Climate Elasticity Research Articles

Impacts of climate change on regional hydrological regimes of the Wujiang River watershed in the Karst area, Southwest China

Abstract Background The impacts of climate change on streamflow in the Wujiang River watershed of Guizhou Province, Southwest China, were investigated by using a monthly distributed hydrological model and the two–parameter climate elasticity of streamflow approach. Results Results showed two different approaches obtained almost identical results in term of precipitation elasticity of streamflow, which is about 1.42 across different emission scenarios. Precipitation is the primary factor controlling runoff generation. However, the effects of temperature on the streamflow cannot be neglected with evidences of opposite signs of future precipitation and streamflow; the slight decline of streamflow is associated with an increase of precipitation and a higher temperature. Conclusion While the magnitudes of annual mean streamflow responses are minor, there would be a seasonal shift: drier spring and wetter summer would potentially result in the increasing frequency of spring drought events and summer flooding, and would produce serious challenge for water resources planning and management for Southwest China.

Effects of Climate Change and Human Activities on Surface Runoff in the Luan River Basin

Quantifying the effects of climate change and human activities on runoff changes is the focus of climate change and hydrological research. This paper presents an integrated method employing the Budyko-based Fu model, hydrological modeling, and climate elasticity approaches to separate the effects of the two driving factors on surface runoff in the Luan River basin, China. The Budyko-based Fu model and the double mass curve method are used to analyze runoff changes during the period 1958~2009. Then two types of hydrological models (the distributed Soil and Water Assessment Tool model and the lumped SIMHYD model) and seven climate elasticity methods (including a nonparametric method and six Budyko-based methods) are applied to estimate the contributions of climate change and human activities to runoff change. The results show that all quantification methods are effective, and the results obtained by the nine methods are generally consistent. During the study period, the effects of climate change on runoff change accounted for 28.3~46.8% while those of human activities contributed with 53.2~71.7%, indicating that both factors have significant effects on the runoff decline in the basin, and that the effects of human activities are relatively stronger than those of climate change.

Separation of the impacts of climate change and human activity on runoff variations

A practical approach to separate the impact of the processes of climate change (CC) and human activities (HA) on streamflow is presented. A non-parametric Mann-Kendall-Sneyers test, combined with moving t test and Yamamoto methods, was used to recognize abrupt change points in the runoff time series to determine a baseline period. A new algorithm to separate CC and HA influence on streamflow was deduced based on the climate elasticity concept. Application to the Chao River, China, shows that CC imposed a positive impact on streamflow in this region (25%, on average), while HA exerted a continuous negative impact of –75% in the period after the 1950s. These results are of great use in understanding the variation of CC and HA impacts under different human development patterns.Editor Z.W. Kundzewicz; Associate editor H. Aksoy

Using the aridity index to assess recent climate change: a case study of the Lancang River Basin, China

As one of the most important climatic variables, annual evapotranspiration (E) reflects the complex interactions between atmosphere, vegetation, soil and hydrological process at global and regional scales. It is largely determined by potential evapotranspiration (E0) and precipitation (P). Aridity index (E0/P) which can be defined as the ratio of annual potential evapotranspiration to annual precipitation, can be used to represent annual evapotranspiration. As result it has become an important indicator to assess water-related climate change. This study utilizes the aridity index to reveal the recent climate change patterns in the Lancang River Basin, China. A new non parametric estimator of climate elasticity has also been developed. Using the daily meteorological records (1961–2005) of precipitation, air temperature, wind speed, relative humidity and sunshine hours from 35 stations, changes in spatial and temporal characteristics of P, E0, E, and E0/P are analyzed. The results reveal some important new findings, which can be summarized as: (a) new findings show that the spatial distribution of, and the correlation coefficients between P, E0, E, and E0/P possess strong latitude zonality; (b) high consistency in the temporal variation of P and E has been detected. The main periodicity of the E and E0/P series varies greatly for the three sub basins, and an anti-phase relationship between them has also been found; (c) our newly developed nonparametric estimator of climate elasticity can be successfully used in assessing the sensitivity of climate system. Climate elasticity of E in relation to E0 and P increases for most of the regions in the study area, suggesting that E becomes more sensitive to changes in the corresponding climatic variable during the study period. The study demonstrates the importance of the aridity index in the water-related climate change studies which has been neglected for a long time by most hydrologists and managers.

Quantitative contribution of climate change and human activities to runoff changes in the Wei River basin, China

Abstract. Surface runoff from the Wei River basin, the largest tributary of the Yellow River in China, has dramatically decreased over last 51 years from 1958 to 2008. Climate change and human activities have been identified as the two main reasons for the decrease in runoff. The study period is split into two sub-periods (1958–1989 and 1990–2008) using the Mann–Kendall jump test. This study develops an improved climate elasticity method based on the original climate elasticity method, and conducts a quantitative assessment of the impact of climate change and human activities on the runoff decrease in the Wei River basin. The results from the original climate elasticity method show that climatic impacts contribute 37–40% to the decrease in runoff, while human impacts contribute 60–63%. In contrast, the results from the improved climate elasticity method yield a climatic contribution to runoff decrease of 22–29% and a human contribution of 71–78%. A discussion of the simulation reliability and uncertainty concludes that the improved climate elasticity method has a better mechanism and can provide more reasonable results.

The mechanism and scenarios of how mean annual runoff varies with climate change in Asian monsoon areas

Understanding the effects of climate change on runoff is important for the sustainable management of water resources. However, the mechanism of such effects in the Asian monsoon region remains unclear. This study revisits Fu's two-parameter climate elasticity index and enhances it by using the Gardner function to strengthen the former's prediction reliability when the future climate condition is beyond the historical range. Then the improved method was applied to study the elasticity change with temperature and precipitation in the eastern monsoon basins of China, whereas to explore the mechanism of climate change on runoff. Furthermore, the runoff change and the elasticity of the study area from 2020 to 2050 under representative concentration pathways (RCPs) were predicted. Results show that the trend of elasticity change assumes a centrosymmetric picture with the symmetric point (0,0). Different catchments respond differently to the same climate change scenario: the sensitivity of the Haihe Basin is the highest; those of Yellow, Huaihe, Liaohe, Songhua, Pearl, Yangtze, and Southeast Rivers are lower, in descending order. The changing mode of precipitation and temperature differs greatly to keep the runoff unchanged. For semi-humid regions in which the mean annual temperature ranges from 0.71 degrees C to 9.0 degrees C, such as the basins of Songhua, Liaohe, Haihe, and Yellow, a 1 degrees C increase in temperature requires a corresponding 3.2-4.0% increase in precipitation to keep the runoff unchanged. However, in wet regions, such as the basins of Yangtze, Southeast Rivers, and Pearl, the same change in temperature requires a less than 2.8% increase in precipitation to keep the runoff unchanged. In the future, the runoff in most basins may decrease in different degrees. The decreasing velocity of the runoff is the fastest in the RCP8.5 scenario and the decreasing trend of the runoff slows down under the RCP4.5 and RCP2.6 scenarios. The proposed method can be applied to other basins to assess potential climate change effects on annual runoff. The results of the basins studies can inform planning of long-term basin water management strategies taking into account global change scenarios. (C) 2014 Elsevier B.V. All rights reserved.

The regional variation in climate elasticity and climate contribution to runoff across China

Summary The climate elasticity of runoff is an important indicator that is used to quantify the relationship between changes in runoff and changes in climate variables. It is a function of both climate and catchment characteristics. Recently, Yang and Yang (2011) proposed an analytical derivation of climate elasticity (YY2011), in which a parameter n was used to represent the impact of the catchment characteristics. In China, both climate and catchment characteristics have large spatial variations. To understand the spatial variation of hydrologic response to climate change, this paper divided China into 210 catchments, further calculated the parameter n, and then estimated the climate elasticity and evaluated the contribution of climate change to runoff for each catchment. The results show that n ranges from 0.4 to 3.8 (with a mean of 1.3 and a standard deviation of 0.6), which has a logarithmic relationship with catchment slope; the precipitation elasticity ranges from 1.1 to 4.8 (with a mean of 1.9 and a standard deviation of 0.6), which shows a large regional variation, smaller values (1.1–2.0) mainly appearing in Southern China, the Songhua River basin and the Northwest, and larger values (2.1–4.8) mainly appearing in the Hai River basin, the Liao River basin and the Yellow River basin. In addition, climate contribution to runoff exhibits a large regional variation, the largest positive values (1.1–3.1%/a) occurring in the Northwest, the largest negative values (−1.0 to −0.5%/a) occurring in the Hai River basin and the middle reach of the Yellow River basin. In theory, the YY2011 method is a first-order approximation. The approximation underestimates the precipitation (P) contribution to runoff when P increases and overestimates that when P decreases, and the relative error has a median of ∼3% and a maximum of ∼20% when 10% precipitations change in those catchments of China.

Investigation of the dramatic changes in lake level of the Bosten Lake in northwestern China

Bosten Lake, located in the arid region of northwest China, is the largest inland freshwater lake in China. Water resources in Bosten Lake are of great importance for the regional drinking water supply, agricultural irrigation, and economic development of Xinjiang province. In this study, the dynamics of the lake level in Bosten Lake were investigated from 1956 to 2010. We found that the lake level experienced three different periods of change due to the combined influences of climate variation and human activities. Generally, the lake level has shown a significant downward trend since the first observation started in 1956 and dropped to its lowest level in 1987. Thereafter, the lake level presented a continuous upward trend and rose to its highest value in 2002. Then, the level decreased dramatically from 2002 to 2010. A water balance model and the climate elasticity method were used to estimate the reasons for the lake level changes of Bosten Lake. The results showed that an increase in lake evaporation led to the continuous decrease in lake level from 1958 to 1987. Then, human-controlled lake outflow and increasing lake inflow together led to the increase in lake level from 1988 to 2002. During 2003 to 2010, the emergency project of transferring water to Tarim River led to the increase in lake outflow, while the lake inflow obviously decreased because of a decrease in precipitation. These factors resulted in a sharp decrease in the lake level from 2003 to 2010. The changes in lake level indicate changes in available water resources from Bosten Lake. This reason for the analysis of the change in lake level in this study is to support the water resources management of Bosten Lake.

Attribution analysis based on the Budyko hypothesis for detecting the dominant cause of runoff decline in Haihe basin

• The elasticity of runoff was derived based on the Choudhury–Yang equation. • Quantify impacts of changes in climate and land use/cover on the catchment runoff. • Attributing the dominant cause for runoff decrease in 33 hilly catchments in the Haihe River. Catchment hydrological processes have been greatly influenced by the intensive variability in land use/cover, precipitation and air temperature due to climate change and local human activities. It is desired to understand catchment hydrological response to these changes. Observations show that annual runoff had a significant decreasing trend during the past 50 years (1956–2005) in Haihe basin of northern China. In order to detect the major cause for this runoff decline, we first theoretically derived the elasticity of runoff from the Choudhury–Yang equation that is a water-energy balance equation based on the Budyko hypothesis. The elasticity of runoff was calculated in 33 selected mountainous catchments in Haihe basin based on their climate condition (represented by the aridity index, E 0 / P ) and landscape condition (represented by the parameter, n ). We analyzed the breakpoint of the annual runoff of the 33 catchments over the past 50 years and split the whole study period into two sub-periods at the breakpoint (period 1: before the breakpoint; period 2: after the breakpoint). Then we attributed the runoff change between the two sub-periods to the impacts of climate variability and land use/cover change. The change of climate is represented by changes in precipitation ( P ) and potential evaporation ( E 0 ) and the change of land use/cover is represented by the parameter n in Choudhury–Yang equation. The change of annual runoff from period-1 to period-2 was the catchment hydrological response to the change of precipitation, potential evaporation and land use/cover (represented as Δ P , Δ E 0 and Δ n ), and we calculated the runoff change based on the elasticities of runoff. For the 33 catchments, the mean annual runoff decreased by 43.0 mm from the period-1 (91.4 mm) to period-2 (48.4 mm). Impacts of climate variation and land use/cover change were accountable for the runoff decrease by 26.9% and 73.1% on average, respectively. Impact of climate variation mainly came from the decrease in precipitation, and impact of land use/cover change mainly came from the vegetation increase. Vegetation increase was mainly due to the reforestation during the soil–water conservation practice during the past 30 years and also partially due to climate variability especially the temperature increase. This methodology can also be used to predict the runoff change in these catchments without direct influence of local human activities under the future climate scenario based on the climate elasticity of runoff estimated from the historical hydroclimatic data.

Inter-annual variation of streamflow, precipitation and evaporation in a small humid watershed (Chengcun Basin, China)

For sustainable water resource management, it is important to determine the relationship between streamflow and other variables that influence availability of water resources. However, many catchments do not have sufficient data to allow for a more detailed study of these relationships. We faced a similar challenge in the Chengcun Basin (limited historical data: from 1986–1999); and therefore we used a new approach to overcome this. We found that, using nonparametric trend methods in conjunction with the climate elasticity analyses and the 2D visualization of hydrologic data, it is possible to assess the relationships between streamflow and other hydro-climatic variables. In the past, streamflow trends in the basin were more correlated with precipitation than with potential evapotranspiration (PET). In addition, there is a gradual shift in the hydrological regime of the catchment, which may affect the occurrence of available water resources and activities that depend on them. In addition, based on our climate sensitivity analyses, the streamflow is dependent and more sensitive to variations in precipitation than to PET (δQ=0.79δP+0.42δE; precipitation elasticity, ɛP =1.32; PET elasticity, ɛE =−2.10). Therefore pending more detailed studies, the use of our approach will provide a rapid means to assess the variation of water resources (streamflow) in a watershed. In the future, we hope to carry out related research in other watersheds and also perform a more detailed studies to improve upon the results of this study.

A global assessment of climate–water quality relationships in large rivers: An elasticity perspective

To uncover climate–water quality relationships in large rivers on a global scale, the present study investigates the climate elasticity of river water quality (CEWQ) using long-term monthly records observed at 14 large rivers. Temperature and precipitation elasticities of 12 water quality parameters, highlighted by N- and P-nutrients, are assessed. General observations on elasticity values show the usefulness of this approach to describe the magnitude of stream water quality responses to climate change, which improves that of simple statistical correlation. Sensitivity type, intensity and variability rank of CEWQ are reported and specific characteristics and mechanism of elasticity of nutrient parameters are also revealed. Among them, the performance of ammonia, total phosphorus–air temperature models, and nitrite, orthophosphorus-precipitation models are the best. Spatial and temporal assessment shows that precipitation elasticity is more variable in space than temperature elasticity and that seasonal variation is more evident for precipitation elasticity than for temperature elasticity. Moreover, both anthropogenic activities and environmental factors are found to impact CEWQ for select variables. The major relationships that can be inferred include: (1) human population has a strong linear correlation with temperature elasticity of turbidity and total phosphorus; and (2) latitude has a strong linear correlation with precipitation elasticity of turbidity and N nutrients. As this work improves our understanding of the relation between climate factors and surface water quality, it is potentially helpful for investigating the effect of climate change on water quality in large rivers, such as on the long-term change of nutrient concentrations.

Impacts of climate variability and human activities on decrease in streamflow in the Qinhe River, China

Under the impacts of climate variability and human activities, there are statistically significant decreasing trends for streamflow in the Yellow River basin, China. Therefore, it is crucial to separate the impacts of climate variability and human activities on streamflow decrease for better water resources planning and management. In this study, the Qinhe River basin (QRB), a typical sub-basin in the middle reach of the Yellow River, was chosen as the study area to assess the impacts of climate variability and human activities on streamflow decrease. The trend and breakpoint of observed annual streamflow from 1956 to 2010 were identified by the nonparametric Mann–Kendall test. The results showed that the observed annual streamflow decreased significantly (P < 0.05) and a breakpoint around 1973 was detected. Therefore, the time series was divided into two periods: “natural period” (before the breakpoint) and “impacted period” (after the breakpoint). The observed annual streamflow decreased by 68.1 mm from 102.3 to 34.2 mm in the two periods. The climate elasticity method and hydrological model were employed to separate the impacts of climate variability and human activities on streamflow decrease. The results indicated that climate variability was responsible for 54.1 % of the streamflow decrease estimated by the climate elasticity method and 59.3 % estimated by the hydrological modeling method. Therefore, the climate variability was the main driving factor for streamflow decrease in the QRB. Among these driving factors of natural and anthropogenic, decrease in precipitation and increase in water diversion were the two major contributions of streamflow reduction. The finding in this study can serve as a reference for regional water resources management and planning.

Relative importance of climate and land surface changes on hydrologic changes in the US Midwest since the 1930s: Implications for biofuel production

The US Midwest is an important area of first generation biofuels, accounting for 80–90% of US corn and soybean production (2009–2011). However, there are potential adverse impacts of biofuel production on water resources in this area. The objective of this study was to assess potential impacts of biofuel production on water resources by exploring relationships between hydrologic changes and climate and land surface changes based on long-term (∼1930s–2010) stream gage and climate data from 55 unregulated watersheds in the US Midwest. Long-term trends in climate (precipitation and potential evapotranspiration) and flow were evaluated. Sensitivity of changes in annual streamflow and baseflow to climate was evaluated using climate elasticity (sensitivity) and the residuals were attributed to land surface changes. Results show that streamflow increased significantly (p < 0.05) in 35% (19/55) of watersheds (median 2.4 ± 0.3 mm/year), baseflow increased in 58% of watersheds (median 1.1 ± 0.4 mm/year), and baseflow index (baseflow/streamflow, BFI) increased in 42% of watersheds (median 0.2 ± 0.1%/year). Overall, climatic variability contributed more than land surface change to streamflow change (61 ± 19% vs. 40 ± 18%), while land surface change contributed much more to baseflow (74 ± 10% vs. 27 ± 10%; 2.7 times higher) and to BFI (119 ± 14% vs. 27 ± 18%; 4.4 times higher) than climate change. Watersheds (25/55, 45%) with no significant trend in climate but with significant flow trends provide direct evidence that the Midwest land surface change (cropping system and related land management) significantly impacted flow processes. Restricting analysis to these watersheds shows that land surface change contributed 2.0 times more than climate variability/change to streamflow change, 3.2 times more to baseflow change, and 7.7 times more to BFI change. The importance of past land surface changes on hydrology suggests that any future land surface changes, such as biofuel expansion or changing biofuel feedstocks, should consider impacts on the hydrology.

Hotspots of the sensitivity of the land surface hydrological cycle to climate change

Due to the shortage of the global observational data of the terrestrial hydrological variables, the understanding of how surface hydrological processes respond to climate change is still limited. In this study, the Community Land Model (CLM4.0) with high resolution atmospheric forcing data is selected to simulate the global surface hydrological quantities during the period 1948–2006 and to investigate the spatial features of these quantities in response to climate change at the regional scales. The sensitivities of evaporation and runoff with respect to the dominant climate change factors (e.g. temperature and precipitation) derived from the concept of climate elasticity are introduced. Results show that evaporation has a declining trend with a rate of 0.7 mm per decade, while runoff shows a weak increasing trend of 0.15 mm per decade over the global land surface. Analyses of the hotspots in the hydrological cycle indicate that the spatial distributions for evaporation and runoff are similar over many areas in central Asia, Australia, and southern South America, but differ largely in high latitudes. It is also found that, the evaporation hotspots in arid regions are mainly associated with the changes in precipitation. Our sensitive analysis suggests that the hydrological quantities show a rather complicated spatial dependency of response of the water cycle to the different climate factors (temperature and precipitation).

Assessing the impacts of climate variability and human activities on annual runoff in the Luan River basin, China

Regional hydrological processes have been greatly influenced by human activities and climate variability. The inflow of Panjiakou Reservoir, which is the largest reservoir located on the Luan River, has shown a significant decreasing trend over the past 50 years. A large-scale hydrological model, namely the geomorphology-based hydrological model (GBHM), and a climate elasticity model were applied to perform quantitative attributing analysis of runoff change in the study catchment. Annual runoff decreased by 19.5 mm from 65.7 mm in the period 1956–1979 to 46.2 mm in the period 1980–2005. Annual direct water intake increased by 22.5 mm from 3.6 to 26.1 mm. Climate impact was accountable for the runoff increase of 8.8 and 9.2 mm simulated by GBHM and the climate elasticity model, respectively. Impacts of land use and vegetation change accounted for the runoff decrease of 2.5 mm. Change of precipitation and vegetation cover contributed to annual runoff change for the upper catchment (grassland-dominated). Change of antecedent precipitation (a proxy of soil moisture) also contributed to annual runoff change for the lower catchment (forest-dominated) and the whole catchment (mixture vegetation).

Impacts of climate variability and human activity on streamflow decrease in a sediment concentrated region in the Middle Yellow River

The Kuye River is the primary tributary located in the sediment concentrated regions in the Middle Yellow River in China. Significant decrease in streamflow has been observed in the Kuye River. The non-parametric Mann-Kendall test was applied to detect the change in annual streamflow for the period of 1960 to 2006. Mean annual streamflow in the Kuye River was 84.9 mm from 1960 to 1979 (period I), while it decreased to 58.2 mm from 1980 to 1998 (period II) and 20.5 mm from 1999 to 2006 (period III), respectively. The climate elasticity method and the hydrological modeling method were individually employed to assess the impact of climate variability and human activities on the decrease in streamflow . The results showed that climate variability was responsible for 29.6 and 27.1 % of the streamflow decrease from the climate elasticity method and the hydrological modeling method, respectively; while human activities accounted for 70.4 and 72.9 % of the streamflow decrease in period II. In period III, climate variability contributed 40.9 and 39.3 % of the streamflow decrease from the climate elasticity method and the hydrological modeling method, respectively; while human activities accounted for 59.1 and 60.7 % of the streamflow decrease. Therefore, human activities were the main reason of the streamflow decrease. Soil conservation measures (planting trees, improving pastures, building terraces and sediment-trapping dams) and coal mining led to the streamflow reduction in the Kuye River.

Responses of runoff to climatic variation and human activities in the Fenhe River, China

The Fenhe River is the second largest tributary of the Yellow River in China. Climatic variation and human activities have impacted the runoff significantly in the Fenhe River in recent decades. In this study, the runoff trend from 1957 to 2010 was analyzed and the impacts of climatic variation and human activities on runoff were attributed by the climate elasticity method and hydrological modeling method. The observed annual runoff decreased significantly (P < 0.05) during the past 54 years in the Fenhe River basin. A change point was identified around the year 1979 for the annual runoff series by the Mann–Kendall test. The observed average annual runoff in the Period II (from 1980 to 2010) decreased by 24.94 mm compared with the Period I (from 1957 to 1979). The attribution results show that the average annual amount of water diversion from the river in the Period II increased significantly by 7.88 mm compared with the Period I, accounting for 31.6 % of the total decrease in the observed annual runoff. In addition, other human activities such as land use and cover change led to the decrease in annual runoff by 6.31 mm from the climate elasticity method and 6.92 mm from the hydrological modeling method, which accounting for 23.8 and 27.7 % of the total decrease in the observed annual runoff, respectively. Therefore, human activities together were responsible for 55.4 % of the total observed runoff reduction estimated by the climate elasticity method and for 59.3 % estimated by the hydrological modeling method. Climatic variation such as changes in precipitation and evapotranspiration led to the decrease in runoff by 10.14 and 10.75 mm from the two methods, accounting for 40.7 and 44.6 % of the total observed runoff reduction. Therefore, human activities were the main driving factor for the runoff decrease in the Fenhe River basin.

Assessing the impacts of climate variability and human activities on streamflow in the water source area of Baiyangdian Lake

As the largest wetland in the North China Plain (NCP), the Baiyangdian Lake plays an important role in maintaining water balance and ecological health of NCP. In the past few decades, the decreasing streamflow in the Baiyangdian Basin associated with climate variability and human activities has caused a series of water and eco-environmental issues. In this study, we quantified the impacts of climate variability and human activities on streamflow in the water source area of the Baiyangdian Lake, based on analyses of hydrologic changes of the upper Tanghe river catchment (a sub-basin of the Baiyangdian Basin) from 1960 to 2008. Climate elasticity method and hydrological modeling method were used to distinguish the effects of climate variability and human activities. The results showed that the annual streamflow decreased significantly (P>0.05) by 1.7 mm/a and an abrupt change was identified around the year 1980. The quantification results indicated that climate variations accounted for 38%–40% of decreased streamflow, while human activities accounted for 60%–62%. Therefore, the effect of human activities played a dominant role on the decline of the streamflow in the water source area of the Baiyangdian Lake. To keep the ecosystem health of the Baiyangdian Lake, we suggest that minimum ecological water demand and integrated watershed management should be guaranteed in the future.

Effects of climate change on annual streamflow using climate elasticity in Poyang Lake Basin, China

Hydrological processes depend directly on climate conditions [e.g., precipitation, potential evapotranspiration (PE)] based on the water balance. This paper examines streamflow datasets at four hydrological stations and meteorological observations at 79 weather stations to reveal the streamflow changes and underlying drivers in four typical watersheds (Meigang, Saitang, Gaosha, and Xiashan) within Poyang Lake Basin from 1961 to 2000. Most of the less than 90th percentile of daily streamflow in each watershed increases significantly at different rates. As an important indicator of the seasonal changes in the streamflow, CT (the timing of the mass center of the streamflow) in each watershed shows a negligible change. The annual streamflow in each watershed increases at different rates, with a statistically significant trend (at the 5 % level) of 9.87 and 7.72 mm year−1, respectively, in Meigang and Gaosha watersheds. Given the existence of interactions between precipitation and PE, the original climate elasticity of streamflow can not reflect the relationship of streamflow with precipitation and PE effectively. We modify this method and find the modified climate elasticity to be more accurate and reasonable using the correlation analysis. The analyses from the modified climate elasticity in the four watersheds show that a 10 % increase (decrease) in precipitation will increase (decrease) the annual streamflow by 14.1–16.3 %, while a 10 % increase (decrease) in PE will decrease (increase) the annual streamflow by −10.2 to −2.1 %. In addition, the modified climate elasticity is applied to estimate the contribution of annual precipitation and PE to the increasing annual streamflow in each watershed over the past 40 years. Our result suggests that the percentage attribution of the increasing precipitation is more than 59 % and the decreasing in PE is less than 41 %, indicating that the increasing precipitation is the major driving factor for the annual streamflow increase for each watershed.

Comparison of the streamflow sensitivity to aridity index between the Danjiangkou Reservoir basin and Miyun Reservoir basin, China

The central route of China’s South-to-North Water Diversion Project would divert water from the Danjiangkou Reservoir basin (DRB) to Beijing beginning in the year 2014. The current main surface water source for Beijing is the Miyun Reservoir basin (MRB). The observed streamflows into the DRB and the MRB decreased significantly due to climatic variation and human activities from 1960 to 2005. The climate elasticity method is widely used to quantitatively separate the impacts of climatic variation and human activities on streamflow. One of the uncertainties of the method is that the impacts of changes in precipitation and potential evapotranspiration on streamflow are separated with the assumption that they are independent. However, precipitation and potential evapotranspiration are not totally independent. Aridity index, as the ratio between potential evapotranspiration and precipitation, could be considered as the representative indicator of climatic variation. In this study, the sensitivity of streamflow to aridity index is evaluated to assess the impact of climatic variation on streamflow in the DRB and the MRB. The result shows that streamflow in the MRB is more sensitive to climatic variation than that in the DRB. However, the effective impact of aridity index on streamflow is the product of the sensitivity and the change rate of aridity index. The attribution results show that change in aridity index contributed 68.8 % of the decrease in streamflow in the DRB while it contributed 31.5 % of the decrease in streamflow in the MRB. This indicated that the impact of climatic variation was the main reason of decrease in streamflow in the DRB while human activities such as increasing water consumption and land use change were the main reasons of decreasing streamflow in the MRB.