Trends In Annual Streamflow Research Articles

Modeling streamflow responses to land use and land cover change using MIKE SHE model in the upper Omo Gibe catchment of Ethiopia

AbstractThe land use and land cover (LULC) changes in the upper Gibe catchment were studied intricately using the MIKE SHE model and analyzed through statistical tests. The Mann–Kendall test was used to identify potential trends, while the Pettit test was used to detect abrupt changes in rainfall, temperature, and streamflow. A set of three maps of LULC change (1990, 2003, and 2018) was developed to observe how they affect the hydrological pattern of the catchment. Statistical analyses were conducted at mean annual time scales to establish relationships among the anomalies. It has been noted that certain temperature gauges showed statistically significant increases in temperature. Change points in the 1980s and 1990s were identified during the study period. The annual streamflow trends displayed an increasing trend that was not that significant. LULC changes contributed to increased surface runoff, attributed to agricultural, settlement, and water body expansion, as well as reductions in bare land, forest, shrubland, and grassland. The MIKE SHE model performed well during both the calibration and validation periods on the monthly time scale. The alterations in LULC had a noticeable impact on stream flows during both wet and dry seasons, resulting in increased mean monthly stream flows during the wet season and decreased flows during the dry season. The MIKE SHE study and related statistical analysis is quite a different method to perceive the results.

Spatiotemporal Analysis of Hydrometeorological Factors in the Source Region of the Dongting Lake Basin, China

The Dongting Lake basin, located in the middle Yangtze River region, has long been under the threat of climate change. However, there has been a lack of comprehensive analysis and research on the long-term trends and interactions among hydrometeorological factors within the region. To address this gap, this study collected data from 31 meteorological stations in the region and employed statistical analysis methods, including the non-parametric Mann–Kendall test, Sen’s slope test, and cross-wavelet analysis. The results revealed significant increases in temperatures, especially in the spring season, while summer, winter, and annual rainfall also exhibited a significant increase. However, spring and autumn rainfall showed a non-significant decrease, and there was a clear decreasing trend in annual streamflow. Interestingly, evaporation demonstrated a significant increasing trend. The annual average temperature and annual runoff exhibited approximately negative correlations in the 6–10-year resonance period and positive correlations in the 4–6-year resonance period. There are significant positive resonance periods in the relationship between annual precipitation and annual runoff within the range of 0–12 years, indicating that precipitation has a substantial impact and serves as the primary source of runoff. Furthermore, there was a transition between “abundance” and “dry” periods in the annual runoff around 4 a, occurring before and after 1973 and 2005. The change points in annual precipitation and runoff were identified as 1993 and 1983.

Effects of Vegetation Restoration on the Hydrological Regimes of the Chinese Loess Plateau: A Comparative Analysis of Forested and Less-Forested Catchments

Large-scale vegetation restoration can significantly affect catchment hydrology. Assessing the impact of vegetation restoration on hydrological regimes is important for water resource management. We chose three less-forested catchments (LFCs, forested area <30%) undergoing major vegetation restoration, i.e., Wuqi, Zhidan, and Liujiahe, and two forested reference catchments (FCs, forested area >77%) that have had secondary forests for more than 150 years, i.e., Zhangcunyi and Huangling, of the Beiluo River basin located in the Loess Plateau (LP) to compare and analyze the stationary and variation characteristics of streamflow and its components from 1958 to 2019. Results show that the mean annual streamflows were 25.07~34.21 and 21.62~48.02 mm in the LFCs and FCs, respectively. The mean streamflow in the LFCs decreased by 50% on average from before the year 2000 to after. The decreasing trend of high flows and increasing trend of low flows is represented in the daily flow duration curves of the LFCs. The result of baseflow separation shows that the average percentages of baseflow in the streamflow were 31.89~43.36% in the LFCs and 58.23~60.14% in the FCs. The Mann–Kendall tests showed significant decreasing trends in annual streamflow (−0.27~−0.70 mm/a) and stormflow (−0.29~−0.64 mm/a) in the LFCs from 1958 to 2019, while the baseflow exhibited increasing trends except for in the Zhidan catchment. The seasonal streamflow and stormflow showed significant decreasing trends in the summer and non-flood season, while the winter and non-flood season’s baseflow increased in LFCs. In FCs, however, the streamflow and its components showed only slight fluctuations over the study period in annual trends, decadal variability, and seasonal trends over the study period, suggesting that FCs have stable hydrological regimes. These results indicate that 20 years of large-scale vegetation restoration greatly influenced hydrological regimes by reducing stormflow and increasing baseflow, and played an important role in streamflow regulation. Conversely, areas with well-preserved vegetation can effectively mitigate the effects of weather and other factors on runoff with stable hydrological regimes. This study can help vegetation restoration and water resource management on the LP.

Complex streamflow responses to climate warming in five river basins in South Yakutia, Russia

The climate is warming much faster than the global average at the northern mid–high latitudes, leading to intensified hydrological cycles. However, it is unclear whether the response of streamflow to climate change is uniform across river basins with areas of 104–105 km2. In this study, monthly streamflow data from five river basins (Bol’shoy Patom, Chara, Olekma, Timpton, and Uchur) and gridded monthly temperature and precipitation data from the Russian South Yakutia at 53.5–61.5°N were analysed to investigate changes in their annual streamflow from 1934 to 2019 and their responses to climate warming. The results showed significant increasing trends in air temperature for all five basins at rates of 0.20°C–0.22°C/decade (p < 0.001), with faster warming after the 1980s. Apart from the Uchur River Basin, increasing trends in annual precipitation were observed in the other four river basins at rates of 9.3–15.7 mm/decade (p < 0.01). However, temporal changes in streamflow were much more complex than those in air temperature and precipitation among the five basins. Only two of the five basins showed significant increasing trends in annual streamflow with change rates of 17.1 mm/decade (p < 0.001) for the Chara River and 7.7 mm/decade (p < 0.05) for the Olekma River. Although the other three basins showed slightly increasing trends in annual streamflow (1.8–4.0 mm/decade), these trends did not pass significance tests (p > 0.05). By analysing the temperature-precipitation-streamflow relationships, we determined that the annual streamflow positively responds to precipitation, while winter streamflow is most sensitive to temperature. With climate warming, the streamflow during the winter period (October-April) increased significantly in four of the five river basins at rates of 1.4–3.1 mm/decade (p < 0.001), suggesting that warming-induced permafrost thawing increases baseflow. Although the streamflow response of large Siberian rivers to climate change is consistent, our results suggest that the streamflow response to climate change in relatively small river basins (104–105 km2) is much more complex.

Upper Gila, Salt, and Verde Rivers: Arid Land Rivers in a Changing Climate

Abstract The major tributary of the lower Colorado River, the Gila River, is a critical source of water for human and natural environments in the southwestern United States. Warmer and drier than the upper Colorado River basin, with less snow and a bimodal precipitation regime, the Gila River is controlled by a set of climatic conditions that is different from the controls on upper Colorado River flow. Unlike the Colorado River at Lees Ferry in Arizona, the upper Gila River and major Gila River tributaries, the Salt and Verde Rivers, do not yet reflect significant declines in annual streamflow, despite warming trends. Annual streamflow is dominated by cool-season precipitation, but the monsoon influence is discernable as well, variable across the basin and complicated by an inverse relationship with cool-season precipitation in the Salt and Verde River basins. Major multiyear streamflow droughts in these two basins have frequently been accompanied by wet monsoons, suggesting that monsoon precipitation may partially offset the impacts of a dry cool season. While statistically significant trends in annual streamflow are not evident, decreases in autumn and spring streamflow reflect warming temperatures and some decreases in spring precipitation. Because climatic controls vary with topography and the influence of the monsoon, the impact of warming on streamflow in the three subbasins is somewhat variable. However, given relationships between climate and streamflow, current trends in hydroclimate, and projections for the future, it would be prudent to expect declines in Gila River water supplies in the coming decades. Significance Statement This research investigates the climatic controls on the Gila River and its major tributaries, the Verde and Salt Rivers, to gain insights on how trends in climate may impact future water supply. The Gila River is the major tributary of the lower Colorado River, but, unlike the situation for the upper Colorado River, no significant decreasing trends in annual streamflow are evident despite warming temperatures. Climate–streamflow relationships are more complex in this part of the Colorado River basin, and several factors may be buffering streamflow to the impact of warming. However, given the key climatic controls on streamflow, current and emerging trends in climate, and projections for the future, declines in streamflow should be expected in the future.

Streamflow trends during recent decades at some near-natural catchments in Iran

ABSTRACT In this study, we assessed the impacts of climate variations on streamflow in 28 near-natural catchments in Iran. To this end, we analysed the trend of annual streamflow, precipitation, and temperatures using the Mann-Kendall test and Sen’s slope between water years 1982 and 2011. We evaluated the frequency of precipitation in different classes, i.e. below 5, 5–10, 10–15, and above 15 mm/day. Our results indicate a decline in streamflow at 25 catchments, at a rate of −5.66 to −0.19 mm/year. The annual precipitation amount did not decrease significantly, while the frequency of light precipitation events (<5 mm/day) increased. About 60% of the upward trend was significant. Mean temperature increased at all studied catchments, at an average rate of 0.055°C/year. In short, our results indicate that increases in temperature and the frequency of light precipitation events are two leading factors in streamflow reduction across studied catchments.

Quantitative assessment of hydrological alteration over multiple periods caused by human activities at the Jingjiang Three Outlets, China

Abstract The Jingjang Three Outlets (JTO) play a major role in the water-sediment transport from the Yangtze River to Dongting Lake. The hydrological regimes at the JTO (Songzi, Taiping, and Ouchi) had been changed due to the Jingjiang Cutoffs (JC), the Gezhou Dam (GD), and the Three Gorges Dam (TGD). Based on hydrological data from 1955 to 2019, the variation trend in annual streamflow was detected using three techniques, and the hydrological alteration was assessed with the Range of Variability Approach. Conclusions are as follows: (1) the inflection points consistent with human activities and the time series were divided into periods of P1 (1955–1971), P2 (1972–1985), P3 (1986–2002), and P4 (2003–2019); (2) human activities made a greater contribution to streamflow change than climate change; (3) the hydrological alteration degree caused by the JC, GD, and TGD projects were 56%, 47%, and 52% at the Songzi outlet; 57%, 41%, and 57% at the Taiping outlet; and 57%, 41%, and 57% at the Ouchi outlet; and (4) the ability of division from the Yangtze River to Dongting Lake is weakening and the hydrological regimes at the JTO are deteriorating due to the JC, GD, and TGD, resulting in negative impacts on the biotic composition, structure, and function of riparian ecosystems. This study provides useful insight for ecosystem protection under hydrological alteration.

Freeze-Thaw cycle representation alters response of watershed hydrology to future climate change

Hydrologic models are widely used for projecting influences of changing climate on water resources. In this study, we compared the original Soil and Water Assessment Tool (SWAT) model and an enhanced version of SWAT model with physically based Freeze-Thaw cycle representation (SWAT-FT) for simulating future annual ET, stream flow, water yield, surface runoff, and subsurface runoff in the Upper Mississippi River Basin (UMRB). SWAT-FT projected fewer frozen days than the original SWAT model due to its better representation of snow cover insulation effects. Both models derived declining trends in annual streamflow and terrestrial water yield in the late 21st century due to increased ET under warmer climate. However, these two models exhibited contrasting mechanisms underlying the streamflow decline. For original SWAT model, the decrease in surface runoff was the major driver, while for SWAT-FT, reduced subsurface runoff was the main cause. In general, the original SWAT model predicted more surface runoff and less subsurface runoff than SWAT-FT. Further geospatial inspection shows large discrepancies between these two models, particularly in the northern colder parts of the UMRB, where the maximum differences in annual surface and subsurface runoff reached 130 mm yr−1 and 140 mm yr−1, respectively. Collectively, the results demonstrate the importance of accounting for Freeze-Thaw cycles for reliable projection of future water resources.

Flow regime changes in three catchments with different landforms following ecological restoration in the Chinese Loess Plateau

The Chinese Loess Plateau is known as one of the most severe soil erosion regions in the world. Two ecological restoration projects, i.e., the integrated soil conservation project since the 1970s and the “Grain for Green” project since 1999, have been progressively implemented to control the soil erosion in this area. Ecological restoration has greatly changed flow regime over the past five decades. However, the mechanism of how flow regime responds to ecological restoration among landforms remains poorly understood. In this study, we investigated the temporal dynamics of flow regime in three catchments, i.e., Wuqi, Honghe and Huangling hydrological stations, respectively representing the loess hilly-gully, loess table-gully and rocky mountain (covered by secondary forest) areas in the Chinese Loess Plateau, using daily hydrological data during the 1960s–2010s. The nonparametric Mann-Kendall test, Pettitt’s test and daily flow series were used to investigate the changes of flow regime. Significantly negative trends of annual streamflow were detected at the Wuqi and Honghe stations, except for the Huangling station. The annual baseflow at the Wuqi station showed a significantly positive trend whereas a significantly negative trend was observed at the Honghe station, and there was no significant trend at the Huangling station. It was interesting that baseflow index significantly increased during the whole period in all catchments. However, the trends and change points of daily flow series derived by different percentages of exceedance and extreme series in different consecutive days varied among individuals. Based on the change points analysis of annual streamflow, we divided data series into three periods, i.e., the baseline period (from 1959 and 1963 to 1979, PI), the integrated soil conservation period (1980–1999, PII) and the “Grain for Green” period (2000–2011, PIII). We found that streamflow decreased due to the reduction of high streamflow (exceeding 5% of time within a year) and median streamflow (50%) in PII and PIII at the Wuqi and Honghe stations. However, low flow (95%) increased in PII and PIII at the Wuqi station while decreased at the Honghe station. Streamflow change at the Huangling station was more stable, thus potentially resulting in much less soil erosion in the forestry area than in the other areas. The great improvement in ecological environment on the Chinese Loess Plateau revealed the advantages of ecological restoration in reducing flood amount and compensating streamflow at a regional scale.

Is there an underestimation of long-term variability of streamflow across the continental United States?

Analysis of the long-term variability of terrestrial streamflow is important for a wide range of studies in hydroclimatology and environment. However, the common practice of detecting only the monotonic trend cannot actually reflect the long-term variability and change in streamflow, thus resulting in an insufficient or biased understanding. This study focuses on the non-monotonic trends of streamflow and its spatial variability across the continental United States (US). Annual streamflow data observed during 1951–2002 at 530 stations across the continental US are studied. The discrete wavelet spectrum (DWS) is used to detect the non-monotonic trend of streamflow and evaluate its statistical significance. The results indicate significant non-monotonic trends in annual streamflow at 172 stations in the northeast Zone and the northern part of the southeast Zone (in the regions east of 100°W). However, considering only the monotonic trends (being significant at only 38 stations) causes a biased understanding of the long-term variability of streamflow in the northeast zone. The results also reveal that the non-monotonic trend of streamflow in the continental US was mainly controlled by the climatic conditions and that the effects of landscape conditions were weak. The average aridity index (AI) of 0.86–1.35 and its DWS-based significance level >0.1 can indicate the significant non-monotonic trend of streamflow at 95% confidence level. The regions that can meet the above two conditions account for 16% of the global terrestrial surfaces. By considering non-monotonic trends, the change ratio of streamflow is found to be double of that of AI, while similar change ratios are obtained from the monotonic trend results, as the reason of significant underestimation. Due to the partly equal roles of low-frequency oscillation and monotonic trend, identification of the non-monotonic trend should be more desirable for the detection and attribution of the long-term variability and change in streamflow.

On the cumulative dam impact in the upper Changjiang River: Streamflow and sediment load changes

Climate change and anthropogenic activities such as dam construction alter basin-scale hydrological regime of a river. The upper Changjiang River (uCR) stands out as one of the most heavily dammed rivers in the world after the construction of the Three Gorges Dam (TGD) and other large dams in its mainstem. Quantification of the cumulative dam impact is prerequisite for better river management. In this work, we provide a rigorous appraisal of the changes in streamflow, sediment load, and sediment composition at multiple time scales throughout the uCR based on data in 1950–2017. We observed that a decreasing trend in annual streamflow has emerged since 2015 at Yichang, the outlet of the uCR basin, although the changes were statistically insignificant for the first 65 years. The annual sediment load has decreased progressively and substantially, e.g., by 97% in 2010s compared to 1950s at Yichang. The Three Gorges Dam and the new large dams in the upstream mainstem accelerated the sediment load reduction in 2003 and 2014, respectively. As a result, the suspended sediment became finer, with a decrease in mean diameter from 17 μm in the 1960s to 8 μm in the 2010s at Yichang. We established a reservoir storage capacity index, which is the ratio of the total reservoir storage capacity to annual streamflow, and identified a threshold of 4% larger than which the cumulative dam impact will induce profound sediment load reduction. We concluded that climate change and anthropogenic activities, in particular the large dams in the mainstem, have transformed the uCR system from a turbulent and muddy river to a placid one, which can affect fluvial processes as well as aquatic ecosystems by altering sediment and nutrient concentrations and ratios. These hydro-morphological changes merit the urgent attention of concerned authorities.

Streamflow change on the Qinghai-Tibet Plateau and its impacts

The Qinghai-Tibet Plateau (QTP), also often called the Third Pole, is considered the Water Tower of Asia because it is the source of many major Asian rivers. The environmental change on the QTP can affect the climate system over the surrounding area, and the changes in glacier and river streamflow on the QTP will lead to cascading impacts in downstream area where billions of people live. This paper reviews the hydrological observations and streamflow changes of the major Asian rivers originating from the QTP. From the 1950s to the beginning of the 21st century, streamflow on the QTP overall shows large interannual variations but no significant trends. The monthly mean streamflows during the flooding seasons are the largest in the 1960s for the outlet stations on the QTP. Annual streamflow in the source region of the Yellow River decreased while that in the source region of the Yangtze River increased slightly. No significant trends of annual streamflow have been reported for the other river source regions. The mean streamflows during peak season are relatively large in the 2000s at the river source region (upper reaches) of most rivers on the QTP. An increasing trend of streamflow in spring has been found in the upper reaches of the Yellow River, the Lancang River, the Tuotuo River (of the Yangtze River), and the Lhasa River (of the Yarlung Zangbo River). The largest month of streamflow often appears in July for most stations, but in August at the Lhasa and Nuxia stations which are located in the Yarlung Zangbo River. Streamflow changes on the QTP could be mainly attributed to changes in snow and ice, as little influence from direct human activities were found. However, the examination of the streamflow changes largely relies on the hydrological observations. So far, due to data unavailability, we are still unclear about the long-term change in the streamflow on the QTP, especially the changes in recent years. The changes in ice and snow pack on the QTP could have significant impact on the downstream water resources and ecosystem. As more water resources have been generated from ice/snow melting, from a long-term perspective, water resources would be reduced along with shrinking and disappearing glaciers. Hydrological projections under future climate change suggest that streamflow in most river source regions would increase along with precipitation and increases in ice/snow melting, and hydrological extremes such as flooding would occur more frequently. Large uncertainties across Generic Circulation Models (GCMs) and hydrological models have been found in future projections of streamflow on the QTP. Reduction of ice/snow melting would aggravate the water stress conditions for both the ecosystem and human society on the QTP and its downstream areas. Sparse hydrometeorological observations in the past, particularly in the remote region of the QTP, are a major limiting factor to studies on streamflow change and its impacts. Further efforts are urgently needed to combine the advanced observation and modeling technologies to improve the observation and simulation capabilities of the water cycle over the QTP, and to provide scientific and technological support for coping with the accelerated ice/snow melting, increasing hydrological extremes and their impacts over the QTP.

Impact of climate change on surface water availability and crop water demand for the sub-watershed of Abbay Basin, Ethiopia

In the present study, climate change effects on surface water availability and crop water demand (CWD) were evaluated in the Birr watershed (a sub-watershed of Abbay Basin), Ethiopia. The Coordinated Regional Climate Downscaling Experiment (CORDEX)-Africa data output of Hadley Global Environment Model 2-Earth System (HadGEM2-ES) was selected under the representative concentration pathways (RCP) scenarios. The seasonal and annual streamflow trends in the watershed were assessed using the Mann–Kendall (MK) test and Sen’s slope at 5% significance level. The surface water availability was assessed using the Hydrologiska Byrans Vattenbalansavdelning (HBV) model. The HBV model showed a satisfactory performance during calibration (R2 = 0.89) and validation (R2 = 0.85). The future water availability was simulated under climate change scenarios. The future projected streamflow indicates that minimum flow may decrease under RCP4.5 and RCP8.5 scenarios, revealing significant downward shifts in the years 2035 and 2055, respectively. Similarly, the 1 day and 7 days maximum flow under RCP8.5 and 90 days flow under RCP4.5 are expected to decrease significantly and a considerable shift may occur in the 2060s and 2030s, respectively. Contrarily, both the minimum and maximum flow may not change significantly under the RCP2.6 scenario. Current and future water demand for the maize crop was estimated using the CROPWAT. The result indicated that irrigation water requirement (IWR) for maize crop may be increased throughout the growing periods, especially, during the development stage. Therefore, this study may contribute to the planning and implementation of the sustainable water resources development strategies and help to mitigate the consequences of climatic change, especially on commonly grown crops in the region.

Quantifying the Performances of the Semi-Distributed Hydrologic Model in Parallel Computing—A Case Study

The research features how parallel computing can advance hydrological performances associated with different calibration schemes (SCOs). The result shows that parallel computing can save up to 90% execution time, while achieving 81% simulation improvement. Basic statistics, including (1) index of agreement (D), (2) coefficient of determination (R2), (3) root mean square error (RMSE), and (4) percentage of bias (PBIAS) are used to evaluate simulation performances after model calibration in computer parallelism. Once the best calibration scheme is selected, additional efforts are made to improve model performances at the selected calibration target points, while the Rescaled Adjusted Partial Sums (RAPS) is used to evaluate the trend in annual streamflow. The qualitative result of reducing execution time by 86% on average indicates that parallel computing is another avenue to advance hydrologic simulations in the urban-rural interface, such as the Boise River Watershed, Idaho. Therefore, this research will provide useful insights for hydrologists to design and set up their own hydrological modeling exercises using the cost-effective parallel computing described in this case study.

Analysis of trends in annual streamflow to the Arctic Ocean

AbstractThere is increasing interest in the magnitude of the flow of freshwater to the Arctic Ocean due to its impacts on the biogeophysical and socio‐economic systems in the north and its influence on global climate. This study examines freshwater flow based on a dataset of 72 rivers that either directly or indirectly contribute flow to the Arctic Ocean or reflect the hydrologic regime of areas contributing flow to the Arctic Ocean. Annual streamflow for the 72 rivers is categorized as to the nature and location of the contribution to the Arctic Ocean, and composite series of annual flows are determined for each category for the period 1975 to 2015. A trend analysis is then conducted for the annual discharge series assembled for each category. The results reveal a general increase in freshwater flow to the Arctic Ocean with this increase being more prominent from the Eurasian rivers than from the North American rivers. A comparison with trends obtained from an earlier study ending in 2000 indicates similar trend response from the Eurasian rivers, but dramatic differences from some of the North American rivers. A total annual discharge increase of 8.7 km3/y/y is found, with an annual discharge increase of 5.8 km3/y/y observed for the rivers directly flowing to the Arctic Ocean. The influence of annual or seasonal climate oscillation indices on annual discharge series is also assessed. Several river categories are found to have significant correlations with the Arctic Oscillation, the North Atlantic Oscillation, or the Pacific Decadal Oscillation. However, no significant association with climate indices is found for the river categories leading to the largest freshwater contribution to the Arctic Ocean.

Understanding land use and cover change impacts on run‐off and sediment load at flood events on the Loess Plateau, China

AbstractThe Loess Plateau has been experiencing large‐scale land use and cover changes (LUCCs) over the past 50 years. It is well known about the significant decreasing trend of annual streamflow and sediment load in the catchments in this area. However, how surface run‐off and sediment load behaved in response to LUCC at flood events remained a research question. We investigated 371 flood events from 1963 to 2011 in a typical medium‐sized catchment within the Plateau in order to understand how LUCC affected the surface run‐off generation and sediment load and their behaviours based on the analysis of return periods. The results showed that the mean annual surface run‐off and sediment load from flood events accounted for 49.6% and 91.8% of their mean annual totals. The reduction of surface run‐off and associated sediment yield in floods explained about 85.0% and 89.2% of declines in the total annual streamflow and sediment load, respectively. The occurrences of flood events and peak sediment concentrations greater than 500 kg/m3showed a significantly downward trend, yet the counterclockwise loop events still dominated the flood event processes in the catchment. The results suggest that LUCC over the past 50 years resulted in significant changes in the water balance components and associated soil erosion and sediment transportation in the catchment. This was achieved mainly by reducing surface run‐off and sediment yield during floods with return period of less than 5 years. Run‐off–sediment load behaviour during the extreme events with greater than 10‐year return periods has not changed. Outcomes from this study are useful in understanding the eco‐hydrological processes and assisting the sustainable catchment management and land use planning on the Loess Plateau, and the methodologies are general and applicable to similar areas worldwide.

Ecohydrological Index, Native Fish, and Climate Trends and Relationships in the Kansas River Basin.

This study quantified climatological and hydrological trends and relationships to presence and distribution of two native aquatic species in the Kansas River Basin over the past half-century. Trend analyses were applied to indicators of hydrologic alteration (IHAs) at 34 streamgages over a 50-year period (1962-2012). Results showed a significant negative trend in annual streamflow for 10 of 12 western streamgages (up to -7.65 mm/50 yr) and smaller negative trends for most other streamgages. Significant negative trends in western Basin streamflow were more widespread in summer (12 stations) than winter or spring (6 stations). The negative-trend magnitude and significance decreased from west to east for maximum-flow IHAs. Minimum- flow IHAs, however, significantly decreased at High Plains streamgages but significantly increased at Central Great Plains streamgages. Number of zero-flow days showed positive trends in the High Plains. Most streamgages showed negative trends in low- and high-flow pulse frequency and high-flow pulse duration, and positive trends in low-flow pulse duration. These results were consistent with increasing occurrence of drought. Shift in occurrence from present (1860-1950) to absent (2000-2012) was significantly related (p<0.10) to negative trends of 1-day maximum flows (both species) and indices associated with reduced spawning-season flows for Plains Minnow and shifting annual-flow timing and increased flow intermittency for Common Shiner. Both species were absent for all western Basin sites and had different responses to hydrological index trends at eastern Basin sites. These results demonstrate ecohydrological index changes impact distributions of native fish and suggest target factors for assessment or restoration activities.

How streamflow has changed across Australia since the 1950s: evidence from the network of hydrologic reference stations

Abstract. Streamflow variability and trends in Australia were investigated for 222 high-quality stream gauging stations having 30 years or more continuous unregulated streamflow records. Trend analysis identified seasonal, inter-annual and decadal variability, long-term monotonic trends and step changes in streamflow. Trends were determined for annual total flow, baseflow, seasonal flows, daily maximum flow and three quantiles of daily flow. A distinct pattern of spatial and temporal variation in streamflow was evident across different hydroclimatic regions in Australia. Most of the stations in southeastern Australia spread across New South Wales and Victoria showed a significant decreasing trend in annual streamflow, while increasing trends were retained within the northern part of the continent. No strong evidence of significant trend was observed for stations in the central region of Australia and northern Queensland. The findings from step change analysis demonstrated evidence of changes in hydrologic responses consistent with observed changes in climate over the past decades. For example, in the Murray–Darling Basin, 51 out of 75 stations were identified with step changes of significant reduction in annual streamflow during the middle to late 1990s, when relatively dry years were recorded across the area. Overall, the hydrologic reference stations (HRSs) serve as critically important gauges for streamflow monitoring and changes in long-term water availability inferred from observed datasets. A wealth of freely downloadable hydrologic data is provided at the HRS web portal including annual, seasonal, monthly and daily streamflow data, as well as trend analysis products and relevant site information.

Streamflow Regime Variations Following Ecological Management on the Loess Plateau, China

The continuous ecological management of the Loess Plateau is known throughout the world for two strategies: the integrated soil conservation project that began in the 1970s, and the “Grain for Green” project that began in the 1990s. Six sub-catchments nested in the Beiluo River basin were selected to investigate streamflow regime variations during the two project periods. The annual streamflow trends and change points were detected using a bootstrap-based Mann-Kendall test and Pettitt test. Annual streamflow (from the 1950s to 2011) exhibited significantly negative trends in five out of six catchments, varying from −0.15 to −0.30 mm/a. During the integrated soil conservation period, the annual streamflow was reduced due to high flow decreases (5% of time exceeded), whereas in the low flows (95%) it increased in all sub-catchments. During the “Grain for Green” period, the annual streamflow decreased due to daily streamflow reductions at four stations. In addition to high flow and low flow decreases at the Wuqi and Liujiahe stations during the “Grain for Green” period, it is significant that the low flows continuously increased. Compared with trends from the forestry area, which includes the Zhangcunyi and Huangling stations, incremental annual streamflow reductions were observed in other sub-catchments, which can be linked to ecological management. This result implies that streamflow can be moderated by appropriate management options, even in semiarid areas. It was concluded that a stable streamflow regime can be achieved in vegetated areas, and streamflow moderation is dependent on ecological management practices.

Long‐term streamflow trends in the middle reaches of the Yellow River Basin: detecting drivers of change

AbstractThe catchments in the Loess Plateau, in China's middle reaches of the Yellow River Basin, experienced unprecedented land use changes in the last 50 years as a result of large‐scale soil conservation measure to control soil erosion. The climate of the region also exhibited some levels of change with decreased precipitation and increased temperature. This study combined the time‐trend analysis method with a sensitivity‐based approach and found that annual streamflow in the Loess Plateau decreased significantly since the 1950s and surface runoff trends appear to dominate the streamflow trends in most of the catchments. Annual baseflow exhibited mostly downward trends, but significant upward trends were also observed in 3 out of 38 gauging stations. Mean annual streamflow during 1979−2010 decreased by up to 65% across the catchments compared with the period of 1957−1978, indicating significant changes in the hydrological regime of the Loess Plateau. It is estimated that 70% of the streamflow reduction can be attributed to land use change, while the remaining 30% is associated with climate variability. Land use change because of the soil conservation measures and reduction in precipitation are the key drivers for the observed streamflow trends. These findings are consistent with results of previous studies for the region and appear to be reasonable given the accelerated level of the soil conservation measures implemented since the late 1970s. Changes in sea surface temperature in the Pacific Ocean, as indicated by variations in El Niño–Southern Oscillation and phase shifts of the Pacific Decadal Oscillation, appear to have also affected the annual streamflow trends. The framework described in this study shows promising results for quantifying the effects of land use change and climate variability on mean annual streamflow of catchments within the Loess Plateau. Copyright © 2015 John Wiley &amp; Sons, Ltd.