and hydrologic data from the Rio Grande and Pecos River basin are analyzed over an approximately 40-year period (1960 to 2000). Mann-Whitney tests for changes between halves of the record and between more recent decades, and Mann-Kendall tests for trend over the 40 years of record, are applied to monthly averages from 35 temperature stations and 63 precipitation stations. Similarly, the 15 hydrometric stations meeting the criteria of the Hydro-Climatic Data Network are examined using Mann-Whitney and Mann-Kendall tests to 5-day averages of daily mean streamflow. To distinguish regions that exhibit similar patterns of climatic variation, temperature and precipitation results from the Mann-Kendall test are used as inputs to a cluster analysis. Climatic variations in the region are consistent neither through time nor across space. Some areas have demonstrated recent increases in temperature or precipitation while others have displayed decreases in these same elements. In addition, many areas reveal climatic shifts in specific periods of the year that are in marked contrast with the trends observed in other periods and other places. Hydrologic variations are also not spatially homogeneous, but generally indicate higher streamflow, earlier onset to freshet, and generally larger freshet volumes in more recent decades.

Assessing Land Cover Change in Hydro-Climatic Data Network Watersheds Using NALC Imagery

Land cover conversion is known to alter the hydrologic regimes of watersheds. While connections between land cover and runoff are generally known, not all land cover alterations result in detectable changes in streamflow, and the quantity of land cover change required to yield a detectable change in streamflow is unknown over a range of watersheds. The connection between land cover change and streamflow was explored for a Hydro-Climatic Data Network (HCDN) watershed. HCDN is a database of USGS gauged streams commonly used to assess the influence of climatic change on streamflow. Watersheds included in the HCDN have been screened to represent "unimpaired" streamflow. Implicit in this definition is the assumption that land cover is relatively unaltered over the streamflow time series. Imagery from the North American Landscape Characterization (NALC) project was analyzed to detect land cover change from 1972 to 1992 in an Oregon watershed selected from the HCDN. A post-classification change detection yielded a 44% rate of landscape change over 20 years. Changes in land cover classes by dominant soil types were paired with the L-THIA model of Purdue University to quantify the effect of land cover change on runoff. Despite land cover changes, simulations confirmed that runoff remained unchanged. This report summarizes recommended steps for applying NALC imagery to detection of landscape change in other watersheds.

A semi-distributed, physics-based hydrologic model using remotely sensed and Digital Terrain Elevation Data for semi-arid catchments

A practical, hydrologic model (DPHM-RS) is developed for the semi-arid climate of the Canadian Prairies that could adequately account for a river basin's terrain features by sub-dividing it to sub-basins of uneven shapes and sizes (semi-distributed) based on topographic information derived from the digital terrain elevation (DTED) data. Even though computationally modest, DPHM-RS is scientifically vigorous, can effectively assimilate remotely sensed (RS) data, and has most of its parameters determined through RS data and measurements. The hydrologic processes are estimated for each land cover and then aggregated according to percentage of each land cover present within each sub-basin. As evapotranspiration (ET) usually dominates the hydrology of the Canadian Prairies, ET from each land cover is estimated at three levels by the two-source model that separately considers evaporation from soil and plants. The soil moisture at the top active and the transmission zones are estimated by a water budget approach, while the groundwater dynamics by the topographic soil index obtained from DTED. The surface runoff from each sub-basin is routed to the channel network by a kinematic wave response function, and then routed to the basin outlet by the Muskingum-Cunge model. DPHM-RS, is applied to the Paddle River Basin (265 km2) of Central Alberta divided to five sub-basins. It was calibrated with hourly hydroclimatic and RS data collected in the summer of 1996 and validated with data of 1997 and 1998. In both stages, there are good agreements between simulated runoff at the basin outlet with the observed, between simulated surface temperature and net radiation with the observed, between soil moisture and that retrieved from Radarsat-SAR data, and between simulated ET and that estimated by water balance. Encouraging results from these multi-criteria assessments demonstrate the feasibility of semi-distributed, physics-based hydrologic modelling in the dry climate of Canadian Prairies, and the usefulness of RS and DTED data in basin hydrology.

THE INFLUENCE OF CLIMATE VARIATION ON THE ESTIMATION OF LOW FLOWS USED TO PROTECT WATER QUALITY: A NATIONWIDE ASSESSMENT1

ABSTRACT: Historical flow records are used to estimate the regulatory low flows that serve a key function in setting discharge permit limits through the National Pollutant Discharge Elimination System, which provides a nationwide mechanism for protecting water quality. Use of historical records creates an implicit connection between water quality protection and climate variability. The longer the record, the more likely the low flow estimate will be based on a broad set of climate conditions, and thus provides adequate water quality protection in the future. Unfortunately, a long record often is not available at a specific location. This analysis examines the connection between climate variability and the variability of biologically based and hydrologically based low flow estimates at 176 sites from the Hydro‐Climatic Data Network, a collection of stream gages identified by the USGS as relatively free of anthropogenic influences. Results show that a record of 10 to 20 years is necessary for satisfactory estimates of regulatory low flows. Although it is possible to estimate a biologically based low flow from a record of less than 10 years, these estimates are highly uncertain and incorporate a bias that undermines water quality protection.

Low Frequency Streamflow Regimes over the Central United States: 1939–1998

Intra- to multi-decadal (6-30 year) streamflow regimes over the central United States during the late 20th century are identified and investigated here through a two-stage analysis. The first stage ranks mean annual flow rates during 1939-1998, calculates Mann-Whitney U statistics from samples of those rankings over running time windows, and then tests those U statistics for significance. This analysis of the records of 42 Hydro-Climatic Data Network stations over the Great Plains and Midwest reveals consistent patterns of highly ranked annual streamflow during time windows at the end of the century, with most beginning during the late 1960s and early 1970s and ending in either 1997 or 1998. Many of these stations are located in a critical agricultural region known as the Corn Belt. The second stage of analysis compares both the duration of abnormal flow periods and the frequency of hydrological surplus and drought conditions during the high flow years indicated by the first stage, relative to the remaining years of 1939-1998. Among gage stations in the climatologically drier western Corn Belt during the 1980s and 1990s there is a clear tendency toward extended periods of above normal flow, which results in more than a doubling in the average annual frequency of hydrological surplus days relative to previous years. These stations also show more than a 50% reduction in the average annual frequency of hydrological drought days relative to previous years. Similar but less pronounced shifts in hydrological regime are evident in the central and eastern Corn Belt, and in the Mississippi River at Vicksburg during 1973-1998. These results indicate that many areas of the central United States have shifted toward a climate regime of relative hydrological surplus during the closing decades of the 20th century.

Developing a Watershed Characteristics Database to Improve Low Streamflow Prediction

Information regarding topographic, meteorologic, geologic, and geomorphic characteristics is increasingly available in spa- tially explicit digital formats. Of interest is whether enhanced spatial processing of newly available digital grids can lead to new estimators of watershed characteristics which may in turn, improve our ability to predict extreme hydrologic events. Regional hydrologic models of low-flow processes often produce estimators with unacceptably large errors. Using a continuous digital elevation model ~DEM! of the conterminous United States, watershed boundaries were developed for the streamflow gauges of the USGS's Hydro-Climatic Data Network. Using these watershed boundaries, many watershed characteristics were developed from digital grids, including: the original DEM, the USDA's State Soil Geographic grids, and the Spatial Climate Analysis Service's orographically weighted precipitation and temperature grids of varying spatial and temporal resolution. Digital processing of grids leads to improvements in estimation and reproducibility of spatial statistics over traditional manual processing approaches. Low-flow regional regression models were developed for regions across the conterminous United States. Inclusion of the new watershed characteristics led to improvements in regional regression models for all regions. The inclusion of hydrogeologic indices, in particular a new smoothed baseflow recession constant estimator, led to dramatic improvements in low-flow prediction.

Channel changes in the Jarama and Tagus rivers (central Spain) over the past 500 years

Long-term channel changes of the Tagus and the Jarama Rivers in central Spain were studied in relation to variations in hydroclimatic factors, such as rainfall and flooding, and also with respect to human activities undertaken in their valleys. Data were taken from historical (1580–1823) and topographical (1877–1988) maps, as well as aerial photographs (1945–1999). The available hydroclimatic data consists of a series of monthly rainfall totals (1859–1994) and mean river flow values recorded at gauging stations (1911–1985). In addition, a historical flood record (1550–1947) was produced from documentary sources. Some of the data was incorporated into a geographical information system (GIS) to quantify the changes in the course of the rivers. The results show there have been two distinct periods: before and after human intervention in the river system, which took place around 1950. During the earlier period (1550–1950), a correlation exists between climate, frequency and magnitude of flooding and changes in fluvial geomorphology. Between 1860 and 1892 an increase in flood frequency and magnitude occurred, which produced half of the cut-offs recorded in the study area between 1823 and 1877. The meanders length ( L), width ( W) and radius of curvature (RC) of the Tagus River have decreased since 1750. However, those of the Jarama reached their maximum values during flood periods. Both rivers have different geomorphological responses during flood events, which can explain these different trends. Floods in the Jarama not only led to the cut-offs, but also enlarged the channel size ( L, W and RC). In the second period (1956—present), flow regulation via dams and gravel mining modified the system completely and impeded the natural development of these rivers.

Modeling the Dynamics of Long-Term Variability of Hydroclimatic Processes

The stochastic analysis, modeling, and simulation of climatic and hydrologic processes such as precipitation, streamflow, and sea surface temperature have usually been based on assumed stationarity or randomness of the process under consideration. However, empirical evidence of many hydroclimatic data shows temporal variability involving trends, oscillatory behavior, and sudden shifts. While many studies have been made for detecting and testing the statistical significance of these special characteristics, the probabilistic framework for modeling the temporal dynamics of such processes appears to be lacking. In this paper a family of stochastic models that can be used to capture the dynamics of abrupt shifts in hydroclimatic time series is proposed. The applicability of such “shifting mean models” are illustrated by using time series data of annual Pacific decadal oscillation (PDO) indices and annual streamflows of the Niger River.

Decision Support System for Adaptive Water Supply Management

Recent advances in computer technology and water resource modeling, availability of real-time hydroclimatic data, and improvements in our ability to develop user-friendly graphical model interfaces have led to significant growth in the development and application of decision support systems ~DSSs! for water resource systems. This study provides an example of the development of a real-time DSS for adaptive management of the reservoir system that provides drinking water to the Boston metropolitan region. The DSS uses a systems framework to link watershed models, reservoir hydraulic models, and a reservoir water quality model with linear and nonlinear optimization algorithms. The DSS offers the ability to optimize daily and weekly reservoir operations toward four objectives based on short-term climate forecasts: ~1! maximum water quality, ~2! ideal flood control levels, ~3! optimum reservoir balancing, and ~4! maximum hydropower revenues. Case studies document the value of the DSS as an enhancement of current rule curve operations. The study shows that simple tools, in this case, familiar spreadsheet software, can be used to improve system efficiencies.

A hydroclimatic threshold for landslide initiation on the North Shore Mountains of Vancouver, British Columbia

Landslides triggered by rainfall are the cause of thousands of deaths worldwide every year. One possible approach to limit the socioeconomic consequences of such events is the development of climatic thresholds for landslide initiation. In this paper, we propose a method that incorporates antecedent rainfall and streamflow data to develop a landslide initiation threshold for the North Shore Mountains of Vancouver, British Columbia. Hydroclimatic data were gathered for 18 storms that triggered landslides and 18 storms that did not. Discriminant function analysis separated the landslide-triggering storms from those storms that did not trigger landslides and selected the most meaningful variables that allow this separation. Discriminant functions were also developed for the landslide-triggering and nonlandslide-triggering storms. The difference of the discriminant scores, ΔCS, for both groups is a measure of landslide susceptibility during a storm. The variables identified that optimize the separation of the two storm groups are 4-week rainfall prior to a significant storm, 6-h rainfall during a storm, and the number of hours 1 m 3/s discharge was exceeded at Mackay Creek during a storm. Three thresholds were identified. The Landslide Warning Threshold (LWT) is reached when ΔCS is −1. The Conditional Landslide Initiation Threshold (CTL I ) is reached when ΔCS is zero, and it implies that landslides are likely if 4 mm/h rainfall intensity is exceeded at which point the Imminent Landslide Initiation Threshold (ITL I ) is reached. The LWT allows time for the issuance of a landslide advisory and to move personnel out of hazardous areas. The methodology proposed in this paper can be transferred to other regions worldwide where type and quality of data are appropriate for this type of analysis.

A REVISED VERSION OF PnET‐II TO SIMULATE THE HYDROLOGIC CYCLE IN SOUTHEASTERN FORESTED AREAS1

ABSTRACT: The PnET‐II model uses hydroclimatic data on maximum and minimum temperatures, precipitation, and solar radiation, together with vegetation and soil parameters, to produce estimates of net primary productivity, evapotranspiration (ET), and runoff on a monthly time step for forested areas. In this study, the PnET‐II model was employed to simulate the hydrologic cycle for 17 Southeastern eight‐digit hydrologic unit code (HUC) watersheds dominated by evergreen or deciduous tree species. Based on these control experiments, model biases were quantified and tentative revision schemes were introduced. Revisions included: (1) replacing the original single soil layer with three soil layers in the water balance routine; (2) introducing calibrating factors to rectify the phenomenon of overestimation of ET in spring and early summer months; (3) parameterizing proper values of growing degree days for trees located in different climate zones; and (4) adjusting the parameter of fast‐flow (overland flow) fraction based on antecedent moisture condition and precipitation intensity. The revised PnET‐II model, called PnET‐II3SL in this work, substantially improved runoff simulations for the 17 selected experimental sites, and therefore may offer a more powerful tool to address issues in water resources management.

Recent Trends in Precipitation and Streamflow in the Rio Puerco Basin

Abstract River systems in semiarid regions are susceptible to rapid and dramatic channel erosion and arroyo formation. Climate plays an important role in arroyo development through changes in precipitation intensity, seasonality, and variability. Here, trends in precipitation and streamflow at the annual, monthly, and daily timescales for the last 50 yr are analyzed for the Rio Puerco Basin in northwestern New Mexico, and connections with recent watershed and channel changes are examined. The increasing trend in annual precipitation in the basin is shown to be part of larger-scale climatic variability that affects the U.S. Southwest region, which is associated with climatic anomalies in the northern Pacific. Results of hydroclimatic data analyses point to a general increase in wetness in nonsummer months—an increase in the number of rainy days and in the frequency of flow days in the stream system is observed. There are substantial shifts in the distributions of both daily precipitation and streamflow. Ra...